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Legumes improve soil fertility through the symbiotic association with microorganisms, such as rhizobia, which fix the atmospheric nitrogen and make nitrogen available to the host and other crops by a process known as biological nitrogen fixation (BNF). Legumes included in the cropping system improve the fertility of the soil and the yield of crops. The advantages of legumes in the cropping system are explained in terms of direct nitrogen transfer, residual fixed nitrogen, nutrient availability and uptake, effect on soil properties, breaking of pests' cycles, and enhancement of other soil microbial activity. The best benefits from the legumes and BNF system can be utilized by integrating them into cropping systems. The most common practices to integrate legumes and their associated BNF into agricultural systems are crop rotation, simultaneous intercropping, improved fallows, green manuring, and alley cropping. However, the level of utilizing nitrogen fixation requires improvement of the systems, such as selecting appropriate legume genotypes, inoculation with effective rhizobia, and the use of appropriate agronomic practices and cropping systems. Therefore, using legumes at their maximum genetic potential, inoculation of legumes with compatible rhizobia, and using appropriate agronomic practices and cropping systems are very important for increasing food production. Importantly, the utilization of legumes as an integral component of agricultural practice in promoting agricultural productivity has gained more traction in meeting the demand of food production of the world populace. Priority should, thus, be given to value the process of BNF through more sustainable technologies and expansion of knowledge to the system.

The evolution of natural ecosystems is controled by a high level of biodiversity, In sharp contrast, intensive agricultural systems involve monocultures associated with high input of chemical fertilisers and pesticides. Intensive agricultural systems have clearly negative impacts on soil and water quality and on biodiversity conservation. Alternatively, cropping systems based on carefully designed species mixtures reveal many potential advantages under various conditions, both in temperate and tropical agriculture. This article reviews those potential advantages by addressing the reasons for mixing plant species; the concepts and tools required for understanding and designing cropping systems with mixed species; and the ways of simulating multispecies cropping systems with models. Multispecies systems are diverse and may include annual and perennial crops on a gradient of complexity from 2 to n species. A literature survey shows potential advantages such as (1) higher overall productivity, (2) better control of pests and diseases, (3) enhanced ecological services and (4) greater economic profitability. Agronomic and ecological conceptual frameworks are examined for a clearer understanding of cropping systems, including the concepts of competition and facilitation, above- and belowground interactions and the types of biological interactions between species that enable better pest management in the system. After a review of existing models, future directions in modelling plant mixtures are proposed. We conclude on the need to enhance agricultural research on these multispecies systems, combining both agronomic and ecological concepts and tools.

Aim: This study assessed whether growing cowpea can increase phosphorus (P) availability in the rhizosphere and improve the yield of legume-cereal systems. In alkaline Mediterranean soils with P deficiency, it is assumed that legumes increase inorganic P availability.Methods: A field experiment was conducted at the Staoueli experimental station, in Algiers province, Algeria, to compare the growth, grain yield, P availability, and P uptake by plants with sole-cropped cowpea (Vigna unguiculata L. cv. Moh Ouali) and maize (Zea mays L. cv. ILT), intercropped cowpea-maize, and fallow. Results: P availability in the rhizosphere was increased in both sole cropping and intercropping systems compared with fallow. It was highest in intercropping. The increase in P availability was associated with (i) significant pH changes of the rhizosphere of cowpea in sole cropping and intercropping systems, with the rhizosphere acidification significantly higher in intercropping (−0.73 units) than in sole cropping (−0.42 units); (ii) significant increase in the rhizosphere pH of intercropped maize (+0.49 units) compared to fallow; (iii) increased soil respiration (C-CO2 from microbial and root activity) in intercropping compared with sole cropping and fallow; and (iv) higher efficiency in utilization of the rhizobial symbiosis in intercropping than in sole-cropped cowpea. Conclusion With cowpea-maize intercropping, cowpea increased the P uptake, by increasing the P availability by rhizosphere pH changes in an alkaline soil. Overall, this study showed that intercropping cowpea improved the plant biomass and grain yield of maize in this soil.

