Spatial Analysis of Species Diversity in Pastures Using GIS and GPS Technologies

The Rhodes research farm with its large topographic variability and extensive pasture acreage is an ideal site to evaluate the application of precision agriculture technologies to forage production and management. In previous studies at Rhodes it has been shown that forage legumes are adapted to sites with higher slopes (15 - 20%), and increasing species diversity with legumes at these sites improves productivity and forage quality. In the current study we are using global positioning systems (GPS) and geographic information systems (GIS) technologies to describe and map the spatial variability in pasture vegetation and examine its relationship to maps generated for slope, drainage, and electrical conductivity. Our objective is to determine whether these technologies can be used successfully to predict grass and legume distribution within the pastures based on topography and soil properties

ADAPTATION OF ANNUAL FORAGE LEGUMES IN THE SOUTHERN GREAT PLAINS

Our objective was to evaluate adaptation and compatibility of cool-season annual legumes overseeded into perennial grasses in the southern Great Plains. Freeze damage, vigor, and standing crop of 14 annual legume species were evaluated during spring at three locations in Oklahoma and Texas from 2006 to 2008. Across locations and years, standing crop of hairy vetch (Vicia villosa Roth) and Austrian winter pea (Pisum sativum L. ssp. arvense (L.) Poir.] averaged 3,513 and 3,210 kg dry matter (DM) ha-1, respectively. Standing crop of crimson clover (Trifolium incarnatum L.) and arrowleaf clover (T. vesiculosum Savi) averaged 1,138 and 1,071 kg DM ha-1, respectively. Although subject to freeze damage, annual medics produced more spring forage than annual clovers on soil with pH \u3e 8.0. Most of the annual legumes survived winter, demonstrating their adaptability to pastures in the southern Great Plains, but hairy vetch and Austrian winter pea consistently provided the most spring forage

ADAPTATION OF ANNUAL FORAGE LEGUMES IN THE SOUTHERN GREAT PLAINS

Our objective was to evaluate adaptation and compatibility of cool-season annual legumes overseeded into perennial grasses in the southern Great Plains. Freeze damage, vigor, and standing crop of 14 annual legume species were evaluated during spring at three locations in Oklahoma and Texas from 2006 to 2008. Across locations and years, standing crop of hairy vetch (Vicia villosa Roth) and Austrian winter pea (Pisum sativum L. ssp. arvense (L.) Poir.] averaged 3,513 and 3,210 kg dry matter (DM) ha-1, respectively. Standing crop of crimson clover (Trifolium incarnatum L.) and arrowleaf clover (T. vesiculosum Savi) averaged 1,138 and 1,071 kg DM ha-1, respectively. Although subject to freeze damage, annual medics produced more spring forage than annual clovers on soil with pH \u3e 8.0. Most of the annual legumes survived winter, demonstrating their adaptability to pastures in the southern Great Plains, but hairy vetch and Austrian winter pea consistently provided the most spring forage

Distribution of Legumes along Gradients of Slope and Soil Electrical Conductivity in Pastures

Legumes establish and persist on backslope landscape positions but fail on summits and toeslopes in southeastern Iowa pastures, suggesting that these pastures be managed site specifically. Visual delineation of landscape positions, however, can be difficult, and char- acterization of spatial variability through soil sampling is expensive. Creation of digital elevation models (DEM) and apparent soil electrical conductivity (ECa) mapping are inexpensive alternatives to de- scribing field conditions. Our objective was to examine the relationships of DEM-derived slope, soil ECa, and legume distribution in pastures.We examined these relationships across four 1.4-ha pastures. Each pasture was divided into 0.46-ha plots that were assigned one of three stocking treatments: continuous, rotational, and nongrazed. We found that legumes, as a percentage of pasture cover,were greatest at 15 to 20% slopes and intermediate values of soil ECa. The absolute ECa value at which legumes were maximized varied by plot within each stocking system and year ECa was measured. When ECa was standardized by pasture and year, however, a nonlinear response curve explained 23 to 42% of the variation of legume cover across the plots. Grazing reduced competition from smooth brome (Bromus inermis Leyss.) and reed canarygrass (Phalaris arundinacea L). These grasses dominated at 0 to 8% slopes and where ECa was either low or high in value. We concluded that slope and soil ECa data are useful in identifying sites where legumes are successful in pastures and showed potential for use in site-specific management of pastures

