Budgets of non-nitrogen nutrients in a high fertility pasture system

Abstract

Concentrations and transport of non-nitrogen nutrients in surface runoff and subsurface flow were determined under a high fertility pasture system during a multi-year study. Most studies of nutrient loss from grasslands have focused solely or primarily on nitrogen. Nevertheless, maintaining a proper balance of other nutrients is important to healthy plant growth, avoidance of toxicity problems from improper nutrient balances, and reduction of potential water quality problems. Rotationally grazed grass pastures received 224 kg N/ha annually as NH 4NO 3 for a 5-year period and had a legume interseeded into the grasses to be the N source during the following 8-year period. Part of the pastures were grazed during the summer only. The other pastures were used in the winter months with cattle eating fall regrowth and the hay made on that area during the summer. Topsoil pH of 6.5–7.0 and available P and K levels of 56 and 336 kg/ha, respectively, were maintained by soil amendments. Concentrations of P, K, Na, Ca, Mg, Cl, and TOC were measured in surface runoff collected from small watersheds with automated samplers and in water from springs draining each area. Nutrient concentrations in both surface runoff and subsurface flow were strongly influenced by the amounts of fertilizer and lime applied. The majority of P and K were transported via surface runoff. The concentrations and transport of P and K were greater during the 8-year period because of increased rates of application of these fertilizers. Nutrient concentrations in subsurface flow did not vary greatly on a monthly basis but there were some increases during the span of the study. Concentrations of K and Na changed very little; Mg increased slightly; and Ca and Cl had large increases during the 13 years. Increased rates of KCl application during the 8-year period was a primary cause for the increased Cl concentrations in the shallow groundwater. Concentrations and transport of non-nitrogen nutrients from a pasture system were little influenced by the summer vs. winter management of this study or the change in N source from fertilizer to legumes. The application of non-nitrogen fertilizers and lime was the major factor of influence. In a pasture system where balances are maintained, the possibility of detrimental environmental impacts from non-nitrogen nutrients is low.