Yield-scaled N2O emissions were effectively reduced by biochar amendment of sandy loam soil under maize - wheat rotation in the North China Plain

Abstract

It is increasingly recognized that the addition of biochar to soil has potential to mitigate climate change and increase soil fertility by enhancing carbon (C) storage. However, the effect of biochar on yield and nitrous oxide (N2O) emissions from upland fields remains unclear. In this study, a one-year field experiment was conducted in an area of calcareous fluvo-aquic soil to assess and quantify the effect of maize straw biochar in reducing N2O loss during 2014–2015 in the North China Plain. Eight treatments were designed as follows: no nitrogen (N) fertilizer (control, CK); biochar application at rates of 3 (B3), 6 (B6) and 12 (B12) t ha−1; chemical fertilizer (NPK) application at 200 kg N ha−1 (F); and fertilizer plus biochar application at rates of 3 (FB3), 6 (FB6) and 12 (FB12) t ha−1. Crop yield, N2O fluxes, soil mineral N concentrations, and soil auxiliary parameters were measured following the application of treatments during each season. During the maize growing season, N2O emission was 0.57 kg N2O-N ha−1 under CK treatment, and increased to 0.88, 0.93 and 1.10 kg N2O-N ha−1 under B3, B6 and B12, respectively. In contrast, N2O emissions were significantly reduced by 31.4–39.9% (P < 0.05) under FB treatments compared with F, and the N2O emission factor of the applied N was reduced from 1.36% under F to 0.71–0.85% under FB. There was also a significant interaction effect of fertilizer and biochar on N2O emissions (P < 0.01). During the wheat growing season, biochar had no effect on N2O emissions regardless of the fertilizer regime. Biochar application did not affect maize yield; however, a significant increase in wheat yield of 16.6–25.9% (P < 0.05) was observed without N fertilization. Nevertheless, a reduction in wheat yield was measured at a biochar rate of 12 t ha−1 with fertilization. Overall, under maize cropping, N2O emissions per unit yield of grain, biomass, grain N and biomass N (yield-scaled N2O emissions) were significantly reduced by 32.4–39.9% under FB compared with F treatment, regardless of the biochar application rate. Biochar did not affect yield-scaled N2O emissions in wheat. Decreased soil bulk density with biochar is suggested to reduce the denitrification potential and N2O emissions; while increased retention capacity of fertilizer N in biochar-added soil decreased wheat growth and yield. These findings suggest that N fertilization plus biochar application at 3 t ha−1 is a practical strategy for reducing yield-scaled N2O emissions from maize fields in the North China Plain.