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Problem:Using high levels of nitrogen fertilizers in wheat crops can cause negative environmental impacts, such as nutrient leaching and contamination of local and ground water supplies or greenhouse gas emission. Additionally, nitrogen fertilizers are costly for farmers. However, nitrogen stress can cause problems with yield losses and lower quality grains. Solutions:A pre-crop is any crop grown before a succeeding crop within a rotation. Pre-crops can be selected to improve nitrogen nutrition and soil structure for the subsequent crop. Using appropriate pre-crops can reduce the need for water and nitrogen fertilizer inputs by fixing atmospheric N (in the case of legume pre-crops) and building soil organic matter for moisture retention and better soil structure.

ReMIX is a H2020 multi-actor project that will allow to redesign cropping systems based on the agroecological principle of crop diversification for the benefit of farmers and the whole EU agricultural community. ReMIX exploits the benefits of species mixtures to design more diversified and resilient agroecological arable cropping systems. Based on a multi-actor approach, ReMIX produces new knowledge that is both scientifically credible and socially valuable in conventional and organic agriculture. The project tackles practical questions and co-design ready-to-use practical solutions. The project spans from the specification of end-user needs and the co-design of in-field and on-farm experiments to demonstrations with evaluation of new varieties and practices. ReMIX contributes to the adoption of productive and resilient agricultural systems.

Diversification of cropping and farming systems is a central agroecological principle, which may improve resource use efficiency, reduce pests and diseases, diversify income sources, and enhance the resilience of the production. The main objective of this study was to identify challenges related to the sustainability of organic cropping systems that were diversified according to one or several of the following practices: diverse crop rotation, integration of cover crops, and intercropping. The sustainability assessments were made using a multi-criteria decision aid method (MCDA) and a framework based on the FAO Sustainability Assessment of Food and Agricultural Systems (SAFA) guidelines. Social, economic and environmental aspects were integrated in the sustainability assessments and combined with semi-structured interviews to identify and discuss farmer's perceptions of barriers to crop diversification and sustainability transition. The results showed that diversified organic cropping systems could achieve high overall sustainability, especially in the environmental dimension thanks to non-inputs of pesticides or mineral fertilizers and efficient use of resources. On the other hand, social and economic dimensions were more variable, with challenges of lower sustainability in profitability and management complexity for several of the diversified cropping systems. Limited access to knowledge, technology and markets for minor crops, and concerns about the consistency of policies were highlighted by farmers as barriers for crop diversification. We discuss how the identified challenges can be overcome and argue that fostering collaboration among stakeholders may increase investment capacity and improve access to new or alternative markets, thereby stimulating transitions toward more diversified and sustainable cropping systems.

Commercial legume varieties vary in terms of their drought tolerance when grown as sole crops, though relatively little is known about how legume variety selection affects cereal–legume intercrop performance under drought conditions. This study aims to test the hypothesis that positive rhizosphere interactions in faba bean–wheat intercrops will confer a “buffering capacity” on faba bean and wheat performance under water stress and that this effect will (i) depend on faba bean varietal selection and (ii) be enhanced with increasing faba bean varietal diversity. In a greenhouse experiment, three commercial faba bean (Vicia faba L.) varieties [Gloria (G), Alexia (A), Julia (J)] were grown in sole crop or intercropped with spring wheat (Triticum aestivum L.) under well-watered or water-stress conditions. Under intercropping, either one, two, or all three faba bean varieties were grown together with wheat to test the effect of intraspecific diversity on a cereal–legume intercrop performance. Consistent with the proposed hypothesis, we found that, under well-watered and water-stress conditions, wheat and faba bean shoot biomass production and nitrogen (N) acquisition improved with intercropping and that faba bean variety and variety mixture strongly modulated the intercropping effect. Interestingly, in both well-watered and water-stress conditions, wheat dry biomass and N accumulation were greatest in intercrops containing Gloria, while nodule number, nodule weight, and N accumulation in faba bean were greatest for intercrops containing Alexia and Julia (AJ). The effect of varietal diversity was inconsistent. Intercrops with two faba bean varieties tended to have positive or neutral effects on measured wheat and faba bean variables. However, overall performance under intercropping was generally reduced when all three faba bean varieties were planted with wheat. The effect of faba bean species diversity can buffer faba bean–wheat intercrop performance against water stress, and intercropping tended to have positive or neutral effects on the measured wheat and faba bean variables, notably with two-varietal faba bean mixtures.

