Summary Application of neem products like neem leaf and neem cake to wetland soil did not have any adverse effect on the population of heterotrophic microflora; nitrifying bacteria, on the other hand, decreased significantly due to addition of neem cake and fresh and dried neem leaf with urea. It is suggested that neem leaf could be used as an inhibitor of nitrification for enhancing nitrogen use efficiency of fertilizers where neem leaf is available in plentiful supply.

The farmers of tropical Asia are applying neem leaves to rice fields as green manure traditionally. Neem cake blending of urea is recommended for inhibition of nitrification and increasing nitrogen use efficiency. Field experiment conducted at the Tamil Nadu Agricultural University, Coimbatore, India, during kharif and rabi seasons in 1984–85 with a short duration (105 days) rice cv. IR 50 showed that application of fresh neem leaf at 5 t/ha or dry neem leaf 1.25 t/ha with urea resulted in higher N recovery per cent and N response ratio and gave increased grain yield compared to the yield obtained due to the application of urea alone. Besides increasing the grain yield, neem leaf application could save about 50 per cent N application and give greater net returns to the farmer.