Use of DGPs, Yield Monitors, Soil Testing, and Variable Rate Technology to Improve Phosphorus and Potassium Management

New technologies such as differential global positioning systems (DGPS), yield monitors and other sensors, variable rate technology, and associated practices (such as grid soil sampling) have potential to improve soil fertility management. Soil sampling in the field is one of the most important sources of error in soil testing. A very small amount of soil needs to appropriately represent thousands of tons of soil and usually there is significant spatial variability of nutrient levels. The expectation of many producers and agronomists is that grid sampling will adequately describe field nutrient availability and that variable rate fertilization will result in better soil fertility management and increased profits to producers. Many also believe that variation in nutrient levels explains much of the yield variability within fields. Studies of the spatial variability of nutrient supplies, sampling methods, and relationships between nutrient levels and crop yields are essential to assess if these expectations are reasonable. Once reliable and cost-effective sampling schemes are identified, the agronomic and economic advantage of variable rate fertilization can be reasonably estimated from amounts of fertilizer applied, expected yield responses, and the costs involved