Levels and Changes of Soil Phosphorus in Subtropical Beef Cattle Pastures

Abstract

Long-term pasture management is believed to change soil chemical properties, but little is known about whether pasture management, such as fertilizer application, grazing, or haying can initiate such change in sandy and well-drained subtropical beef pastures. The objective of this study was to investigate the long term effect of pasture management (grazing + haying, GZ + HY) on soil phosphorus (P) dynamics (levels and changes) in subtropical beef cattle pastures with bahiagrass (BG, Paspalum notatum) and rhizoma peanut (RP, Arachis glabrata) with (WP) or without (WNP) P fertilization in Brooksville, FL from 1988 to 2000. Soil P dynamics in Subtropical Agricultural Research Station (STARS) was significantly affected by P fertilization (p ≤ 0.001) and pasture management (p ≤ 0.0001). The soil P levels across years from the fertilized fields of 119.0 ± 4.9 mg kg−1 was significantly higher than those pasture fields with no P fertilization (62.8 ± 7.8 mg kg−1). However, during the past 12 years, there was no P build up despite of the annual application of P-containing fertilizers in addition to the daily in-field loading of animal waste bi-products like fecals and urine. The average soil test values for P in STARS had declined by about 28.3%. The soil test values of P in BG-GZ was about 23% higher than that of BG-GZ + HY, suggesting that GZ followed by HY could have lowered levels of soil P. Soil testing program in the station should continue to measure the amount of soil P that is proportional to what is available to BG and RP, and also continue looking at alternative soil P tests that are better predictors of the loss and/or build up of total and dissolved P to soil and water systems.