Using Grid Soil Sampling to Determine Profit Maximizing Phosphorus Application Rates in Wheat

Past research on the profitability of precision phosphorus (P) application has used a small number of fields and a short time frame. Data on grid-sampled fields provided by producers are used to define the distribution of phosphorus within fields. Expected yields and net present value (NPV) are simulated to compare variable and uniform rate P. The highest NPV used a variable rate that changed each year based on yield and predicted carryover. A variable rate using the same rates for 4 years was inferior to simply applying a little extra P at a uniform rate.