Jarrod Miller, Extension Agronomist & James Adkins, Irrigation Engineer

One method to uncover soil variability and crop response is to use precision soil sampling, including either grid or zone methods. These maps can then be used to make variable rate applications, where application rates will change as you cross the field, and GPS helps guide the rates. For this study, soil samples were taken from the upper eight inches of soil on our irrigation research farm in Harbeson, DE. Samples were taken on a 90 by 90-foot grid in April 2022 (Figure 1).

From these grids, maps of nutrients and soil properties were created, including soil pH and buffer pH (Figure 2). Soil pH is measured using water and is the pH your crop will react to. So you use the soil pH measurement to decide if you want to raise or lower your pH. The buffer pH helps figure out any acidity within the soil that will react with lime, causing the need for a higher lime rate (Figure 2b). These two pH measurements were combined using UD recommendations to create a variable rate lime map (target pH = 6.2), which was applied in 2023.