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 (N2) fixation and soil-derived nitrogen acquisition using a meta-analysis of 29 field-scale studies. We estimated and compared effects of different intercrop compositions (proportion of each species in the intercrops), fertilization rates, crop species, soil properties, and other management practices on the symbiotic N2 fixation and the acquisition of soil-derived nitrogen by the cereals and grain legumes. The proportion of N derived from N2 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 N2 fixed (kg ha−1) by about 15 %, when N2 fixation in inter- and sole cropped legumes was expressed at equivalent density by compensating for the sown legume proportion in intercrops relative to their sole crop sowing rate. The results were mainly influenced by the intercrop composition, legumes species and the method used to quantify N2 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 N2 fixation by grain legumes 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.
Approximately 65% of anthropogenic emissions of N2O, a potent greenhouse gas (GHG), originate from soils at a global scale, and particularly after N fertilisation of the main crops in Europe. Thanks ...to their capacity to fix atmospheric N2 through biological fixation, legumes can reduce N fertilizer use, and possibly N2O emissions. Nevertheless, the decomposition of crop organic matter during the crop cycle and residue decomposition, and possibly the N fixation process itself, could lead to N2O emissions. The objective of this study was to quantify N2O emissions from a dry pea crop (Pisum sativum, harvested at maturity) and from the subsequent crops in comparison with N2O emissions from wheat and oilseed rape crops, fertilized or not, in various rotations. A field experiment was conducted over 4 consecutive years to compare the emissions during the pea crop, in comparison with those during the wheat (fertilized or not) or oilseed rape crops, and after the pea crop, in comparison with other preceding crops. N2O fluxes were measured using static chambers. In spite of low N2O fluxes, mainly due to the site's soil characteristics, fluxes during the crop were significantly lower for pea and unfertilized wheat than for fertilized wheat and oilseed rape. The effect of the preceding crop was not significant, while soil mineral N at harvest was higher after the pea crop. These results should be confirmed over a wider range of soil types. Nevertheless, they demonstrate the absence of N2O emissions linked to the symbiotic N fixation process, and allow us to estimate the decrease in N2O emissions by 20–25% through including one pea crop in a three-year rotation. On a larger scale, this reduction of GHG emissions at field level has to be added to the decrease due to the reduced production and transport of the N fertilizer not applied to the pea crop.
•Intercropping legumes with oilseed rape modified the dynamic of nitrogen uptake in the cash crop.•At the end of flowering, the N surplus in rape, derived from legumes, reached 20 to 40kgNha−1 for ...some legume species.•The use of 15N-labelled fertiliser made it possible to quantify the nitrogen derived from legumes in the rape crop.•The presence of legumes in autumn resulted both in higher N mineralisation and in improved fertiliser-N recovery.
The use of legume cover crops as green manure is often seen as an effective means of supplying nitrogen to the following crop. As winter oilseed rape requires a large amount of N in the spring, the introduction of frost-sensitive legume living mulch (killed off during the winter) is a promising way of decreasing mineral N fertiliser inputs. The aim of this study was to assess the supply of biological N to rape during the spring from several frost-sensitive legumes, grown as intercropped living mulches.
We carried out a field trial over two growing seasons before sowing, comparing seven legume species and three legume mixtures intercropped with rape, and two levels of soil mineral N. The presence of legumes, living during the autumn and dead during the spring, resulted in 20–40kgNha−1 more nitrogen uptake in oilseed rape, by the end of flowering, compared to rape grown as a sole crop. Moreover, the use of 15N-labelled nitrogen fertiliser showed that this increase in rape N accumulation was due to the mineralisation of legume residues, but also to other mechanisms such as increase in fertiliser-N recovery and in soil organic matter mineralisation.
