Dynamic biochar effects on nitrogen use efficiency, crop yield and soil nitrous oxide emissions during a tropical...

The application of biochar to soil combined with synthetic fertilizers has been proposed for enhancing N availability to plants and crop yields while reducing nitrous oxide (N₂O) emissions. However, little is known about those interactions for tropical soils. Thus, this study evaluated the effects of sugarcane straw biochar on tropical soil attributes, crop productivity, N₂O emissions and N use efficiency. It was conducted a greenhouse pot experiment with wheat cultivation using a¹⁵N-labelled source (NH₄¹⁵NO₃). The treatments evaluated were: Soil, with N, no biochar; Soil, with N and biochar at rates equivalent to 0.4%, 0.8% and 1.9% (w/w); and a control (soil only). Increasing biochar amendments decreased cumulative N₂O emissions by 71% compared to the fertilized, no-biochar soil. Moreover, increasing biochar rates to soil increased available P up to 30% and led to 8-fold higher exchangeable K⁺ concentrations. Grain yield and shoot biomass increased by 27 and 16%, respectively, with the rate of 1.9% biochar to soil, which also resulted in higher tillering and number of heads compared to fertilized, no-biochar soil. The amount of ¹⁵N in grains was 28% higher with 0.8 and 1.9% of biochar compared to no-biochar soil, which correspond to 25% of the total ¹⁵N-labelled fertilizer applied to soil. The ¹⁵N loss by volatilization did not differ between treatments. Nevertheless, the biochar amended soils produced less N₂O than the no-biochar treatment, indicating that biochar amendment to tropical soil led to gaseous N losses in forms other than N₂O. The application of biochar to soil improved N utilization and the efficiency with which N is acquired by the plants and converted to grain yield, thereby enhancing crop performance, while simultaneously reducing N₂O emissions from N fertilization, thus mitigating GHG emissions to the atmosphere under tropical conditions.