Crop residue management for lowland rice-based cropping systems in Asia

Intensification of rice-based cropping systems in Asia has substantially increased production of food and associated crop residues. The interval between crops in these systems is often brief, making it attractive for farmers to burn residues in the field to hasten and facilitate tillage for the next crop. Open-air burning causes serious air quality problems affecting human health and safety, and it has been banned by many Asian governments. In this chapter, we evaluate for rice-based cropping systems existing and emerging in-field alternatives to burning residues based on criteria of productivity, profitability, environmental impact, and sustainability. In intensive rice monocropping systems, residue is typically managed under conditions of soil flooding and anaerobic decomposition during the rice crop. In systems, where rice is rotated with an upland (non-flooded) crop, there are two major categories: residue of upland crop managed during flooded rice and rice residue managed during the upland crop. One option during the flooded rice crop is incorporation of residues from the previous rice or upland crop into the soil. Many studies have examined incorporation of crop residue during land preparation for flooded rice. In the vast majority of cases there was no significant increase in yield or profit. Residue decomposition in anaerobic flooded soil substantially increases methane (CH4) emission relative to residue removal. Surface retention of residue during rice cropping is challenging to implement because residue must be removed from the field during conventional tillage with soil flooding (i.e., puddling) and then returned. Alternatively, rice must be established without the traditional puddling that has helped sustain its productivity. Mulch is a good option for rice residue management during the upland crop, especially with reduced and no tillage. Mulch can increase yield, water use efficiency, and profitability, while decreasing weed pressure. It can slightly increase nitrous oxide (N2O) emission compared with residue incorporation or removal, but N fertilization and water management are typically more important factors controlling NO emission than residue management. Long-term studies of residue removal have indicated that removing residue from continuous rice systems with near continuous soil flooding does not adversely affect soil organic matter (SOM). The use of crop residue as a mulch with reduced or no tillage for upland crops should be promoted in rice-based cropping systems. On the contrary, residues from the crop preceding rice on puddled and flooded soil can be considered for removal for off-field uses.