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Agronomy Masters Theses Collection

Theses from 1963 1963.

Effects of nitrogen supply on the cation exchange capacity of cereal roots and its relation to Ca adsorption from Ca-H bentonite clay systems by excised roots. , Ronald Paul White, Agronomy

Theses from 1962 1962

The effects of some environmental factors on growth and control of northern nutgrass. , Eugene Raymond Hill, Agronomy

Theses from 1961 1961

The use of fish by-product materials as fertilizers - alone and in mixtures or formulations. , Roy Augustus Barrett, Agronomy

Theses from 1959 1959

Interaction between height of cut and various nutrient levels on the development of turfgrass roots and tops. , Evangel John Bredakis, Agronomy

Theses from 1958 1958

A comparison of liquid and solid fertilizer for turf. , Norman Henry MacLeod, Agronomy

Theses from 1957 1957

Relationship of root cation exchange capacity to calcium uptake. , John M. White, Agronomy

Theses from 1956 1956

The role of nitrogen on the increased availability of fertilizer phosphorus. , William Makepeace Atwood, Agronomy

An investigation into the relation of soil compaction and soil fertility as affecting root development in soils. , Philip R. Pearson, Agronomy

Theses from 1955 1955

Effect of degree of saturation and nature of clay colloid upon the availability of calcium to tomatoes and the effect of type of colloid upon the migration of cations from plant root to clay colloids. , Paul Eck, Agronomy

A study of the physical properties of eolian influenced soils in the central lowland of Connecticut and Massachusetts. , A. Ritchie, Agronomy

Theses from 1953 1953

The effect of several organic salts with hydrogen ion in solubilizing rock phosphate. , Joseph Angelini, Agronomy

Studies on cation exchange capacity of plant roots with reference to their ecological phenomena. , Eliot Epstein, Agronomy

The curing of cigar tobacco with the use of kerosene as a source of heat, in comparison with the use of liquified petroleum gas for the purpose. , Claus Hans Tameling, Agronomy

The effect of soil fertility, rate of planting and variety on the value of corn for silage. , Hrant M. Yegian, Agronomy

Theses from 1952 1952

Potassium competition in grass-legume associations as a function of root cation exchange capacity. , Bryce Carroll Gray, Agronomy

Theses from 1951 1951

The precipitation of phosphorus by iron and aluminum as influenced by pH and pure organic substances. , Donald Bigelow Bradley, Agronomy

Solubilization effect of citric acid on some insoluble phosphate salts. , Jean Joseph Lucien Leclerc, Agronomy

Theses from 1950 1950

The chemical composition of the foliage of different plant species as affected by soils derived from different rocks. , Jean-Marie Lapensee, Agronomy

Effects of rates and ratios of calcium, magnesium, and potassium on composition and yield of Ladino clover. , Philip Beaumont Turner, Agronomy

Theses from 1949 1949

Up-take of selenium by carnations, loss of selenium from treated soils by leaching, and occurrence of selenium in Massachusetts soils. , Robert John Allen, Agronomy

The elimination of white clover (Trifolium repens) from turf with particular reference to nitrogen levels. , Geoffrey S. Cornish, Agronomy

Spent hops for construction of turf areas. , Moyle E. Harward, Agronomy

The influence of parent material on the base exchange of soils. , Michael Neznayko, Agronomy

The availability to plants of applied phosphorus as influenced by the presence of organic materials and fluoride. , Glenn C. Russell, Agronomy

Color as a soil amendment. , Roy Edward Sigafus, Agronomy

The influence of organic anions on the replacement of fixed phosphates at various pH levels. , Paul Herbert Struthers, Agronomy

The toxicity of the copper ion in the growth of soy beans and the influence of the copper ion on the transfer of magnesium in soy bean seedlings from seed and growing medium to the aerial parts of the plant. , Gordon Franklin Thomas, Agronomy

Theses from 1948 1948

The fixation of phosphorus by iron and its replacement by organic and inorganic ions. , Richard Merrill Swenson, Agronomy

Theses from 1947 1947

The relative effect on the nitrogen content of buckwheat plants grown in a medium treated by varied concentrations and combinations of boron, manganese, and copper ions. , Garland Booker Bass, Agronomy

The relative effect of various types of vegetative tissues on the total base exchange capacity, exchangeable bases and pH value of a laminated clay. , Ivan Hope Tomlinson, Agronomy

Theses from 1942 1942

The influence of family relationships upon the uptake of nitrogen in the soil by plants. , A. Boy Pack, Agronomy

Theses from 1941 1941

A study of absorption and excretion of potassium and calcium by the roots of barley in different solution media and changes in hydrogen-ion concentration. , George Wenzel, Agronomy

Theses from 1940 1940

The effect of certain organic compounds on the flocculation of clay suspension. , Edward Theodore Clapp, Agronomy

The relative toxicity of certain ions and the function of the calcium ion as an antagonist, as indicated by soybean roots. , Plese Corbett, Agronomy

The lignin and methoxyl content of some common crops. , John Wendell Hurdis, Agronomy

The effect of the calcium ion on the development of soy bean seedling and the antagonism of this ion to arsenic, boron, and selenium ions. , Elvin Ted Miles, Agronomy

The effect of certain plant residues upon the buffer capacity of two Massachusetts soils. , Moody Francis Trevett, Agronomy

Theses from 1939 1939

A study of the percentage and total intake of certain elements by calciphilic and calciphobic plants grown on soils varying in pH. , William H. Bender, Agronomy

Some factors influencing the activity of Aspergillus niger. , Charles H. Moran, Agronomy

The relative rate of nitrification of nitrogen materials on certain tobacco soils from Canada. , Julien Richard, Agronomy

Theses from 1938 1938

Nitrification in soils of Massachusetts as influenced by soil type and source of nitrogen , Raymond B. Farnsworth, Agronomy

Rates of decomposition of various bedding materials. , John M. Zak, Agronomy

Theses from 1937 1937

Increasing the iron content of hay grown on soils producing nutritional anemia in Massachusetts livestock , Karol Joseph Kucinski, Agronomy

Theses from 1936 1936

The effect of additions of calcium hydroxide upon the solubility of phosphorus in certain Massachusetts soils , John Nelson Everson, Agronomy

Theses from 1934 1934

Oxidation-reduction potentials and their application to soils , Matthew Cotton Darnell, Agronomy

Theses from 1932 1932

Studies of methods for determination of magnesium deficiency in soils , Jay L. Haddock, Agronomy

Theses from 1931 1931

Some factors affecting the flora of pastures , Richard Carol Foley, Agronomy

The effect of some forms of nitrogen on the growth and nitrogen content of wheat and rice plants , Guy. Thelin, Agronomy

Theses from 1930 1930

The Ammonification and nitrification of cottonseed meal and the nitrification of ammonium sulphate , Harold R. Knudsen, Agronomy

A study of varietal and cultural factors affecting stand and yield of soybeans , Rhea E. Stitt, Agronomy

Theses from 1928 1928

The salt requirement of Havana tobacco with nitric and ammonic nitrogen , Oliver W. Kelly, Agronomy

Nitrate nitrogen accumulation in soils as affected by soil reaction and certain treatments , George J. Larsinos, Agronomy

The effect of boron and manganese on the growth of tobacco plants , T. Robert Swanback, Agronomy

Theses from 1927 1927

On the nitrate accumulation as affected by soil type, soil management and cropping system , Alwyn C. Sessions, Agronomy

Theses from 1924 1924

Physical properties of fertilizer materials , Raymond Alson Mooney, Agronomy

Theses from 1920 1920

Factors affecting the pop-ability of pop corn , James A. Purington, Agronomy

Theses from 1917 1917

The decomposition of organic matter in soils , Fred G. Merkle, Agronomy

Effect of one crop upon another and upon the fertility of the soil , S. G. Mutkekar, Agronomy

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MSc Thesis on Economic Efficiency and the Determinants in Major Food Crops Production

Ethiopian agriculture is characterized by its subsistence and low productivity and hence low level of efficiency that leads to food insecurity. Therefore, this study was undertaken with an objective of providing empirical evidence on the TE, AE and EE levels of major food crops (wheat, barley maize and teff) production in Albuko woreda using data collected from 151 randomly selected sample respondents during 2016/17 production year. Applying the a parametric Cobb Douglas SFA, the MLE result revealed that elasticities of inputs included to the production were statistically significant implying increase in these inputs will increase output and the average TE, AE and EE levels of households is found to be 73.49%, 54.61% and 38.01% respectively. The average efficiency levels entails that, food crops producing farmers in the study area have a yield potential and cost saving advantage for the available inputs. Further, this paper explored those factors that influence the efficiency levels by employing Tobit regression model. Thereby the outcome revealed that education level, farming experience and family size were found as to be positive and significant factors affecting TE whereas proximity is found to be a significant factor influencing TE negatively. The study also revealed that AE is influenced by education level, credit received, access to extension service and off farm income positively and significantly while land fragmentation and farm land owned negatively and significantly. Further, the study revealed that education level, credit received, access to extension service and off farm income were factors positively and significantly influencing EE while age, farm size and land fragmentation were found to be negative and significant factors. Thus, it is recommended that for improved efficiency levels there is need for better policies and strategies that gives due attention on expansion of education, provision of credit and extension service focusing on efficient use of resources, and generation of off farm income side by side to farming activity. Furthermore, arranging farmers in groups can play vital role in experience and knowledge sharing among them. Key words: Food crops; stochastic frontier; Wheat Equivalent Yield; economic efficiency;

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• Open access
• Published: 12 October 2020

A scoping review of adoption of climate-resilient crops by small-scale producers in low- and middle-income countries