Plant breeders are increasing yields and improving agronomic traits in several perennial grain crops, the first of which is now being incorporated into commercial food products. Integration strategies and management guidelines are needed to optimize production of these new crops, which differ substantially from both annual grain crops and perennial forages. To offset relatively low grain yields, perennial grain cropping systems should be multifunctional. Growing perennial grains for several years to regenerate soil health before rotating to annual crops and growing perennial grains on sloped land and ecologically sensitive areas to reduce soil erosion and nutrient losses are two strategies that can provide ecosystem services and support multifunctionality. Several perennial cereals can be used to produce both grain and forage, and these dual-purpose crops can be intercropped with legumes for additional benefits. Highly diverse perennial grain polycultures can further enhance ecosystem services, but increased management complexity might limit their adoption.

BACKGROUND AND SCOPE: Multi-cropping approaches in production systems, where more than one crop cultivar or species are grown simultaneously, are gaining increased attention and application. Benefits can include increased production, effective pest, disease and weed control, and improved soil health. The effects of such practices on the range of interactions within the plant-soil system are manifest via plant interspecific competition, pest and disease attenuation, soil community composition and structure, nutrient cycling, and soil structural dynamics. Interplant diversity and competition effectively increases the nature and extent of root networks, tending to lead to more efficient resource use in time and space. Increased competitive ability at a system level, and allelopathic interactions, can reduce weed, pest and disease severity. Soil biotic communities are affected by plant diversity, which can increase abundance, diversity and activity of functional groups. Attendant rhizosphere-located processes can facilitate nutrient uptake between component crops. Whilst there are few studies into multi-cropping effects on soil structure, it is hypothesised that such processes are manifest particularly via the role which the belowground biota play in soil structural dynamics. A deeper understanding of eco-physiological processes affecting weed, pest and disease dynamics in the context of multiple cropping scenarios, and breeding cultivars to optimise mutualistic and allelopathic traits of crop mixtures could significantly increase productivity and adoption of more sustainable farming practices. CONCLUSIONS: Wider consideration needs to be given to plant: soil interactions when crop plants are grown in the context of mixtures, i.e. as communities as opposed to monotonous populations. In particular, a better understanding is required of how root systems develop in the context of mixtures and the extent to which resultant interactions with the soil biota are context-dependent. A significant challenge is that crop cultivars or production systems optimised for monocultural circumstances should not be assumed to be most suited for multi-cropping scenarios, and hence alternative strategies for developing new production systems need to take this into account.

Food security has become a global issue, seriously threatening developing countries owing to fast-growing human populations and declining availability of land for agriculture. Increasing crop yields could be achieved by intensive systems, but these usually need higher energy and emit more carbon (C). Here, we studied crop productivity, energy yields, and C emissions of intercropping versus sole cropping. We tested maize–wheat, maize–rape, maize–pea, and soybean–wheat intercropping, and sole crops as controls in field experiments at Wuwei experimental station in from 2009 to 2011 in a randomized block design with three replicates. We used an evaluation index integrating yield and environmental factors. Results showed a yield increase of 27 % for maize–wheat, 41 % for maize–rape, and 42 % for maize–pea versus sole crops. Water use efficiency increased by 25 % for maize–wheat intercropping over sole wheat, 152 % for maize–rape over sole rape, and 95 % for maize–pea over sole pea. The three maize–crop intercrops produced 68, 308, and 256 % more energy yield than did the sole wheat, sole rape, and sole pea crops, respectively. They emitted 42, 52, and 45 % less C per unit of water in 2009, 2010, and 2011, respectively, compared with the sole maize crop. The maize-based intercropping received a the highest evaluation index (0.82 out of 1.0) among the systems evaluated, clearly showing that the maize-based intercropping is the most effective and sustainable cropping system for arid irrigation areas.

The forecasted 9.1 billion population in 2050 will require an increase in food production for an additional two billion people. There is thus an active debate on new farming practices that could produce more food in a sustainable way. Here, we list agroecological cropping practices in temperate areas. We classify practices according to efficiency, substitution, and redesign. We analyse their advantages and drawbacks with emphasis on diversification. We evaluate the potential use of the practices for future agriculture. Our major findings are: (1) we distinguish 15 categories of agroecological practices (7 practices involve increasing efficiency or substitution, and 8 practices need a redesign often based on diversification). (2) The following agroecological practices are so far poorly integrated in actual agriculture: biofertilisers; natural pesticides; crop choice and rotations; intercropping and relay intercropping; agroforestry with timber, fruit, or nut trees; allelopathic plants; direct seeding into living cover crops or mulch; and integration of semi-natural landscape elements at field and farm or their management at landscape scale. These agroecological practices have only a moderate potential to be broadly implemented in the next decade. (3) By contrast, the following practices are already well integrated: organic fertilisation, split fertilisation, reduced tillage, drip irrigation, biological pest control, and cultivar choice.

