Nitrogen Availability Indexes for Submerged Rice Soils

Abstract

Publisher Summary This chapter reviews the methods proposed for assaying the nitrogen-supplying capacity of wetland rice soils and recommends those methods that have potential for predicting soil nitrogen (N) availability, thus making possible the judicious and efficient use of fertilizer nitrogen for rice production. It discusses the mineralization process that is basic to soil nitrogen availability to wetland rice. The mineralizable N pool in soils plays a dominant role in N nutrition of wetland rice. Studies using 15 N-labeled fertilizers show that approximately one-half to two-thirds of the total N utilized by a rice crop, even in well-fertilized rice paddies, comes from the soil-mineralizable N pool. Numerous biological and chemical laboratory methods have been proposed for predicting soil N availability to various crops, including rice. Mineralization of organic nitrogen, which does not proceed past ammonium production in wetland rice soils, is the most important biological process that is involved in the availability of soil N to rice grown under submerged conditions. The chapter discusses simple equations describing the relationships between the amounts of NH 4 + –N released under waterlogged conditions and environmental factors such as temperature and other soil characteristics. These relationships have been formulated from studies with diverse soils from a particular region and are limited in that they have not been widely tested.