• Maricelis Acevedo   ORCID: orcid.org/0000-0003-4257-9375 1 ,
• Kevin Pixley   ORCID: orcid.org/0000-0003-4068-7436 2   na1 ,
• Nkulumo Zinyengere 3   na1 ,
• Sisi Meng 4 ,
• Hale Tufan   ORCID: orcid.org/0000-0002-5323-4244 1 ,
• Karen Cichy 5 ,
• Livia Bizikova 6 ,
• Krista Isaacs   ORCID: orcid.org/0000-0002-1335-4516 7 ,
• Kate Ghezzi-Kopel   ORCID: orcid.org/0000-0002-8777-402X 1 &
• Jaron Porciello   ORCID: orcid.org/0000-0002-3179-1971 1  

Nature Plants volume  6 ,  pages 1231–1241 ( 2020 ) Cite this article

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• Agriculture
• Plant breeding
• Plant sciences

Climate-resilient crops and crop varieties have been recommended as a way for farmers to cope with or adapt to climate change, but despite the apparent benefits, rates of adoption by smallholder farmers are highly variable. Here we present a scoping review, using PRISMA-P (Preferred Reporting Items for Systematic review and Meta-Analysis Protocols), examining the conditions that have led to the adoption of climate-resilient crops over the past 30 years in lower- and middle-income countries. The descriptive analysis performed on 202 papers shows that small-scale producers adopted climate-resilient crops and varieties to cope with abiotic stresses such as drought, heat, flooding and salinity. The most prevalent trait in our dataset was drought tolerance, followed by water-use efficiency. Our analysis found that the most important determinants of adoption of climate-resilient crops were the availability and effectiveness of extension services and outreach, followed by education levels of heads of households, farmers’ access to inputs—especially seeds and fertilizers—and socio-economic status of farming families. About 53% of studies reported that social differences such as sex, age, marital status and ethnicity affected the adoption of varieties or crops as climate change-adaptation strategies. On the basis of the collected evidence, this study presents a series of pathways and interventions that could contribute to higher adoption rates of climate-resilient crops and reduce dis-adoption.

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Agriculture and food production are highly vulnerable to climate change. Extreme weather events such as droughts, heat waves and flooding have far-reaching implications for food security and poverty reduction, especially in rural communities with high populations of small-scale producers who are highly dependent on rain-fed agriculture for their livelihoods and food. Climate change is expected to reduce yields of staple crops by up to 30% due to lower productivity and crop failure 1 . Moreover, the projected global population growth and changes in diets toward higher demand for meat and dairy products in developing economies will stretch natural resources even further, increasing demands on food production and food insecurity 2 . To cope with climate change, farmers need to modify production and farm management practices, such as adjusting planting time, supplementing irrigation (when possible), intercropping, adopting conservation agriculture, accessing short- and long-term crop and seed storage infrastructure, and changing crops or planting more climate-resilient crop varieties.

This scoping review examines the conditions that have led to the adoption of climate-resilient crops over the past 30 yr in lower- and middle-income countries. For all countries, but especially those that rely on domestic agriculture production for food security, one of the most critical and proactive measures that can be taken to cope with food insecurity caused by unpredictable weather patterns is for farmers to adopt climate-resilient crops. Climate-resilient crops and crop varieties have enhanced tolerance to biotic and abiotic stresses 3 (Box 1 ). They are intended to maintain or increase crop yields under stress conditions and thereby provide a means of adapting to diminishing crop yields in the face of droughts, higher average temperatures and other climatic conditions 4 . Adoption of climate-resilient crops, such as early-maturing cereal crop varieties, heat-tolerant varieties, drought-tolerant legumes or tuber crops, crops or varieties with enhanced salinity tolerance, or rice with submergence tolerance, can help farmers to better cope with climate shocks. Climate-resilient crops and crop varieties increase farmers’ resilience to climate change, but despite their benefits, adoption rates by small-scale producers are not as high as expected in some cropping systems 4 , 5 , 6 . In this study, we focus on scoping (reviewing and synthesizing) the published evidence on the adoption of climate-resilient crops and crop varieties from climate-vulnerable countries and countries that have experienced climate-related impacts as determined by 45 indicators established by the Notre Dame Global Adaptation Initiative.

Overall, we find that the most important determinants of adoption of climate-resilient crops are the availability and effectiveness of extension services and outreach, education level of heads of households, including some awareness of climate change and adaptation measures, and farmers’ access to inputs, especially seeds and fertilizers. On the basis of the collected evidence, this scoping review presents a series of pathways and interventions that can contribute to higher adoption rates of climate-resilient crops and reduce dis-adoption (Box 2 ).

Box 1 Definitions and assumptions

Small-scale food producers. Definitions of small-scale food producers in the literature are mostly based on four criteria: land size, labour input (especially of family members), market orientation and economic size 2 . Land size is the most commonly used criterion. The clear majority of definitions of small-scale food producers are based on the acreage of the farm and/or a headcount of the livestock raised. Sometimes an arbitrary size is created (commonly 2 hectares or less), but otherwise a relative measure is used, which considers the average size of landholdings in the country, as well as a poverty measure (farms that generate 40% or less of the median income). A second important criterion of small-scale producer is the source of the labour used on the farm (whether it is provided by the household that runs the farm or workers who are paid a wage). A third criterion is the extent to which the farm output is sold to market rather than consumed by the farm household or bartered with neighbours (some authors caution that this is also contextual and many small-scale producers are engaged in commercial markets). A fourth criterion is economic size (the value of the farm’s production) 56 .

Climate-vulnerable countries are countries that are considered to be vulnerable to climate change. The ND-GAIN index presents a list of countries ranked by vulnerability to climate change and readiness to respond ( https://gain.nd.edu/our-work/country-index/rankings/ ).

Climate resiliency is the capacity for a socio-ecological system to absorb stresses and maintain function in the face of external stresses imposed on it by climate change, and adapt, reorganize and evolve into more desirable configurations that improve the sustainability of the system, leaving it better prepared for future climate change impacts.

Climate change adaptation includes planned or autonomous actions that seek to lower the risks posed by climatic changes, either by reducing exposure and sensitivity to climate hazards or by reducing vulnerabilities and enhancing capacities to respond to them. Adaptation also includes exploiting any beneficial opportunities presented by changing climates.

Climate-resilient crops are crops and crop varieties that have enhanced tolerance to biotic and abiotic stresses. They are intended to maintain or increase crop yields under stress conditions such as drought, flooding (submergence), heat, chilling, freezing and salinity, and thereby provide a means of adapting to diminishing crop yields in the face of droughts, higher and lower than seasonal temperatures, and other climatic conditions 3 , 57 .

Climate-smart agriculture is an approach or set of practices aimed at increasing agricultural productivity and incomes sustainably, while building resilience and adapting to climate change conditions and reducing and/or removing greenhouse gas emissions where possible 6 .

Conservation agriculture is a farming system that promotes minimum soil disturbance (that is, no tillage), maintenance of a permanent soil cover, and diversification of plant species; for instance, through crop rotation 58 .

Adoption is the stage at which technology has been selected and is being used over a sustained period by an individual or an organization. Adoption is more than acceptance; it is inclusion of a product or innovation among the common practices of the adopter.

Gender refers to the social relations between men and women, boys and girls, and how this is socially constructed. Gender roles are dynamic and change over time.

Agricultural extension is a form of outreach that shares research-based knowledge with farmers and communities in order to improve agricultural practices and productivity. The approach to delivering these services varies in terms of farmer participation and engagement. This range includes technology transfer, advisory, experiential and iterative learning, farmer-led extension services (such as farmer field schools), and facilitation, in which farmers define their own problems and develop their own solutions.

Box 2 Summary methods

A double-blind title and abstract screening was performed on 5,650 articles that were identified through a comprehensive search of multiple databases and grey literature sources and then uploaded to the systematic review software Covidence. The full search protocol is described in the Supplementary Information .

The resulting 886 articles were subjected to a second round of full-text screening, and 684 articles that did not meet the inclusion criteria were excluded, leaving 202 articles that were read in full and included in the qualitative synthesis.

We performed data extraction on each of the 202 included studies. A data-extraction template (available in the Supplementary Information ) was developed to document the data, study type and context of each citation and all themes of interest.

The extracted data were qualitatively summarized on the basis of emerging themes and with the aim of providing recommendations to donors and policy makers.

Among the 684 articles that were excluded at the full-text screening phase, 230 were excluded because they did not include an explicit analysis of factors for climate-resilient crop adoption and 204 were excluded because there was no explicit focus on crops, varieties, seed, planting materials or germplasm.

The inclusion criteria for this study were:

The study focus includes population of small-scale food producers, as defined in the protocol

The study was published after 1990 (1990 was the year the Intergovernmental Panel on Climate Change (IPCC) produced its first report on climate change).

The study includes original research (qualitative and quantitative reports) and/or a review of existing research, including grey literature.

An explicit focus or clear relevance on climate change resilience or climate change adaptation, as defined in the protocol.

An explicit focus on crops, varieties, seed, planting materials or germplasm.

The study mentions factors for adoption, as defined in the protocol.

The area of focus of the study includes target populations in lower- and middle-income countries, as defined by the World Bank.

A scoping review aims to explore the key concepts underpinning a research area and the main sources and types of evidence available 7 . Established scoping review methods provide an evidence-based framework for systematically searching and thematically characterizing the extent, range and nature of existing evidence. A PRISMA-P protocol for this scoping review 8 was registered on 4 June 2019 on the Open Science Framework. We performed double-blind title and abstract screening of 5,649 citations, selecting 568 papers for full-text screening using a priori inclusion and exclusion criteria; 202 papers met the inclusion criteria for data extraction. The inclusion and exclusion criteria are available in the protocol (Methods and Supplementary Information ), and the data-extraction procedure and the PRISMA flow diagram of included and excluded studies are presented in the Supplementary Information .

Of the 202 papers included, 89% were published in peer-reviewed journals and 11% were published in the grey literature. Eighty-seven studies used mixed methods, 82 used quantitative methods and 33 studies used qualitative methods.

