Summary of Rice Response to Phopshorus Fertilization in Mississippi.

Phosphorus deficient rice was identified in MS in the late 1990’s, with soil test correlation and calibration trials established in 2002.  Across the rice belt yield increases have been shown to P fertilization, however traditional soil test methods have been poor predictors of yield responsiveness.  This data will summarize and explore phosphorus correlation/calibration research from the last 13 years in Mississippi. Our objective is to better predict when a yield response to phosphorus fertilization will occur based on routine soil testing.Field Experiments were established between 2002-2015 at the Delta Research and Extension Center (DREC), and on production farms in the Mississippi Delta area. Soybean [Glycine max (Merr.) L.] was the previous crop grown at all site-years.. Most trials received P fertilization between planting and the 2-LF stage of rice growth and development. A limited number of trials evaluated timing in the structure with P application timing ranging from fall to midseason.  In all trials phosphorus application rates ranged from 0 to 100 lb P₂O₅ ac^-1 in 25 lb P₂O₅ ac^-1 increments. Rice grain yield was significantly influenced by P fertilization rate at 16 of 34 site-years.  Averaged across both responsive and non-responsive site-years, P fertilization increased rice grain yield by 225 lb ac^-1.  When considering only sites that responded positively (p<0.20) to P fertilization yields were increased above the untreated control by approximately 585 lbs ac^-1.  Evaluation of distribution of soil test levels at responsive sites (n = 16) suggested that approximately 46% fell below 10 ppm soil test P, 62% < 20 ppm soil test P, and 85< 30 ppm soil test P. For non-responsive sites (n=18) approximately 75% of sites had soil test P below 30 ppm P.  On non-responsive sites relative yield from the untreated control ranged from 94 to 100%.  This data further illustrates the need for additional research centered on determining additional methods to determine crop responsiveness to soil test P.