ABSTRACT

Most regions of the U. S. cotton belt make use of multiple irrigation scheduling procedures with few instances found in which one universally adopted method is used among growers. Both plant and soil based scheduling methods are being used with reasonable success throughout the cotton growing regions with numerous types of technologies used. Plant based approaches that make use of measurements of canopy temperature and leaf water potential have been highly successful in areas that do not rely on summer rainfall as a major component of ET. Growers and researcher that favor this method note the rapid and far-reaching information that integrates evaporative demand with plant available soil moisture to establish peak levels of crop water stress to develop scheduling thresholds.

Soil based irrigation scheduling methods are more widely accepted because they need not rely on current climatic conditions, instruments generally produce repeatable results and the timing of measurements is relatively flexible. Soil moisture methods for irrigation scheduling typically make use of estimates of plant available water (PAW) derived from field capacity (FC), crop permanent wilting point (PWP) and rooting depth. A percent depletion value is applied, above which there is an increasing risk of high water stress impacting crop losses. While this approach can be very useful to the agronomist, good initial estimates of rooting depth, field capacity and wilting point are necessary to minimize the risk of incorrectly estimating soil water reserves. During the process of establishing the soil specific parameters, it is also useful to develop an understanding of how these parameters change with time and location. This studies focus is to provide information that describes variation in cotton rooting depth during the season at specific sites and contrasts multiple sites that differ mainly in their soil conditions.