Diversifying cropping systems by increasing the number of cash and cover crops in crop rotation plays an important role in improving resource use efficiency and in promoting synergy between ecosystem processes. The objective of this study was to understand how the combination of crop diversification practices influences the performance of arable crop sequences in terms of crop grain yield, crop and weed biomass, and nitrogen acquisition in a temperate climate. Two field experiments were carried out. The first was a 3-year crop sequence with cereal or grain legume as the first crops, with and without undersown forage legumes and forage legume-grass crops, followed by a cereal crop. The second experiment was a 2-year crop sequence with cereal or legume as the first crops, a legume cover crop, and a subsequent cereal crop. For the first time, crop diversification practices were combined to identify plant-plant interactions in spatial and temporal scales. The results partly confirm the positive effect of diversifying cereal-based cropping systems by including grain legumes and cover crops in the crop sequence. Legume cover crops had a positive effect on subsequent cereal grain yield in one of the experiments. Using faba beans as the first crop in the crop sequence had both a positive and no effect on crop biomass and N acquisition of the subsequent cereal. In cover crops composed of a forage legume-grass mixture, the grass biomass and N acquisition were consistently increased after the grain legume, compared to the cereal-preceding crop. However, differences in the proportion of legume to grass in mixture did not influence crop yield or N acquisition in the subsequent cereal. In conclusion, these results support that increased crop diversity across spatial and temporal scales can contribute to resource-efficient production and enhance the delivery of services, contributing to more sustainable cropping systems.

Cropping system diversification is a key factor in developing more sustainable cropping and food systems. The agroecological practice of intercropping, meaning the simultaneous cultivation of two or more species in the same field, has recently gained renewed interest as a means of ecological intensification in European agricultural research. We discuss some recent research developments regarding 1) intercropping for ecological intensification in agroecological and conventional cropping systems, 2) studies on nitrogen resource use by cereal-grain legume intercropping cultivation, 3) the role of intercropping in the management of biotic stressors, especially weeds, and 4) intercropping as a means of creating cropping systems that are more resilient to the abiotic and biotic stress associated with climate change. Finally, we propose methods for the greater adoption of intercropping in European agriculture by unlocking farming systems from upstream and downstream barriers, with the aim of developing more sustainable agricultural and food systems.

Grain legumes are known for their benefits to deliver ecosystem services on provisioning of protein-rich food and feed, reducing greenhouse gas emissions through the symbiotic nitrogen fixation function and diversification of cropping systems. Intercropping is an agroecological practice in which two or more crop species are grown simultaneously in the same field, thereby maximizing the use of resources to enhance yields in low input systems and the resilience of cropping systems. We quantified the effect of grain legume-cereal intercropping on the use of N resources in temperate agroecosystems, focusing on dinitrogen (N 2) fixation and soil-derived nitrogen acquisition using a meta-analysis of 29 field-scale studies. We estimated and compared effects of different in-tercrop compositions (proportion of each species in the intercrops), fertilization rates, crop species, soil properties , and other management practices on the symbiotic N 2 fixation and the acquisition of soil-derived nitrogen by the cereals and grain legumes. The proportion of N derived from N 2 fixation was on average 14 % (95 % CI = [11, 16]) higher in intercropped grain legumes (76 %) compared to legume sole crops (66 %). On the other hand, intercropping reduced the amount of N 2 fixed (kg ha −1) by about 15 %, when N 2 fixation in inter-and sole cropped legumes was expressed at equivalent density by compensating for the sown legume proportion in in-tercrops relative to their sole crop sowing rate. The results were mainly influenced by the intercrop composition, legumes species and the method used to quantify N 2 fixation. Soil-derived nitrogen acquisition in intercropped grain legumes was significantly reduced (−47 %, 95 % CI = [−56, −36]) compared to sole crop legumes, expressed at equivalent density, while the soil N acquired by intercropped cereals was much higher (+61 %, 95 % CI = [24, 108]) than in sole crop cereals. Total soil N acquisition (legume + cereal) was significantly higher in intercrops than in legume sole crops (+25 %, 95 % CI = [1, 54]), while there was no significant difference between intercrops and cereal sole crops. The meta-analysis confirms and highlights that intercropping consistently stimulates complementary N use between legumes and cereals by increasing N 2 fixation by grain le-gumes and increasing soil N acquisition in cereals. Based on the results of this analysis it would be suggested that cropping systems diversification via intercropping can be used for simultaneous production of both cereals and grain legumes, while increasing the use of N-sources and reducing external inputs of N fertilizers, thereby enhancing the sustainability of agriculture.

