Nitrous oxide, methane emissions and grain yield in rainfed wheat grown under nitrogen enriched biochar and straw in a semiarid environment

BACKGROUND: Soil application of biochar and straw alone or their combinations with nitrogen (N) fertilizer are becoming increasingly common, but little is known about their agronomic and environmental performance in semiarid environments. This study was conducted to investigate the effect(s) of these amendments on soil properties, nitrous oxide (N(2)O) and methane (CH(4)) emissions and grain and biomass yield of spring wheat (Triticum aestivum L.), and to produce background dataset that may be used to inform nutrient management guidelines for semiarid environments. METHODS: The experiment involved the application of biochar, straw or urea (46% nitrogen [N]) alone or their combinations. The treatments were: CN(0)–control (zero-amendment), CN(50) –50 kg ha(–1) N, CN(100)–100 kg ha(–1) N, BN(0) –15 t ha(–1) biochar, BN(50)–15 t ha(–1) biochar + 50 kg ha(–1) N, BN(100)–15 t ha(–1) biochar + 100 kg ha(–1) N, SN(0) –4.5 t ha(–1) straw, SN(50) –4.5 t ha(–1) straw + 50 kg ha(–1) N and SN(100)–4.5 t ha(–1) straw + 100 kg ha(–1) N. Fluxes of N(2)O, CH(4) and grain yield were monitored over three consecutive cropping seasons between 2014 and 2016 using the static chamber-gas chromatography method. RESULTS: On average, BN(100)reported the highest grain yield (2054 kg ha(–1)), which was between 25.04% and 38.34% higher than all other treatments. In addition, biomass yield was much higher under biochar treated plots relative to the other treatments. These findings are supported by the increased in soil organic C by 17.14% and 21.65% in biochar amended soils (at 0–10 cm) compared to straw treated soils and soils without carbon respectively. The BN(100)treatment also improved bulk density and hydraulic properties (P < 0.05), which supported the above results. The greatest N(2)O emissions and CH(4) sink were recorded under the highest rate of N fertilization (100 kg N ha(–1)). Cumulative N(2)O emissions were 39.02% and 48.23% lower in BN(100) compared with CN(0) and CN(100), respectively. There was also a ≈ 37.53% reduction in CH(4) uptake under BN(100)compared with CN(0)–control and CN(50). The mean cumulative N(2)O emission from biochar treated soils had a significant decrease of 10.93% and 38.61% compared to straw treated soils and soils without carbon treatment, respectively. However, differences between mean cumulative N(2)O emission between straw treated soils and soils without carbon were not significant. These results indicate the dependency of crop yield, N(2)O and CH(4) emissions on soil quality and imply that crop productivity could be increased without compromising on environmental quality when biochar is applied in combination with N-fertilizer. The practice of applying biochar with N fertilizer at 100 kg ha(−1) N resulted in increases in crop productivity and reduced N(2)O and CH(4)soil emissions under dryland cropping systems.