INTERACTIVE EFFECT OF IRRIGATION AND NITROGEN-FERTILIZATION ON COTTON, SOIL, AND GROUNDWATER NITROGEN

Two field experiments were carried out at Sakha Agricultural Research Station during the 1988 and 1989 seasons to determine the effect of ir rigation regime, nitrogen (N) fertilization, and their interactions on N content of both cotton plant and soil as well as N losses into grou ndwater. The data showed that irrigation at 14 days after the wilting leaves had a negative effect on growth, bell weight, and nutrient conc entrations [N, phosphorus (P), potassium (K)]. Irrigation at the initi al sign of wilting had a positive effect. It was found that increasing N application rates increased dry matter and N uptake by the plant. T he highest rate (traditional) of 70 kg N/Fad gave the highest growth ( plant dry weight) and N uptake by the cotton plant. Examination of the interactions between irrigation and N treatments revealed that the hi ghest boil weight was due to application of irrigation at the initial sign of wilting and N fertilization at the rate of 70 kg N/Fad (166.7 kg/ha, 1 Fad=0.42 ha).