Potentially mineralizable nitrogen in West African lowland rice soils

Abstract

Nitrogen (N) deficiency is a major constraint to rice production in West Africa. Little information is available on the N supplying capacity of soils used for wetland rice production in West Africa. Potentially mineralizable N, as a measure of N supplying capacity, was determined employing an anaerobic incubation test in 15 diverse soils from 5 major rice producing countries in the sub region. Mineralized N contents of the soils varied widely (21 to 166 mg kg −1 of soil) and the ammonium N released constituted 2 to 7% of the total N. Mineralized N was significantly correlated with pH, organic C, total N, clay and CEC but not with extractable iron and C/N ratio of the soils. Multiple regression analysis of mineralized N with soil characteristics showed that inclusion of C/N ratio and extractable iron improved the prediction of mineralized N. The results underscore the importance of organic matter (organic C and total N) in controlling potentially mineralizable N in wetland rice soils. The main soil factors affecting N mineralization, identified by principal components analysis, accounted for over 97% variation in potentially mineralizable N in the soils.