Soil Nutrient Survey for Phosphorus and Potassium in the Texas Blacklands and Coastal Plains Production Regions

In most of the high clay content soils, phosphorus (P) and potassium (K) are not generally thought to be major limiting factors for cotton production. However, higher yield potential increases in cotton the demand for nutrients both in the surface layer and sub-surface soils. Nitrogen fertilizer application rates have paralleled the increase in yield potential; however, P and K inputs have remained relatively constant for the past 50 years. This increased crop removal paired with low nutrient applications is causing depletion of P and K in the sub-soil layers. The low mobility of P and K in the soil retains them in the upper layers near the surface where uptake can be minimal, especially under dry conditions.  Additionally, previous nutrient calibration curves were based of surface soil nutrient levels, while in reality, a significant amount of the P and K were being contributed by the sub-soil.  Deep profile soil samples (0-48 inches) were collected in every major row crop production county in the Blacklands and Coastal Plains production regions and will be compiled to determine the P and K sub-soil levels.  This soil survey will demonstrate to producers and scientist the amount of nutrient mining that has occur and may impact future nutrient management recommendations.