Evidence of adoption of climate-resilient crops

Of the 29 evaluated potential social and economic factors related to adoption, interventions related to the availability, effectiveness and access to agricultural extension services were the most prominent determinants of the adoption of climate-resilient crops in low- and middle-income countries. Nearly 50% of the studies identified extension services and awareness outreach as important factors for the effective adoption of climate-resilient crops in low- and middle-income countries (Fig. 1 ). The individual figures per characteristic are presented in detailed summary graphs in Extended Data Figs. 1 – 5 . The determinants are plotted in bar charts to provide additional context and visualization. The unit of analysis is per study, and a single study can report on multiple determinants.

The inner ring outlines the five broad categories to which the 29 social and economic factors are mapped. The outer ring shows the factors within each broad category that were most frequently mentioned across the included studies. The relative area occupied by categories indicates their relevance. Charts with the full data and frequencies for each category are presented in the Supplementary Information . For illustrative purposes, factors mentioned in less than 20% of studies as determinants of adoption were excluded from this figure.

The principal factors determining adoption of climate-resilient crops or crop varieties were largely consistent across the three regions with robust numbers of publications: sub-Saharan Africa, South Asia and East Asia. The most important determinants across these regions were, in order of importance: (1) access to extension services or information about options, (2) education level of head of household, (3) access to needed farm inputs, (4) experience and skills of farmer, (5) social status, and (6) access to climate information (Fig. 2 ). Access to extension services and information about options, and education level of head of household were among the top five determinants for adoption for all three regions. Access to farm inputs was the first and second most important determinants for adoption in South Asia and sub-Saharan Africa, respectively, but was only sixth most important for East Asia. Experience and skills of farmers were first and third most important determinants for adoption in East Asia and sub-Saharan Africa, respectively, and sixth most important in South Asia. Social status was highly important in South Asia and sub-Saharan Africa, but only moderately important for determining adoption of technologies in East Asia. Although there were few papers and thus limited information for Latin America and Middle East and North Africa regions, the education level of the head of household was cited as the most important determinant for adoption in both regions.

a – e , Individual determinants are ranked from highest to lowest number of studies in the regions: East Asia and Pacific ( a ), Latin America and the Caribbean ( b ), Middle East and North Africa ( c ), South Asia ( d ) and sub-Saharan Africa ( e ).

The climate-resilient crops are included in this scoping review on the basis of data found in the included papers (Fig. 3 ). We classified them as cereals (maize, rice, grain (general), wheat, millet, sorghum barley and teff), legumes (soybean, chickpeas, cowpea, common beans, mung beans and groundnut), vegetables and fruits (tomato, eggplant, pepper, cocoa, mango, clover, garlic, mustard, pea, onion, saffron, green grams and cola nut) and roots, tubers and bananas (banana, plantain, yam, sweet potato, cassava and potato). Thirty-three per cent of the studies did not report on a specific crop or variety in their research; of the studies that did report on a specific crop or variety, 67% reported on cereals only. Despite their importance for food security and nutrition, less than 1% of the studies reported on legumes only and 25% reported on a combination of cereals and legumes, roots, tubers, bananas, vegetables and fruits. We also assessed the 202 papers to determine the purpose of the crops as primarily for human consumption (44%), for human consumption and animal feed (26%) or not clearly stated (30%).

a – d , Countries are colour-coded from yellow to red based on number of relevant studies involving cereal ( a ), legumes ( b ) vegetables ( c ) and roots, tubers and bananas ( d ).

Climate-resilient crops and crop varieties were adopted to cope with abiotic stresses such as drought, heat, flooding, salinity and shorter growing season (early-maturing crops), as well as pests associated with changes in weather or climate patterns (disease and pest resistance) (Fig. 4 ). Climate-resilient crops and crop varieties were also adopted to address general challenges associated with climate change and crop system sustainability, such as to improve moisture retention in soil, improve soil quality, and reduce erosion (planting of cover crops and legumes and to reduce vulnerability to food insecurity). The most studied trait in the dataset was drought tolerance, followed by water-use efficiency and earlier maturity. Adoption of early-maturing crops enables farmers to cope with climate change-induced weather variability by allowing them to adjust planting dates when rains are delayed and reducing the chances of yield losses caused by drought or heat waves late in the growing season. Changing of planting dates was identified in 32% of the papers as a strategy to cope with climate change.

Studies are divided into the same geographical regions as in Fig. 2 .

In general, the evidence suggests that farmers do not adopt a new crop or crop variety without changing other practices. A total of 136 papers (67%) describe that farmers adopt climate-resilient crops in conjunction with other climate-resilient technologies such as climate-smart agriculture (CSA) schemes and conservation agriculture (CA). Other climate-resilient technologies included: planting of trees and shrubs, reduced or increased investment in livestock and modified planting dates and irrigation (Table 1 ).

Seed and adoption of climate-resilient crops

Seventy-three papers mentioned the topic of seed. The major themes associated with seed that emerged with direct evidence drawn from the papers are summarized in Table 2 . Access to and availability of seed were the most prevalent themes, with 60% of papers mentioning these as issues in the adoption of climate-resilient strategies. Social networks such as farmers’ organizations or co-operatives, as well as access to information, were also reported as facilitators of adoption. These themes refer to different social groups and ways in which farmers can exchange seed or get information about seed.

Social differences and adoption of climate-resilient crops

About 53% of studies reported that social differences (such as sex, education and age of household head) influence adoption of varieties or crops as mitigation strategies against the effects of climate change, whereas 30% of studies did not report any effect of social difference. Fifteen per cent of studies did not include data on social differences. Of the studies that identified social differences as influencing adoption of climate-resilient crops and crop varieties, education (22%), sex (28 %), age (24%) and family size (14%) emerged as the most important factors. Income (6%), access to information (5%), marital status (2%) and experience (2%) were also mentioned, but much less frequently. We examined the papers for sex disaggregation of data, in which sex of household heads was considered. Forty-five per cent of studies reported on the sex of respondents, with 39% reporting on both male and female household heads, 5% including men only, and only 1% of studies including only female respondents. Most of the studies explored social differences only superficially, by including variables in surveys, but few substantiated these findings with follow-up qualitative research to understand the social dynamics driving the observed adoption decisions.

The studies largely concur that socio-economic status of farmers plays a large part in their adoption of climate-resilient technologies. Thirty-one per cent of the studies highlighted the socio-economic status of farmers. Various studies indicated that a nuanced understanding of the socio-economic status of farmers is vital for the targeting of climate-resilient crop technology interventions and their adoption and sustainability in practice. Thirteen studies reported a positive effect of farmer income on adoption. Farmers with access to finance, such as risk transfers (for example, insurance or remittances) and credit (for example, bank loans or community loans), were more likely to adopt climate-resilient crop technologies. Farmers who reported constrained credit were less likely to grow modern crops and more likely to cultivate local varieties 9 . This is partly because the lack of cash or credit may prevent farmers from using purchased inputs 10 .

Evidence on the dis-adoption of climate-resilient crops

Dis-adoption of climate-resilient crops and crop varieties was discussed in 12 of the 202 papers included in our evidence synthesis. The major reasons for dis-adoption included technology not meeting expectations due to poor performance or quality of the technology or variety (8 papers), government policies (3 papers), technical constraints (2 papers), labour shortages (1 paper) or financial constraints (1 paper). Eight of the twelve studies indicated that dis-adoption was specifically due to the performance of a crop variety, and four of these eight studies indicated that the varieties’ performance under stress conditions did not meet farmers’ expectations 10 , 11 , 12 , 13 .

The primary goal of this scoping review was to identify factors in adoption of climate-resilient crops in climate-vulnerable countries. Insights into these factors may inform the design of interventions aimed at equipping farmers to adopt climate-resilient technologies before experiencing devastating impacts of climate change and encourage adoption best practices 14 , 15 .

We show that there is a predominance of cereals in reported studies on adoption of climate-resilient crops (67%). Only 1% of the studies report on legumes only; otherwise, they are considered only in combination with other crops. This may reflect the dominance of cereals in staple foods across the world and biases towards the study of such crops and in the development of improved climate-resilient crop varieties. However, this is a concerning trend given that some legumes, roots and tuber crops (for example, cassava, bambara groundnuts and beans) that are largely neglected in the studies have known climate resilience, are sources of high-quality nutrition and provide more well-established environmental benefits than cereals, such as soil enrichment.

About 50% of the studies included in this scoping review identified agricultural extension and awareness outreach as the most relevant factor for adoption of climate-resilient technologies in low- and middle-income countries. Agricultural extension links farmers with the latest research and engages in a translational practice to make complex information more accessible to farmers. It has been shown that farmers who have access to early-warning systems such as weather forecast systems can better cope and adapt to a changing climate 16 . Farmers plan better for farming activities, including choice of crop varieties to plant, after having had access to weather forecast information (for example, from a community-managed weather station). Emerging digital technologies provide an opportunity to use information and communications technology-enhanced extension and climate services that can provide timely information that farmers can use for decision making and to adapt their farming practices. These could also improve efficiencies of extension services while also reducing their cost. Poor funding for extension services in the developing world have limited farmers’ access to training and expert guidance on emerging technologies 17 . Partnerships with other emerging players in information exchange, such as telecommunications companies and non-governmental organizations, will be key.

Farmers generally tend to be risk averse, which leads to limited investment and adoption of improved agricultural production technology 18 . Experienced farmers use precautionary strategies to protect against the possibility of catastrophic loss in the event of a climatic shock and thus optimize management for average or likely conditions, but not for unfavourable conditions. These ex ante, precautionary strategies include selection of crops and cultivars and improved production technology 18 .

