Water transport characteristics of cotton as affected by drip irrigation layout

To reduce drip irrigation equipment costs, dripper lines are laid in alternate interrow spaces. This study examined the effect of this practice on cotton (Gossypium hirsutum L.) water relations. Measurements of water uptake and water potential of plants grown in the held were conducted during four rainless summers at two locations. During the first summer, drippers in every interrow space delivered about 50 mm of water, the exact amount depending on estimated evapotranspiration (ET), every 10 d. The following summer, drip lines were laid in alternate interrow spaces, applying frequent (2-4 d) and small (10-20 mm) amounts of water, based on estimated ET. Treatments were repeated the following two summers. Measurements included water uptake (F), leaf water potential (psi(1)), and soil water content. Whenever a linear relationship between diurnal psi(1) and F was found, we determined the hydraulic conductance (K-T) of the plants as the line's slope reciprocal, and the intercept (psi(0)) as the water potential at the root-soil interface. A linear relation was found in the treatment with drippers in every interrow space. Water stress developed toward the end of the irrigation interval, causing K-T to decrease without affecting psi(0). Irrigation restored K-T to its initial value. With the alternate interrow-space pattern, the relationship between psi(1) and F remained linear only until midday. Afternoon (psi(1), F) points were below those of the morning, suggesting a lowering of the soil water potential near the roots. It was concluded that drippers laid in alternate interrow spaces expose cotton to frequent short periods of water stress.