Seasonal Dynamics of Minerals in Forages at the Texas Experimental Ranch

Abstract

Range livestock derive the bulk of their dietary mineral intake from forages that are often deficient in one or more essential minerals. The objective of this study was to quantify the seasonal dynamics of phosphorus (P), potassium (K), calcium (Ca), and magnesium (Mg) concentrations in the dominant native forages at the Texas Experimental Ranch. Concentrations were estimated by class of tissue (live and dead) for 5 species/ species groups: sideoats grama (Bouteloua curtipendula Michx.), Texas wintergrass (Stipa leucotricha Trin. and Rupr.), annual grasses, other warm-season grasses, and forbs. The study spanned a period of 2 years and included 16 sample dates. Although P, Mg, and K concentrations varied significantly among species and date, they varied primarily as a function of class of tissue. Averaged across dates and species, concentrations of P, Mg, and K in live tissue averaged 0.12, 0.13, and 2.02%, respectively, while concentrations in dead tissue averaged 0.04, 0.09, 0.57%, respectively. As a result, seasonal differences in whole plant concentrations of P, Mg, and K were closely linked to seasonal growth dynamics as they affect live/ dead ratios. Ca concentrations were affected more by species than class of tissue. Averaged across dates, Ca concentrations in live tissue averaged 0.55, 0.40, 0.42, 0.35, and 1.80%o in annual grasses, Texas wintergrass, sideoats grama, other warm-season grasses and forbs, respectively, while concentrations in dead tissue averaged 0.41, 0.40, 0.41, 0.36, and 0.96%, respectively. It is concluded that considerations must be given to the potential effect that a given treatment may have on plant growth dynamics to properly interpret its effect on whole plant concentrations of minerals.