Improving the Efficiency of Cattle Manure Utilization
for Forage Production

by Augustine Obour, M.S. Student, University of Florida/IFAS

The rapid growth of concentrated animal feeding operations (CAFOS) in many areas of the world in recent years has caused a tremendous increase in the amount of manure produced annually. The major sources of manure in the USA are beef cattle, dairy, poultry and swine production. The beef cattle industry generates approximately 24.4 million metric tons of manure per year, dairy farming 19 million tons of manure, poultry 12.7 million tons of litter and manure, and swine production generates manure equivalent of 14.5 million tons. The nitrogen and phosphorus generated from these livestock enterprises are equivalent to that supplied annually by inorganic nitrogen and phosphorus. It is estimated that about 7.5 million tons of N and 2.3 million tons of P are generated in the USA annually by the livestock industry compared to 9 million tons N and 1.6 million tons P applied to agricultural land in the form of commercial fertilizers. The enormous increase in manure production from these cattle production enterprises has generated environmental concerns due to limited land area for efficient manure application and spreading.

Proper incorporation of cattle manure into forage production systems would be an effective way of manure recycling to reduce environmental problems, and also provide a low cost alternative to mineral fertilizer to farmers. Forage production removes and recycles more nutrients from the soil than other crops especially when plants of high biomass yield with relatively high N uptake capacity, tolerance to wet soil conditions, prolonged vegetative growth, and tolerance to frequent harvest are used. This will maximize manure nutrient utilization and reduce N and P movement to surface and ground water.

Manure application rates are usually based on crop N requirement which greatly increases soil P levels because the N: P ratios of manure (2:1 to 4:1) are significantly smaller than N: P uptake ratios (6:1 to 8:1) for most crops. The excess P and NO3-N from manure application can be transported in runoff or leached into the groundwater. Phosphorus and NO3-N accumulation in soils and subsequent contamination of water bodies have become an environmental concern in many regions of the world. The U.S Environmental Protection Agency (EPA) has shown that agricultural nonpoint source pollution is a significant cause of stream and lake contamination that prevents the attainment of the water quality goals set by the Clean Water Act (USEPA 2002). The excess P in soil resulting from N-based manure application has led to growing public demand for P-based manure application. Recent Florida legislation requires P-based application of biosolids in watersheds associated with P-sensitive water bodies. The Lower Suwannee River Basin of Florida has been designated by the Florida Department of Environmental Protection as a Group 1 basin because of the increase in nitrate concentration of surface and groundwater in the Upper Floridan Aquifer. The NO3-N concentration in water from the basin exceeds the maximum contaminated level of 10 mg L-1 set by the U.S Environmental Protection Agency. Additionally, Beef ranching and dairy farming in the Lake Okeechobee Basin in South Florida have been identified as major contributors of P to the lake. The Green Swamp and the Okeechobee Basin are designated as P limited by legislation and these areas are to have P-based nutrient budgets irrespective of the nutrient source. The P-based nutrient management approach will reduce excess P accumulation in the soil hitherto resulting from N-based application. However, a P-based manure nutrient management means substantially lower waste and manure application rates, larger land area requirements for spreading and higher cost to transport waste outside sensitive watersheds.

The uniqueness of present work is to evaluate the environmental impacts of different application strategies of dairy manure for forage production under field conditions. The specific objectives of this study are.

  1. Assess the effects of single vs. split, and manure vs. manure combination with inorganic N on productivity, quality and persistence of bahiagrass (Paspalum notatum. L. Flugge) forage.
  2. Quantify N and P uptake by bahiagrass hay following manure vs. supplemental inorganic N application.
  3. Quantify potential offsite leaching and runoff losses of N and P in groundwater, and onsite loading of nutrients and pH changes in soil following manure vs. manure/supplemental inorganic N application.

Field experimental plots( 6.02 m x 6.02 m) will be bermed down to the spodic soil layer (about 1 m deep) with a 7 mil thick water proof plastic sheet and each plot will be an isolated hydrological unit (6.02 m perimeter alley) having two PVC wells ( one above and one below the spodic layer) and a surface runoff collector. This will provide an effective way of monitoring N and P movement in soil, surface, and ground water and facilitate development of nutrient budgets.

The development of efficient N-based application strategies into forage production systems will help reduce groundwater pollution and take advantage of the rich nutrient content of manures to promote forage production. Ultimately, this project provides the baseline data for developing and promoting a new technology for manure/inorganic-N blends to optimize the N: P ratio for crop uptake and utilization --- a technology that ensures maximum utilization of the excess P available in manures for crop production, and one which allows for the preservation of current scarce mineral soil-P deposits for our future generation.

Augustine Obour
Field layout of experiment showing bermed plots.

Augustine Obour
PVC well for monitoring water quality.