The impact of modern agriculture on natural resources has become a major global concern. Population growth and expanding demand for agricultural products constantly increase the pressure on land and water resources. A major point of concern for many intensively managed agricultural systems with high external inputs is the low resource-use efficiency, especially for nitrogen. A high input combined with a low efficiency ultimately results in environmental problems such as soil degradation, eutrophication, pollution of groundwater, and emission of ammonia and greenhouse gases. Evidently, there is a need for a transition of current agricultural systems into highly resource-use efficient systems that are profitable, but at the same time ecologically safe and socially acceptable. Here, opportunities to improve nitrogenuse efficiency in cropping and farming systems are analyzed and discussed. In the past and present, increased productivity of the major plant production systems has been derived from genetic improvement, and from greater use of external inputs such as energy, fertilizers, pesticides and irrigation water. Aiming at improving resource-use efficiencies, in high-input systems the focus should be on more yield with less fertilizer N. In low-input systems additional use of N fertilizer may be required to increase yield level and yield stability. Developing production systems that meet the goals of sustainable agriculture requires research on different scales, from single crops to diverse cropping and farming systems. It is concluded that N supply should match N demand in time and space, not only for single crops but for a crop rotation as an integrated system, in order to achieve a higher agronomic N-use efficiency. A combination of quantitative systems research, development of best practices and legislation will be needed to develop more environmentally-friendly agricultural systems. The growing complexity of managing N in sustainable agricultural systems calls for problem-oriented, interdisciplinary research.

Background and aims It is so far a gap in knowledge to assess nitrate (NO₃⁻) leaching loss linking with crop yield for a given cereal cropping system. Methods We conducted a meta-analysis on 32 published studies reporting both NO₃⁻ leaching losses and crop yields in the maize (N=20) and wheat (N=12) systems. Results On average, 22 % and 15 % of applied fertilizer N to wheat and maize systems worldwide are leached in the form of NO₃⁻, respectively. The average area-scaled NO₃⁻ leaching loss for maize (57.4 kg N ha⁻¹) was approx. two times higher than for wheat (29.0 N ha⁻¹). While, if scaled to crop yields, the average yield-scaled NO₃⁻ losses were comparable between maize (5.40 N ha⁻¹) and wheat (5.41 N ha⁻¹) systems. Across all sites, the lowest yield-scaled NO₃⁻ leaching losses were observed at slightly suboptimal fertilization rates, corresponding to 90 % and 96 % of maximum maize or wheat yields, respectively. Conclusions Our findings suggest that small adjustments of agricultural N management practices can effectively reduce yield-scaled NO₃⁻ leaching losses. However, further targeted field experiments are still needed to identify at regional scale best agricultural management practices for reducing yield-scaled NO₃⁻ leaching losses in maize and wheat systems.

Background and aims Recent studies have shown that tree-based intercropping (TBI) systems support a more diverse soil microbial community compared to conventional agricultural systems. However, it is unclear whether differences in soil microbial diversity between these two agricultural systems have a functional effect on crop growth. Methods In this study, we used a series of greenhouse experiments to test whether crops respond differently to the total soil microbial community (Experiment 1) and to arbuscular mycorrhizal (AM) fungal communities alone (Experiment 2) from conventionally monocropped (CM) and TBI systems. Results The crops had a similar growth response to the total soil microbial communities from both cropping systems. However, when compared to sterilized controls, barley (Hordeum vulgare) and canola (Brassica napus) exhibited a negative growth response to the total soil microbial communities, while soybean (Glycine max) was unaffected. During the AM fungal establishment phase of the second experiment, 'nurse' plants had a strong positive growth response to AM fungal inoculation, and significantly higher biomass when inoculated with AM fungi from the CM system compared to the TBI system. Soybean was the only crop species to exhibit a significant positive growth response to AM fungal inoculation. Similar to the total soil microbial communities, AM fungi from the two cropping systems did not differ in their effect on crop growth. Conclusion Overall, AM fungi from both cropping systems had a positive effect on the growth of plants that formed a functional symbiosis. However, the results from these experiments suggest that negative effects of non-AM fungal microbes are stronger than the beneficial effects of AM fungi from these cropping systems.