In general, there is widespread agreement that aside from the useful experience that farmers gain from the time they have spent in farming, their experience with climatic shocks is key to their adoption of climate-resilient technologies. Many studies showed that farming experience is influential in adoption and utilization, and previous experiences with environmental shocks such as drought can influence adoption of climate-resilient crops and crop varieties. The more experience farmers have with climatic shocks, the more likely they are to be receptive to the adoption of related climate-resilient technologies. For example, experience with drought shock in the agro-ecological zone of Brong Ahafo, Ghana, increased the probability of adoption of drought-tolerant varieties by 15%, and farmers reported that drought shock was the primary reason for adoption of drought-tolerant varieties 19 .

It has been widely acknowledged that education levels of farmers have a positive correlation with technology adoption, and our synthesis demonstrates that this is also relevant for the adoption of climate-resilient crops 16 , 20 , 21 , 22 . Highly educated heads of households are more likely to readily accept and access information about new technologies in a shorter period of time than less educated heads of households; education was measured as educational attainment and reported in 49% of the studies. A study based in Zimbabwe showed a 52% decrease in production of traditional sorghum varieties in favour of new varieties better suited to drier conditions for every additional year of schooling, and a 5% increase in growing new early-maturing varieties 23 .

Changing crop varieties is one of the most frequently cited climate-resiliency strategies for both men and women farmers, but women are more likely to adopt such strategies when they are aware of climate-adaptation options 24 . Other intersectional variables such as marital status, education and age, in combination with gender, influenced whether improved seed was grown by households 25 . A major shortcoming of the reviewed literature is that most studies included women only when they were household heads. Definitions of household headship are variable, and when women are only included as household heads, their views do not necessarily represent the views of women who live in male-headed households 26 . A large majority of women live in male-headed households, and their views are rendered invisible through this practice 27 . For example, young, poor women who were household heads were the least likely to adopt drought-tolerant maize in Uganda, whereas spouses of male household heads influenced adoption decisions on their husbands’ fields 9 . Only a few studies paid attention to intra-household dynamics, gender roles and relations, and how these shape adaptation decisions 9 , 28 . This limited attention on intra-household gender dynamics and decision making around climate-resilient seed adoption skews the conclusions and recommendations, as the literature does not equally represent the challenges and views of women.

Seed policies in many countries focus on strengthening formal, national seed systems that rely on variety-release mechanisms, seed certification policies and seed companies for distribution. These types of seed systems remain difficult to access for many farmers, and evidence from the papers in this scoping review suggests that strengthening local seed systems is essential. Local seed systems rely on social networks to ensure multiple options to access seed of a range of climate-resilient crops and varieties, including local landraces and improved seed. Thus, context specificity is important for seed systems, as it is for almost all factors influencing adoption of climate-resilient crops and varieties.

The determinants of adoption that we identified are, in many cases, context-specific and therefore implementation of specific interventions is most successful when they are tailored to their environment and the cropping system. Seemingly contradictory or opposing (positive and negative) effects of each determinant of adoption were commonly reported among—and sometimes within—studies. Sex, age, education, years of farming experience and indicators of socio-economic status or wealth (assets) all affected decisions to adopt climate-resilient technologies in context-specific and sometimes opposite ways, depending on interacting environmental, policy and household factors. For example, equal and sizable numbers of studies (13 each) identify positive and negative effects of age on adoption. Whereas some studies identified older farmers to be more reluctant to adopt new technologies, other studies found that the earned experience, broad social networks and accumulation of wealth associated with older farmers may explain a positive effect on adoption. Extension and access to information about climate-resilient technologies and weather might be exceptions to this trend, as these determinants seem to transcend context-specific implementation. The resulting conclusion is that there is no ‘one size fits all’ recommendation to ensure adoption of climate-resilient crops and crop varieties, and interventions are unlikely to uniformly benefit all climate-vulnerable farmers (Table 3 ). This is consistent with the large number of papers in this study that reported farmers adopting climate-resilient crops as part of broader climate-resilient strategies.

Climate resiliency at farm level is essential to achieve food security and improve livelihoods of rural communities, especially in countries and communities that depend on local agricultural production to ensure household income and achieve daily adequate caloric intake and balanced nutrition. Understanding the factors contributing to adoption and dis-adoption of climate-resilient crops provides opportunities to increase adoption and reduce the impact of climate change on rural communities in developing countries. The most important determinants of adoption of climate-resilient crops based on our analysis are the availability and effectiveness of extension services and outreach, followed by education levels of heads of households, farmers’ access to inputs, especially seeds and fertilizers, and socio-economic status of farming families. Building resilience to climate change requires a cropping-systems, and more often a farming-systems approach. The results from this scoping review show that the adoption of climate-resilient crops and varieties, in most cases, happens as part of whole-farm and climate-smart agriculture strategies to cope with changing climate. Farmers adopting multiple complementary strategies under climate-smart agriculture help to build highly resilient and sustainable agriculture systems that can respond to shocks associated with climate change and other agricultural challenges 29 , 30 , 31 . Single component intervention programmes or projects are therefore less likely to realize widespread adoption and improvement of resource-poor farmers’ resilience to climate change compared with more holistic, multifaceted approaches that take into consideration the physical, human and socio-economic circumstances of the targeted farmer or farming community. Specific policy recommendations are presented in Box 3 .

Box 3 Recommendations

Access and availability of climate-resilient crops seeds must be combined with relevant and timely advisory services, such as early-warning systems for weather.

Ensuring that farmers have multiple options to access seeds for a range of climate-resilient crops and varieties is essential. This can be achieved by empowering existing social networks, such as farmer organizations.

There is no single profile that applies to all farmers. Therefore, extension services will need to continue to evolve to be (1) participatory, (2) information and communications technology enhanced, and (3) partnerships based. This partnership should include various actors, such as women’s groups, universities, the private sector and non-governmental organizations in order to provide customized and appropriate information for diverse needs.

High-quality studies are needed on how members of households—and not just heads of households—make decisions about how to respond to climate change. This research will fill in the evidence gaps on gender and social differences and reasons for dis-adoption of climate-resilient crops and related technologies, and promote a more diverse group of climate-resilient crops that also provide food security and nutrition, such as legumes and root crops.

National policies need to support farmers’ access to other assets and services, such as education, land, finance services and diverse income-earning opportunities. Without these provisions, especially education, the adoption of climate-resilient crops and technologies will be limited.

A multiple-interventions approach is needed if countries want to promote adoption of climate-resilient crops. Farmers do not adopt climate-resilient crop or crop varieties without changing other practices, such as planting dates, water-conserving technologies, planting trees and shrubs, or increasing or decreasing livestock.

Farmers will not adopt climate-resilient crops solely on the basis of environmental-adaptation qualities. Development and breeding programmes must consider farmer and market trait preferences.

Mandating disaggregated data collection to identify strategies that are working and who they are working for in agricultural surveys and research will enable policy makers and donors to respond with more appropriate and informed interventions.

Unlike a typical narrative review, a scoping review strives to capture all the literature on a given topic and reduce authorial bias. Scoping reviews offer a unique opportunity to explore the evidence in agricultural fields to address questions relating to what is known about a topic, what can be synthesized from existing studies to develop policy or practice recommendations, and what aspects of a topic have yet to be addressed by researchers.

Evidence synthesis methodology and protocol pre-registration

This scoping review was prepared following guidelines from the PRISMA extension for scoping reviews (PRISMA-ScR) 32 . This framework comprises five steps: identifying the research question; identifying relevant studies; study selection; extracting and charting the data; and collating, summarizing, and reporting the results 33 . The protocol for this scoping review was registered on the Open Science Framework before study selection 8 . The full protocol is available in the Supplementary Information .

Research question

The guiding question for this scoping review was, ‘what are determinants that lead small-scale producers in low-and middle-income countries to adopt climate-resilient crops and crop varieties?’.

Information sources, search methods and citation management

An exhaustive search strategy was developed to identify all available research pertaining to facilitators that lead small-scale producers in low- and middle-income countries to adopt climate-resilient crop varieties. Search terms included variations of the key concepts in the research question: small-scale producers, germplasm and climate resilience. The search algorithms were formatted for compatibility with each database so that they may be reproduced in their entirety, and they can be accessed at https://osf.io/sfzcm/ . Searches were performed in the following electronic databases by K.G.K.: CAB Abstracts and Global Health (accessed via Web of Science), Web of Science Core Collection (accessed via Web of Science) and Scopus (accessed via Elsevier). A comprehensive search of grey literature sources was also conducted. Search results were de-duplicated to remove redundant citations identified from multiple sources. To facilitate acceleration of the screening process, machine-derived metadata were added to individual citations, for example, identifying populations, geographies, interventions and outcomes of interest. This enabled accelerated identification of potential articles for exclusion at the title- or abstract-screening stage.

Eligibility criteria and study selection

Studies were included for data extraction and analysis if (1) their focus included a population of small-scale food producers; (2) they were published between 1990 and the start of the search (1990 is when the IPCC first met and produced their first report on climate change); (3) they presented original research (qualitative and quantitative reports) and/or reviewed existing research, including grey literature; (4) they explicitly focused on or were clearly relevant to climate change resiliency or climate change adaptation; (5) they explicitly focused on crops, varieties, seed, planting materials or germplasm; (6) they mentioned factors for adoption; (7) they included target populations in countries classified as lower and middle-income by the World Bank. Studies that did not meet all of the aforementioned inclusion criteria were excluded.

Study selection was performed in two stages. In a first step, articles were uploaded to the systematic review software Covidence, and title and abstract screening was performed by all authors to exclude articles that did not meet all inclusion criteria. Each article was reviewed by two independent authors, and discrepancies were resolved by a third independent author. Full-text screening was then performed by M.A., K.C., S.M., N.Z., H.T., K.P., L.B. and K.I., and inclusion decisions were made by a single reviewer. Studies included in full-text screening were those that met all inclusion criteria or those whose eligibility could not be established during title and abstract screening. The PRIMSA flow diagram in the Supplementary Information presents the study selection process and indicates the number of articles excluded at each phase of screening.

