A Chemical Index for Predicting Ammonium Production in Submerged Rice Soils

Abstract

Nitrogen (N) deficiency limits rice production and productivity in tropical soils. The escalating cost of chemical fertilizers warrants an efficient use of external inputs of N. This can be achieved by estimating a soil's indigenous N supply. There is an urgent need for developing simple, rapid and effective methods of assessing N supplying capacity of soils. Ammonium production is the key process in the N nutrition of wetland rice because N mineralization halts at ammonium production in submerged soils. Previous work showed that organic matter and reducible iron control ammonium production in submerged soils. In this paper results are presented for 15 diverse West African rice soils, which show that regression equation connecting organic carbon (C) and reducible iron (extracted by EDTA or ammonium oxalate) with ammonium released under waterlogged condition, can be used for predicting ammonium production in these soils. Soils with higher N supplying capacity had relatively higher contents of organic C and reducible iron. There was a close agreement between the observed values of ammonium released and those predicted by organic C and reducible iron for the soils studied. These results suggest that the chemical index based on organic C and reducible iron contents of soils can be used as a simple and rapid index for estimating N supplying capacity of wetland rice soils.

Keywords:

• Electron acceptors
• Nitrogen index
• Prediction of ammonium production
• Organic matter
• Reducible iron
• Rice soils

Acknowledgments