There is an increasing need for diagnostic tools that can assess the crop nitrogen (N) nutrition status during the growth cycle. In addition to the leaf chlorophyll (Chl) content, we proposed here ...the use of the leaf content of polyphenolics (Phen) as a potential indicator of crop N status. Because of their absorption features in the visible and in the UV part of the spectrum, both Chl and Phen can be measured by rapid and non-destructive optical methods. Therefore, we used two leaf-clip devices, the Minolta SPAD-502 for Chl, and the Dualex for Phen. The latter is a prototype (patent pending) that measures the UV absorbance of the leaf epidermis, which is related to the leaf Phen content. Dynamics of Phen and Chl were measured on the last fully developed leaves of two winter wheat cultivars subjected to different levels of N availability, from tillering to flowering, in 2001, 2002 and 2003. Both Phen and Chl contents were found to increase along the leaf, starting from the ligula, regardless of the stage of development. Both variables were highly correlated with the N concentration of leaves. The average Chl content of the leaf increased, and the average Phen content decreased, with the increased application of N to the field, irrespective of the growth stage, the cultivar and the year of experiment. Therefore, both Phen and Chl can be considered as probes of the crop N nutrition status. Still, the relationship between Chl and the nitrogen nutrition index (NNI), used as a reference indicator of N deficiency, was influenced by the growth stage, whereas the year of experiment affected the relationship between Phen and the NNI. We also propose the use of the simple Chl/Phen ratio as an indicator of leaf N content at the canopy level, for future application in precision agriculture. This ratio would alleviate, at least partially, the problem of gradients along leaves, and would even accentuate the differences among levels of crop N deficiencies because of the Chl and Phen inverse dependence on the crop N nutrition status.
•Intercropping legume living mulch with winter oilseed rape helps weed control.•Seven legume species and three mixtures undersown in winter oilseed rape were compared.•The most efficient legume ...species decreases weed abundance up to 75% before winter.•Legume/WOSR biomass ratio is a good indicator of the potential efficacy of weed control.•Soil nitrogen availability is a key factor explaining the competition between species.
Living mulches are generally seen as a possible way to decrease the reliance on pesticides. We investigated the effect of a frost-sensitive legume living mulch on weed control during the autumn and cash crop performance, in winter oilseed rape crops. A field trial was carried out over two years, comparing seven legume species—fenugreek, spring faba bean, grass pea, lentil, field pea, berseem clover and spring common vetch—and three legume mixtures, as living mulches, in crops with two levels of soil mineral nitrogen content before sowing. The presence of the legume living mulch decreased weed abundance before winter. Field pea, berseem clover, common vetch and the common vetch/faba bean/berseem clover mixture were particularly effective, regardless of the growing conditions, decreasing weed abundance by 20–75% with respect to that in the crop grown alone, in the absence of herbicide application. Weed abundance before winter was negatively correlated with total intercrop biomass, and this relationship was dependent on the legume species considered and soil mineral nitrogen content. As with other legume intercrops, the level of soil mineral nitrogen had a strong influence on intercrop structure, modifying the proportion of legume biomass produced. The legume/oilseed rape biomass ratio was also found to be a useful indicator in all growing conditions: the higher the ratio, the more efficient the weed control. However, a high ratio was associated with a higher risk of competition with the cash crop. The choice of the most appropriate legume living mulch is therefore a compromise between the anticipated ecosystem services and the potential disservices provided by the legume mulch. The introduction of a legume living mulch did not entirely prevent weed growth, but was clearly a relevant agroecological solution for decreasing herbicide, while increasing the sustainability and diversity of weed-control strategies in cropping systems.
