Seasonal Variation of Water Soluble and Total Zinc in Cool‐Season Grasses1

Zinc concentrations in temperate origin perennial grasses do not always meet recommended nutritional requirements for animals. Availability could be affected by factors which contribute to lignification which reduce forage digestibility, and possibly, availability of minerals including Zn. A field plot study was established on Hagerstown silt loam (Typic Hapludalf fine, mixed, mesic) where Zn concentration and Zn water solubility was determined in vegetative material of two cultivars of each of six temperate origin perennial grasses collected in May, August, and October of 1971 and 1972. Total Zn concentrations were positively correlated (P < 0.01) with water soluble Zn especially in material produced in August and October. Total Zn concentrations and percentage Zn solubility [(water soluble Zn/total Zn) ✕ 100] were inversely related among species; for example, reed canarygrass (Phalaris arundinaceaL.) ranked first among the species for total Zn (23 ppm) and last for percent solubility (61%), while tall fescue (Festuca arundinaceaSchreb.) ranked last among the cultivars for total Zn (15 ppm) and first for solubility (84%). Total Zn concentrations were positively correlated (P < 0.01) with in vitro dry matter digestibility; Zn solubility (%) was not. The data show Zn concentrations vary with season and that all species and cultivars do not exhibit the same pattern of variation. Therefore, careful species and cultivar selection should be considered, particularly where there is evidence of Zn inadequacy in ruminant diets.