Biochar stimulates NH4+ turnover while decreasing NO3− production and N2O emissions in soils under long-term vegetable cultivation

Abstract

A 15N-tracer incubation experiment was conducted to investigate the short-term effects of biochar on gross N transformation rates and nitrous oxide (N2O) emissions in soils under 1-year and 10-year vegetable cultivations. Biochar was applied at three rates: 0 (control), 10, and 30 t ha−1. Gross N transformation rates in the two vegetable soils varied in response to biochar application. Specifically, organic N oxidation into NO3− (ONorg) was almost negligible in the biochar-amended soils, and biochar application at 10 t ha−1 did not change either the rate of mineralization of organic N into NH4+ (MNorg) nor the inorganic N supply capacity (INS, ONorg + MNorg) in both soils, when compared to the control. However, 30 t ha−1 biochar decreased INS significantly, by inhibiting MNorg, in the 1-year vegetable soil but increased INS, by stimulating MNorg, in the 10-year vegetable soil. The rates of NH4+ oxidation into NO3− (ONH4), NO3− immobilization into organic N, and dissimilatory NO3− reduction into NH4+ were not influenced significantly by biochar application in the 1-year vegetable soil, resulting in no significant differences in NO3− production potential. Conversely, biochar decreased NO3− production potential significantly in the 10-year vegetable soil, by inhibiting ONH4 and increasing NH4+ immobilization into organic N (INH4), with more obvious effects under higher biochar application rates. Overall, the results demonstrate the capacity of biochar to stimulate NH4+ turnover and to decrease NO3− production potential in soil under long-term vegetable cultivation; however, the effect is limited under short-term vegetable cultivation. In addition, N2O emissions decreased significantly in biochar-amended vegetable soils.