Data extraction and analysis

A data-extraction template (available in the Supplementary Information ) was developed to document the data and study type and context of each citation and all themes of interest. The data extraction first collected data on the paper quality, study location, population socio-economic data of the population and crop and cropping system characteristics. Second, the data-extraction template was used to collect information about the determinants of adoption and associated socio-economic factors influencing the adoption or dis-adoption of the climate-resilient crops. In total, 29 factors and determinants were selected. Additional rater observations and comments were included to increase analysis depth. Finally, raters also recorded policy and programmatic information and recommendations mentioned in the papers to support the adoption of climate-resilient crops. The data-extraction template was tested by the review team before use and data were extracted by the authors. The extracted data were qualitatively summarized on the basis of emerging themes and with the aim of providing recommendations to donors and policy makers. An assessment of study quality is not typically carried out as part of a scoping review 7 , 34 .

Data availability

The data that support the findings of this study are available from the corresponding author upon request.

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Acknowledgements

We thank the Federal Ministry of Economic Cooperation of Germany (BMZ) and the Bill and Melinda Gates Foundation for the support to conduct this study under the Ceres2030: Sustainable Solutions to End Hunger programme.

Author information

These authors contributed equally: Kevin Pixley, Nkulumo Zinyengere.

Authors and Affiliations

Cornell University, Ithaca, NY, USA

Maricelis Acevedo, Hale Tufan, Kate Ghezzi-Kopel & Jaron Porciello

CIMMYT, Mexico City, Mexico

Kevin Pixley

World Bank, Washington, DC, USA

Nkulumo Zinyengere

University of Notre Dame, Notre Dame, IN, USA

USDA-ARS, East Lansing, MI, USA

Karen Cichy

International Institute for Sustainable Development, Winnipeg, Manitoba, Canada

Livia Bizikova

Michigan State University, East Lansing, MI, USA

Krista Isaacs

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M.A., K.C., S.M., N.Z., H.T., K.P., L.B., K.I. and J.P. provided expertise on content, extracted data and wrote the manuscript. K.G.-K. and J.P. provided systematic review methods and information retrieval.

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Extended data

Extended data fig. 1 access to advisory networks and knowledge about climate change..

Social determinants captured in this graph are a small-scale producers access to demonstration plots, access to weather and climate info, education of the head of household or respondent if not head of household, experience and skills of head of household or respondent, access to extension and outreach, access to social networks including co-operatives, and a knowledge and perceptions of crops and traits.

Extended Data Fig. 2 Crops fit for purpose.

Social determinants captured in this graph include farmer’s selection of a CR crop or variety based on environmental and agro-ecological conditions, cultural practices and preferences about CR crops and varieties, and selection based on knowledge about a crop traits.

Extended Data Fig. 3 Education, experience and household characteristics.

The social determinants captured in this graph include age of head of household or respondent, family size, gender, social and economic status of household, and diversification of household income.

Extended Data Fig. 4 Enabling environment.

The determinants captured in this graph include a farmer’s reported power and agency, access to institutions, and access to government programs.

Extended Data Fig. 5 Access to finance and technical resources (not advisory).

The determinants in this chart include access to energy and electricity, access to labour, access to water, distance to market for inputs and outputs, farm infrastructure, farm inputs (seeds and fertilizer), land (size and tenure), non-farm infrastructure, access to finance (transfers and credit).

Extended Data Fig. 6

Prisma Flow Diagram.

Supplementary information

Supplementary information.

List of included studies, scoping review protocol and data-extraction template.

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Acevedo, M., Pixley, K., Zinyengere, N. et al. A scoping review of adoption of climate-resilient crops by small-scale producers in low- and middle-income countries. Nat. Plants 6 , 1231–1241 (2020). https://doi.org/10.1038/s41477-020-00783-z

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Diverse approaches to crop diversification in agricultural research. A review

• Review Article
• Open access
• Published: 20 April 2020
• Volume 40 , article number  14 , ( 2020 )

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• Johannes Hufnagel 1 ,
• Moritz Reckling 1 , 2 &
• Frank Ewert 1 , 3  

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Agricultural intensification increased crop productivity but simplified production with lower diversity of cropping systems, higher genetic uniformity, and a higher uniformity of agricultural landscapes. Associated detrimental effects on the environment and biodiversity as well as the resilience and adaptability of cropping systems to climate change are of growing concern. Crop diversification may stabilize productivity of cropping systems and reduce negative environmental impacts and loss of biodiversity, but a shared understanding of crop diversification including approaches towards a more systematic research is lacking. Here, we review the use of ‘crop diversification’ measures in agricultural research. We (i) analyse changes in crop diversification studies over time; (ii) identify diversification practices based on empirical studies; (iii) differentiate their use by country, crop species and experimental setup and (iv) identify target parameters to assess the success of diversification. Our main findings are that (1) less than 5% of the selected studies on crop diversification refer to our search term ‘diversification’; (2) more than half of the studies focused on rice, corn or wheat; (3) 76% of the experiments were conducted in India, USA, Canada, Brazil or China; (4) almost any arable crop was tested on its suitability for diversification; (5) in 72% of the studies on crop diversification, at least one additional agronomic measure was tested and (6) only 45% of the studies analysed agronomic, economic and ecological target variables. Our findings show the high variability of approaches to crop diversification and the lack of a consistent theoretical concept. For better comparability and ability to generalise the results of the different primary studies, we suggest a novel conceptual framework. It consists of five elements, (i) definition of the problem of existing farming practices and the potential need for diversification, (ii) characterisation of the baseline system to be diversified, (iii) definition of the scale and target area, (iv) description of the experimental design and target variables and (v) definition of the expected impacts. Applying this framework will contribute to utilizing the benefits of crop diversification more efficiently.

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1. Introduction

2. Methodology

2.1 Search term strategy

2.2 analysed information.

3. Global analysis of crop diversification studies

3.1 Historical development and scope of the term ‘crop diversification’

3.2 Baselines of crop diversification

3.3 countries of crop diversification experiments, 3.4 types of crop diversification, 3.5 agronomic measures accompanying crop diversification, 3.6 target variables of the crop diversification experiments.

4. The lack of a concept of crop diversification

5. Methodological considerations

6. Conclusion

Acknowledgments

1 introduction.

Agriculture has developed towards intensive but simplified production systems over the last decades, especially in the northern Hemisphere. While this trend significantly increased agricultural productivity, it also had detrimental effects on the cropping systems themselves and on the environment (Tilman et al. 2002 ). A multitude of driving forces led to lower diversity of cropping systems like, e.g. easy availability of mineral fertilisers and pesticides, concentration of breeding efforts on the economically most important crops and changes in agricultural policies that allow producers to respond more freely to market signals, incentives and technology change (Fausti 2015 ). These processes supported a higher genetic uniformity within crop species (Kahiluoto et al. 2019 ), less crop species in rotations (Stein and Steinmann 2018 ; Barbieri et al. 2017 ) and higher uniformity within agricultural landscapes (Fig. 1 ) with large field sizes (Bianchi et al. 2006 ; Rusch et al. 2016 ). This development also caused environmental problems such as nitrate pollution of water, eutrophication of ecosystems, climate-relevant emissions of greenhouse gases (Bommarco et al. 2013 ; Therond et al. 2017 ; Bowles et al. 2018 ; Stoate et al. 2009 ) and an overall loss of habitats and biodiversity (Tscharntke et al. 2012 ; Kleijn et al. 2012 ; Buhk et al. 2017 ; Frison et al. 2011 ; Therond et al. 2017 ; Bommarco et al. 2013 ).

Aspect of a large field of winter rye in a simplified cropping system in Northern Brandenburg, Germany. Copyright Johannes Hufnagel

Simplification of farming systems and growing environmental problems led to concerns about the future functionality of today’s cropping systems with regard to resilience, adaptability to climate change, multifunctionality of agricultural landscapes, provisioning of ecosystem services and biodiversity (Lichtenberg et al. 2017 ; Rusch et al. 2016 ).

Crop diversification can be considered as an attempt to increase the diversity of crops through, e.g. crop rotation, multiple cropping or intercropping (Fig. 2 ), compared to specialized farming with the aim to improve the productivity, stability and delivery of ecosystem services (Kremen et al. 2012 ; Garbach et al. 2017 ; Wezel et al. 2014 ). It can be one measure to develop more sustainable production systems, develop value-chains for minor crops (Meynard et al. 2018 ) and contribute to socio-economic benefits (Feliciano 2019 ). Crop diversification practices can include higher crop diversity (Renard and Tilman 2019 ), more diverse crop rotations (Reckling et al. 2016 ), mixed cropping (Bedoussac et al. 2015 ; Malézieux et al. 2009 ), cultivation of grain legumes in otherwise cereal dominated systems (Watson et al. 2017 ), perennial leys or grassland (Haughey et al. 2018 ; Phelan et al. 2015 ; Weißhuhn et al. 2017 ) and regionally adapted varieties or variety mixtures (Yang et al. 2019 ; Vijaya et al. 2019 ). Crop diversification and/or additional diversification measures like variation of seeding time or changing cropping patterns have the potential to lead to higher and more stable yields, increase profitability and lead to greater resilience of agro-ecosystems in the long term (Rosa-Schleich et al. 2019 ; Meynard et al. 2018 ; Liu et al. 2019 ; Raseduzzaman and Jensen 2017 ; Renard and Tilman 2019 ; Urruty et al. 2016 ). These practices have the potential to make cropping systems more divers in space, time and genetics. Consequences of diversification are temporal shifts and ranges of phenological stages (relevant for biodiversity and adaptation to climate change), more frequent or continuous soil cover and more diverse management strategies, i.e. ‘tillage’, ‘sowing dates’, ‘fertilization’, ‘irrigation’, ‘harvesting’ and also reducing labour peaks and economic risk.

