The effect of neem (Azadirachta indica a juss) kernel powder on the release of NH+4-N and NO-2+ NO-3 -N from urea in a savannah ecological zone of Nigeria

An incubation study was conducted to evaluate the potential of powder made from neem (Azadirachta indica A Juss) kernel as an alternative nitrification inhibitor for increased utilisation and efficiency of urea fertiliser in soils. Three soil textural classes, namely: loamy sand, sandy clay loam and clay soils in Bauchi State, Nigeria were used for the study. Seven sets of 20 g soil samples were made in triplicate for each soil. Each of the seven sets respectively received seven rates of neem kernel powder (NKP) (i.e. 0, 1, 2, 3, 4, 5 and 6 mg.g-1of soil) and arranged in a completely randomised design for each of the seven incubation periods (0, 3, 7, 15, 30, 45 and 60 days). All the samples received 4 ml of urea solution (50 ug ml') and incubated at field capacity and at laboratory temperature (30 °C ± 2 °C). At the end of each incubation period, samples were analysed for NH+4, -N and (NO-2+ NO-3)-N. Results of the incubation study revealed that neem kernel powder treatments significantly (p<0.01) increased the retention of NH+4 -N presumably released through hydrolysis of applied urea by slowing its nitrification. This was observed in all the soils from 7 up to 30 days incubation period. Beyond this period, however, application of NPK ceased to be effective in slowing the nitrification process in loamy sand and sandy clay loam soils but continued to be effective in clay soil up to the end of the study (60 days).