Project Title: Agro-Ecosystems Indicators of Sustainability as Affected by Cattle Density in Ranch Management Systems

Principal Investigators: K. L. Campbell, J. C. Capece, J. J. Mullahey, M. D. Fanning, D. A. Graetz, J. Holt, R. McSorley, R. M. Muchovej, K. M. Portier, F. M. Roka, A. D. Steinman, and G. W. Tanner

Grant Number: 97-35108-5125 Proposal Number: 9703960 Reporting Year: 1999

Specific Aims: The objectives of this multidisciplinary project are to:

1. investigate the effect of cattle stocking rate on the following indicators of cattle ranching system sustainability:

• animal performance,
• seasonal forage biomass production and quality in summer and winter pastures,
• changes in soil test P, soil P sorption capacity over time, and their implications for P transport,
• avian community structure and biodiversity, and
• nematode community structure and biodiversity.

• track the economic performance of cow-calf operations in south Florida for a given set of agronomic and animal performances relationships, and

• improve our understanding of ranching systems by identifying the agronomic and animal management decisions that have important economic consequences.

Stocking density treatments for the summer pastures (April-November) were 0, 1.4 (high), 2.5 (medium), and 3.3 (low) acres per cow. In the winter pastures (November-April) the stocking density treatments were 0, 2.3 (high), 4.0 (medium), and 5.3 (low) acres per cow. Winter pastures were burned in November 1998 and grazed from February-April 1999. Forage production (dry matter) was similar in all pastures prior to grazing (657-840 kg/ha). In the winter pastures in April, the available forage was highest in the control (816 kg/ha) followed by the low (764 kg/ha), medium (744 kg/ha) and high (425 kg/ha) stocking density. Percent utilization during this time was 51.4% for the low treatment, 52.8% for medium, and 61.7% for high. Burning the winter pastures in November resulted in a decline in standing forage from about 8000 kg/ha before the burn to about 400 kg/ha in January 1999. However, by August 1999, all treatments had similar amounts of standing forage (2126-2583 kg/ha). Summer pastures were mowed in October/November 1998, burned in February 1999, and grazed from April-November 1999. In June 1999, the available forage was highest in the control treatment (3495 kg/ha) followed by the low (1055 kg/ha), medium (597 kg/ha) and high (247 kg/ha) stocking density. Percent utilization for all treatments (except the control) during June increased (46, 74, and 86%) with an increase in stocking density. In September 1999, utilization was near zero for all treatments indicating that forage production was higher than consumption.

Soil sampling has continued as described in previous reports. Data are presently being statistically examined for cattle stocking rate effects. An additional study was conducted to determine the phosphorus status of seasonal wetlands within selected grazing treatments in the summer and winter pastures. The detrital layer and upper 15 cm of underlying mineral soil were sampled at three randomly selected locations in the interior and along the edge of each wetland. Soil analyses included water soluble phosphorus (WSP), total P (TP) and P fractions. P fractions measured were: NH₄Cl-extractable P (labile P), NaOH-extractable P (Fe-Al associated inorganic P and organic P), HCl-extractable P (Ca-Mg associated P) and residual P (recalcitrant P is considered to be primarily organic in nature). TP concentrations were higher (240-660 mg P/kg) in the detrital layer compared to the mineral layer (16-180 mg P/kg). WSP comprised 1-9% of the TP and was higher in the wetland interior compared to the edge of the wetland. TP and WSP concentrations were greater in the improved pastures (summer) than in the semi-native range (winter) pastures. There was a significant relationship (P < 0.01) between WSP and TP for both the detrital layer and the mineral soil. The greatest portion of the TP was present in the residual P fraction which is considered to be recalcitrant. Relatively small percentages of TP were found in the labile form (NH₄Cl-P), however, greater percentages were found as NaOH-OP which is often considered to be "easily mineralizable P".

Currently, soil samples are being examined for nematode populations to determine the effects of the stocking rate treatments. In addition, differences in nematode community structure will be compared between winter pastures (which tend to be wetter overall) and summer pastures (which tend to be somewhat drier). Soil samples contain a great variety of nematodes, particularly those that are involved in decomposition, feeding on bacteria and fungi. Varying numbers of plant-feeding nematodes, predatory nematodes, and omnivores nematodes are found in most samples, even in April 1999 when extremely dry conditions prevailed. Since previous work indicates that nematode population levels may respond to inputs of organic matter, fertilizers, and other nutrients, nematodes are considered to be excellent bioindicators of non-target effects on native fauna from various types of agricultural activities, such as grazing or manipulation of stocking rates.

