Phosphorus Fertility Evaluation in Graham County

Abstract

A series of three phosphorus (P) fertility experiments were conducted in 2001 in Graham County. These studies follow similar experiments conducted over the past three seasons. Results from 2001 were consistent with previous results indicating a positive relationship between yield and P fertilizer applications in relation to soil test indices. Modest yield increases were observed from a minimum of 25 to 80 lbs. lint per acre with an application of approximately 70 lbs. of P as P₂O₅ per acre. Yield differences from previous years have been as great as 170 lbs. of lint per acre. With the increased use of UAN-32 as a primary fertilizer source and a reduction in the application of P fertilizers, which is typically associated with a rotation of small grains, a depletion of soil P is a potential result. A continuation of this research with varying rates of P fertilizer will take place in 2002 in an attempt to relate soil test P levels to yield increases observed in recent years. The results of this research demonstrate the possible need for a return to use of fertilizers with supplemental P for optimum yields that would be predictable based on soil test results.