ABSTRACT

Interest is growing in expanding the use of COTMAN to assist in end-of-season recommendations such as irrigation termination. Current recommendations in subsurface drip irrigated cotton are inadequate to determine the optimum timing to stop irrigation. This study was conducted to determine if crop based recommendations could be used for timing the final irrigation in subsurface drip irrigated cotton in West Texas. Treatments were made by shutting off the drip irrigation in an 8 acre zone at approximately 200, 400 and 600 Heat Units (HU) after cutout (based on 4 nodes above white flower). Evaluations included percent open boll, yield and fiber characteristics.

Continuing to irrigate the crop slowed boll opening and may have impacted the final yield of the crop. Shutting off the water too early can drastically affect yield. The 200 HU treatment had 536 and 369 lbs lint / acre less than the 400 HU and 600 HU treatments, respectively. Both the 400 HU and 600 HU treatments had increased lint and seed weights over the 200 HU treatment. The 600 HU treatment also had a higher seed weight than the 400 HU treatment.

With respect to fiber characteristics of the composite sample, micronaire was unaffected. The 400 HU treatment had higher fiber strength values than the 200 HU treatment, but the 600 HU treatment was not different from either of the other treatments. Of the fiber characteristics, fiber length was most affected by shutting the water off early. In the composite sample and all but the first harvest date, the 200 HU treatment had shorter fibers than both the 400 and 600 HU treatments.

No advantage was gained by watering subsurface drip irrigated cotton beyond the point of 400 HU past cutout. The COTMAN rules for HU accumulation appear to be beneficial in determining the final irrigation of subsurface drip irrigated cotton in West Texas. However, additional studies need to be conducted on when irrigation should cease in drip irrigated cotton that include the measurement of other factors in addition to HU accumulation since cutout.