We use a meta-analysis approach to assess the effects of intercropping on the N use by grain legume and cereal plants in temperate agroecosystems.

In the face of climate change and to achieve global food security, the resilience of agricultural systems is gaining increasing attention, and is often considered as important as their productivity (Olesen et al., 2011). Temporal yield stability is one indicator of the economic resilience of cropping systems and its analyses have become more important as a decrease in yield stability has been observed for different crops at regional and global scale (Döring and Reckling, 2018). The temporal and spatial diversification of cropping systems with legumes, perennial crops, cover crops and intercrops can be expected to increase crop yield stability and offers an adaptation strategy to the increased climate variability (Liu et al., 2019). The objectives of this study were to assess the effect of cropping system diversification strategies on yield stability, through (i) integration of perennial leys with and without legumes, (ii) increasing proportion (length, i.e. number of years) of the perennial grass-clover leys relative to the entire crop rotation, (iii) varying the order in which crops are positioned in the rotation, (iv) integration of grain legumes and (v) integration of cover crops during fallow periods.

National audience; A better understanding of how plant growth, N nutrition and symbiotic nitrogen fixation (SNF) are influenced by soil inorganic N availability, for a wide range of legume species, is crucial to optimise legume productivity, N2 fixation, while limiting environmental risks such as N leaching. A comparative analysis was performed for ten legume crops, grown in a field experiment and supplied with four levels of N fertiliser. Dry matter, N concentration and SNF were measured. Parallely, root traits were studied in a greenhouse experiment. For most species, inorganic N inputs had little effect on plant growth and N nutrition. SNF was negatively affected by soil inorganic N available at sowing but with large differences among species. The response varied according to plant N requirements for growth and plant inorganic N uptake ability. Legumes root systems differed according to root exploration of the soil, root branching and their response to inorganic N inputs; these observations were in great accordance with observations of plant ability to uptake inorganic N measured in the field experiment. Combining SNF response to soil inorganic N, shoot N and plant ability to uptake inorganic N, allowed a robust evaluation of species differential response to soil inorganic N.

International audience; Crop diversification in space and time is a key component in the design of resource -efficient cropping systems with reduced dependency on synthetic inputs. A well - known example of crop diversification is the practice of intercropping, i.e. growing two or more crops together in the same field. Intercropping grain legumes and cereals in low-input systems makes use of complementary acquisition of light, water and nutrients to enhance the crop’s resource use efficiency and competitiveness against weeds. Within-species diversification in variety mixtures may also increase yield stability, via e.g. complementary tolerance to abiotic or biotic stress. As part of the European LEGATO project, our study has investigated whether a mixture of pea (Pisum sativum L.) varieties with two types of leaf morphology can increase the legume crop’s standing ability and competitiveness against weeds. The pea varieties Dukat (normal-leafed) and Partner (semi-leafless) were grown as single varieties and variety mixtures with and without a wheat intercrop in field experiments at four locations in Europe: Serbia (Novi Sad), Sweden (Alnarp) and France in central (close to Paris) and southern (Toulouse) regions. Lodging, weed biomass and crop/intercrop grain yields were recorded during two growing seasons per location. The results showed that a variety mixture of pea can combine the beneficial traits of the single varieties with maintained legume grain yield relative to the highest-yielding variety. However, the benefits in terms of weed reduction and standing ability were not as strong in variety mixtures as in pea-wheat intercrops, which remained the most efficient mixtures.

Linser har låg stjälkstyrka och svag konkurrensförmåga och blir därför lätt övervuxna av ogräs, speciellt i ekologisk produktion. Skörden försvåras också ofta på grund av liggsäd, det vill säga att plantorna lägger sig ner mot marken. Genom att samodla linser med spannmål, till exempel havre, uppnås effektivare konkurrens mot ogräs samtidigt som linserna får stöd, så att problemen med liggsäd undviks.

