Project Partners

• SFWMD
• FCA
• FDACS
• UF/IFAS
• USDA-STARS
• Southern Datastream

Project Products

• Final Report

History and Rationale

Improved pastures associated with beef cattle ranches are now the most prevalent source of phosphorus from the the Okeechobee watershed to Lake Okeechobee.  Based on the recent phosphorus budget developed for the northern Lake Okeechobee watershed, this land use accounted for 33% of the total phosphorus imports into the watershed, from 1997 to 2001. Animal densities and runoff phosphorus concentrations associated with beef cattle pastures are relatively low; however, the vast acreage of this land use, which comprises more than 180,000 hectares or approximately 36% of the northern Lake Okeechobee watershed, makes them a major contributor of phosphorus. Improved pastures accounted for almost 60% of the total P loading to the lake from 1997 to 2001 for an estimated runoff load of over 280 metric tons of phosphorus per year. These findings emphasize the need to develop management strategies to further reduce phosphorus runoff from improved beef cattle pastures. Controlling phosphorus losses from this source would help achieve the in-lake target phosphorus concentration of 40 parts per billion (ppb) and would hasten the lake’s recovery. 

This project will examine on-farm water management to reduce P losses from experimental cattle pasture plots at the MacArthur Agro-ecology Research Center (Fig. 1).These pastures were used in a previous study that examined the effects of cattle stocking density on nutrient concentrations and loads in surface runoff.  The new project on pasture water management is the first project that will be conducted under the newly-established MOU (2004-2008) among the SFWMD, ARCHBOLD, UF-IFAS, the USDA Agricultural Research Service (USDA-ARS), the USDA Natural Resources Conservation Service (USDA-NRCS), the Florida Department of Agriculture and Consumer Services (FDACS), the Florida Department of Environmental Protection (FDEP), and the Florida Cattlemen’s Association (FCA).  This project complements other efforts to retain more water and restore wetland conditions throughout the Lake Okeechobee watershed.  The project will involve holding water back in the pastures during periods of flow and flooding to allow for enhanced uptake of P within the pasture by the sediment, algae, and aquatic plants.  There is evidence that more P is retained when water flows more slowly or is held back relative to when it drains off quickly.  The key to effective water management on beef cattle ranches would be maintaining a water table that will provide optimal crop and animal production while minimizing water quality impacts, i.e. nutrient runoff. 

Objectives.

The overall objective of the project is to evaluate the technical feasibility and economic viability of on-farm retention/detention of water in controlling phosphorus losses from beef cattle ranches. Water control structures will be installed in the ditches to allow management of water in the pastures during high and low flow periods.  The specific project objectives are to:

• Document the effects of water storage and reduced flow on the quality of water leaving the pastures. 
• Determine nutrient load reductions from the pastures by integrating flow and nutrient concentration data for surface runoff.
• Evaluate forage yield and quality, and animal performance as influenced by water retention treatments. 
• Identify specific water management practices that could be implemented on a watershed-wide basis. These best management practices (BMPs) would have to be practical from a producer’s point of view and have a potential for significantly reducing phosphorus loads. 

Experimental Design    top

This study will be conducted on eight 50-acre plots in a block of improved pastures located at the Buck Island Ranch. The surface runoff from each plot is isolated from adjacent plots by the construction of ditches and beams along their mrgins. At the downstream end of each  plot there is a trapezoidal flume that is equipped with an automatic sampler for collection of flow-weighted surface drainage water leaving the plot.  The trapezoidal flumes have a peak flow capacity of seven cubic feet per second (cfs).  There are stilling wells, floats and digital encoders that monitor flume upstream and downstream water depth, from which flow rates and volumes can be determined.  There is a 15-ft groundwater well on each plot for monitoring of water table depth and groundwater quality.  

Plots 1-4 and Plots 5-8 will be blocked separately to simplify engineering design and for a better-balanced design from a demonstration perspective. Two water treatments will be evaluated; reduced flow and uninterrupted flow.  Reduced flow would involve holding water back in the pastures while maintaining a pre-determined minimum depth of surface water in the main drainage ditch in each pasture using riser board water control structures. Increasing the water level in drainage ditches of reduced flow pastures is expected to increase the groundwater level in the pastures, which will be monitored with an array of instrumented groundwater wells.  This treatment will be imposed on Plots SP1-SP4 (Block 1) by installing two flashboard riser control structures in the main drainage ditch of each plot, one structure close to the existing flume and another at midway up the ditch.  The water level in the ditch will be controlled by inserting or removing flashboards in the structures.  There will be a total of eight structures, two each in Plots SP1-SP4.  No structures will be installed in Plots SP5-SP8 (Block 2), which will serve as the uninterrupted flow treatment.  Animals will be allowed to graze the pastures at a stocking density of 40 cow-calf pairs per pastures or 1.69 cow-calf pairs per hectare, except for Plots 1 and 8, which serve as long-term grazing controls. 

A water retention structureinstalled just upstream of the flume that collects runoff from the south end of pasture SP2

Funding Sources      top

South Florida Water Management District

USDA National Research Initiative Competitive Grants Agricultural Systems 

Florida Department of Environmental Protection/USEPA 319

Florida Department of Agriculture and Consumer Services