Effect of Site and Fertilization on Protein Content of Native Grasses

Abstract

Protein content of selected native range grass and sedge species was followed during the course of the growing season over a 6-year period on four major range sites in western North Dakota. The study included three rates of nitrogen fertilizer plus some added treatments of phosphorus alone and in combination with nitrogen during the study. Protein content varied appreciably between the same species on different sites, different species on the same site, and between the same species on the same site due to fertilization. Certain species were inherently high in protein content (Agropyron smithii), while others were intermediate (Stipa comata and Stipa viridula), and still another was comparatively low (Bouteloua gracilis). The presence of nitrogen fertilizer generally increased protein content of all species regardless of level of treatment or site; the magnitude of increase, however, varied greatly between sites and species. Decline in protein content is progressive in all species with the advance in maturity regardless of fertilizer treatment level or site. However, the rate of protein loss is accelerated with fertilization and becomes more rapid with a decline in summer moisture. Cool-season species show a more rapid protein loss than was observed from warm-season Bouteloua gracilis. The length of the grazing period when forage values remain near the minimum protein requirement is appreciably extended on some sites with certain species, especially Bouteloua gracilis. Proper range management must take into consideration the potential of each major range site and the inherent species capabilities to produce and maintain a high level of protein for an extended period of grazing.