Nitrogen Transformation of Neem Oil Coated Urea in Alfisols

摘要

Nitrogen trnasformations from neern oil coated urea (2% w/w, NOCU) and prilled urea (PU) was studied in four Alfisols. The soils had a pH of 5.7-6.9, organic carbon content of 0.49-1.21 per cent, cation exchange capacity of 6.3-13.9 cmol (p~+) kg~(-1)and texture ranging from sandy clay to clay. The urease activity ranged from 2.03-18.23 mu g NH_4~+ g~(-1) hr~(-1) and dehydrogenase activity of 6.61-47.67 ug TPF g~(-1) hr~(-1). The gaseous loss of NH_3 increased during 27 days of incubation from 0.9-1.7 to 6.9-7.2 per cent in different soils. The amnoniacal form in the soil was the dominant form that increased from 42.5-5 2.0 per cent on the 3rd day to 47.4-56.2 per cent on the 10th day and gradually declined to 41.4-34.4 per cent up to the 27th day.Urease activity at 10 days of incubation was significantly reduced under NOCU compared to PU. Nitrite content in the soil built up from traces to 2.3-3.0 per cent on the 15th day and stabilized at 3.1-3.4 per cent till the end of incubation. Nitrate content in the soil steadily increased throughout the period of study from 7.7-9.2,per cent (3rd day) to 38.9-45.0 per cent (27th day). The total amount of urea that was transformed was 51.1-62.8 to 89.7-90.5 per cent during incubation. At all the stages, neem oil coated urea (NOCU) showed significantly lower gaseous loss of NH_3 as well as different N-fractions in the soil compared to PU indicating that neem oil inhibited both ammonification and nitrification. Neem oil coated urea was found to persist for a longer duration than PU in soil and supply N needs of the plant more effectively.