Moritz Reckling

Trade-Offs between Economic and Environmental Impacts of Introducing Legumes into Cropping Systems.

Europes agriculture is highly specialized, dependent on external inputs and responsible for negative environmental impacts. Legume crops are grown on less than 2% of the arable land and more than 70% of the demand for protein feed supplement is imported from overseas. The integration of legumes into cropping systems has the potential to contribute to the transition to a more resource-efficient agriculture and reduce the current protein deficit. Legume crops influence the production of other crops in the rotation making it difficult to evaluate the overall agronomic effects of legumes in cropping systems. A novel assessment framework was developed and applied in five case study regions across Europe with the objective of evaluating trade-offs between economic and environmental effects of integrating legumes into cropping systems. Legumes resulted in positive and negative impacts when integrated into various cropping systems across the case studies. On average, cropping systems with legumes reduced nitrous oxide emissions by 18 and 33% and N fertilizer use by 24 and 38% in arable and forage systems, respectively, compared to systems without legumes. Nitrate leaching was similar with and without legumes in arable systems and reduced by 22% in forage systems. However, grain legumes reduced gross margins in 3 of 5 regions. Forage legumes increased gross margins in 3 of 3 regions. Among the cropping systems with legumes, systems could be identified that had both relatively high economic returns and positive environmental impacts. Thus, increasing the cultivation of legumes could lead to economic competitive cropping systems and positive environmental impacts, but achieving this aim requires the development of novel management strategies informed by the involvement of advisors and farmers.

A Comparative Nitrogen Balance and Productivity Analysis of Legume and Non-legume Supported Cropping Systems: The Potential Role of Biological Nitrogen Fixation.

The potential of biological nitrogen fixation (BNF) to provide sufficient N for production has encouraged re-appraisal of cropping systems that deploy legumes. It has been argued that legume-derived N can maintain productivity as an alternative to the application of mineral fertilizer, although few studies have systematically evaluated the effect of optimizing the balance between legumes and non N-fixing crops to optimize production. In addition, the shortage, or even absence in some regions, of measurements of BNF in crops and forages severely limits the ability to design and evaluate new legume–based agroecosystems. To provide an indication of the magnitude of BNF in European agriculture, a soil-surface N-balance approach was applied to historical data from 8 experimental cropping systems that compared legume and non-legume crop types (e.g., grains, forages and intercrops) across pedoclimatic regions of Europe. Mean BNF for different legume types ranged from 32 to 115 kg ha−1 annually. Output in terms of total biomass (grain, forage, etc.) was 30% greater in non-legumes, which used N to produce dry matter more efficiently than legumes, whereas output of N was greater from legumes. When examined over the crop sequence, the contribution of BNF to the N-balance increased to reach a maximum when the legume fraction was around 0.5 (legume crops were present in half the years). BNF was lower when the legume fraction increased to 0.6–0.8, not because of any feature of the legume, but because the cropping systems in this range were dominated by mixtures of legume and non-legume forages to which inorganic N as fertilizer was normally applied. Forage (e.g., grass and clover), as opposed to grain crops in this range maintained high outputs of biomass and N. In conclusion, BNF through grain and forage legumes has the potential to generate major benefit in terms of reducing or dispensing with the need for mineral N without loss of total output.

Poor farmers - poor yields: socio-economic, soil fertility and crop management indicators affecting climbing bean productivity in northern Rwanda

Climbing bean is the key staple legume crop in the highlands of East and Central Africa. We assessed the impact of interactions between soil fertility characteristics, crop management and socio-economic factors, such as household resource endowment and gender of the farmer, on climbing bean productivity and yield responses to basal P fertiliser in northern Rwanda. Through a combination of detailed characterisations of 12 farms and on-farm demonstration trials at 110 sites, we evaluated variability in grain yields and responses to fertiliser. Grain yields varied between 0.14 and 6.9 t ha −1 with an overall average of 1.69 t ha −1 . Household resource endowment and gender of the farmer was strongly associated with climbing bean yield, even though these were partly confounded with Sector. Poorer households and women farmers achieved lower yields than wealthier households and male farmers. Household resource endowment and gender were likely to act as proxies for a range of agronomic and crop management factors that determine crop productivity, such as soil fertility, current and past access to organic manure and mineral fertiliser, access to sufficient quality staking material, ability to conduct crop management operation on time, but we found evidence for only some of these relationships. Poorer households and female farmers grew beans on soils with poorer soil fertility. Moreover, poorer households had a lower density of stakes, while stake density was strongly correlated with yield. Diammonium phosphate (DAP) fertiliser application led to a substantial increase in the average grain yield (0.66 t ha −1 ), but a large variability in responses implied that its use would be economically worthwhile for roughly half of the farmers. For the sake of targeting agricultural innovations to those households that are most likely to adopt, the Ubudehe household typology – a Rwandan government system of wealth categorisation – could be a useful and easily available tool to structure rural households within regions of Rwanda that are relatively uniform in agro-ecology.

Potential effects of biochar-based microbial inoculants in agriculture

Biochar has been used widely as a soil amendment to improve plant growth, nutrient acquisition, stress tolerance and to improve soil biological, chemical and physical properties. Several studies suggest biochar as a carrier for bacterial inoculants under various climatic and environmental conditions because of the properties that favour microbial life. Biochar is rich in organic carbon, contains nutrients, such as N, P, K, has a high porosity, and high water-holding capacity. In this review, we synthesise results on the effectiveness of biochar as a carrier for inoculum in pot and field conditions. Biochar as a carrier supported a high survival rate of introduced bacteria and significantly increased colonization in the plant rhizosphere. Soil microbes are known to play an essential role in soil biochemical processes, and nutrient cycles; improve plant stress tolerance, and nutrient acquisition through their ability to fix atmospheric nitrogen, solubilize phosphate, or by enhancing decomposition of plant residues. Moreover, biochar-based inoculants increased root and shoot biomass, nodulation and nutrient uptake of plants in pot and field experiments. Biochar-based inoculants were also effective in enhancing plant growth and grain yield in pot and field experiments. These studies demonstrate that biochar can be considered as a suitable carrier or formulation of bacterial inoculants even in hostile environments and might contribute to replace other commercially used materials successfully. Biochar-based rhizobial inoculants can significantly improve the symbiotic performance of legumes with rhizobia which may reduce N fertilizer demand and thus promote the sustainability of crop production.

Introducing legumes into European cropping systems: farm-level economic effects.

F.L. Stoddard and C.A. Watson) 209 Abstract Legume cultivation in Europe has declined in recent decades due to decreased farm-level economic competitiveness compared with cereal and oil crop production. The increase in soybean prices in recent years and the public benefits expected from diversified production systems are reasons to reconsider legumes in Europe. Farm-level economic assessments, based on gross margin analysis of individual crops, often underestimate the contribution that legumes make to the farm business. We addressed this deficit using assessments made at the crop rotation level. We explored the possibilities resulting from: (i) the consideration of the management and yield of subsequent crops; (ii) systematic cropping system design; and (iii) changed price relations for legume feed grain. We identified several situations where legume-supported crop rotations are competitive and can create economic and environmental win–win situations to support a sustainable intensification of European cropping systems.