Relationships between N, P, and K in corn biomass for assessing the carryover effects of winter pasture to corn

Pasture fertilization may influence the subsequent corn crop in integrated crop-livestock systems, but few tools exist to assess the likelihood and magnitude of this carryover effect. Our goals were to determine whether a previous pasture with N fertilization could supply adequate N nutrition to a succeeding corn crop and affect its P and K nutrition using the concept of N dilution curve and relationships between N, P, and K in corn shoot biomass. The experiment consisted in a winter grazed pasture followed by a corn crop in summer. Treatments were N fertilization of a black oat (Avena strigosa) winter pasture (0 and 200 kg N ha⁻¹) as main plots and four sidedress N fertilization rates (0, 100, 200, and 300 kg N ha⁻¹) applied to corn as sub-plots in a randomized complete block design with split-plot restriction. The N nutrition index, that is, the ratio of observed shoot N concentrations to critical N concentration determined by a critical N dilution curve, adequately identified situations of deficient N nutrition in corn following a pasture with or without N fertilization. This carryover effect from a winter pasture should therefore be accounted for in N fertilizer recommendations for corn in tropical soils. Corn P nutrition, based on critical P concentrations derived as a function of N concentration, was nearly optimal when no N was applied to the pasture, but it was less than optimal when N was applied. Although no critical K curves have been published, our results confirm that the relationship between shoot K and N concentrations varies with the level of N nutrition as does the relationship between shoot P and N concentrations. Our results confirm that the concept of critical N and P concentrations serves as a useful reference to assess the status of N and P nutrition during corn growth in tropical soils with the potential to improve nutrient management of corn following a pasture in an integrated crop-livestock system.