Delineating Cotton Irrigation Management Zones and Monitoring Station Locations in Variable Water Holding Capacity Soils Based on 5 Years of Experimental Yield Data

From 2010 to 2014, optimum cotton yield was determined from seven irrigation treatments in three soils with distinctly different water holding capacities (WHC) at the West Tennessee Research and Education Center in, Jackson, TN.  From these results potential field scale yields can be estimated from any mix of these three soils in a hypothetical field based on one of five water regimes: rainfed, a single irrigation decision based on optimizing yield in one of the three soil types, or a variable irrigation decision that optimizes yield in all soil types.  Irrigating to meet the water needs of the sandiest soil (lowest WHC) often optimizes yield for the entire field even when sandy soil is only 25% of a field because the yield response to irrigation is greater in sand than in the other soil types.  At the same time, sandy soils require more irrigation than the other soils and these higher rates of irrigation cause some cotton yield reduction in the higher WHC soils.  These yield responses are being analyzed to determine how to delineate Cotton Irrigation Management Zones (IMZ) and where to locate sensors (which soil type) within an IMZ or within a whole field in order to maximize yield for that field.  Of course, economics can shift IMZ delineation because it is more expensive to irrigate the sandy soils.