Intercropping maize with climbing beans diversifies current crop rotations in Northern Germany. Here, maize serves as a pole for the red-flowering scarlet runner bean ( Phaseolus coccineus L. cv Preisgewinner) before both crops are harvested for silage (Fischer et al. 2020 ). Copyright: Jenny Fischer/Thünen Institute of Organic Farming

Davis et al. ( 2012 ) showed that diverse cropping systems provided similar or even higher yields than simplified systems whilst environmental impacts were lower. Renard and Tilman ( 2019 ) found that arable crop species diversity at national level is correlated with greater year-to-year stability of the total national harvest of all edible crops. Nevertheless, measures of diversification are rarely implemented because of lack of required investments in machinery, infrastructures and expertise and research evidence (Meynard et al. 2018 ; Roesch-McNally et al. 2018 ; Ponisio and Ehrlich 2016 ; Geels 2011 ).

A closer look on ‘diversification’ reveals that the term lacks a clear definition and from this reason, it is used in very different meanings. Some authors only use the term to describe diversification by crops, e.g. mixed cropping; others restrict it to diversification by management strategies, e.g. varying seeding time. Some use it for a combination of cropping and management approaches. The same applies for the scale analysed: Investigations are done from on field, farm and landscape level.

The very complex diversification approach of ‘diversified farming systems’ as described, e.g. by Kremen et al. ( 2012 ) and Rosa-Schleich et al. ( 2019 ), rely on diversification concepts that apply individual steps of crop diversification, e.g. cover crops, and diversification by management strategies, e.g. reduced tillage at the field level, production systems at the farm level (e.g. ‘organic farming’, ‘conservation agriculture’) and selected measures at the landscape level (e.g. ‘structural elements’). In the diversified farming approach, it is not obvious which diversification measures are chosen under what conditions. The choice of the combination of measures seems to rely on diversity concepts and depends on, inter alia, which ecosystem services (ES) are in focus.

As diversification is a relatively new as a concept, many authors may not use the term diversification at all although their main focus is on diversification. An extensive meta-study at global scale analysed the effects of crop diversification on numerous parameters (Beillouin et al. 2019a ), and many of the articles evaluated do not use the term diversification. Although the term has recently been shown more frequently in agronomic studies (Hatt et al. 2018 ; Haro et al. 2018 ; Kumar et al. 2017 ; Hondrade et al. 2017 ), many publications still mention only the tested diversification measure, e.g. intercropping.

In many different contexts, there is no clear separation between the concepts of diversification and ‘diversity’. Although research on crop diversity has increased, it mainly refers to natural and semi-natural systems. In most cases, ecologists analysed the simultaneous occurrence of system diversity with biodiversity (Cardinale et al. 2007 ; Gross et al. 2014 ). As a consequence, authors suggest to apply (agro) ecological principles of diversity to agricultural systems to make these more resilient (Wezel et al. 2014 ; Landis 2017 ; Altieri et al. 2015 ; Barot et al. 2017 ; Therond et al. 2017 ; Isbell et al. 2017 ). In many cases, the concept of diversity is seen as equal to the concept of diversification. From an agronomic point of view, that is not the case: while the former deals with biological principles such as genetic diversity, the latter deals with agronomic principles such as crop rotation or mixed cropping that subsequently might lead to higher biodiversity and associated ecosystem services. Diversification is the process that leads to the state of diversity. Depending on the initial situation, the same measure of crop diversification might lead to completely different states of biodiversity or ecosystem services. Although diversification is claimed to be a fundamental solution for many problems of today’s agricultural systems (Renard and Tilman 2019 ), sufficient quantitative evidence is lacking from long-term studies (Reckling et al. 2019 ).

In this review, we focus on crop diversification and define it as ‘a process that makes a simplified cropping systems more divers in time and space by adding additional crops’. Crop diversification can lead to greater genetic and/or structural diversity in time and/or space. Common examples for crop diversification are crop rotations, double cropping or intercropping, bee crops, nurse crops or variety mixtures. Diversification by agronomic measures, e.g. tillage, shall not be considered unless it is tested in combination with crop diversification. Our analysis was restricted to crop diversification at the field level. In contrast to many studies, we have taken an agronomic perspective on crop diversification as a basis for this review.

This review aims to elucidate the current use of crop diversification in research and support a common approach to utilize its full potential. We argue that a common understanding of the diversification concept in the context of crop production is needed for enabling the comparison of results and to enhance the empirical evidence of the effects of diversification as a measure to make cropping systems more resilient and to reduce negative impacts on the environment. Generally spoken, our main questions were: Is there a common understanding of crop diversification as a concept within the scientific community of agronomist regarding topic, scope and ‘successful’ application? And do we agree on the methods to test crop diversification in field experiments in order to achieve scientifically sound and transferable results? The objectives of this paper were to (i) review the use of crop ‘diversification measures’ in agricultural research; (ii) describe changes in using the term diversification over the last 40 years; (iii) identify the most common temporal and spatial practices of crop diversification like crop rotation or intercropping based on empirical studies; (iv) differentiate their use by country, crop species and experimental setup and (v) identify target parameters that were analysed.

2 Methodology

Since we did not find a classification system of crop diversification, we defined a list of crop diversification measures that consider the most important steps of crop diversification. The search terms used were based on different references (Connor et al. 2011 ; Wezel et al. 2014 ; Malézieux et al. 2009 ; Hole et al. 2005 ) and focused exclusively on crop diversification (e.g. expansion of crop rotation, implementation of flower strips) at the field scale. The search terms were not exhaustive and overlaps between categories were unavoidable.

The material for the review was selected by searching the Scopus database ( www.scopus.com ). The relevant search terms were applied to ‘article title’, ‘abstract’ and ‘keywords’. The search was restricted to Source type ‘journals’; to Document types ‘article’, ‘review’ and ‘articles in press’ and to Language ‘English’. The decisive search was done the 18th of June 2018 and included all references available in the Scopus database to this date.

The selection of the literature analysed followed a three-step procedure: (i) searching for publications tagged with different target terms for ‘measures of crop diversification’ using specific terms for each measure and related terms differentiated by temporal and spatial crop diversification (Table 1 ), (ii) filtering the publications from step 1 that were tagged with diversification or related search terms (Table 2 ) and (iii) selecting the publications from the remaining sample that documented results from field experiments in arable farming. If the main focus of the experiment was on arable farming publications of adjacent fields like ‘field vegetables’, ‘pastures’ or ‘alley cropping’ were selected too.

The search terms we used for selecting publications on crop diversification (Table 1 ) are the iterative outcome of more than 30 provisional searches done with the objective to explore and understand the topic area and find the most suitable search terms.

The search for measures of crop diversification resulted in 43,680 hits (step 1), 19,305 for ‘temporal’ and 24,375 for ‘spatial crop diversification’. Selecting those publications that were tagged with diversification (step 2) led to 680 hits, thereof 16 were totally out of focus, 417 treated the topic with a non-experimental view such as meta-analysis, reviews, models, farmer surveys or reported about diversification in adjacent subject areas like aquaculture, pure agroforestry, fruits or forests. The remaining 247 publications reported about field experiments in arable farming. Some of them reported about two or three different measures of crop diversification thus been selected twice or three times by the selection procedure described. For this reason, in the end, the review is based on 193 primary studies.

The subsequent analysis of the selected literature was performed manually extracting information from article titles, keywords and abstracts available in Scopus. When information was lacking or too vague, ‘material and methods’ of the full article was consulted.

Based on the extracted information, the following questions were to be answered:

1) How did the number of articles about ‘crop diversification’ develop over time, are there differences between temporal and spatial diversification?

(2) How did experiments on crop diversification develop over time?

(3) What was the experimental baseline (‘control’) against which crop diversification was compared to?

(4) Where (which countries) were experiments on crop diversification executed and what were the main baselines in these countries?

(5) What measures of crop diversification were analysed experimentally?

(6) Was crop diversification combined with additional agronomic measures and if so, by which?

(7) Which target variables were analysed to evaluate the impact of crop diversification?

3 Global analysis of crop diversification studies

3.1 historical development and scope of the term crop diversification.

The number of publications with the focus on crop diversification that use the term diversification increased slowly from far below 10 per year in the 1980s to about 25 in the 2010s and tripled to almost 100 in 2017 (Fig.  3 ). The share of publications on temporal vs. spatial diversification was similar over the years with an average of 47% and 53%, respectively. Only in years with very few publications (e.g. 1985, 1995), the share varied significantly between 0 and 100% (Fig. 3 ). The number of experiments on diversification developed more or less parallel to the number of studies on crop diversification in general. There were only 8 years without any studies reporting experiments that tested measures of diversification and referring to the concept of diversification, between 1981 and 1995 (Fig. 3 ). The share of publications reporting about experiments in years with 10 and more publications varies between 9 and 69% with an average of 44%. Over the whole period, on average, 51% of the experiments focussed on temporal and 49% on spatial diversification. The absolute number of 193 primary studies was surprisingly low compared to the high number of publications selected by our search terms on measures of crop diversification (43,680 hits) and the fact that diversification seems to be a very popular concept (Meynard et al. 2018 ; Rosa-Schleich et al. 2019 ; Beillouin et al. 2019a ; Renard and Tilman 2019 ). Beillouin et al. ( 2019a ) found almost 20-fold more primary studies on crop diversification measures with a focus on meta-analysis and different search equations. Even though Beillouin et al. ( 2019a ) analysed additional strategies of diversification such as agroforestry and landscape heterogeneity in many articles, they extracted analysed rotations, intercropping, cover crops etc. without mentioning the concept of diversification explicitly.

