Tina Gray Teague

Determining the Optimum Timing for the Final Furrow Irrigation on Mid-South Cotton

A common question from cotton farmers in the U.S. Mid-South is when to stop irrigating the crop. U.S. Cotton growers are adopting COTMAN to monitor crop development and aid in making end-of-season decisions concerning the optimal dates for safe termination of insect control and application of defoliants. The objective of this research was to investigate a similar crop-based recommendation for timing the final irrigation on cotton. Data sets from 28 Mid-South cotton fields conducting irrigation termination studies during the 2000 through 2007 growing seasons were analyzed. Day of year, days after planting, and growing degree days after planting, all until the last irrigation, did not provide a strong enough relationship with yield to guide late-season irrigation decisions. Days after nodes above white flower (NAWF)=5 (DA5) and growing degree days after NAWF=5 (GDDA5) of the last irrigation in the northern portion of the Mid-South did provide a yield impact estimate suitable for developing recommendations, but a relationship for fields south of 34° N latitude could not be established. Based on the resulting equations for a cotton price of

Cotton Insect Pest Management

1.15 kg-1 of lint, an irrigation applied after 18 days or 192 GDD, 15.6°C base, after NAWF=5 would not be expected to produce enough additional yield to be profitable. The derived equations can also be used to determine the GDDA5 and DA5 of the last profitable irrigation for a known lint price and diesel cost, allowing the producer to react to his or her individual situation. Six of the fields were harvested twice and a later crop (i.e., a lower % first harvest) was associated with later irrigation, though the differences were not always significant. When fiber quality was measured, significant differences were seldom observed and no consistent trend relating to final irrigation was observed. However, because of the price discounts associated with low or high micronaire and the relationship between micronaire and crop maturity, additional research is needed to refine the fiber-quality relationship for the Mid-South.