After consultation with leading avian ecologists within the US, we changed our sampling protocol from using spot counts within the pastures to censusing birds within two 500-m transects within each pasture. This method will provide a more robust data set for statistical analysis. Birds were sampled using strip counts within each pasture during the winter, spring and fall seasons. Summer counts were not made due to changing of personnel. During winter, mean avian species richness ranged from 14.0 to 23.5 among the four grazing treatments within the summer pastures and between 9.0 and 14.5 within the winter pastures. During the spring count, these means were 8.5 to 11.5 for the summer pastures and 6.5 to 9.0 for the winter pastures. During the fall, these means were 12.0 to 16.0 in the summer pastures and 11.5 to 14.0 in the winter pastures. There was no pattern of species richness with stocking density during any of the seasons for both pasture areas. Presence of small, isolated wetlands and scattered trees seemed to have the strongest association with species composition. Data from the summer 1999 season indicated that the resident avian community within the pastures is comprised of two primary species (eastern meadowlark and red-wing black bird). The increased diversity in the other seasons is from winter/spring residents and neotropical migrants passing through the region.

Balance sheets and cash flow reports were added to the economic simulation model to more completely represent financial implications of management changes on a cow-calf operation. University faculty in the animal science and range science departments were consulted further about the overall structure of the model. Version one of the model has been patented and it was distributed to county extension faculty. The model has been introduced to the ranching community through one county agent meeting, a presentation during the Florida Cattleman's Association, and during a workshop at Buck Island Ranch.

Plans for the Coming Year: Experimental treatments will be continued on the 16 pastures at assigned stocking rates throughout the coming year. We will continue measuring body condition score, calf weaning weight, pounds of beef produced per acre, and the pregnancy rate while the animals are in the winter and summer pastures. Forage production and quality and forage utilization will be monitored during the remainder of the winter grazing season and during the upcoming summer grazing period. Soil sampling will be continued in the summer and winter pastures in the same manner as described previously. During the coming year, a final sampling of nematode numbers is anticipated, along with a detailed examination and analysis of previously collected data. The avian community will be censused four times during the next year. The various stocking levels may begin to alter the composition and structure of the vegetation, and thus the bird community may begin to respond to the treatments. Tasks planned for the economic simulation model studies include: 1) loading financial information from MacArthur Agro-ecology Research Center at Buck Island Ranch and analyzing production/financial trends, 2) increasing contact with individual ranches by working with county extension faculty to identify and solicit cooperation from commercial ranches in south Florida, 3) writing a user's guide for the simulation model, and 4) using data collected from ranch simulation exercises to develop enterprise budgets for cow-calf operations in south Florida. Hydrologic/water quality data will be measured continuously throughout the year from all 16 experimental pastures with support from a Florida Department of Environmental Protection/EPA Section 319 grant. An agro-ecology professional development program is scheduled for late February 2000. The intended audience is elected officials and county extension agents. The program will focus on the ecological, environmental, and economic values of a commercial ranch operation. Research results from grazing of the winter and summer pastures will be presented.

Publications:

Earman, J. and F. Roka. "What If I Changed My Ranching Operation?" The Florida Cattleman and Livestock Journal 63(11):65-67, August 1999.

Other Products: The following technology transfer workshops were conducted:

• May 26, 1999. Grazing in-service training, Gainesville, FL, for 25 University of Florida county extension staff and extension specialists.

 
• November 16, 1999. Workshop for ranchers, Buck Island Ranch. Six ranchers attended, representing operations from LaBelle to Lake City, FL.

• Graetz, D. A. and P. J. Bohlen. 1999. Phosphorus status of wetland soils in subtropical rangelands. Agronomy Abstracts. p. 327, American Society of Agronomy 1999 Annual Meeting.

 
• Graetz, D. A., K. L. Campbell and P. J. Bohlen. 1999. Agro-ecosystem indicators of sustainability as affected by cattle density in ranch management systems. Agronomy Abstracts. p. 367, USDA-NRI Poster Session, American Society of Agronomy 1999 Annual Meeting.

http://www.agen.ufl.edu/~maerc

Information available at this location includes project status, summary data, progress reports, work plans, meeting notes, experimental plot layouts, and other similar information.

Students Supported: None