Cotton gas exchange response to standard and ultra-narrow row systems under conventional and no-tillage

The availability of soil water to crops is a major limitation to crop production. We measured soil moisture and cotton (Gossypium hirsutum L.) leaf level photosynthesis, stomatal conductance, and transpiration during reproductive growth under different row spacing [standard 102 cm row (SR) and ultra-narrow row of 20 cm (UNR)] and tillage [conventional (CT) and no tillage (NT)] conditions during the summers of 1999 to 2001. In 1999, SR cotton under CT maintained higher photosynthetic rates during early reproductive growth when soil water was not limiting. However, during dry periods photosynthetic rates were higher in NT especially under SR. The benefits of NT were sporadic in 2000 and 2001 due to frequent rainfall. Cotton in UNR typically had lower photosynthesis compared to SR. Stomatal conductance and transpiration measurements generally mirrored those of photosynthesis. The results suggest that during periods of infrequent rainfall, photosynthesis can be maintained in NT since soil water is conserved during critical reproductive stages.