Temporal Nutrient Dynamics in Grazed Cool-Season Pastures.

Achieving optimal mineral nutrition and animal performance in pastured-based livestock systems requires maintaining adequate mineral concentrations in both soils and plant tissue. Assessment of pasture fertility is commonly preformed through soil testing, but analysis of plant tissue may provide more accurate information. The objective of this study was to analyze relationships between soil and forage tissue nutrient concentrations in grazed pastures and evaluate how well they predict the mineral requirements of beef cattle. Twelve sets of 8 or 9 rotationally-stocked tall fescue- (Schendonorus phoenix (Schreb.) Dumort.) predominated paddocks at the Virginia Tech Shenandoah Agriculture Research and Extension Center in Steele’s Tavern, VA were grazed by cow-calf pairs across a 5-year experimental period. Soil was sampled from the 96 paddocks during late fall of each year and herbage tissue was sampled monthly during the growing season. Concentrations of soil nutrients remained stable across the 5-year grazing period. Herbage tissue concentrations fluctuated throughout each growing season, with lowest average mineral concentrations occurring in July. With no additional feed during the growing season or added fertilizer, all average herbage mineral concentrations, except Zn and Cu, remained above the mineral requirements recommended for gestating beef cows. The results of this study indicate that, as expected, soil nutrients are mostly recycled within pasture systems. In terms of predicting forage mineral concentrations for livestock feed, forage tissue analysis provides little additional information as compared to soil test results that indicate adequate nutrient concentrations for pasture production.