Nitrous oxide emissions from kharif and rabi legumes grown on an alluvial soil

Nitrous oxide (N2O) emissions were monitored for a period of 60 days in a pot culture study, from two kharif (June–September) and two rabi (October–March) season legumes, which were grown on a Typic Ustochrept, alluvial sandy loam soil. Black gram (Vigna mungo L. Hepper), var. T-9, and soybean (Glycine max L. Merril), var. Punjab 1, were taken up in kharif season whereas lentil (Lens esculenta Moench), var. JLS-1, and Bengal gram (Cicer arietinum L.), var. BGD-86, were grown in rabi season. All the crops were grown with and without urea and one pot (containing soil but with no fertilizer or crop) was used as a control. Nitrous oxide emissions were significantly higher in unfertilized cropped soil than in the control, while the addition of urea to the crops further increased the emissions. Significant emissions occurred during third and seventh week after sowing for all the treatments in both kharif and rabi seasons. In kharif, soil cropped with soybean had higher total N2O-N emission than soil sown with black gram both under fertilized and unfertilized conditions; while in rabi, lentil had a higher total N2O-N emission than Bengal gram under both fertilized and unfertilized conditions. In kharif, total N2O-N emissions ranged from 0.53 (control) to 3.84 kg ha–1 (soybean+urea), while in rabi it ranged from 0.45 (control) to 3.06 kg ha–1 (lentil+urea). Higher N2O-N emissions in kharif than in rabi was probably due to the favorable effect of temperature on nitrification and denitrification in the former season. The results of the study indicated that legume crops may lead to an increase in N2O formation and emission from soils, the extent of which varies from crop to crop.