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.
- 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.
- Quantify N and P uptake by bahiagrass hay following manure vs. supplemental inorganic N application.
- 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.
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| Field layout of experiment showing bermed plots. |
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| PVC well for monitoring water quality. |
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