Be aware, however, that overapplying P to soils can enhance decline in surface water quality by providing increased levels of P to surface waters and aquatic plants. Many Iowa producers are interested in finding ways to squeeze profit out of their input dollars while avoiding negative impacts related to the environment and water quality. Managing soil P levels is one way to address profitability and environmental sustainability. And it is an important one. To make informed decisions about P application, producers need to know what plant-available levels exist in their soil.
Soil tests are the only reliable way to determine the status of available nutrients in a field.
Reliable soil test results and recommendations depend upon good soil sampling, calibrated soil analysis procedures, and research-based fertilizer recommendation guidelines. With accurate soil test results, producers can calculate their specific fertilization needs and make good decisions about the application of P to meet reasonable crop yield expectations. Phosphorus losses Phosphorus is strongly adsorbed by soil particles and readily retained in soil. Therefore, if P moves to surface waters, it does so primarily with eroded soil, but it also is dissolved in runoff water. Avoiding P movement to streams, rivers, and lakes is largely dependent upon maintaining agronomically optimum and not excessively high levels of plant-available P in the soil, and then keeping that soil in place.