Nitrogen supplying capacity of lowland rice soils in Southern India

Abstract Effective indigenous nitrogen (N) supply (EINS) was estimated in ‐N plots (no fertilizer N addition) of a multi‐location field experiment with irrigated rice conducted in India. Dynamic soil tests, namely anaerobic incubation without (AI) or with K+‐saturated cation exchange resin (AIR) and N release to a mixed‐bed ion‐exchange resin capsule (PST), were used and compared with total soil N, organic carbon (C), initial NH4‐N and alkaline KMnO4‐N as predictors for EINS. The pattern of net N mineralization was similar in all soils of 10 sites and fitted the two‐pool first and zero order model: a rapid early phase from 0–14 d, a transition phase from 14–35 d and a slow, nearly linear phase from 35–56 d. In the rapid phase, average net NH4‐N release with K‐resin was 125% greater than the net NH4‐N without K‐resin. Static soil N tests were significantly correlated with net NH4‐N of AIR only up to rapid and transition phases and also with the cumulative NH4‐N adsorption measured by PST. Grain yield in th...