Comparison of soil phosphorus extractants as affected by fertilizer phosphorus sources, lime recommendation and time among four Arkansas soils

Phosphorus (P) sources were evaluated for their usefulness as P fertilizers in four acid Arkansas soils. Soils were amended with acidulated rock phosphorous, Florida rock phosphate, liquid ammonium phosphate, North Carolina rock phosphate, and triple superphosphorous, at 50 mg P kg(-1). After application, the soils were incubated for two years at 33 kPa soil moisture potential, with samples taken periodically. At each sampling Mehlich III (M-III) and Bray-Kurtz PI (BK1) extractants were used to measure available P levels. Acidulated rock phosphate was consistently the best P source for all soils, although P levels were significantly raised above the check by all P sources. Mehlich III extracted significantly more P than did BK1 for all soils. Phosphorus release varied among amendments during the incubation period. Acidulated rock phosphate, liquid ammonium phosphate, and triple superphosphate exhibited rapid initial release. The Florida and North Carolina rock phosphates did not achieve their maximum P release until one year of incubation. The correlation between extractants for P was M-III= 1.2 + 1.06 (BK1) with r(2) = 0.94.