Number of publications on temporal and spatial crop diversification per year between 1978 and 17th of June 2018 (total n  = 664) and number of publications that are based on experimental data ( n  = 247): black dots: based on experiments

In our analysis, we found that on average, only 1.6% of the publications on common measures of crop diversification we selected in step 1 were tagged with the term diversification with only small differences (0.4–5.1%) between the different categories of crop diversification (Fig.  4 ). Among the selected categories on crop diversification (Table 1 ), the most common measures were ‘crop rotation’ (12,693 in total and 240 associated with diversification), ‘intercropping’ (7659 and 141), ‘companion crops’ (6756 and 63), ‘mixed cropping’ (5531 and 106), ‘catch crops’ (4020 and 33), ‘bee plants’ (2803 and 11) and ‘double crops’ (2421 and 32). Less common were the measures ‘alley crops’ (717 and 7), ‘trap crops’ (615 and 9), ‘variety mixtures’ (294 and 15) and ‘relay crops’ (171 and 7). The small number of publications tagged with diversification could be an indication that the concept of diversification is still relatively new in the scientific agricultural community.

Number of publications based ( n  = 247) and not based ( n  = 417) on experiments broken down by ‘measures of crop diversification’. Column of figures on the right: number of publications by search term × 1000 (total n  = 43.6 × 1000); in brackets: percentage of publications that are tagged with the term ‘diversification’

In sum, only 193 of the 664 selected publications refer to experiments. The proportion of experiments varies considerably between the different crop diversification strategies and is usually well below 50% (Fig. 4 ).

Here, we define ‘baseline’ as the current cropping practice for a given region that is to be diversified in order to improve the performance of an existing system. In most cases, the baseline is part of an experiment and usually regarded as control treatment. In most publications, the baseline of an experiment is explicitly mentioned (control), but in some cases, we had to deduce the baseline by checking further information provided by an article. In many cases, baseline is a simplification of a complex cropping system. Based on our analysis, we identified three simplified types of baselines (Table 3 ) which comprise approximately the same proportion of publications: pure stands of single crops ( n  = 59), continuous cropping of a single crop ( n  = 58) and simple crop rotations with 2 or maximally 3 crops ( n  = 76).

Pure stands of arable crops ( n  = 35) and field vegetables ( n  = 24) account for the largest types of baselines (Fig.  5 ). Publications on continuous cropping of a single crop are mainly restricted to wheat, corn or rice while publications on continuous cropping of crops like cotton, soybean or millet play a minor role (Fig. 5 ). Rotations with two crops are widely represented by rice–wheat ( n  = 34) or corn–soybean or wheat ( n  = 21) while ‘wheat and a second crop’ is tested less frequently ( n  = 6). The group of ‘other simple crop rotations’ ( n  = 15) is very heterogeneous with various sequences of two to three crops. In experiments with pure stands as baseline, the starting point for experiments is on genetic homogeneity of one field in a single year. In these experiments, mostly, the focus is on spatial diversification and not on crop rotation. The main crops tested in pure stands are arable crops like pulses including soy ( n  = 19), corn ( n  = 12) and field vegetables like cabbages ( n  = 15) in particular broccoli ( n  = 9) (Table 4 ). The results show that the starting point for crop diversification experiments is globally restricted to very few crops. In more than 54% of the primary studies, the main focus is on rice, corn or wheat, which, although economically very important, only represent part of the manifold global cropping situations.

Number of publications on crop diversification experiments broken down by ‘baselines’ (total n  = 193)

Most publications ( n  = 144) on crop diversification experiments were found in Asia ( n  = 81) and North America ( n  = 63) (Table 5 ), followed by Europe ( n  = 20), South America ( n  = 18) and Africa ( n  = 11). Countries with most studies are India ( n  = 61), the USA ( n  = 47), Canada ( n  = 16), Brazil ( n  = 13) and China ( n  = 10). Each of the remaining 25 countries alone plays a minor role—at least as far as the number of publications is concerned ( n  = 46, all remaining countries together).

According to the analysed literature, experiments with pure stands of arable crops as baselines were mainly carried out in USA, Brazil, India, Finland and China, while those with pure stands of field vegetables were found mainly in the USA, followed by Australia, China and Brazil. Experiments on continuous wheat concentrate in the USA and Canada; very few were carried out in Kazakhstan, China and Australia. In India, 71% of the experiments were dedicated to diversify continuous rice and rice–wheat rotations while crop rotations with corn and soybean or wheat were mainly tested in the USA, some in India, Argentina and China. Most of the diversification experiments on ‘simple crop rotations’ were located in Europe and Canada. It seems that the number and kind of baselines that were to be diversified in experiments reflects very much the simplified cropping situation that is widespread in the respective country or region. It was a surprising result of the review that a relevant number of experiments on crop diversification were conducted only in a few countries and thus agroecological situations. This fact limits the ability to generalise the results of the primary studies.

The vast majority of analysed experiments (90%) were diversified through introducing a ‘new’ crop into the baseline cropping system: either by temporal diversification ( n  = 102)—expanding continuous cropping of a single crop or a simple crop rotation—or by spatial diversification ( n  = 71) of a pure stand on a single field through, e.g. intercropping, mixed cropping or companion cropping. The groups of crops used for diversification include the whole range of crop plants like cereals, pulses, fodder legumes, grasses, field vegetables and flowers or a combination of 2 or 3 groups of the latter (Fig.  6 ).

Number of publications on crop diversification experiments broken down by baselines and groups of crops used for diversification (total n  = 193)

Crop diversification by non-legumes was widespread in experiments of pure stands of field vegetables and arable crops and was still relevant both in continuous corn and wheat and in simple crop rotations (Fig. 6 ). Both, legumes and non-legumes, were tested to diversify baselines—either alone or both; diversification by pulses and/or fodder legumes alone plays a minor role in crop diversification. The introduction of both non-legumes and pulses is a central diversification step in rice–wheat rotations, in continuous wheat, continuous rice and continuous corn, in simple crop rotations and in pure stands of arable crop. The introduction of both non-legumes and fodder legumes is tested in corn–soybean or wheat rotations, rice–wheat and pure stands of field vegetables, while the introduction of pulses, fodder legumes and non-legumes is widespread in rice–wheat rotations and is of certain importance in continuous corn and continuous wheat and in simple crop rotations (Fig. 6 ).

Crop diversification by flowers is mainly applied in experiments of field vegetables in pure stands and only sometimes in pure stands of arable crops.

Diversification that was not explicitly based on the introduction of a new crop occurred only in 10% of the experiments, almost exclusively in pure stands of arable crops, some in other simple crop rotations. In these cases, the diversification measures comprise two approaches: replacement of the genetically homogeneous baseline crop by variety mixtures of this crop or mixtures of pure stands of widespread baseline crops of a region on the same field.

In the publications analysed, we found the following groups of agronomic measures (Table 6 ) that were tested additionally to crop diversification or—in some cases—exclusively.

In 22% of the experiments, the introduction of new crops or variety mixtures (Fig.  7a ) was not accompanied by diversifying agronomic measures (Fig. 7a ). In 71% of the experiments, crop diversification went along with at least one additional agronomic measure like variation of cropping patterns; seeding or harvesting time; weed, pest or fertilizer treatment; soil tillage; irrigation or integration fodder production or animals into arable farming (Fig. 7b ). In 58% of these, experiments were tested one, in 33% two and in 9% three diversifying agronomic measures.

Number of crops and variety mixtures tested without additional measures ( a , n  = 43) or in combination with at least one additional measure ( b , n  = 136) broken down by baselines and groups of measures ( n  = 179). Many publications ( n  = 136) refer to experiments with at least one accompanying measure to crop diversification. Thus, the number of cases ( n  = 245) shown in the figure exceeds the number of publications. Experiments with measures ‘others than crop diversification’ are not presented in Fig. 7 ( n  = 14)

The introduction of only a new crop was most important in rice–wheat, corn–soybean or wheat and continuous wheat and continuous rice, variety mixtures only as single diversification measure were tested in pure stands of arable crops, as additional measure in combination with others in continuous rice and in rice–wheat experiments.

In all baselines, the variation of growing patterns was an agronomic measure to obtain spatial diversification within a field, more importantly in pure stands of arable crops and field vegetables, and to a lower extent in continuous corn and rice. Variation of cropping patterns was implemented by intercropping, e.g. pulses, fodder legumes or vegetables or by establishing spots or borders with flowering plants or herbs (Fig. 7b ). Especially in experiments with corn–soybean or wheat and to a lesser extent in experiments with continuous wheat, continuous corn and with pure stands of vegetables, different levels of inputs were tested. The variation of tillage systems was an important issue in continuous wheat, in other simple crop rotations and in rice–wheat. Irrigation was tested in some experiments of rice–wheat, in continuous rice and wheat–millet, cotton etc., but in total irrigation played a minor role as additional measure of diversification. The testing of green manure was an important measure in experiments with rice–wheat, other simple crop rotations, corn–soybean or wheat, continuous corn and in pure stands of vegetables. Only in rice–wheat rotations the introduction of fodder production for animals was an additional and important measure of diversification.

In many publications, it was hard to know if the term diversification is restricted to the introduction of a new crop or if additional agronomic measures are also regarded as part of the diversification approach. Some articles used the term diversification exclusively for the introduction of a new crop (crop diversification); in others, the term diversification also was applied to diversification by additional agronomic measures (‘diversification by measure’).

In fact, in 7% of the experiments, diversification was obtained by only introducing new agronomic measures. This diversification approach was chosen especially for pure stands of arable crops and to a small extent for other simple crop rotations. Especially one diversification measure without crop diversification was tested: the variation of growing patterns, where a new spacing of ‘old’ crops was subject to analysis. Other measures like variation of tillage or cultivation period, irrigation or input management played a minor role in experiments restricted to diversification by agronomic measures.

