Management strategies for dryland cotton production in west texas
Ralston, Wesley R.
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Over 1.8 million acres of dry-land cotton production exist annually on the Southern High Plains of Texas and another 1.0 million exist in the Rolling Plains. As Conservation Reserve Acreage is returned to row crop production, and as irrigation water supplies continue to dwindle, the dry-land cotton acreage will grow to well over 3.5-4.0 million acres. Dry-land cotton production is the only agricultural enterprise with any profit potential in this semi-arid region. Analyses of the past 30 years historical county yields indicate considerable year-to-year variability, but the long-term trend is flat. Analyses of rainfall patterns and dry-land cotton yield within each county results in no apparent linear relationship between yield and annual rain nor growing season rain. This lack of a strong correlation provides significant hope that management systems can be developed to increase yields. Most of the dry-land cotton production in the area reflects a cotton monoculture using a skip-row planting pattern on a 40-inch row spacing management system. Analyses of the rainfall pattern reveals that 70% of the annual precipitation occurs from mid-April through mid-October, the cotton growing season. Analyses also reveals that over 70% of the rainfall events are less than 0.5 inch per event. Low volume rains per event coupled with the high evaporative demand (over 0.30 inches per day) during the growing season results in over 50% of the rainfall being wasted to bare soil evaporation in the current skip-row pattern. Only about 2 years out of 10 does sufficient winter precipitation occur to fill the soil profile for use by the subsequent cotton crop. Therefore the crop is growing on current rainfall rather than on stored water supplies. The blank row in the skip-row pattern is essentially wasted space that costs the producer to maintain. Due to blowing sand problems and occasional hailstorms, seeding rates are usually greatly in excess of that required to produce maximum yield within the constraints of the water supply. In fact, the excessive populations within the row exaggerate plant water stress and cause yields to be lower than the water supply should support. Our hypothesis is that by using solid-planted cotton on a narrow row spacing (30-32 inch) at a lower seeding rate per unit row length, and by using the current 33% of the land area in the blank row to grow grain sorghum in rotation, we will make more cotton and more farm profit over a 10 year period than the current system. The goal of this project is to develop a comprehensive management system that will result in increased cotton yields due to reduced risk of excessive water stress during the growing season for dry-land cotton production on the Texas Southern High Plains. Specific Objectives include: 1). Evaluation of individual management strategies which enhance utilization of the rainfall for cotton production. 2). Combining the 'Best Management Strategies' into a production system which increases yield and profit through better utilization of the total water resource. The experimental system used to test this hypothesis was established in 1995 and occupies over 50 acres of land area. The soil is a loamy, fine-sand typical of the vast dry-land acreage in the Southern High Plains of Texas. A split-split plot arrangement is used to test the major components of the experiment, (ie) row direction (north-south versus east-west) and continous skip-row cotton versus solid-planted cotton in rotation with grain sorghum. These variables are not replicated in space but rather in time. Within each year, the experimental design is a randomized block with four replications. Within each system, we compare row spacing, plant population, variety, and fertility.