High-frequency level basin irrigation for cotton.

Abstract

High-Frequency level basin irrigation of cotton was studied. The objectives were to determine the effects of small, frequent irrigations on level basin design parameters and performance, and to evaluate the economic feasibility of a high-frequency level basin irrigation design for cotton production in the southwestern United States. Field measurements were made in level basin and small-plot studies spanning two seasons with a short-staple cotton (Gossypium hirsutum, L., cv. Deltapine 20) in central Arizona. The measurements were used to evaluate and analyze the effects of light, frequent water application on the infiltration and soil surface roughness characteristics, irrigation uniformity, and the water use, growth, and yield of cotton. The high-frequency applications were generally confined to a four-to-five-week period, coinciding with most rapid fruiting. The Kostiakov infiltration equation constants, k and a, and the Manning n, used to describe infiltration and surface roughness, respectively, decreased significantly with time, reflecting the seasonal changes in cultural practices and field conditions. During rapid fruiting, the Kostiakov k was significantly reduced when irrigations were given at frequent intervals (5-to-7-days), compared to the k determined for conditions of less frequent irrigation (12-to-15-day intervals). However, the effect of irrigation frequency on the Kostiakov a and the Manning n was not significant during rapid fruiting. An analysis of the low-quarter distribution uniformity (defined as the average low-quarter infiltrated depth divided by the average depth of water infiltrated) showed that when the effect of surface water retention variation was considered, the uniformities attained for high-frequency irrigation during rapid fruiting were reduced from 4 to 10% below those attained for large, less frequent, irrigation. However, final lint yields were increased from 6 to 21% with high-frequency irrigation. An economic analysis indicated that a level basin designed for high-frequency irrigation in central Arizona might realize an increase in annual net income of $156 per hectare above that expected for a conventional system. Properly designed and managed high-frequency level basin irrigation offers an opportunity to increase yields and reduce grower vulnerability to net losses in the Southwest.