Submitted to: Government Publication/Report
Publication Type: Government Publication
Publication Acceptance Date: November 3, 2010
Publication Date: November 3, 2010
Citation: Sassenrath, G.F. 2010. Irrigation scheduling for humid environments. Government Publication/Report. Fact Sheet No. 2010-03. Interpretive Summary: Irrigation can increase crop yields when water is applied correctly. Unpredictable rainfall and highly variable soils make water management in humid growing areas such as the Mississippi Delta particularly challenging. To ensure adequate yields, farmers are increasingly using irrigation to supplement the sporadic and often insufficient rain during the growing season. Mississippi receives high rainfall throughout the year, but the alluvial aquifer, the source for irrigation water, is being mined since more water is pumped from the aquifer than is recharged. Wise water management requires knowledge of how much water the crop needs and when the water is needed. Irrigation scheduling is a method of managing water to better match the timing and application of irrigation with crop water use. Several methods are available to monitor or estimate the loss of water through evaporation from the soil surface or transpiration from the crop, termed evapotranspiration (ET) and schedule irrigation. One method of scheduling irrigation is based on estimating crop water use from weather conditions and calculating total available soil moisture. A water balance is then determined as the initial water in the soil, plus water from rainfall or irrigation, minus water used by the crop or evaporated from the soil (ET). This “checkbook” method sums the water balance of the soil and indicates the need for irrigation when the available soil water falls below that which is readily available for the plant (Figure 2). The checkbook method relies on knowledge of crop water use, soils, and weather during the growing season to make an estimate of crop water use and show the need for irrigation. An irrigation scheduling tool using the checkbook method is currently under development for Mississippi.
Technical Abstract: Increased reliance on supplemental irrigation in the humid Mid-South has resulted in declining levels of the alluvial aquifer. While the area receives high rainfall levels, the intermittent and unreliable rainfall reduces crop yields in certain years. Methods of detecting the onset of water stress based on crop temperature or reflectance have been successfully employed in arid regions. However, the high humidity levels, frequent cloud cover and low evaporative cooling potential make detection of crop water stress challenging in the Mid-South. Estimating crop water use is possible by using weather information to calculate crop water use, correcting for specific crops with crop coefficients. These estimates of crop water use can then be used in a water balance method to determine when irrigation is required. A team of researchers is developing a irrigation scheduling tools for use in the Mid-South. The tools will be delivered through a web-based interface, allowing farmers real time access to information in the field.