Crop Residue Management and Greenhouse Gases Emissions in Tropical Rice Lands

Abstract

There are about 4 million tons of lignocellulosic crop residues generated in the world every year. Most of them (~ 25%–35%) are rice residues produced in the tropics, which have a huge potential to act as a carbon sink. Unfortunately 25%–40% of rice residues are burnt in open air in order to clear the field for the next crop in intensive tropical rice-based cropping systems. It is a paradox that on the one hand we have a shortage of animal feed, biofuel, and manure, while on the other hand a considerable amount of crop residue is either wasted or burnt. This is not only a big loss of natural renewable resources, but also a source of greenhouse gas (GHG) emissions and environmental pollution. However, these residues can effectively be used as mulch and for the production of manure, ethanol, biodiesel, biochar, etc., as well as employed in conservation agriculture. In a rough estimate, if 20% of the world's rice straw is used for the production of ethanol annually, about 40 billion liters could be generated, which can replace 25 billion liters of fossil fuel-based gasoline. In this way, net GHG emissions would be reduced to a tune of 70 billion tons of CO2 equivalent. Therefore the effective and alternate management of crop residues would not only reduce GHG emissions, but simultaneously offset fossil fuel use. It could also sink atmospheric CO2 for a larger period of time if it were judiciously retained and subsequently incorporated in topsoil, composted, or used for biochar production, thereby building a defense against climate change.