FAS Abstracts 2004 Meeting Page

Agricultural Sciences (AGR): AGR-17

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Effects of applied phosphorus (P), lime and gypsum on Stargrass forage yield and quality, and water quality.  M.B. ADJEI (1), J.E. RECHCIGL (2), and I.S. ALCORDO (1).  (1) Univ. of Florida, Range Cattle Research, Ona, FL 33865, (2) Univ. of Florida, Gulf Coast Research and Education Center, Bradenton, FL 34203.  Phosphorus is the primary cause of eutrophication and algae blooms of lakes in south-central Florida and excessive P fertilization on pasture may contribute to the problem.  Treatments for a field experiment conducted in the Lake Okeechobee Basin consisted of 0, 12.5, 25.0, and 50.0 kg P ha^-1 yr^-1 from triple super phosphate.  Additionally, the soil amendments calcium carbonate (CaCO₃) and mined gypsum (CaSO₄)  were applied at 0.2 and 4.0 Mg ha^-1 yr^{- 1} based on 100% CaCO₃ to other plots that received 50.0 kg P ha^-1 yr^-1. Each P or P and soil amendment treatment was applied to 15.2 x 30.4 m plots on a stargrass (Cynodon  nlemfuensis Vanderyst) pasture arranged in a RBC with four replicates.  Stargrass forage yield, crude protein and digestibility were not impacted by P fertilizer for 3 yr.  Although applied P improved tissue P concentration, most cattle producers routinely feed a balanced mineral mix.  Applied P caused significant buildup of P in the Ap, E and Bh soil horizons, increased soluble P concentration in shallow and deep wells by 400% and 1500%, respectively, and in surface runoff by 50%.  Gypsum was not beneficial in reducing P in surface runoff.  Although Ca-lime amendment reduced total P in surface runoff, its long-term benefits are not clear due to equilibrium effects.  This study collaborated results from other multi-county studies to provide strong support for the recent reduction in IFAS P fertilizer recommendation on improved grass pastures in south Florida from 40 to 20 kg P ha^-1 yr^-1 at no cost to forage production.