Dairy production accumulates large quantities of effluent in lagoons. Sometimes, lagoons overflow causing the nutrients and other contaminants in effluent to pollute the land and associated water bodies. Alternative uses of effluent are urgently needed for a more sustainable and environment-friendly dairy production. This study determined the sustainable effluent application rate and assessed the effects of effluent irrigation on the retention, accumulation and movement of nutrients, especially phosphorus (P), in the soil (Cumulic Haplustoll). Four tropical grasses—bana (Pennisetum purpureum K.), signal (Brachiaria decumbens S.), star (Cynodon nlemfuensis V.), and suerte (Paspalum atratum S.)—were subsurface drip irrigated with dairy effluent at two rates based on potential evapotranspiration (ET_p) at the site (Waianae, Hawaii)—2.0 ET_p (7-44 mm d^-1) and 0.5 ET_p (2-11 mm d^-1). Treatments were arranged in an augmented completely randomized design. Forage was harvested and soil and soil solution were collected every month. Changes in P sorption with time were determined. Soil P was extracted with recommended (Olsen) and acid extractants (Modified Truog and HCl). Extractable soil P and soil solution total P did not significantly increase despite daily irrigation for two years, even at twice the ET_p. No substantial downward movement of P was observed. These findings suggest that this plant and soil system can be irrigated with effluent at 2.0 ET_p–-a substantially higher rate than that designed for irrigation objectives. Calcium-phosphate precipitation in the soil was indicated by the calculated phosphate potentials for dicalcium phosphate dihydrate, octacalcium phosphate and tricalcium phosphate, and higher extractable soil P with acidic extractants. Additional monitoring is needed to determine the longer-term impacts of effluent application on plant and soil properties, especially on P accumulation and movement in the soil profile. The information generated will allow dairy producers to reduce feed costs while minimizing pollution associated with effluent application—thus, creating a win-win option.