Feasibility of early fertilization of maize with 15 N application to preceding cover crop

Early nitrogen (N) application on live cover crops or their residues is a potential alternative for supplying N demand while enhancing the yield of subsequent cash crops in tropical regions. The objective of applying N on live forage grasses or their residues to no-till (NT) systems is to promote the gradual release of N via straw decomposition to the subsequent crop. However, the N use efficiency by the subsequent crop under early fertilization has not been determined in the end of growing season. The aim of this study was to evaluate whether the most cultivated tropical forage grasses can supply the N demand and enhance the grain yields of maize via the N recovery when N is applied with different timings than the conventional method. A 3-year field experiment was performed using palisade grass [(Urochloa brizantha (syn. Brachiaria)] and ruzigrass (U. ruziziensis) as cover crops with four N application timings to agricultural system: (i) no-N, zero N application; (ii) CC+N, 120 kg N ha−1 applied on live cover crops 35 days before maize seeding; (iii) St+N, 120 kg N ha−1 applied on cover crops straw 1 day before seeding; and (iii) Nv4, conventional method of sidedress N application at the maize V4 (four leaf) growth stage. Except control, all N treatments received 40 kg N ha−1at maize seeding, totalizing 160 kg N ha−1. Straw decomposition and cover crop N accumulation were greater in the treatments in which N fertilizer was applied on palisade grass compared with ruzigrass. High maize yields were achieved with N application on palisade grass or its residues or according to the conventional method, with yields of 13.2, 13.2 and 13.6 Mg ha−1, respectively. Similarly, high maize yields were obtained when N was applied on ruzigrass residues or according to the conventional method (12.1 and 11.8 Mg ha−1, respectively). However, regardless of cover crop species, N recovery was highest when N fertilizer was applied via the conventional method. Additionally, most of the N in maize at harvest came from the soil when N fertilizer was applied to live palisade grass. Thus, best recovery of N fertilizer in the grain occurred in maize fertilized using the conventional method. Our results indicate that agricultural systems characterized by high dry matter from palisade grass have the potential to recycle and supply N to subsequent maize. Although palisade grass combined with early N fertilizer application may enhance maize response and yield, the current conventional method of N fertilizer application on maize allows higher recovery from N fertilizer while increasing the maize yield in tropical food production.