Environmental impacts of land application of biosolids to perennial pastures

Land application of biosolids to pastures confers multiple agronomic and environmental benefits, particularly in coarse-textured soils with low nutrient and organic matter levels. However, concerns over potential water quality have led to more stringent regulations that will limit beneficial reuse of biosolids in Florida. This 3-year field study evaluated the impacts of biosolids application strategies on N and P leaching losses, and soil P availability in an established bahiagrass (Paspalum notatum Flueggé) pasture. Treatments consisted of 2 P sources (biosolids and inorganic fertilizer) applied at 0, 20, 40, and 60 kg total P ha^-1. Inorganic fertilizer treatments received the same N loads as the corresponding biosolids treatments. Biosolids and inorganic fertilizer increased in situ soil P availability and pore-water P concentrations relative to the control. Pore-water P concentrations increased linearly with P rate with the greatest values generally associated with inorganic fertilizer. Relatively low leachate P concentrations (below the detection limit of 0.025 mg L^-1 in 596 out of 777 samples) observed in the current study indicates minimum P offsite movement risk regardless of the P management strategy. Annual P mass leached was not affected by treatments; however, inorganic fertilizer resulted in modest but significant greater annual NO₃-N mass leached than the other treatments. Lack of biosolids application rate effect on P and N leaching losses indicates that reduction in biosolids imposed by new state regulation will likely have no positive impact on water quality. Data demonstrated that, when properly managed, biosolids can be an environmentally sound fertilizer source for pastures.