Predicting potential Anaerobic Nitrogen mineralization of rice–rice and rice–wheat soils of Asia

Abstract

Nitrogen (N) supplying capacity of soils in rice (Oryza sativa L.)-based cropping systems has been reported to be in decline in some sites in Asia. Studying the relationship between N mineralization, rice cropping intensity and soil properties may help us understand changes in N supplying capacity. We conducted short- and long-term laboratory incubations in flooded, anaerobic conditions to measure N mineralization in a range of rice–rice and rice–wheat (Triticum aestivum L.) cropped soils. Our objectives were to determine: (1) what soil properties affect potential anaerobic N mineralization, and (2) whether potential anaerobic N mineralization is affected by rice cropping system. Several soil properties, especially total organic N (TON) and total organic C (TOC), were positively correlated with N mineralization potential at 30°C (N0) and with 7-d production of NH4 at 40°C (N-7-d). Nitrogen mineralization was only weakly correlated with TON or TOC if the initial large flush during the first 14 d was ignored. Rice–rice soils on average had greater N mineralization than rice–wheat soils, mostly due to higher TON concentrations. Seven-day production of NH4 at 40°C was so similar to N0 estimated after 84 d of anaerobic incubation at 30°C that the 7-d incubation could possibly substitute for the long-term one in developing N fertilizer recommendations.