Optimizing agronomic efficiency (AE) of nitrogen (N) fertilizer use by crops and enhancing crop yields are challenges for tropical no-tillage systems since maintaining crop residues on the soil surface alters the nutrient supply to the system. Cover crops receiving N fertilizer can provide superior biomass, N cycling to the soil and plant residue mineralization. The aims of this study were to (i) investigate N application on forage cover crops or cover crop residues as a substitute for N sidedressing (conventional method) for maize and (ii) investigate the supply of mineral N in the soil and the rates of biomass decomposition and N release. The treatments comprised two species, i.e., palisade grass [Urochloa brizantha (Hochst. Ex A. Rich.) R.D. Webster] and ruzigrass [Urochloa ruziziensis (R. Germ. and C.M. Evrard) Crins], and four N applications: (i) control (no N application), (ii) on live cover crops 35 days before maize seeding (35 DBS), (iii) on cover crop residues 1 DBS, and (iv) conventional method (N sidedressing of maize). The maximum rates of biomass decomposition and N release were in palisade grass. The biomass of palisade grass and ruzigrass were 81 and 47% higher in N application at 35 DBS compared with control in ruzigrass (7 Mg ha⁻¹), and N release followed the pattern observed of biomass in palisade and ruzigrass receiving N 35 DBS (249 and 189 kg N ha⁻¹). Mineral N in the soil increased with N application regardless of cover crop species. Maize grain yields and AE were not affected when N was applied on palisade grass 35 DBS or 1 DBS (average 13 Mg ha⁻¹ and 54 kg N kg⁻¹ maize grain yield) compared to conventional method. However, N applied on ruzigrass 35 DBS decreased maize grain yields. Overall, N fertilizer can be applied on palisade grass 35 DBS or its residues 1 DBS as a substitute for conventional sidedressing application for maize.

优化作物使用氮 (N) 肥的农艺效率 (AE) 和提高作物产量是热带免耕系统面临的挑战，因为将作物残留物保持在土壤表面会改变系统的养分供应。接受氮肥的覆盖作物可以提供优良的生物量、氮循环到土壤和植物残留物矿化。本研究的目的是 (i) 调查在牧草覆盖作物或覆盖作物残留物上施氮作为玉米施氮的替代方法（常规方法），以及 (ii) 调查土壤中矿物质氮的供应和比率生物量分解和氮释放。处理包括两个物种，即栅栏草 [ Urochloa brizantha (Hochst. Ex A. Rich.) RD Webster] 和 ruzigrass [ Urochloa ruziziensis](R. Germ. 和 CM Evrard) Crins]，以及四次施氮：(i) 控制（不施氮），（ii）在玉米播种前 35 天在活覆盖作物上（35 DBS），（iii）在覆盖作物上残留物 1 DBS，和 (iv) 常规方法（玉米施氮肥）。生物量分解和氮释放的最大速率在栅栏草中。与在 ruzigrass (7 Mg ha ^-1 ) 中的对照相比，在 35 DBS 下施氮的栅栏草和 ruzigrass 的生物量分别高 81% 和 47% ，并且氮释放遵循观察到的栅栏草和 ruzigrass 接受 N 35 DBS 的生物量模式249 和 189 kg N ha ^-1）。无论覆盖作物种类如何，土壤中的矿物质氮都随着施氮而增加。与常规方法相比，当在栅栏草 35 DBS 或 1 DBS（平均 13 Mg ha ^-1和 54 kg N kg ^-1玉米籽粒产量）上施氮时，玉米籽粒产量和 AE 没有受到影响。然而，在 ruzigrass 35 DBS 上施氮会降低玉米的产量。总的来说，氮肥可以在栅栏草 35 DBS 或其残留物 1 DBS 上施用，以替代玉米的常规侧施。