Evaluation of rice cultivation systems for greenhouse gases emission and productivity
T Ramesh, S Rathika
A field experiment was conducted at Tamil Nadu Rice Research Institute, Aduthurai during two consecutive Kharif season to evaluate the different rice cultivation systems for greenhouse gases (CH4, CO2 and N2O gas flux) and grain productivity. Rice cultivation systems viz., transplanted rice (TR), wet seeded rice (WSR), system of rice intensification (SRI), drip irrigated rice and aerobic rice (dry seeded rice) were tested. Gas sample was collected at critical stages of rice by static chambers installed in the field. Gas Chromatography (GC) Varian 450 was used for analysis of gas. The results revealed that CO2 emission was less during tillering stage and reached maximum during flowering stage and thereafter declined under transplanted, wet seeded rice and SRI cultivation. Whereas, drip irrigated and aerobic rice emitted higher CO2 during tillering stage and thereafter it started to decline. Transplanted rice emitted higher methane at all the stages of observation whereas aerobic rice and drip irrigated rice emitted lesser methane as compared other methods of rice cultivation. During flowering stage, transplanted rice emitted higher CH4 (8.20 mg/m2/day), followed by wet seeded rice (7.70 mg/m2/day), SRI (6.05 mg/m2/day). Aerobic rice (2.13 mg/m2/day) and drip irrigated rice (1.82 mg/m2/day) emitted lesser CH4 over other methods of rice cultivation. SRI paddy emitted an average of 26.8% lesser CH4 and 3.8% higher N2O over conventional flooded paddy. Wet seeded rice showed 16.6 and 18.1% lesser CH4 and N2O emission than transplanted rice. In case of drip irrigated rice, an average of 68.6 and 34.4% lesser CH4 and N2O emission was noticed over conventional flooded paddy. Changing rice cultivation from conventional flooded rice to aerobic rice emitted an average of 79.8% lesser CH4. But, it was emitted 14.4% more N2O over transplanted paddy. Wet seeded rice produced significantly more number of productive tillers (392 m-2) over transplanted, aerobic and drip irrigated paddy. However, it was on par with SRI. Significantly more number of filled grains (157.5 m-2) was recorded under SRI over other methods of rice cultivation. The highest mean grain yield of 5855 kg/ha was recorded under SRI over other methods of cultivation which was 10.5% higher over transplanted rice. Drip irrigated rice and aerobic rice registered 17.9 and 29.5 per cent lesser grain yield respectively. Even though, these new systems of rice cultivation (drip irrigated and aerobic rice) had better advantages in reducing greenhouse gases emission, the crop establishment was under aerobic condition did not favour enhanced growth and yield over SRI and wet seeded rice. Thus, SRI method of rice cultivation is considered as best method to reduce CH4 emission (26.8%) with increased grain productivity (10.5%) over transplanted rice in the present context of climate change.