Pot experiments on urea as a fertilizer

Summary

In a series of pot experiments the effect of soil applications of urea on the aerial growth of various crops was compared with that of ammonium nitrate and ammonium sulphate.

When the nitrogen sources were uniformly incorporated in the soil at the time of sowing the pattern of response was essentially the same for the twelve crops examined. Applications of urea, ammonium nitrate and ammonium sulphate at the lowest rates gave similar yields. At the intermediate rates, yields from urea were considerably lower than from the other nitrogen sources and were often equal to or less than those of the no-nitrogen controls. At the highest rates of application, urea gave much lower yields than the other sources. In most crops these smaller yields were associated with urea-induced damage which was followed by the death of established plants.

Topdressing applications of urea and ammonium nitrate caused very slight damage and increased the yields of all five crops. The responses from urea were lower than those from ammonium nitrate, especially at the higher rate of applied nitrogen.

However, within each method of nitrogen application, the pattern of response to urea was similar for all the crops tested. Maize was selected as a suitable indicator plant for potential investigations on the effects of urea as a fertilizer.