Field studies were conducted in 1986 and 1987 with cv. Stoneville 825 to determine the effect of chlordimeform yield enhancement on leaf N, leaf photosynthesis, and lint yield of cotton (Gossypium hirsutum L.) grown under different N fertility and irrigation levels. Treatments in the experiment were irrigation (none and furrow irrigation when leaf water potential reached -2.0 MPa), applied N (0, 40, 80, and 120 kg ha^-1), and chlordimeform (o and 0.14 kg a.i. ha^-1 applied at six weekly intervals). Leaf samples for N analysis were collected 80 and 105 days after planting in 1986 and 74, 95, and 110 days after planting in 1987. Midday photosynthetic rates of fully expanded leaves at the top of the canopy were measured on sunny days throughout June and July both years. Lint yield was determined by hand-picking three m of row in 1986 and six m of row in 1987.

Leaf N increased with increasing N fertility rates at all sampling dates both years, but irrigation and chlordimeform treatment had little effect on leaf N either year. Increased leaf photosynthesis occurred in the July measurements at higher N fertility levels both years under irrigated conditions. As soil moisture became limiting under dryland conditions in 1986, leaf photosynthesis of untreated plants was reduced before photosynthesis of chlordimeform treated plants at the higher N fertility rates. Photosynthetic rates were correlated with leaf conductance. Averaged over all N and irrigation treatments both years, photosynthetic rates of chlordimeform treated plants were generally numerically higher, but rarely statistically higher, than untreated plants. Lint yield increased with increasing N rate both years. Higher yields with chlordimeform treatment occurred only under irrigated conditions in 1986. There were no N x chlordimeform interactions for yield either year.