Methane emissions from irrigated rice fields in northern India (New Delhi)

Methane (CH4) emission fluxes from rice fields as affected by water regime, organic amendment, and rice cultivar were measured at the Indian Agricultu ral Research Institute, New Delhi, using manual and automatic sampling tech niques of the closed chamber method. Measurements were conducted during fou r consecutive cropping seasons (July to October) from 1994 to 1997. Emissio n rates were very low (between 16 and 40 kg CH4 m(-2) season(-1)) when the field was flooded permanently. These low emissions were indirectly caused b y the high percolation rates of the soil; frequent water replenishment resu lted in constant inflow of oxygen in the soil. The local practice of interm ittent flooding, which encompasses short periods without standing water in the field, further reduced emission rates. Over the course of four seasons, the total CH4 emission from intermittently irrigated fields was found to b e 22% lower as compared with continuous flooding. The CH4 flux was invariab ly affected by rice cultivar. The experiments conducted during 1995 with on e cultivar developed by IRRI (IR72) and two local cultivars (Pusa 169 and P usa Basmati) showed that the average CH4 flux from the intermittently irrig ated plots without any organic amendment ranged between 10.2 and 14.2 mg m( -2) d(-1). The impact of organic manure was tested in 1996 and 1997 with va rieties IR72 and Pusa 169. Application of organic manure (FYM + wheat straw ) in combination with urea (1:1 N basis) enhanced CH4 emission by 12-20% as compared with fields treated with urea only. The site in New Delhi represe nts one example of very low CH4 emissions from rice fields. Emissions from other sites in northern India may be higher than those in New Delhi, but th ey are still lower than in other rice-growing regions in India. The practic e of intermittent irrigation-in combination with low organic inputs-is comm only found in northern India and will virtually impede further mitigation o f CH4 emissions in significant quantities. In turn, the results of this stu dy may provide clues to reduce emissions in other parts of India with highe r baseline emissions.