It is well known that the uptake of fertilizer-N by crops is relatively inefficient, often amounting to less than half the quantity applied. Some becomes unavailable by combining with soil organic matter and some is lost from the system by surface runoff, leaching, denitriiication or ammonia volatilization. Most research has shown urea to be less effective than other sources of N when applied under conditions where ammonia volatilization becomes significant, especially when broadcast on the surface of alkaline and calcareous soils. Devine & Holmes (1964) found that ammonium sulphate was less effective than ammonium nitrate for wheat on a calcareous soil. Nitrogen recovery by wheat and barley tended to be similar for various N-fertilizers but further recovery in the following year was highest from calcium nitrate followed by ammonium sulphate and ammonium nitrate (Alessi & Power, 1973). On the other hand the efficiency of nitrate-N for flooded rice is less than that of ammoniacal fertilizers, owing to denitrification and leaching. Sarkar et al. (1978) found that rice grain yields with ammonium sulphate were significantly higher than with urea whereas Narain & Datta (1974) reported that urea and ammonium sulphate were equivalent and gave significantly higher yields of rice than ammonium nitrate. Therefore, yield responses to different sources of N vary depending upon soil, crop, climate and management factors; the study reported here was initiated to provide information on the relative performance of various N carriers applied to wheat and rice in the Punjab.
Ammonia volatilization from enhanced-efficiency urea on no-till maize in brazilian cerrado with improved soil fertility
