Irrigation Termination in Cotton

The 2011 cotton crop is progressing nicely in spite of being somewhat late.  Defoliation applications have taken place on some of the earliest planted cotton near Port Gibson as well as on small acreage near Benoit.  In general, open bolls are beginning to appear in more and more fields.

To that end, a quick review of irrigation termination timing in cotton is warranted.  Generally speaking, furrow irrigation applications should be terminated once cotton reaches first cracked boll.  Although some prefer to terminate irrigation somewhat earlier or later, shutting down furrow irrigation at first cracked boll appears to be the optimum timing.  Terminating furrow irrigation prior to the onset of cracked bolls may lead to inconsistencies in development of uppermost bolls.  Terminating furrow irrigation after first cracked boll may help with development of those uppermost bolls; however, increased moisture combined with a lush canopy may lead to problems with boll rot and hardlock.  While some may be tempted to push furrow irrigation after first cracked boll, the potential losses due to hardlock and bollrot should be considered if you are going to make a final irrigation application.

When considering irrigation termination for pivot irrigated fields several factors should be taken into consideration.  First and foremost, pivot irrigation systems do not deliver the same volume of water to a given field as furrow irrigation.  In most cases, 0.75” to 1” of water per acre are being applied through a pivot irrigation system at each irrigation timing.  Furrow irrigation applications generally deliver 2” to 3” of water per acre each time a given field is watered.  Due to the discrepancy in amount of water delivered between a pivot irrigation system and furrow irrigation, termination of pivot irrigation is generally somewhat later than termination of furrow irrigation.  Recommendations for terminating pivot irrigation generally occur about 7 – 10 days after first cracked boll.  While applying water through a pivot irrigation system may lead to issues with hardlock and bollrot as described above, lack of water late in the season may lead to reduced weight and quality of fiber in the uppermost bolls which can translate into yield and quality losses.

Keep in mind that these are general guidelines.  When deciding when to terminate irrigation on any field, one should examine the crop in the field, the root system of the plant, and moisture status in the soil.  Once you are confident adequate soil moisture exists in the soil (or will be received through rainfall) to finish out the crop in your field, irrigation termination should occur.