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

Abstract

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 (N₂O) and methane (CH₄) 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: CN₀-control (zero-amendment), CN₅₀ -50 kg ha^-1 N, CN₁₀₀-100 kg ha^-1 N, BN₀ -15 t ha^-1 biochar, BN₅₀-15 t ha^-1 biochar + 50 kg ha^-1 N, BN₁₀₀-15 t ha^-1 biochar + 100 kg ha^-1 N, SN₀ -4.5 t ha^-1 straw, SN₅₀ -4.5 t ha^-1 straw + 50 kg ha^-1 N and SN₁₀₀-4.5 t ha^-1 straw + 100 kg ha^-1 N. Fluxes of N₂O, CH₄ and grain yield were monitored over three consecutive cropping seasons between 2014 and 2016 using the static chamber-gas chromatography method.

Results: On average, BN₁₀₀reported 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 BN₁₀₀treatment also improved bulk density and hydraulic properties (P < 0.05), which supported the above results. The greatest N₂O emissions and CH₄ sink were recorded under the highest rate of N fertilization (100 kg N ha^-1). Cumulative N₂O emissions were 39.02% and 48.23% lower in BN₁₀₀ compared with CN₀ and CN₁₀₀, respectively. There was also a ≈ 37.53% reduction in CH₄ uptake under BN₁₀₀compared with CN₀-control and CN₅₀. The mean cumulative N₂O 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 N₂O emission between straw treated soils and soils without carbon were not significant. These results indicate the dependency of crop yield, N₂O and CH₄ 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 N₂O and CH₄soil emissions under dryland cropping systems.

Keywords: Carbon amendments; Fertilization; Grain yield; Greenhouse gas; Loess plateau; Rain-fed; Semi-arid.