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2000 Florida Cotton Production Guidelines: Water Requirements for Cotton1 Fred Rhoads2 1. This document is NFREC9, one of a series of the North Florida Research and Education Center, Florida Cooperative Extension Services, Institute of Food and Agricultural Sciences, University of Florida. Date first printed Jan. 2000. Please visit the EDIS Website at http://edis.ifas.ufl.edu. 2. Fred Rhoads, Professor, Department of Soil Science, Institute of Food and Agricultural Sciences, University of Florida, North Florida Research and Education Center, Quincy FL 32351. The Institute of Food and Agricultural Sciences is an equal opportunity/affirmative action employer authorized to provide research, educational information and other services only to individuals and institutions that function without regard to race, color, sex, age, handicap, or national origin. For information on obtaining other extension publications, contact your county Cooperative Extension Service office. Florida Cooperative Extension Service/Institute of Food and Agricultural Sciences/University of Florida/Christine Taylor Waddill, Dean. Water Requirements for Cotton Cotton is an excellent candidate for irrigated land, particularly in areas that frequently have drought periods during July 1 August 20 and when grown on coarse textured, sandy land. During peak blooming, cotton will use about 0.3 to 0.4 inch of water per day. Irrigated cotton yields have been from 0 to more than 800 lbs/Ac greater than non-irrigated yields with the most frequently reported increases being in the 200 to 400 lbs/Ac range. The following procedure is suggested for 900 to 1100 lbs/Ac yields: Prior to first bloom, irrigate with 0.75 1.00 inch of water whenever wilting of plants is observed by midday. After first bloom, irrigate as needed to supply the quantities of water listed below (Table 1). Rain gauges should be used to measure the water received from rain and the amount supplied by irrigation. Examine the crop during the 7th week to determine if irrigation should be continued. Irrigation intervals can be determined by dividing the quantity/day into 50 to 66% of the available moisture holding capacity of the upper two feet of soil in fields. For example, if the available moisture capacity of the soil is 0.7 inch per foot and the quantity/day is 0.3 inch, the interval between irrigations following rain that brings soil moisture to field capacity would be 66% x 2 ft. x 0.7 inch/ft. divided by 0.3 inch/day=3.08 or 3 days. Intervals for most of the season will be 3-4 days for coarse textured sand, 4-6 days for more productive loamy sand and sandy loam, and 5-8 days for fine textured sandy loam or "clay." A 4-6 day interval will fit a large majority of the situations.

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Table 1. Water requirements for cotton. 2000 Florida Cotton Production Guidelines: Water Requirements for Cotton 2 Period Inches/Week Inches/Day Week beginning at 1st bloom 1.0 0.15 2nd week after 1st bloom 1.5 0.22 3rd week after 1st bloom 2.0 0.30 4th week after 1st bloom 2.0 0.30 5th week after 1st bloom 1.5 0.22 6th week after 1st bloom 1.5 0.22 7th week after 1st bloom 1.0 0.15