Cotton Yield and Soil Test P As Influenced By Phosphorus Fertilzation.

A 4-year study was initiated in 2010 to evaluate cotton response to phosphorus (P) fertilization in a continuous rain-fed production system with and without AVAIL® Phosphorus Fertilizer Enhancer from Specialty Fertilizer Products, Inc.  The study consisted of a factorial arrangement of P rates (0, 20, 40, and 60 lb P/acre) and AVAIL (0 or 0.5 gal/ton).  All treatments were included in a randomized complete block design with six replications.  Pre-weighed concentrated superphosphate (CSP, 0-46-0) was applied to the surface in the fall of each year following cotton harvest.  Primary and secondary tillage was then used to incorporate the fertilizer material.  Cotton was grown under uniform cultural practices and harvested following defoliation with a commercial cotton picker adapted for plot harvest.  Grab-samples were collected at the time of harvest and then ginned through a 10-saw micro-gin to determine lint percentage and calculated lint yields.  Soil Samples were then collected immediately following harvest and prior to the next P addition.  Seedcotton and lint yields have shown no significant response to increasing P rates.  Soil test P levels have increased with fertilizer P additions as would be expected.  Adding AVAIL Phosphorus Fertilizer Enhancer was not effective in increasing cotton yields in this study where soil test P levels were high.  This study supports to need to soil test on a regular basis and follow the prescribed recommendations.  Fertilizer additions under high test situations are not likely to occur and buildup on soil test levels are to be expected.  The AVAIL product may be effective in P deficient soils but further evaluations under those conditions.  Fertilizer P additions in excess of crop removal should result in a buildup of soil test P levels as shown.