Peer review

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.

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