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.

对活的覆盖作物或其残留物进行早期施氮 (N) 是满足 N 需求同时提高热带地区后续经济作物产量的潜在替代方案。在免耕 (NT) 系统中对活饲草或其残留物施用 N 的目的是通过秸秆分解来促进 N 逐渐释放到随后的作物中。然而，早期施肥下后茬作物的氮素利用效率在生长期末尚未确定。本研究的目的是评估在与常规方法不同的施氮时机时，种植最多的热带牧草是否可以通过氮回收来满足玉米的氮需求并提高玉米的产量。使用栅栏草 [( Urochloa brizantha(syn. Brachiaria )] 和 ruzigrass ( U. ruziziensis ) 作为覆盖作物，对农业系统有四种施氮时机：(i) 无施氮，零施氮；(ii) CC+N，120 kg N ha ^-1在玉米播种前 35 天施用于活体覆盖作物；(iii) St+N, 120 kg N ha ^-1在播种前 1 天施用于覆盖作物秸秆；(iii) Nv4，在玉米 V ₄ (四叶) 生长阶段施氮肥的常规方法。除对照外，所有 N 处理在玉米播种时接受 40 kg N ha ^-1，总计 160 kg N ha ^-1. 栅栏草施氮肥处理的秸秆分解和覆盖作物氮积累量均高于稗子草。在栅栏草或其残留物上施氮或根据常规方法获得高玉米产量，产量分别为13.2、13.2和13.6 Mg ha ^-1。类似地，当 N 施用于芸香草残留物或根据常规方法（12.1 和 11.8 Mg ha ^-1， 分别）。然而，无论覆盖作物种类如何，当通过常规方法施用氮肥时，氮的回收率最高。此外，当向活栅栏草施用氮肥时，收获时玉米中的大部分氮来自土壤。因此，采用常规方法施肥的玉米籽粒中氮肥的最佳回收率。我们的研究结果表明，以栅栏草的高干物质为特征的农业系统具有回收和供应氮给后续玉米的潜力。尽管栅栏草与早期氮肥施用相结合可以提高玉米的反应和产量，但目前在玉米上施用氮肥的常规方法可以提高氮肥的回收率，同时提高热带粮食生产中的玉米产量。