BUDGETS OF NON-NITROGEN NUTRIENTS IN A HIGH FERTILITY PASTURE SYSTEM

Concentrations and transport of non-nitrogen nutrients in surface runo ff and subsurface flow were determined under a high fertility pasture system during a multi-year study. Most studies of nutrient loss from g rasslands have focused solely or primarily on nitrogen. Nevertheless, maintaining a proper balance of other nutrients is important to health y plant growth, avoidance of toxicity problems from improper nutrient balances, and reduction of potential water quality problems. Rotationa lly grazed grass pastures received 224 kg N/ha annually as NH4NO3 for a 5-year period and had a legume interseeded into the grasses to be th e N source during the following 8-year period. Part of the pastures we re grazed during the summer only. The other pastures were used in the winter months with cattle eating fall regrowth and the hay made on tha t 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 amen dments. Concentrations of P, K, Na, Ca, Mg, Cl, and TOC were measured in surface runoff collected from small watersheds with automated sampl ers and in water from springs draining each area. Nutrient concentrati ons in both surface runoff and subsurface flow were strongly influence d by the amounts of fertilizer and lime applied. The majority of P and K were transported via surface runoff. The concentrations and transpo rt of P and K were greater during the 8-year period because of increas ed rates of application of these fertilizers. Nutrient concentrations in subsurface flow did not vary greatly on a monthly basis but there w ere some increases during the span of the study. Concentrations of K a nd Na changed very little; Mg increased slightly; and Ca and C1 had la rge increases during the 13 years. Increased rates of KCI application during the 8-year period was a primary cause for the increased C1 conc entrations in the shallow groundwater. Concentrations and transport of non-nitrogen nutrients from a pasture system were little influenced b y the summer vs. winter management of this study or the change in N so urce from fertilizer to legumes. The application of non-nitrogen ferti lizers and lime was the major factor of influence. In a pasture system where balances are maintained, the possibility of detrimental environ mental impacts from non-nitrogen nutrients is low. Published by Elsevi er Science B.V.