Abstract
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.
Highlights
Long-term agricultural projections report that the world’s population is growing at a rate of at least one percent per year (USDA 2019; Worldometers 2019)
The dry matter loss and N accumulated from palisade grass and ruzigrass was significantly (p \ 0.05) affected by N application timing on cover crops at 0, 30, 60, 90 and 120 days after termination (DAT) (Table 1, Fig. 1 and Supplementary Table 3)
Palisade grass resulted in similar rates of dry matter loss and N accumulated in all treatments when receiving N fertilizer (35 days before maize seeding (DBS), 1 DBS and conventional) and no-N
Summary
Long-term agricultural projections report that the world’s population is growing at a rate of at least one percent per year (USDA 2019; Worldometers 2019). Plants of the genus Urochloa are commonly used as cover crops in the tropical region due to their high biomass and vigorous, deep root systems (Pacheco et al 2011; Soratto 2011; Moro et al 2013). This deep root architecture increases nutrient uptake from the soil and enables these species to grow in harsh off-season conditions such as drought (Felismino et al 2012; Pacheco et al 2017). The residues of Urochloa spp. offer other benefits, such as improved soil health, weed suppression and nutrient loss avoidance (Castro et al 2015; Buchi et al 2019)
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