Date of Award:

12-2010

Document Type:

Thesis

Degree Name:

Master of Science (MS)

Department:

Plants, Soils, and Climate

Advisor/Chair:

Jennifer W. MacAdam

Abstract

Species diversity achieved by adding novel functional groups (warm-season grasses and non-leguminous forbs) to pasture land, along with traditional grasses and legumes, could aid in the capture of nutrients and water in pasture systems by offering complementary rooting architecture to aid in water and nitrogen uptake and decrease nitrogen leaching. Because these species may differ from commonly used grasses and legumes in their seasonal pattern of productivity, they could also extend or enhance growing-season productivity. The goal of this project is to better understand the role of plant diversity in 1) nitrogen use and 2) distribution of rooting dynamics and forage production. On a larger scale, this project hopes to identify pasture mixtures with greater diversity and management practices that maintain desirable pasture composition and livestock productivity. Herbage dry mass (DM), root surface area (RSA), and 15N uptake of nine species grown individually in the greenhouse were measured in the first experiment. Species which performed well or which were of particular interest to our study were used in mixtures in the second experiment, which contained varying numbers of functional groups. Individual species grown in monoculture varied in DM production over the course of the experiment, but there were no differences among mixtures, which all increased similarly in DM. Herbage DM of mixtures was 72 to 110% of that predicted by Experiment 1. The RSA of tap-rooted species was low and varied little with depth, while the RSA of cool-season grasses was higher closer to the soil surface. The RSA of mixtures decreased linearly with increased depth, and was between 150 and 350% higher than predicted from the RSA of individual species. Legumes, which have higher foliar protein content than grasses, accumulated more 15N in shoot DM than grasses, but mixtures did not differ from one another. It is concluded that the DM production advantage of mixtures is more consistent yield. Furthermore, increasing the diversity of simple grass-legume mixtures by adding non-leguminous forbs or other functional groups will likely improve water-use efficiency, thus reducing the risk of nitrate leaching compared with low-diversity grass-legume mixtures while fully exploiting biological nitrogen fixation.

Comments

This work made publicly available electronically on January 19, 2011.

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