Soil is an heterogeneous and fluctuating environment. Water limitation in agronomic soils is often partial but lead locally to the suppression of symbiotic activity and therefore to reduction of N acquisition by the plant. A split-root system was developed in pea to evaluate the capacities of Pea-Rhizobium leguminosarum bv viciae (Rlv) symbiotic associations to compensate a local reduction of water availability. Root systems are split in two parts watered separately. Soil water content was monitored. Water limitation was exerted by stopping watering of a half root system. Arrest of nitrogen fixation is very rapidly observed in root directly exposed to water stress. This local and partial water limitation of the plant triggered a systemic signaling on well-watered roots of the same plant. The compensatory response occurs by increasing nodule biomass (and therefore nitrogen fixation capacities) of these roots not directly exposed to the water limitation. In preliminary experiments pea plants were inoculated with a reference Rlv strain. Response of and root and nodule development that compensate the local water limitation was confirmed. Interestingly, the compensatory response varies according to the Rlv strain as another Rlv strain, displaying similar nitrogen fixation efficiency in watered conditions, was not able to promote equivalent compensatory response. This experimental system has been used as a screen to select Rlv strains able to promote rapid compensatory responses to water stress.

National audience

Poster Session 3: L3.2 Climate - smart cropping systems; The FACCE-ERA-NET+ project Climate–CAFÉ: Climate change adaptability of cropping and farming systems for Europe. Climate-Smart Agriculture 2015

Despite the agronomical and environmental advantages of the cultivation of legumes, their production is limited by various environmental constraints such as water or nutrient limitation, frost or heat stress and soil salinity, which may be the result of pedoclimatic conditions, intensive use of agricultural lands, decline in soil fertility and environmental degradation. The development of more sustainable agroecosystems that are resilient to environmental constraints will therefore require better understanding of the key mechanisms underlying plant tolerance to abiotic constraints. This review provides highlights of legume tolerance to abiotic constraints with a focus on soil nutrient deficiencies, drought, and salinity. More specifically, recent advances in the physiological and molecular levels of the adaptation of grain and forage legumes to abiotic constraints are discussed. Such adaptation involves complex multigene controlled-traits which also involve multiple sub-traits that are likely regulated under the control of a number of candidate genes. This multi-genetic control of tolerance traits might also be multifunctional, with extended action in response to a number of abiotic constraints. Thus, concrete efforts are required to breed for multifunctional candidate genes in order to boost plant stability under various abiotic constraints.

Organic agriculture faces challenges to enhance food production per unit area and simultaneously reduce the environmental and climate impacts, e.g. nitrate leaching per unit area and greenhouse gas (GHG) emissions per unit mass produced. Eco-functional intensification is suggested as a means to reach these objectives. Eco-functional intensification involves activating more knowledge and refocusing the importance of ecosystem services in agriculture. Organic farmers manage agrobiodiversity by crop rotation (diversification in time). However, sole cropping (SC) of genetically identical plants in organic agriculture may limit resource use efficiency and yield per unit area. Intercropping (IC) of annual grain species, cultivar mixes, perennial grains, or forage species and forestry and annual crops (agroforestry) are examples of spatial crop diversification. Intercropping is based on eco-functional intensification and may enhance production by complementarity in resource use in time and space. Intercropping is based on the ecological principles of competition, facilitation and complementarity, which often increases the efficiency in acquisition and use of resources such as light, water and nutrients compared to sole crops, especially in low-input systems. Here we show that IC of cereals and grain legumes in European arable organic farming systems is an efficient tool for enhancing total grain yields compared to their respective sole crops. Simultaneously, we display how intercropping of cereals and legumes can be used as an efficient tool for weed management and to enhance product quality (i.e. cereal grain protein concentration). We discuss how intercropping contributes to efficient use of soil N sources and minimizes losses of N by nitrate leaching via Ecological Precision Farming. It is concluded that intercropping has a strong potential to increase yield and hereby reduce global climate impacts such as GHG kg-1 grain. Finally, we discuss likely barriers and lock-in effects for increased use of intercropping in organic farming and suggest a roadmap for innovation and implementation of IC strategies in organic agriculture.

International audience