Soil respiration under different N fertilization and irrigation regimes in Bengaluru, S-India

Urban Farm DB summary

This study investigated how three rates of mineral nitrogen addition combined with rainfed versus irrigated conditions affected CO2 emissions from typical crops during the wet (Kharif) and dry (Rabi) seasons on a Nitisol in Bengaluru, South India. Two two-factorial split-plot experiments were conducted under rainfed and irrigated conditions from 2017 to 2021, using maize, finger millet, and lablab, and the vegetables cabbage, eggplant, and tomato or chili. CO2 emissions were measured with a Los Gatos Research multi-gas analyzer from 7:00-11:30 a.m. and 12:30-6:00 p.m., with CH4, NH3, and N2O found negligible. Regardless of irrigation, season, crop, or nitrogen level, afternoon CO2 emission rates were 2-128% higher than morning rates. Diurnal differences ranged from 0.04-1.61 kg CO2-C/ha/h in the irrigated field and 0.20-1.78 kg CO2-C/ha/h in the rainfed field. In the rainfed field, high-nitrogen plots emitted 56.4% more CO2 than low-nitrogen plots, versus only 12.1% more in the irrigated field. A linear mixed model showed nitrogen fertilization enhanced CO2 emissions, most strongly in rainfed crops; soil moisture enhanced emissions in rainfed crops but decreased them under irrigation, while soil temperature at 5 cm depth enhanced emissions in both fields.