Dynamic responses of ammonia volatilization to different rates of fresh and field-aged biochar in a rice-wheat rotation system

Abstract

Biochar, as a soil conditioner to increase soil carbon storage and improve soil quality, has been widely applied to farmland to mitigate climate change and enhance crop productivity. However, many studies have focused on the short-term effects of biochar amendment, while few studies have traced the long-term effects on ammonia (NH3) volatilization. A two-year field experiment was conducted to investigate the effect of different rates of field-aged biochar (applied 3 years before) and fresh biochar reapplication (fresh biochar applied to aged biochar) on NH3 volatilization, crop yield and nitrogen use efficiency (NUE) in a typical rice-wheat rotation system. The results showed that the NH3 loss rate of applied nitrogen fertilizer ranged from 5.9% to 13.2% in the wheat season and from 9.9% to 19.2% in the rice season. The fresh biochar reapplication increased NH3 volatilization losses. However, the low rate of aged biochar decreased NH3 volatilization, but the high rate of aged biochar still increased NH3 volatilization. The NH4+-N concentration and pH were determinant factors for NH3 volatilization. Both field-aged and fresh biochar reapplication improved rice and wheat NUE, although there was no significant increase in rice and wheat yields. Thus, biochar amendment at a low rate of 20 t ha−1 beneficially mitigated NH3 volatilization and enhanced crop NUE in rice-wheat rotation systems during field aging.