Regulated Deficit Irrigation Application and the Physiological Responses of Cotton (Gossypium hirsutum L. ) in Southwest Texas

The urban water demand in Southwest Texas is increasing rapidly in recent years due to the population increase in this area. One possible way to assist in solving this problem is to reduce the agricultural water use without affecting crop yield. Regulated deficit irrigation (RDI) is a widely used measure for saving water and maintaining crop yield. An experiment with seven treatments, including five ‘fixed’ (X) and two ‘dynamic’ (D) irrigation schemes, was developed in the summers of 2008 and 2009 and tested on several different varieties to determine whether more irrigation water could be saved by a RDI method.

The data analyses showed that: 1) the cultivar effects are minor, and the cultivar by irrigation interaction was not significant; and 2) the fixed RDI threshold (the maximum water saving point) should remain between 70% and 80%. With reference to the dynamic RDI, 50% of the irrigation water can be saved without affecting the lint yield during the pre-flowering season, which may contribute to a 35-40% water savings. Within a year, almost no significant effect was detected on the net photosynthetic rate (Pn) or the water use efficiency (WUE). In the year 2009, due to the continuous heat in June and July with no rainfall, the Pn and WUE are both lower than that of 2008, indicating the plants were under heat stress. Based on the results, it appears that the the 50D irrigation scheme is a good alternative for cotton production in SW Texas.