Plant species richness in relation to pasture position, management, and scale

The objective of this research was to describe how landscape position, grazing management, and scale affected overall plant species richness and species richness per functional group in temperate pastures located in the central United States. The effects and interactions of summit, backslope, and toeslope positions and continuous, rotational, and nongrazed stocking systems on species richness were examined at sample scales of 0.18 m2 and 4.5 m2. Landscape position explained 40–63% of species richness variation at 0.18 m2 compared to 3–26% at 4.5 m2 for overall, perennial, perennial grass, vegetative-spreading grass, perennial herb, and perennial N2-fixing herb (legume) functional groups. Grazing management, in contrast, explained 22–35% of species richness variation for overall, perennial, annual–biennial, perennial grass, and perennial bunchgrass functional groups at 0.18 m2 compared to 30–43% of their variation at 4.5 m2. Landscape position and stocking system mostly did not interact. Overall species richness averaged 11.7, 14.3, and 10.3 on summits, backslopes, and toeslopes, respectively, and 14.8, 12.9, and 8.7 within the continuous, rotational, and nongrazed systems, respectively, at the 4.5 m2-scale. Backslope positions supported more species than summits and toeslopes regardless of scale, with differences that appeared related to total vegetation production and aboveground competition. Continuously and rotationally stocked pastures also supported more species than nongrazed pastures, effects that were consistent across functional types and scales. Increased scale enabled detection of a greater number of species per unit area but reduced the percentage of species richness variation explained by pasture position and management

Soil Organic Matter and Root and Rhizome Responses to Management Strategies in Smooth Bromegrass Pastures

Soil organic matter (SOM) is a key component of pasture production. This is study investigated how management strategies that varied amount and form of N input in a long-term experiment affected concentrations and stocks of total-soil organic C and N, particulate organic carbon (POC), particulate organic nitrogen (PON), root and rhizome mass, C and N contents in topsoil of smooth bromegrass (Bromus inermis Leyss.) pastures with silty clay loam soils in a wet (2010) and dry (2012) year. Management strategies included: (i) unfertilized pasture grazed with unsupplemented beef cattle (CONT); (ii) unfertilized pasture grazed with dried distillers grains plus solubles (DDGS)-supplemented beef cattle (SUPP); and (iii) nitrogen-fertilized pasture grazed with unsupplemented beef cattle (FERT). After 8 yr, management strategies had similar concentrations and stocks of total-soil organic C and N, POC, and PON, and there were no management strategy × year interactions. From 2010 to 2012, total-soil organic C and N, POC, and PON stocks increased as soils dried and soil bulk density increased. The CONT and SUPP management strategies had less root and rhizome mass (concentrations and stocks) and greater soil bulk density than FERT. These belowground responses were consistent with earlier research conducted at the site demonstrating greater herbage accumulation and litter deposition in FERT. Management strategies that vary amount and form of N inputs into pasture appear to have low potential to affect total-soil organic C and N concentrations in the short-term, but long-term effects of less root and rhizome contents remain unknown

Litter Deposition and Nitrogen Return in Rotationally Stocked Smooth Bromegrass Pastures

