Cotton productivity on the High Plains of Texas is frequently limited by water and nitrogen availability.

Radin et al (1981) reported that increasing levels of N to cotton plants grown under water stress caused a desensitizing of the stomata, and increased stomatal conductance at ambient CO₂ concentration. The objectives of this study were to determine the effects of nitrogen and water interactions on cotton leaf gas exchange, biochemical composition, leaf area development and dry weight accumulation.

The field experiment was conducted on sandy soil near Brownfield, Texas in which three irrigation treatments by three pre-plant nitrogen treatments were imposed. The irrigation treatments were 0, 50, and 100 percent replacement of estimated evapotranspiration. The pre-plant nitrogen treatments were 0, 50, and 100 kgN/ha. Sampling was conducted at 60, 85, and 110 days of plant age in which carbon exchange rate (CER), leaf conductance, soluble protein content, chlorophyll content, and growth analyses were determined. CER was measured as CO₂ depletion/unit of leaf area/unit of time with a leaf assimilation chamber of 4 liters of volume (closed system). Conductance was measured with a Li-Cor 1600 Steady State Porometer.