Cotton is a relatively drought-tolerant and salt-tolerant crop that generally responds well to irrigation. Cotton can be produced over a range of irrigation levels, from rain-fed (dryland) to deficit to full irrigation. Cotton water use efficiency is generally higher under managed deficit irrigation than under full irrigation; however excessive water deficit or drought stress at critical growth stages can have a considerable negative impact on yield potential for the crop.
- Increase understanding of water requirements (peak water use, seasonal water use, critical growth stages, drought sensitivity/tolerance, and water quality requirements) of cotton.
- Increase water use efficiency and profitability in cotton production through application of appropriate best management practices.
- Key Points:
- Cotton is relatively tolerant to drought and salinity.
- Seasonal water use for cotton in the Texas High Plains is approximately 13 to 27 inches per season. Seasonal water demand is generally 24 to 28 inches. Deficit irrigation management (water available is less than crop demand) is common practice, often due to limited water supply.
- Peak water use occurs during flowering and boll development.
- The most critical period during which water stress will have the greatest effect on yield is early in the season when drought stress can cause square shedding.
- Excessive irrigation and excess available nitrogen can encourage excessive vegetative growth, necessitating use of plant growth regulators.
- Assess your knowledge:
- What is the peak water use of cotton in you area? When (growth stage and calendar range) does this occur?
- What is the maximum effective root zone depth for cotton? Are there other factors in your field or management program that you would expect to limit this effective root zone depth? What practical significance do these limitations have with respect to your irrigation and nutrient management programs?
- Are there water quality (salinity) concerns for cotton production on your farm? If so, what are they? How can they be managed?
- What irrigation method do you currently use to irrigate cotton? What best management practices (BMPs) are you using to optimize water use efficiency? Identify other methods and BMPs that would be applicable to your operation.
- Pre-Plant, Planting and Stand Establishment
Roots grow in moist soil (not in saturated or dry soil); hence good moisture conditions in the root zone are key to establishment of a good root system early in the season. An extensive root system improves the crop’s access to moisture and nutrients from a larger area of the soil profile.
In West Texas, fields are often pre-irrigated because of limited rainfall in the winter and spring. The timing of pre-irrigation depends on water availability, soil texture and the time required for the soil to drain adequately before planting. The amount of water applied depends on rooting depth, available moisture-holding capacity and current soil moisture.
- Emergence to First Bloom
During the emergence to first bloom growth stage, decisions on water, fertilizers and plant growth regulators are important. Water use increases dramatically, from less than 1 inch per week at emergence to 2 inches per week at first bloom. The goal is to avoid water stress early in the season and to have a full soil water profile as the plant reaches peak bloom (usually 3 weeks after bloom for most regions of Texas).
- First Bloom to First Open Boll
The plant’s water use increases dramatically during the stage from first bloom to open boll. Estimated evapotranspiration (water used by the plant and evaporated from soil) water use can be as high 0.4 inches per day or 2.8 inches per week. Because the soil is the storage site for water available to the plant, the primary factors in determining water-holding capacity are soil texture and root zone depth. Soils with course (sandy) textures tend to hold less water than loam and clay soils. Rooting depth is affected by both chemical and physical soil characteristics; water tables, dry layers, hard pans, caliche layers and salt accumulation zones limit rooting depth. Once blooming starts, cotton prefers frequent, low-volume applications of water rather than large, less frequent amounts. This strategy minimizes the degree of water stress between rain or irrigation events and thus increases fruit retention.
In West Texas, very few producers have the irrigation capacity to satisfy crop demands (0.3 to 0.4 inches per day). Highly efficient advanced irrigation technologies, including low pressure center pivot irrigation (LEPA-low energy precision application and LESA- low elevation spray application) and subsurface drip irrigation have proven to be excellent tools in these water-limited production systems. Research indicates that cotton responds very well to high-frequency deficit irrigations, even with amounts as low as 0.20 to 0.25 inch applied every 2 days. When irrigation capacities are above 0.2 inch per day, the frequency of irrigation is not as critical.
- First Open Boll to Harvest
At peak bloom, cotton requires about 0.3 inch of water per day. By harvest, the rate will drop considerably, to less than 0.1 inch per day. Ideally dryland producers would have a full profile of moisture at the third week of bloom, followed by a couple of timely rain showers. Producers with furrow irrigation have more control than dryland producers but still must make the last irrigation before bolls open. Late applications of excessive water can lead to many problems, including boll rot, late season re-growth, an increase in late-season insect pests, added harvest aid inputs and possible grade reductions from late-season re-growth. In West Texas, furrow irrigation should be terminated before September 1. Sprinkler or drip irrigation should be continued for 1 to 2 weeks after open boll or until 20 percent of the bolls are open. The goal is to provide adequate moisture for the last harvestable bolls to mature.
Adapted from: Sansone, Christopher, Thomas Isakeit, Robert Lemon, and Billy Warrick. Texas Cotton Production Emphasizing Integrated Pest Management. Texas AgriLife Extension Service (formerly Texas Cooperative Extension). Available here. (Accessed 12-21-07)