Carbon and Nitrogen Mineralization Dynamics: A Perspective in Rice-Wheat Cropping System

Abstract

Rice-wheat cropping system (RWCS), one of the prominent agricultural production systems, at an area of ~26 M ha is confined to the Indo-Gangetic Plains (IGPs) in South Asia and China. Crop residues obtained from field crops are essential sources of nutrition and organic carbon (40% of total dry biomass constituted by C) for the next crops, and hence they not only increase the agricultural productivity but also are responsible for the better quality of soil, water, and air. Perhaps the most important challenge facing exhaustive RWCS in all regions of the world is effective management of post-harvest crop residues. Disposal of wheat residue is easy as it can be used to feed animals. However, due to the presence of high silica content, rice residue is usually burned. Residue burning is the main method of disposal in areas under combined harvesting in the IGPs of eastern India as it reduces cost. However, burning of crop residue (CR) is not eco-friendly as it results in fast degradation of soil organic matter and nutrients and increased CO2 emission creating intense air pollution as well as global warming. Therefore, exploitation of CR is a crucial element for a sustainable production system, and it has generated much interest in the recent years by reducing the consequence of residue burning and increasing the soil organic matter (SOM) and the nutrient-supplying capacity. CR retention infield can be considered a key element in promoting soil health with increased physical, chemical, and biological properties. In RWCS, residue management can be done by (1) wheat residue retention in rice and its residual effect in succeeding wheat crop, (2) rice straw retention in wheat and its residual impact in following rice, and (3) wheat straw retention in rice and rice straw retention in wheat (cumulative effect). All these crop residue management systems depend on a systematic understanding of the factors that control residue decomposition and their careful application. Significant factors, such as tillage/CR management, influence soil microbial activity and biomass, bulk density, soil moisture content, porosity, soil structure stability, and nutrient-supplying capacity of the soil. Thus, the variations in soil properties consequently bring change in soil C and N dynamics and have an impact on plants’ nutrient uptake capacity.