Research Accomplishment Reports 2010

Spatial and Temporal Characteristics of Grassland Agroecosystems

C. T. Dougherty
Department of Plant and Soil Sciences

 

Non-Technical Summary

Grazing system research is often limited in application because we have not been able to determine where, when, and how livestock are grazing in a grassland landscape that ranges from less than an acre to many thousands of acres, over as little as a few hours to many years. This problem may be addressed by monitoring where the animals are and what they are doing. It may also be addressed by careful sampling of pasture and soil transects and the application of advanced statistical techniques to introduce the dimensions of space and time to the defining data of grassland landscapes. This information will help determine the variables and sampling procedures needed to define the spatial and temporal properties of grassland landscapes.

Spatial statistics can be used to minimize the number of variables needed to define grassland landscapes in space and time. Application of spatial analysis should lead to better experimental designs and reduce the cost of grazing system research compared with those operating under classical designs. These procedures will reinforce research and models necessary to ensure the continued sustainability and profitability of grassland livestock enterprises as well as address present day and future environmental issues.

2010 Project Description

The rotational grazing system based on seeded cold hardy bermudagrass and operating at stocking rates much higher than the industry standard has been used in a number of field days directed towards stakeholders. Most of these were to a segment of the equine industry using small farms, few horses, and with limited capital. A number of posters have been prepared that have been displayed and discussed with small horse farm operators at County meetings through the Kentucky Cooperative Extension Service. Presentation of research results have been made to research and extension personnel and industry leaders at national meetings. Seminars have been presented to academics in plant and soil sciences and in equine sciences. Two graduate students have been involved; one in equine grazing behavior and one in spatial analysis.

2010 Impact

Grazing system research is often limited in application because we have not been able to determine where, when, and how livestock are grazing in a grassland landscape that ranges from less than an acre to many thousands of acres, over as little as a few hours to many years. This problem may be addressed by monitoring where the animals are and what they are doing. It may also be addressed by careful sampling of pasture and soil transects and the application of spatial statistical techniques to introduce the dimensions of space and time to the defining data of grassland landscapes.

Spatial analysis of soil profiles and sward properties of transects indicated that equine grazing behavior had both short and long term effects on soil profiles and sward properties. Dunging and urination redistribute ingested plant nutrients in excess of the needs of grazing horses. Grazing horses grazed over large areas of pasture but urinated only 2 to 3 times each day creating soil patches that were rich in plant nutrients while depleting grazed patches that were not urinated or defecated upon.

Patches of soil enriched with urinary nitrogen promoted active growth of pasture patches if soil water and ambient temperatures were favorable until soil nitrogen was depleted. Pastures growing over urine deposits were leafier and greener than pastures between urine patches and herbage had higher water content, higher biomass, higher nutritive content, and fewer seed heads.

Horses grazed patches over urine deposits in preference to grazing other patches, indicating that they used a strategy in accordance with foraging theory. It was also observed that horses defecated and urinated while grazing so that patches of pasture stimulated by urine were indicators of the spatial pattern of grazing. Further, ordered spatial patterns of urine stimulated pasture also indicated that horses grazed as a herd maintaining a minimum space between grazing mates and in a general north to south orientation apparently influenced by geomagnetic fields.

We used equine nutrient utilization models in conjunction transect data show that grazing horses excreted urinary nitrogen and potassium during single urination events in excess of 2,500 kg per hectare. These amounts indicate that both nitrate and potassium fluxes in soil of urine patches could reach the ground water.

We also concluded that horses grazing bermudagrass at a high stocking rate in a paddock system did not establish patches of grazing and patches restricted to defecation and urination.