AGRO-ECOSYSTEMS INDICATORS OF SUSTAINABILITY AS AFFECTED BY CATTLE DENSITY IN RANCH MANAGEMENT SYSTEMS

Investigators: Campbell, K. L.
Performing Department: AGRI ENGINEERING -- 0060
Start Date: 12/01/1997 Termination Date: 11/30/2000
Reporting period: 10/01/1997 to 09/30/1998

Progress Report:

Installation of flumes and hydrologic instrumentation was completed and the remainder of the year served as an equilibration period to remove the effects of construction disturbance and establish consistent measurement performance and procedures. One hundred forty Brahman-cross, pregnant cows (4-9 years of age) were stratified by age and body condition (5-7; scale 1-9), randomly allotted to the stocking density treatments, and placed in the winter pastures on October 21, 1998. However, cattle subsequently were removed from the winter pastures and the area was burned. Cattle will be returned to the winter pastures in early January and graze until April, when they will be moved to the summer pastures. This year was devoted to background data collection to determine the chemical and biological status of the pastures before any treatments were imposed. Soil samples were taken from the winter and summer pasture arrays to provide pre-treatment soil P characterization. Pastures were divided into five equal components and two soil sampling locations were randomly selected within each. Soil was sampled to a depth of 30 cm in increments of 0-5, 5-10, 10-20, and 20-30 cm. Each sample was analyzed for water-soluble P (WSP) and 'Soil Test' (Mehlich I) elements including P, Fe, Al, Ca, and Mg. Analyses have been completed for the winter pasture array. Average WSP concentrations were 19, 4.5, 1.0, and 0.3 mg/kg for the respective depths. Comparable concentrations of P in the Mehlich I extract were 19, 9, 4, and 1 mg/kg. Similarity of concentrations between the two extractants suggests that the sorbed P in these soils is highly labile. Soil samples for nematode analysis were collected from the pastures in February, May, and early October. Analyses of these samples and data are pending. In addition to establishing background levels of nematodes in each of the pastures in the experiment, these samples will be examined for seasonal trends in nematode populations and analyzed for any differences in nematode populations and community structure between winter and summer pastures. Avian communities in the summer and winter pastures were censused in spring and summer. Vegetation structure associated with these censuses also was quantified. Since cattle grazing had not begun, no associations could be drawn between grazing and bird community composition. Work on the ranch economic simulation model during the first year of the project consisted of refining a spreadsheet model developed by John Earman. University faculty in the animal science and range science departments were consulted about the overall structure of the Earman model and specifically reviewed default values describing animal nutritional requirements and forage production coefficients. Several University of Florida research papers were identified and work is ongoing to incorporate those findings into the Earman model. Two ranches were solicited for their respective production data to test the model performance and procedures for gathering ranch-specific data. Overall, the model accurately tracked the cash flow position of each ranch. Work has begun on writing a user's guide.

Publications:

McSorley, R. 1997. Correlation of nematode densities and rainfall in a Florida pasture. Soil Crop Sci. Soc. Florida Proc. 56:55-57.