Crop Residue Recycling for Improving Crop Productivity and Soil Health

Introduction

India produces a huge amount of crop residues biomass (685 MT annually). The crop residues include arable crop residues such as straw, stover/stalk, stubbles and seeds/pods. The processed crop residues include husk, seeds (broken/ shriveled), bagasse, molasses and roots. The crop residues are mainly used as animal feeding and their bedding, thatching of homes and as a source of fuel for domestic and industrial purposes. After putting aside the residues for agricultural and non-agricultural uses, 34% of it remains as surplus, which is either burnt or is being wasted. This surplus crop residue biomass has the potential to generate 4.15 EJ bio-energy, which can meet out 17% of India's total primary energy consumption (Hiloidhari et al., 2014). The stems, leaves, chaff and husks that remain in the fields after crops are harvested for grain, seed or fiber play a critical role in soil quality and environmental issues since they are primary inputs of elemental carbon (C) into soil systems (Fig 1). Crop residues have been referred to as ‘wastes’ but as a natural and valuable resource are also considered to be ‘potential black gold.’ The negative connotation of ‘residues’ may refer to the remains after a part is taken or something leftover or useless. On the contrary, crop residues offer a large, but finite potential mechanism for C sequestration and nutrient cycling (Reicosky and Wilts, 2005).

Figure 1.

Schematic representing the role of crop biomass in the agricultural ecosystems carbon cycle

(Source: Reicosky and Wilts, 2005)

Crop Residue Generation In India

The amount of crop residues produced in India is estimated to be approximately 620 million tons (Mt) and an increasing trend in crop residues generation has been observed with increasing food grain production in the country (Fig. 2). Half the quantity of agro-residues thus produced finds use as roofing material, animal feed, fuel and packing material, while the other half is disposed-off by burning in the field. About 50% of the total residues generated are produced by three crops viz. rice, wheat and oilseed. Rice residues account for 135 Mt annually. The rice-wheat (RW) system accounts for nearly 1/4^th of the total crop residues produced in India. The surplus crop residues (i.e., total residues produced minus the quantity used for various purposes) are typically burned on-farm. The amount of surplus crop residues available in India is estimated to range from 84–141 Mt year^-1 where the cereal crops contribute about 58%. Of the 82 Mt of surplus crop residues from the cereal crops, 44 Mt is from rice followed by 24.5 Mt from wheat, which are mostly burned on-farm.

Figure 2.

Annual crop residue generated in India since 1950-51

The cereal crops contribute the most in total crop residues generation, followed by oilseed and fibre crops. The share of various crop groups in residue generation and the surplus has been shown in Fig. 3.

Figure 3.

Residue generation (A) and the share of unutilized residues in total residues generated (B) by different crops in India (MNRE, 2009)

The major states of India which contribute towards the crop residues generation in different crops has been given in table 1, which indicates that the states producing the highest crop residues are also responsible for huge residue burning. A huge area under cultivation in these states has great potential of the residue use for maintaining higher soil fertility.