ABSTRACT

Optimization of water and nutrients in cotton under drip fertigation is important for semiarid regions of south Tamil Nadu, where drip fertigation is new for cotton. This study investigates the combined effect of water and nitrogen for cotton dry matter production and N uptake. Two levels of water and nitrogen namely; adequate input (100% of crop evapotranspiration + 120 kg N ha^-1) and deficit input (75% of crop evapotranspiration + 90 kg N ha^-1) were tested during winter 2001 and summer 2002 at Madurai Agricultural College Central farm, Tamil Nadu, India. The two treatments studied were part of a larger experiment with different combinations in a factorial randomized design. Adequate and deficit input produced 3293 and 2561 kg ha^-1 seed cotton. The rate of dry matter production was slow until 60 days after seeding. Adequate and deficit input produced 74% and 82% of the total seasonal dry matter in an eight week period from 60 to 120 days after seeding. Although an increase in water and nitrogen increased the dry matter production, the relative proportion of the plant fractions exhibited a little variation between the treatments. Mature plants contained 187 and 140 kg N ha^-1.Peak N uptake occurred between 60 and 90 days after seeding and was 46 and 60 % of total seasonal N uptake for cotton receiving adequate and deficit input. The accumulation of N in adequate treatment followed that of dry matter production, whereas in deficit treatment N reached a peak at 120 after seeding and then decreased. Earliness was induced in deficit treatment.