Non-nitrogen nutrient inputs and outputs for fertilized pastures in silt loam soils in four small Ohio watersheds

Evaluations of non-nitrogen nutrient budgets in pasture systems are limited, and there needs to be greater knowledge of these budgets. Although most nutrient budget studies from grasslands have focused solely or primarily on N, maintenance of a proper nutrient balance is important to healthy plant growth and reduction of potential water quality problems. Budgets of non-nitrogen nutrients were studied in a rotational pasture system during two treatment periods, which received different levels of nitrogen (N) fertility. Rotationally grazed grass pastures in Ohio (USA) received 56 kg N ha^-1 as NH4NO3 for a 5-year period and then 168 kg N ha^-1 for a 10-year period. A topsoil pH of 6.0 and available P and K levels of 28 and 168 kg/ha, respectively, were maintained. Cattle grazed four paddocks during the summer and were fed hay in one of the paddocks during the winter. Inputs of phosphorus (P), potassium (K), calcium (Ca), magnesium (Mg), sodium (Na), and chlorine (Cl) from precipitation, fertilizer, and hay were determined. Losses of these nutrients plus total organic carbon (TOC) were measured in surface runoff and in water from springs draining each area. The majority of the nutrients from the summer only grazed (SG) paddocks were transported in subsurface flow. Hay was the major source of P and K in the winter feeding/summer grazing (WF/SG) paddock, and surface runoff was the major transport pathway for them and TOC. Most of the transport of Ca, Mg, Na, and Cl from the WF/SG area occurred via subsurface flow. Concentrations of P in subsurface flow were low; Na concentrations changed little during the 15-year study; Mg, Ca, and Cl concentrations increased slowly from the SG area but much more rapidly from the WF/SG area. When large amounts of nutrients are brought into an area with hay, there can be a soil buildup of P and K. This increases the possibility for adverse water quality impacts. Nevertheless, the evaluation of nonnitrogen nutrients in pasture systems showed that when they are balanced and meet the plant requirements for the N fertility level, the possibility of detrimental environmental impact is low.