It was one goal of our review to compile target variables that were used in the analysed primary studies to assess the impact of crop diversification, whereas we did not quantify the impact itself. We found the following groups of target variables listed in Table 7 .

About 10% of the experiments concentrated only on agronomic and or economic target variables, only half of them raising both. Forty-five per cent analysed mainly biotic and abiotic target variables without integrating agronomic or economic aspects (Fig.  8 ). The remaining 45% of the experiments analysed the impact of crop diversification measures both on agronomic and/or economic target variables and on abiotic and/or biotic variables describing the impact on the production site, e.g. soil and/or the environment, e.g. ground water or food webs (Fig.  9 ). There was no obvious preference for certain variables as a function of the different baselines—with two exceptions: first, experiments in pure stands of both field vegetables and arable crops focussed very much on food webs (mostly insects), in arable crops additionally on pests, diseases and weeds (Fig. 8 ); and second, a small share of experiments analysed two or more groups of target variables beside agronomic and economic parameters or even tried to characterize the ‘whole system’ (Fig.  9 ). This applies both to continuous corn and corn–soybean or wheat baselines and to experiments with ‘continuous rice’ or rice–wheat rotations (Fig. 9 ); the first ones are mostly located in North America and the second ones in India.

Number of publications on crop diversification experiments analysing only non-agronomic/non-economic groups of target variables broken down by baselines and groups of target parameters

Number of publications on crop diversification experiments analysing both agronomic/economic and non-agronomic/economic groups of target variables broken down by ‘baselines’ and groups of target parameters

In any other cases, experiments only focussed on one group of target variables while neglecting others (Figs.  8 and 9 ). It is difficult to get an idea about the reasons why which parameters in which experiment have been selected. We suppose that the selection of the respective target variables depends very much on the professional focus of the experimenters and the common agreement of a particular scientific school.

4 The lack of a concept of crop diversification

Though we found thousands of scientific papers on crop diversification like crop rotation or intercropping in the field of agronomy (Table 1 ), only a fraction of these publications relate to diversification as a concept. Despite our global assessment on the use of crop diversification in the literature, we did not find a theoretical and overarching concept of crop diversification. Hence, the implementation of diversification experiments is not concise concerning the problems to be solved, the baseline situation to allow comparisons, the kind and number of crop diversification measures applied and the target variables analysed.

In many of the analysed publications, authors did not explain explicitly under which circumstances and prerequisites which measures of crop diversification would be most efficient to solve a given problem (problem definition). Our analysis also showed that most articles do not describe explicitly the current farming practice of specialized or non-diversified farming (baseline definition). This information is relevant to allow comparisons with the novel diversified systems. Only a few studies have been repeated at more than one site or even in different agroecological zones which limits the applicability (definition of scale). The design of the experiments is often insufficiently explained to understand why certain measures are tested and why not others (experimental design). Not all of the studies have a clear definition of the target parameters to be analysed (define impact), and only 50% of them raised both agronomic/economic and ecological parameters; it is necessary to evaluate crop diversification both from an agronomic and ecological point of view and to compare it to the baseline. In most cases, the implementation of experiments seems very much driven by practical problems in agriculture of a given country or region We suspect that in these cases, the tested diversification steps were selected by local experts to answer applied problems. In other cases studied, diversification steps are selected by researchers who have set up the experiments for a pressing research question. Hence, such experiments are highly context-specific and based on a broad base of regional experience. They surely may help to solve specific local or regional problems, but it is difficult to compare the different studies and generalise from the results of these studies on diversification. This would be necessary to contribute efficiently to the development of scientifically based and more importantly transferable approaches to crop diversification. In addition, generalisation also is made difficult by the fact that 76% of the experiments were executed in five countries and 56% in only two (USA and India). Furthermore, most of the experiments within a country are restricted to one agroecological zone.

From the range of problems to be addressed by crop diversification studies, we can identify three types of perspectives that motivated the respective studies:

The first one is based on an explicit theoretical concept: e.g. diversification is useful to improve biological pest control (Hooks and Johnson 2001 ; Haro et al. 2018 ). This perspective applies for most of the experiments that analyse the possibilities to influence and understand interactions in food webs by crop diversification (‘agroecological perspective’). The second one tries to find alternative or additional agricultural products (Kachroo et al. 2014 ; Jacob et al. 2016 ) that might rise and stabilize farmer’s income (e.g. many of the diversification experiments in India—rice–wheat) (‘agro-economic perspective’). The third perspective is driven by the fact that current cropping practices go along with stagnating yields, deterioration of soils, increase of environmental problems, rise of pests, diseases or weed problems following an ‘agronomic-ecological’ perspective (Liebman and Davis 2000 ; Hati et al. 2013 ; Sharma et al. 2017 ). Perspective 1 mostly focusses on furthering the understanding of agroecological principles; most of these studies are made in diversified pure stands and do not consider the effect of preliminary crops. The focus of perspectives 2 and 3 is mostly on stabilizing income, developing new cropping methods and/or to reduce environmental problems.

A well-defined concept of crop diversification is a prerequisite to make results among studies comparable and to avoid arbitrary use of the term diversification. Likewise, Beillouin et al. ( 2019b ) state that ‘most of the meta-analyses studied cannot be considered fully transparent and reproducible’. A defined concept should clarify what is understood by diversification, what types of measures are regarded as diversification, which target parameters are useful to assess the impact of diversification and what the relevant scales of investigation are. The concept of crop diversification should be framed along five elements, following the limitations identified in the analysed literature:

Problem definition: Describe the reason for diversification and the diversification target

Baseline definition: Characterise the baseline system to be diversified.

Scale definition: Describe the target area of diversification: field, farm or landscape and expected interactions, define the system boundary.

Experimental design: Explain the decisions on diversification treatments, crop choice, mixtures, rotations etc. and the target variables. Ensure comparison with the baseline.

Define impact: Systematically compare the baseline with diversified systems in absolute and relative terms for defined impact variables to evaluate the effects of the diversification measures. To do that, a minimum set of agronomic, economic and ecological target variables is necessary.

This framework can be a starting point for a guideline which supports experimentalists to answer the main question on diversification. Some studies such as Plaza-Bonilla et al. ( 2017 ) provide most of the aspects in our framework in more or less detail. They described the problem of current farming in southwestern France, as the high environmental degradation due to the uncoupling of carbon and N cycles in specialized cropping systems (problem definition). Current farming is represented by a cereal-sunflower rotation without legumes (baseline definition); the analysis is conducted at the rotational level (scale definition) and the experiment explores the diversification effect of grain legumes with and without cover crops (experimental design). To describe the system and its impact sufficiently, both agronomic, e.g. yield, grain protein concentration and ecological variables, e.g. soil water, mineral N-content (Plaza-Bonilla et al. 2018 ) were quantified and compared with the baseline system (define impact).

5 Methodological considerations

In contrast to many other studies, we have taken an agronomic perspective on crop diversification as a basis for this review. Our focus was on diversification and not on diversity. That means our scientific question differed considerably to that in diversity studies, e.g. Haro et al. ( 2018 ), Buhk et al. ( 2017 ) and Wezel et al. ( 2014 ). Diversity studies analyse diversity of cropping or natural systems concerning flora and fauna and ask for the main characteristics of these systems. That means most studies on diversity compare different levels of diversity as a result of diversification. They do not analyse the initial situation, the necessary steps and the importance of time to achieve the level of diversity they found. Implicitly, they assume that it is sufficient to establish cropping systems that show the found characteristics of diversity to be sustainable, environmentally friendly or biodiversity supporting though some authors emphasise that the performance of diversification practices is highly context-specific (Rosa-Schleich et al. 2019 ; Kremen and Miles 2012 ).

We are well aware that our review shows some important limits; some of them can be explained by the topic itself: since there is no consensus on what crop diversification comprises, it was not possible to compile a complete list of adequate search terms. Hence, we may not have found some measures of crop diversification that have been addressed in other analysis, e.g. Beillouin et al. ( 2019a ). Furthermore, we excluded arbitrarily some diversification measures like ‘agroforestry’ or ‘intergraded crop-livestock systems’. Also, because our analysis is based mainly on information in title, abstract and keywords, considering information of the whole articles might have led to other results at least with regard to quantity. Furthermore, the low percentage of found publications on the topic suggests that probably many agronomic experiments are carried out with ‘diversification in mind’ without labelling them with diversification, e.g. Reckling et al. ( 2016 ) and Stein-Bachinger et al. ( 2015 ). It is therefore not surprising that other review studies on crop diversification found more experiments, e.g. the almost 20-fold higher number of primary studies in the meta-analysis by Beillouin et al. ( 2019a ). And last but not least, our review is restricted to crop diversification at field level.

6 Conclusion

Our analysis reveals that so far, there is no theoretically well-founded concept of crop diversification. The current use of the term diversification depends very much on the country, regional current problems caused by agriculture, the focus of the scientific discipline, the particular scientific school and local expert knowledge, and it is restricted to relatively few baselines and agroecological situations.

If crop diversification is to be developed as a tool for improving cropping systems, developing novel value-chains and providing other socio-economic benefits, it is necessary to develop a shared conceptual understanding. Without such concept, the numerous results of the different scientific communities on the topic (diversification) will use different terms for the same thing or same terms for different things (e.g. diversification, diversity, crop rotation, mixed cropping). This will prevent synergetic effects and generalisation of results.

We suggest first steps towards a conceptual framework on crop diversification expletively distinguishing and providing information on (i) problem definition, (ii) baseline definition, (iii) scale definition, (iv) characterisation of the experimental design including a minimum set of target variables and (v) defining the impact systematically to assess and report the effects of the diversification measures.

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Hufnagel, J., Reckling, M. & Ewert, F. Diverse approaches to crop diversification in agricultural research. A review. Agron. Sustain. Dev. 40 , 14 (2020). https://doi.org/10.1007/s13593-020-00617-4

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