Date of Award
Doctor of Philosophy
Kenneth J. Moore
Legumes improve the quality and production of forage in pastures. Their distribution and abundance, however, depend on landscape position and grazing management, and their productivity, as percentage of dry matter, is correlated positively to the number of legume species found across pasture landscapes. The objectives of my dissertation were to: (i) evaluate why legumes exhibit site-specific adaptations in pastures; (ii) determine the effect of landscape position and grazing management on plant species composition and diversity; and (iii) quantify the relationship between the distribution and abundance of legumes and gradients of slope and soil electrical conductivity in pastures. I addressed these objectives with three experiments. In the first experiment, I measured the emergence and survival of legumes on summit and backslope landscape positions under varying N fertilization and sward cutting height treatments. I found legume establishment on summit landscape positions is limited by poor survival of seedlings. On backslopes, grass competition is less, and legume establishment is successful in swards cut at 5 cm. In the second experiment, I used a multi-scale sampling method to measure the effects of landscape position and grazing management on the occurrence and diversity of legume and grass species in pastures. I found legume and grass species diversity was greatest on backslope landscapes. Diversity increased with scale but at a greater rate in grazed than nongrazed pastures. Increasing sample scale enables greater detection of minor forage species. In the final experiment, I found legumes in pastures, as a % of vegetative cover, are most successful at 15 to 20% slopes and intermediate values of soil EC. Competition from grass limits the occurrence of legumes at slopes <10% and at low and high values of soil EC. The results from these studies support the hypotheses that the distribution of legumes and plant diversity in pastures is strongly related to topography, and that sound grazing management is essential to the maintenance of legumes and plant diversity in pastures. I recommend a diverse assemblage of legumes be seeded on backslope landscape positions to optimize pasture production and the availability of nutrients over space and time.
Digital Repository @ Iowa State University, http://lib.dr.iastate.edu
John Andrew Guretzky
Guretzky, John Andrew, "Distribution of legumes and plant diversity in pastures that vary in landscape position and grazing management " (2002). Retrospective Theses and Dissertations. 513.