Understanding how management systems impact nutrient cycling is important to pasture sustainability. From 2010 to 2011, we investigated how supplementation of beef cattle (Bos taurus) with corn (Zea mays L.) dried distillers grains plus solubles (DDGS) on unfertilized, rotationally stocked smooth bromegrass (Bromus inermis Leyss.) pasture (SUPP) affected the litter pool, residual herbage mass, litter deposition, and litter quality relative to unsupplemented beef cattle rotationally stocked on unfertilized control (CONT) and N-fertilized (FERT) smooth bromegrass pastures. As hypothesized based on management for greater herbage mass and animal demand during the grazing season, litter deposition was 48% greater in FERT than CONT and SUPP. Management effects, however, depended on year and rotation. Differences in the litter pool, residual herbage mass, and litter deposition typically were greatest before and after the third and fourth rotations, time periods coinciding with peak herbage mass. Meanwhile, deposited litter contained 16.5, 18.1, and 18.9 g N kg–1 and returned 27, 30, and 46 kg N ha–1 through the 158-d grazing season, equivalent to 35, 23, and 34% of total N returning through litter and excreta in CONT, SUPP, and FERT, respectively. Trampling during the 4- to 6-d grazing periods and senescence of herbage contributed to litter deposition. Increase of litter deposition and N return during the grazing season in FERT indicated this system may maintain better soil quality than CONT and SUPP. More research is necessary to examine how changes in litter deposition and N return affect litter decomposition, N losses, and soil organic matter dynamics

Soil Organic Matter and Root and Rhizome Responses to Management Strategies in Smooth Bromegrass Pastures

Soil organic matter (SOM) is a key component of pasture production. This is study investigated how management strategies that varied amount and form of N input in a long-term experiment affected concentrations and stocks of total-soil organic C and N, particulate organic carbon (POC), particulate organic nitrogen (PON), root and rhizome mass, C and N contents in topsoil of smooth bromegrass (Bromus inermis Leyss.) pastures with silty clay loam soils in a wet (2010) and dry (2012) year. Management strategies included: (i) unfertilized pasture grazed with unsupplemented beef cattle (CONT); (ii) unfertilized pasture grazed with dried distillers grains plus solubles (DDGS)-supplemented beef cattle (SUPP); and (iii) nitrogen-fertilized pasture grazed with unsupplemented beef cattle (FERT). After 8 yr, management strategies had similar concentrations and stocks of total-soil organic C and N, POC, and PON, and there were no management strategy × year interactions. From 2010 to 2012, total-soil organic C and N, POC, and PON stocks increased as soils dried and soil bulk density increased. The CONT and SUPP management strategies had less root and rhizome mass (concentrations and stocks) and greater soil bulk density than FERT. These belowground responses were consistent with earlier research conducted at the site demonstrating greater herbage accumulation and litter deposition in FERT. Management strategies that vary amount and form of N inputs into pasture appear to have low potential to affect total-soil organic C and N concentrations in the short-term, but long-term effects of less root and rhizome contents remain unknown

Litter Deposition and Nitrogen Return in Rotationally Stocked Smooth Bromegrass Pastures

Understanding how management systems impact nutrient cycling is important to pasture sustainability. From 2010 to 2011, we investigated how supplementation of beef cattle (Bos taurus) with corn (Zea mays L.) dried distillers grains plus solubles (DDGS) on unfertilized, rotationally stocked smooth bromegrass (Bromus inermis Leyss.) pasture (SUPP) affected the litter pool, residual herbage mass, litter deposition, and litter quality relative to unsupplemented beef cattle rotationally stocked on unfertilized control (CONT) and N-fertilized (FERT) smooth bromegrass pastures. As hypothesized based on management for greater herbage mass and animal demand during the grazing season, litter deposition was 48% greater in FERT than CONT and SUPP. Management effects, however, depended on year and rotation. Differences in the litter pool, residual herbage mass, and litter deposition typically were greatest before and after the third and fourth rotations, time periods coinciding with peak herbage mass. Meanwhile, deposited litter contained 16.5, 18.1, and 18.9 g N kg–1 and returned 27, 30, and 46 kg N ha–1 through the 158-d grazing season, equivalent to 35, 23, and 34% of total N returning through litter and excreta in CONT, SUPP, and FERT, respectively. Trampling during the 4- to 6-d grazing periods and senescence of herbage contributed to litter deposition. Increase of litter deposition and N return during the grazing season in FERT indicated this system may maintain better soil quality than CONT and SUPP. More research is necessary to examine how changes in litter deposition and N return affect litter decomposition, N losses, and soil organic matter dynamics