Response of Native Grassland Legumes to Water and Nitrogen Treatments

Abstract

The response of native shortgrass prairie legumes to water and nitrogen additions was evaluated utilizing a replicated factorial design of two water and two nitrogen treatments. Responses measured were densities and aboveground biomass by species. Water treatment greatly increased both density and biomass of legumes, presumably because of more favorable conditions for nitrogen fixation and increased competitive advantage under nitrogen deficient conditions. The availability of nitrogen, more than any other mineral element, is a critical determinant of both the structure and productivity of grassland plant communities (Date 1973). Additionally, mineral nitrogen supplies to the plant community largely determine the value of the biomass produced as forage for consumers. In native grasslands nitrogen-fixing plants are presumed to occupy an important position in nitrogen cycling although for most grasslands very little is known about the ecology or functional significance of native legumes (Becker and Crockett 1976). This is particularly true of the semiarid grasslands of the Great Plains of North America. The majority of the information available concerning the ecology of legumes in these grasslands is available as an incidental portion of the data collected on the dominant grassland plants (Albertson 1937; Hanson and Whitman 1938; Dyksterhuis 1946; Brown 1971; Hyder et al. 1975). As a first step in understanding the functional role of legumes in a shortgrass prairie, we provide basic phytosociological data for legumes under ambient environmental conditions and results from experimental manipulation of soil water and mineral nitrogen availability.