Assessment of the soil moisture status of your fields is essential to schedule your first “post-planting” irrigation in cotton. In general, we should be irrigating somewhere around 700-900 HUAP (Heat Units After Planting). That’s a good rule of thumb, but should not be the only consideration. In some areas, high winds might have dried out the soil, so you need to get out and do some digging around and get an estimate of soil moisture. The plants are still fairly small and the roots are not fully developed. For this first irrigation, you should be looking in the top 12 – 18 inches to determine soil moisture levels. Go to http://ag.arizona.edu/crops/cotton/cropmgt/post_plant_irrigation.html (Spanish version at http://cals.arizona.edu/pubs/water/az1220S.pdf) for information on determining soil moisture. Remember, these small cotton plants do not require a large amount of irrigation water. However, they also don’t have access to all the moisture in the soil due to their limited root growth.
Timing the First Post-Planting Irrigation in Cotton