Elucidating the role and contribution of cover crop roots to soil fertility and crop nutrition in organic cropping systems

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Nitrogen budgeting is a complex task in organic cropping systems, because crop fertilization is based on organic fertilizers (animal manures, cover crops, compost, etc.) rather than readily available mineral fertilizers. Many unknowns remain on the contribution of these organic fertilizers to the nutrition of subsequent crops, and particularly on the contribution of cover crop roots to soil N budget. Indeed, generally, only the shoot biomass of cover crops is considered when estimating the contribution of cover crops to nitrogen budget and fertilization plan. However, cover crop roots are hypothesized to contribute considerably to the soil N supply of agricultural soils. No research has previously addressed these important and innovative research questions. ***The long-term objective of the proposed research program is to elucidate the mechanisms of contribution of cover crop roots to soil fertility and crop nutrition. The short-term objectives of the proposed research program are 1) to quantify and differentiate the contribution of cover crop shoots and roots to the soil N dynamics; 2) to improve the current conceptual model of transfer of cover crop residue N into various soil organic and inorganic fractions; 3) to elucidate the temporal dynamics of N derived from the decomposition of cover crop roots in the soil-plant continuum; and 4) to synchronize the N supply from decomposing cover crops with N uptake of cash crops grown under organic management.***Two field experiments and one incubation study will be conducted to achieve the research objectives. The field experiment #1 will compare the shoot and root characteristics of different cover crop species incorporated at different termination stages, and their contribution to organic corn nutrition. The long-term incubation study will quantify the contribution of cover crop roots and shoots to soil N supply. A second field experiment will be conducted using cover crop material grown in 15N-enriched environment, to address specific unknowns about N partitioning in various soil N fractions.***My research will provide a fundamental understanding of cover crop root decomposition and associated soil N supply to plants and to the replenishment of the soil reserve and to plants. This will allow for better estimation of the soil N supply to subsequent crops and, therefore, for better forecasting of the need for other N organic amendments. Knowledge of the actual contribution of cover crop roots will be integrated in farm N budgets, therefore conceptually advancing the cover cropping and nutrient budgeting in organic cropping systems. Moreover, increase in crop yield due to better N management and timing would represent important gains in revenues to farmers. On a broader scale, gathering information on soil N budget may help to reduce N losses from cover crop-based cropping systems like organic farming systems.