Soil mineral nitrogen, soil urease activity, nitrogen losses and nitrogen footprint under machine-planted rice with side-deep fertilization

Abstract

Abstract Reduction of the nitrogen (N) footprint of agroecosystems is currently a hot topic in various research disciplines and fields. However, the effect of machine-plantedrice with side-deep fertilization (MRSF) on nitrogen loss and footprint of double-cropping rice fields in Hunan is still unclear. Here, we established a field experiment in which we applied various N compositions (N 135/148.5–90/99 kg ha− 1) to early-season rice (ESR) and late-season rice (LSR). The loss of different N forms during the whole growth period of double cropping rice was measured. The N footprint of double cropping rice in red soil region of South China was calculated by using life cycle assessment method. Compared with the conventional fertilizer (CF; N 150/165 kg ha− 1) treatment, the MRSF treatments significantly reduced NH4+-N and NO3−-N runoff by 26.2–40.9% and 9.0–36.5%, respectively, for ESR, and by 54.4–79.0% and 6.6–40.7%, respectively, for LSR. Moreover, relative to the CF treatment, the MRSF treatments significantly reduced leaching loss by 21.8–41.2% and 20.5–42.1%, respectively, for ESR, and 26.7–41.8% and 20.9–51.0%, respectively, for LSR. While urease activity decreased with increasing soil depth, MRSF treatments increased relative soil urease activity in the later stages of rice growth. Compared with the CF treatment, they also decreased the total N footprint by 42.3–53.5% and 45.1–57.1% for ESR and LSR, respectively. Correlation analysis further showed that mineral N loss and total N footprint increased exponentially with the N-application rate under the MRSF strategy. Overall, MRSF was found to reduce environmental risks associated with N loss caused by paddy field leaching and runoff while maintaining the topsoil N content. In this manner, MRSF can attenuate the total N footprint of double-cropping rice systems in Southern China.