Role of Starch Polymer-Coated Urea in the Mitigation of Greenhouse Gas Emissions from Rice and Wheat Ecosystems

The excessive use of synthetic nitrogen fertilizer in agriculture interferes in natural ecosystem functioning and pollutes the environment through nitrogen leaching, volatilization, nitrification, and denitrification. The consumption of conventional fertilizer in the agricultural field has increased nitrous oxide (N2O) emission, an important trace gas, which is responsible for stratospheric ozone layer depletion and global warming. Alternatively, the use of slow-release fertilizer (SRF) is considered to ameliorate crop nitrogen use efficiency (NUE) and yields while minimizing problems related to environment caused by inorganic N-fertilizer. For SRF, the coating of urea particles can be done with various coating materials; thus, nutrients release slowly from coated fertilizer and plant can efficiently use it. The degree of N release to soil depends on the coating material being used. Starch is one type of encapsulating polymer which can be used to coat or encapsulate the urea granules to slow the rate of fertilizer release. Although starch is mineralizable, the addition of different cross-linking agents reduces the release rate of entrapped urea from their cross-linking structure. The presence of coating directly retards the ammonium (NH4+) oxidation by reducing the activity of nitrifying bacteria and indirectly reduces the substrate availability for denitrification in soil. In this chapter, we have briefly reviewed about the different types of SRF and its use in the different agroecosystems. The efficiency of SRF for the reduction of greenhouse gas from rice and wheat ecosystems, mainly N2O emission by affecting nitrification and denitrification process in soil, has also been discussed.