The goal of this research was to determine the level of deficit irrigation that provides the highest economic return for cotton. In 2006 and 2007, drip tape was used to create nine deficit irrigation treatments compared to a dryland control in a RCB Design. Irrigation was initiated at square, bloom, and post-bloom by opening manual valves on the drip lines while irrigation levels were created by different drip tapes that supplied 1.5, 1.0, and 0.5 inches per week. Irrigation amounts were reduced if rainfall supplied the required water. Delta Pine 143 was used on a Memphis soil at the West Tennessee Research and Education Center, Jackson, TN.
During the growing season, soil water tension, NDVI, and nodes above white flower and cracked bowl were monitored. At harvest, seed cotton was weighed, fiber samples were collected, plant height was measured, and bowl location was mapped. After harvest, gin out was determined and cotton samples were classed.
In 2006, a five week drought period started three weeks prior to bloom. The highest gross return occurred in plots that received from 2.5 to 4.5 inches of irrigation (1850 lbs of lint per acre at $0.53 per lb). Based on a 200 acre center pivot, these optimum irrigation amounts would have produced an additional $30,000 in cotton value as compared to the dryland treatment (1550 lbs of lint per acre at $0.54 per lb). The treatment that received the highest irrigation, 8 inches, produced only $2,000 in additional cotton value (1725 lbs of lint per acre at $0.495 per lb), a return insufficient to pay for pumping costs let alone the capital cost of a center pivot.
In 2007, drought stress was more severe than in 2006 and occurred at completely opposite growth stages. Results from the 2007 experiment are expected to be available by the 2008 Beltwide Conference.
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