EFFECTS OF SOIL WATER CONDITIONS ON FATE OF UREA NITROGEN

Concerning with applied nitrogen fertilizer. the uptake as well as loss of nitrogen is mainly related to soil water content. The effects of soil water condition in wheat field on the uptake, leach and loss of nitrogen fertilizer were studied in this paper using 15N tracing technique. The results showed that within certain range of soil water supply. from 180 to 360 mm of available water storage, the loss of nitrogen was in direct proportion to the amount of fertilizer application and the nitrogen use efficiency decreased with the increase of nitrogen application. In other words, the nitrogen use efficiency decreased with the nitrogen application increased in an order of 75, 150. 225 kg/hm2. one interesting result was that the nitrogen use efficiencies ranged from 17. 9% to 30. 5% for different water treatments(W1, W1 and W1) receiving the same application N rate of 75kg/hm2.