Comparison of the efficiencies of several nitrogen fertilizers applied to pasture in autumn and winter

Abstract

A comparison was made of the responses to, and nitrogen recoveries from, ammonium sulphate, sodium nitrate, and urea when broadcast on a ryegrass sward in a favourable growing season. A second comparison was made, in a drier season on the same sward, between ammonium sulphate, sodium nitrate, urea, calcium ammonium nitrate, and ammonium nitrate. In both comparisons urea was an inefficient source of nitrogen, but its efficiency depended on the time of application. Differences in the rainfall shortly after application probably caused this variation in efficiency, by affecting the amounts of ammonia lost to the atmosphere. With sources other than urea, variation in the length of time during which the fertilizer remained at the soil surface, awaiting effective rainfall and plant uptake, had little effect on the final recovery of nitrogen. Ammonium sulphate, calcium ammonium nitrate, and ammonium nitrate showed similar efficiencies during the relatively dry season in which they were compared. Sodium nitrate was the most efficient source in both seasons.