In 2015, the Government of India directed that all fertilizer urea manufactured in the country or imported will have to be coated with neem oil at the rate of 0.5 kg per tonne. Urea coated with neem cake (200 kg per tonne) (NCU) or neem oil (NOCU) possesses nitrification inhibition properties and can increase yield and N use efficiency in field crops more than untreated urea, although quality of neem oil and neem cake in terms of concentration of triterpenoids can vary in different lots. So far more than 75 studies have been conducted to study the performance of NCU or NOCU in increasing the yield of rice, wheat, and several other crops. In rice and wheat to which more than 50% of the urea consumed in India is applied, mean increase in grain yield by replacing urea with NCU or NOCU is 5 to 6% in plots managed by researchers. In about 30% comparisons, no increase was observed. As level of crop management and plant protection in farmer's fields is generally lower than in the researcher's plots, the achievable yield increase by using NOCU should be substantially less than that observed in researcher's plots. Farmers applying high and above optimal levels of urea-N in different crops may not observe significant improvement in yield levels by applying NOCU. Positive impact of NOCU in increasing crop production is likely to be further lowered by the fact that effect of nitrification inhibitors depends also upon the soil texture, pH and whether the crops are irrigated or rainfed. Nitrification inhibitors work better in acidic soils than in neutral or alkaline soils, in coarse textured soils than in fine textured soils, and in irrigated crops than in rainfed crops. More than 30% of total urea consumed in India is applied to crops grown under rainfed conditions. Thus, on an overall basis, replacing all urea being supplied to farmers in the country with NOCU is not likely to show a significant impact on food production levels. Till new recommendations for using NOCU are formulated for different crops and regions, no reduction in demand for NOCU should be expected. Possibly, applying NOCU following the site-specific nutrient management principles will lead to crop production of higher or similar levels as observed with untreated urea but with lower fertilizer application rates.
Neem coated urea, nitrogen, plants
