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Iowa pastures are diverse in the landscapes and soil conditions present within small area units. Introducing legumes into these areas has the potential to improve seasonal distribution and quality of the pasture forage. This study was performed to quantify the spatial and temporal variation in legume contribution to the plant community when seeded into established cool-season grass pastures. Pastures were seeded with a mixture of eleven legumes and then divided into three grazing methods (non-grazed, continuous, and rotational), with each grazing method containing five landscape positions (upland, sideslope, bottomland, opposite sideslope, and opposite upland). Legume dry matter composition, legiune species richness, legume diversity, and forage quality were determined during the grazing season and associated with site soil characteristics. Sideslope positions had greater legume dry matter composition (161 g kg ') than either the upland (62 g kg'') or bottomland landscape positions (7 g kg''), and legume concentrations increased as the growing seasons progressed in the grazed treatments. Legume species richness also was greater for sideslope landscape positions. Legume dry matter composition showed a strong, positive linear relationship to species richness in continuous, rotational, and non-grazed treatments (r^O.77,0.84, and 0.74), and may potentially be utilized as a tool to estimate the need for reestablishment in these pastures. Legume dry matter diversity using the Shaimon-Wiener index was greatest for grazed pastures, but was positively linearly related to legume dry matter composition in only rotationally grazed paddocks (r^O.88). Upland and xvi bottomland sites with the greatest total available dry matter herbage production potential contained the lowest legume concentrations and legume herbage. Forage NDF was lowest and IVDMD was greatest on sideslopes (527 g kg*', 630 g kg ") compared to uplands (552 g kg ', 608 g kg ') and bottomlands (568 g kg"', 560 g kg '). Of all spatial and temporal variables, land slope best explained the variation in legume dry matter composition (r^O.66) and species richness (r=0.75). Competition resulting from the greater grass component at lesser slopes appeared to be a limiting factor for legume establishment. Land slope is easily quantified, and could serve as a basis for pasture division for differential fertilization, seeding, and grazing management. I CHAPTER 1. GENERAL INTRODUCTION Background The role of forages in soil conservation on marginal land is of major importance in Iowa. Between 1986 and 1997, approximately two million acres of marginal lands within the state of Iowa were enrolled in the Conservation Reserve Program (CRP) (USDA, 1998). This is land that had been identified as having erosion potential that warranted it being under continuous vegetation. Over 98% of this land had been established with forages which are suitable for grazing purposes, and 1.8 million acres were seeded into simple grass and legume mixtures (USDA, 1998). Most of the land enrolled in CRP will likely be returned by producers back to row crop use unless economic alternatives can be identified when the program ends. Grain crops grown on marginal lands are for the most part utilized as livestock feed. Improving the quality and utilization of forages to the extent that livestock production can compete economically with grain crops on marginal lands will provide an incentive for maintaining these areas in permanent vegetation, thus reducing soil erosion and improving water quality. Forage species which contribute to the composition of CRP lands are mostly warm-season (C4) and cool-season (C3) grasses. Cool-season grasses found in CRP are also the dominant grass species found in permanent cool-season grass pastures throughout the state of Iowa (Bamhart et al., 1998). Smooth bromegrass (Bromus 2 inermis Leyss.), Kentucky bluegrass [Poa pratensis L.), reed canarygrass {Phalaris arundinacea L.), orchardgrass (Dactylis glomerata L.), and tall fescue {Festuca arundinacea Schreb.) are the primary species which may be found in most cool-season grass pastures or cool-season CRP swards. Improvement of these cool-season grass swards, both CRP and permanent grass pasture, potentially could entice producers to leave these lands out of row-crop production and maintain environmentally friendly and economically productive permanent vegetation. Interseeding diverse legume mixtiures into these grass swards is one method which has potential for substantially increasing sward production. The use of legumes grown in mixtures with grasses for pasture offers several advantages over grasses grown alone. Legumes are able to obtain nitrogen from the atmosphere through symbiosis with nitrogen-fixing bacteria that occupy nodules on their roots. This ability to fix nitrogen reduces fertilizer requirements and costs necessary to maintain pasture production at high levels, and minimizes envirormiental risks associated with nitrogen fertilization. Legumes typically have higher protein concentrations and forage quality than grasses and, therefore, improve the nutritive value of the pasture, particularly for high-producing classes of livestock. Although legumes are C3 species, the photosynthetic responses of many forage legumes to temperature are intermediate to those of C3 and C4 grasses. Consequently, the seasonal biomass accumulation of many forage legumes is complementary to that of grasses. Native grasslands contain a great diversity of species. This diversity confers 3 stability to the grassland ecosystem by allowing a natural succession of species in response to seasonal and annual variation in growth environments. The plasticity of native grasslands to the enviroiunent allows them to be productive throughout much of the year, although botanical composition of their biomass varies with season. Native, untilled grasslands in Iowa, however, are not suitable for intensive livestock production because they evolved under intermittent grazing by bison (Bison bison L.) and cannot endure heavy stocking rates for extended lengths of time. As a consequence, much of the native grasslands have been converted to permanent pastures consisting mostly of introduced cool-season grasses grown in monocultures or simple mixtures with temperate legumes. The species diversity of these pastures is narrow, mainly consisting of two to three dominant grass species (Bamhart et al., 1998), and as a result there is large seasonal and armual variation in their productivity. By interseeding a diverse mixture of legumes to create a highly productive pasture, an alternative to tillage and conversion of current CRP acres or other unproductive pasture back to row crops exists. By keeping the soil intact, less soil erosion will occur and thus keep sedimentation of nearby streams and lakes at a minimum. Annual large inputs of fertilizers, chemicals, fuel, and equipment used for row crops would not be necessary. Therefore, this strategy has potential for being both environmentally and economically beneficial. The hypotheses evaluated in this experiment were; 1) the productivity of coolseason grass pastures for grazing livestock can be improved by increasing the

Legume establishment and persistence at sites varying in landscape position, grazing method, and soil characteristics