Retention, Accumulation, and Movement of Phosphorus in a Mollisol Soil Irrigated With Dairy Effluent in a Tropical EnvironmentValencia-Gica, Rowena B.; Yost, Russell S.; Porter, Guy S.; Pattnaik, RosalinSoil Science: October 2010 - Volume 175 - Issue 10 - p 500-510 doi: 10.1097/SS.0b013e3181f79669 Technical Article Abstract Author Information Dairy operations generate large quantities of effluent, which are stored in constructed lagoons. Lagoons, however, have finite storage capacity and can overflow, potentially polluting land and associated water bodies. Alternative uses of effluent are, therefore, needed for a more sustainable and environment-friendly dairy production. This study assesses the effects of effluent irrigation on the retention, accumulation, and movement of phosphorus. Four grasses-Bana (Pennisetum purpureum K. Schumach.), California (Brachiaria mutica [Forssk.] Stapf.), Star (Cynodon nlemfuensis Vanderyst), and Suerte (Paspalum atratum Swallen)-were subsurface (20-25 cm) drip irrigated with effluent at two rates based on potential evapotranspiration (ETp) at the site (Waianae, HI)-2.0 ETp (16 mm d−1 in winter; 23 mm d−1 in summer) and 0.5 ETp (5 mm d−1 in winter; 6 mm d−1 in summer). Treatments were arranged in an augmented completely randomized design. Most of these grasses produced large amounts of dry matter with effluent irrigation. California grass receiving the 2.0 ETp effluent application outyielded all other grass species, producing 60 Mg ha−1 year−1. Olsen soil phosphorus (P) and soil solution P did not significantly increase despite daily irrigation for at least 2 years and when irrigated at 2.0 ETp. A relatively small amount of P was measured at deeper soil depths at the 2.0 ETp irrigation rate (131 kg ha−1 year−1). Calcium-phosphate precipitation was predicted by calculated phosphate potentials. Acid-extractable soil P increased, supporting the hypothesis of Ca-P precipitation. Department of Tropical Plants and Soil Sciences, University of Hawaii at Manoa, 3190 Maile Way, St. John 102, Honolulu, HI 96822. Dr. Rowena B. Valencia-Gica is corresponding author. E-mail: firstname.lastname@example.org Received March 25, 2010. Accepted for publication August 16, 2010. © 2010 Lippincott Williams & Wilkins, Inc.