Cotton growth and production under drip-irrigation restricted soil wetting

Summary

Control of optimal soil water status for high productivity of cotton can be achieved more easily when the volume of the root system is restricted than with an extended root system. The restricted root system was obtained by planting on a pre-dried soil profile and by irrigation with a drip irrigation system applying small quantities of water at high frequencies. The effects of plant population, row and drip lateral densities and the amount of water per application, on soil water distribution and on cotton growth and productivity under these conditions were determined during 3 years of field trials. Cotton (Gossypium hirsutum L. cv. Acala SJ-2) was grown in a loess-brown loam soil in the northern Negev of Israel. The crop was planted on a dry soil profile between the end of May and early June and harvested during October and early November. There was no rainfall during the irrigation season. Water moved to a greater distance vertically than horizontally from the emitter, but there was no movement of water below a depth of 50 cm unless large quantities of water were applied. Maximal lint production was obtained within a narrow range of irrigation water quantities. Quantities below this range reduced production due to water stress, while quantities above this range enhanced vegetative growth and plant height and reduced lint formation. It was concluded that an optimal moisture regime can be obtained more easily by restricting the size of the root zone, but that over-irrigation may easily occur under such conditions. An increase in population over 10 plants/m2 resulted in enhanced vegetative growth associated with a reduction in lint yield with all irrigation regimes. At the optimal plant population and with maximum quantities of water applied, higher lint production and higher rates of water withdrawal were obtained at a row spacing of 50 cm as compared with 100 cm. When sub-optimal quantities of water were applied lint production was less reduced at row spacing of 100 cm. A row-to-lateral ratio of 2, and location of the laterals between alternate rows led to a greater vertical gradient in soil water content as compared with a row-to-lateral ratio of 1. Lint production was increased and vegetative growth was decreased at a row-to-lateral ratio of 2, at both row spacings of 50 and 100 cm.