In wheat (Triticum aestivum L.), nitrogen remobilization from the vegetative organs of the crop to the grains has been shown to depend on environmental factors and genotype. We performed, for a set ...of 10 winter wheat genotypes, field experiments at six sites over a 2-yr period. By measuring nitrogen uptake at flowering (NUF from 32-284 kg ha(-1)), the amount of remobilized nitrogen (REMN from 24-228 kg ha(-1)) and nitrogen remobilization efficiency (NRE from 0.44-0.92) we were able to determine the effect of genotype and environment on the relationship between REMN and NUF. Environment and genotype had significant effects on nitrogen remobilization and nitrogen remobilization efficiency, which mainly depended on treatment (nitrogen and fungicide) and site. For environments without limiting factor during the grain-filling period, we found that REMN was not dependent on the genotype and could be estimated by a single two-parameter linear relationship (REMN = 4.13 + NUF x 0.76, r2 = 0.97). We analyzed the effect of drought stress before and after flowering, high temperature during these periods, nitrogen availability and disease pressure on REMN by comparing observed and estimated REMN. The effect of the environment on the relationship between nitrogen uptake at flowering and nitrogen remobilization depended on nitrogen uptake during grain-filling period and disease pressure and was also affected by genotype. Disease-resistant genotypes seemed to be able to keep remobilization efficiency stable in conditions of strong disease pressure, whereas nitrogen remobilization efficiency decreased strongly in susceptible genotypes under the same conditions.
Although there is increasing awareness of the importance of food legumes in human, animal and soil health, adoption of improved production technologies for food legume crops is not proceeding at the ...same pace as for cereal crops. Over the previous decade, the only food legumes to have shown significant production increases have been chickpea, lentil and faba bean in North America, chickpea in Australia, and faba bean in Europe. In smallholder farming in developing countries, production trends have mostly been static or have declined over the past decade despite the existence of technology that should permit higher and more stable yields. Ability to reverse negative trends is jeopardized by climate change as food legumes are mostly grown rainfed and are being exposed to increasingly variable and extreme weather. This review examines recent innovations in cultivation technology for the major food legumes—chickpea, lentil, dry pea, faba bean, lupin, common bean, mung bean, black gram, cowpea, and pigeonpea—and explores constraints to their adoption, particularly by resource-poor smallholder farmers. Conservation agriculture, involving minimum soil disturbance, maximum soil cover, and diverse rotations, has contributed to sustainable cropping system production in large-scale commercial farming systems in the Americas, Europe, Australia, and Turkey. Temperate food legumes have been incorporated into such systems. Adoption of conservation agriculture is only just beginning for smallholder farming in Asia and Africa, catalyzed by the development of low-cost implements suitable for minimum tillage. Water use efficiency improves with conservation agriculture as it allows for earlier planting, reduced soil evaporation, better weed management, and increased access to nutrients. Ecosystem-based approaches to plant nutrition are evolving which place more reliance on accessing organic and mineral reservoirs than in replenishing the immediately available pool with chemical fertilizers, leading to enhanced nutrient use efficiency of cropping systems. Ecosystem-based approaches are also being applied to management of weeds, diseases, and insect pests of food legumes, again with decreased reliance on synthetic chemicals. In achieving sustainable agricultural production systems, there is increasing realization of the need to move towards the tenets of organic agriculture, as exemplified in conservation agriculture and ecosystem-based approaches to plant nutrition and pest management. This does not necessarily imply a desire to qualify for organic product certification but more a realization of the need for sustainable agriculture. The movement towards conservation and organic agriculture encourages greater inclusion of food legumes, and legumes generally, in cropping systems. Unfortunately, however, technology transfer to resource-poor farming situations, where most food legumes are produced, remains a major bottleneck to meeting global demand. More participatory approaches to technology development, testing, and dissemination are required than hitherto practiced. It is suggested that this process could be enhanced by better focusing on major constraints within the value addition chain for food legumes.
•We developed a Decision-support systems (DSS) for integrated weed management systems.•Farmers and crop advisors took part via online surveys, group meetings and workshops.•The DSS goal, application ...field and structure was defined with future users.•They proposed two DSS, based on meta-decision rules or detailed farming practices.•Biophysical knowledges were fed to the DSS from an existing mechanistic model.
