Project Summaries

11-811TX  Project Manager: E. M. Barnes

EFFECTS OF VARIABLE IN-SEASON IRRIGATION CAPACITY ON COTTON

James P. Bordovsky, Texas AgriLife Research

Within the Ogallala Aquifer region, the available irrigation capacity on a given field can change within a growing season. Typically this is due to declining water tables. More recently, water is diverted from one crop (cotton) to other crops (corn) which may have higher value, or are at a more critical growth stage than cotton, particularly in a year of low rainfall. Furthermore, underground water conservation districts in the Texas High Plains will begin enforcing pumping restrictions, which could cause abrupt changes in irrigation rates as limits are reached. Preplanned timing of irrigations with available water allowances complicated by erratic rainfall will become more critical.

The objectives of this project were to:
1. Determine cotton lint yield, fiber quality, and water use efficiency as a function of combinations of irrigation capacities during three cotton growth periods; and to
2. Develop strategies to improve water management and water value in a semi-arid environment where new policies restrict irrigation volume and irrigation capacities are limited.

The treatment factors included in-season irrigation capacity (maximums of 0 in./d, 0.125 in./d, and 0.25 in./d) and irrigation application within a specific growth period. Periods were determined by heat unit (hu) accumulation and were generally designated as early vegetative/juvenile (< 950 hu), reproductive (950-1350 hu) and maturation period (>1350 hu). Combinations of these factor levels resulted in 27 irrigation regimes or treatments. A 4-span LEPA pivot was used to irrigate 9.5 acres of this field experiment. The pivot was modified so that each 8-row section (40-in circular rows) along the lateral length could automatically provide different irrigation amounts depending on the treatments being irrigated and pivot position. Groups of four valves (irrigating an 8-row plot) were actuated using signals from a controller (Farmscan 7000, Dothan, Alabama) with specific time sequences for each irrigation treatment and distance from the pivot point. Inputs to the controller were pivot location (via GPS signal) and irrigation quantity (via application map) at each 8-row x 16-degree section for each irrigation sequence.

Test results to date were obtained from years representing record breaking extremes – high rainfall in 2010 and low and ineffective rainfall in 2011 and 2012. In all years, cotton yield and water productivity data indicated that building soil water in the profile (i.e., irrigating in excess of the evapotranspiration rate of the cotton plants) reduced irrigation water value compared to applying irrigation later in the growing season. This was attributed to water loss from excessive evaporation (high wind, low humidity) that often occurs in May and June on the Texas High Plains. Irrigation water value during reproductive and maturation periods resulted in water use efficiencies in excess of 100 lb./acre-inch of irrigation applied. Additional field tests can provide the foundation for in-season irrigation recommendations that will optimize lint yield (and water value) based on irrigation pumping and volume restrictions.

 

Project Year: 2012
 

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