COTTON RESPONSE TO NONUNIFORMITY OF CONVENTIONAL SPRINKLER IRRIGATION

Sprinkler irrigation systems are characterized by some degree of non-u niformity. The effect of non-uniformity on crop yield has been modelle d in different ways but experimental studies are scarce. An experiment was conducted comparing the effects of two levels of uniformity (mean Wilkox and Swailes' uniformity coefficients of 80% and 52%) at two le vels of water supply (about 400 and 260 mm for the whole irrigation se as on) on cotton production. Final yield was not affected either by un iformity or by the amount of water supplied. Vegetative growth was hig her in the full irrigation treatments. Maximum leaf area index did not differ statistically between uniformity treatments. The lack of diffe rences was attributed to the curvilinear shape of the yield function a nd to the dampening of the variations in applied water in the soil, as the coefficient of variation in applied water was more than twice the coefficient of variation of infiltrated water. These results suggest that non-uniformity of conventional sprinkler irrigation has a lower i mpact on cotton crop performance than expected from previous simulatio n studies.