Farmers and farm advisors need a decision support system (DSS) to develop multiperformant weed management strategies adapted to economic, social and environmental stakes and farmers' constraints. We worked with future users, farmers, and crop advisors to define the uses and type of DSS they needed, via an online survey, group meetings and workshops. The feedback from future users helped to define the structure of the DSS with two complementary DSS needed: (1) a synthetic tool working with meta-decision rules to help with a complete overhaul of a cropping system, and (2) a precise and detailed tool for fine tuning cropping systems. Here, we present how we interacted with future users to transform an existing research model into a DSS by (1) defining its goal, application field and structure, (2) entering into the DSS knowledge on biophysical processes comprised in the mechanistic weed dynamics model FlorSys. We selected a more appropriate vocabulary for describing agricultural practices and formats with future users. Based on their feedback, a large range of weed impact indicators was included in the DSS so that farmers can choose the most pertinent for their objectives. Based on workshops with farmers, a decision tree format with numerical values of weed impact indicators was chosen to demonstrate the impacts of multiple cultural practices combinations. The DSS also includes an online calculator predicting weed (dis)services from meta-decision rules which was tested by crop advisors. Responses of the DSS were sometimes not expected by users, but were still considered interesting highlighting the need of agronomical support while using the tool.
In a context of economic and environmental concerns in agriculture, legumes appear to be suitable alternative crops to diversify current cropping systems and reduce their dependence on synthetic ...nitrogen (N) fertiliser and protein from imported soya bean. However, legume-based cropping systems may increase N losses through nitrate leaching if the N available from legumes does not coincide with subsequent crop requirements. To help agricultural advisers manage N in these systems, we adapted the decision-support system Syst’N®, designed to assess N losses in cropping systems, to simulate three annual and one perennial legume crops: pea, faba bean, soya bean and lucerne. To this end, we adapted and simplified existing submodels of legume functioning to include them in Syst’N, to keep the latter simple. We adapted the submodels “BNF” (i.e. biological N fixation) from the STICS model and “dormancy” from the CropSyst model. We also added the ability to enter the flowering date to improve predictions (improvement in N fixation’s rRMSE from 57% to 41% and EF from 0.57 to 0.77). The equations and associated parameter set developed for the four legume crops yielded satisfying predictions of crop biomass (rMBE = 9%, EF = 0.82, rRMSE = 39%) and N content (rMBE = 5%, EF = 0.76, rRMSE = 37%). These performances support the philosophy of Syst’N® that requires minimising the number of additional parameters for users when representing new crops or processes.
•The decision-support system Syst’N® was adapted to simulate diverse legume crops.•Submodels of legume functioning were adapted and simplified to keep Syst’N® simple.•The ability to enter the flowering date to improve predictions was added.•Predictions of soil water and N content were less accurate.
Grain-legume plants fix atmospheric nitrogen in the soil and thus do not need nitrogen fertilizers. Therefore, grain-legumes can potentially decrease global warming, as nitrogen fertilization is ...responsible for half of all agricultural greenhouse gas emissions. Moreover, grain-legumes have many functional and nutritional properties both as feed and food. Despite the fact that the European Union has granted considerable subsidies to promote grain-legume cultivation, their production continues to fall and there has been no satisfactory explanation as to why. This study provides an answer by showing that a situation of technological lock-in has resulted from the co-evolution of crop systems, based on an agrochemical paradigm, public policies, and market dynamics that promote cereals. This process began with the historical choice by European and French public institutions to relegate grain-legumes to feed in direct competition with imported soybeans. Moreover, interrelated factors, such as breeding selection, public subsidies, and food systems, have favored increasing returns to adoption for cereals to the detriment of grain-legumes. Finally, the evolutionary economics approach used here identified several actions that must be implemented together, such as agricultural cost-accounting methods, nitrogen management, institutional innovations, and market outlets to promote grain-legumes and move towards more sustainable agriculture.
•Socio-technical interactions between agriculture and economics have evolved into lock-in.•Increasing returns to adoption for cereals have contributed to specialized crop systems.•Greater diversity by using grain-legumes in crop systems is beneficial for the environment.•To increase the use of grain-legumes in agriculture, changes must be made throughout the entire agrifood system.•Combined changes in R&D, fertilization, and market outlets would promote grain-legume use.
PDF
