• Representative compost temperatures for solid dairy cattle waste.
• Project to evaluate the use of dairy cattle solid waste collected by hydraulic flush and dry scrape collection techniques and poultry litter when composted alone or with sawdust as a bulking agent.
• Project to evaluate the use of dairy cattle solid waste collected by hydraulic flush techniques when composted with and without supplemental nitrogen fertilizer and with and without sawdust as a bulking agent.
• Project to evaluate co-composting of dairy cattle solid waste collected by hydraulic flush techniques with coarse and fine textured sawdust and poultry litter used as bulking agents.

Name of Grantee: Texas A&M University-Commerce

TDA file number: 459107

Period covered by report: June 15, 1995 through June 15, 1996

Principal Investigator: Donald L. Cawthon

Project summary: Agriculture has been identified as the single largest contributor to nonpoint source pollution in the United States. Over one-third of all agricultural nonpoint source pollution impairments are caused by waste from livestock confined animal feeding operations (CAFO's). CAFO operators are required to confine all animal waste products and operate under a "no-discharge" policy into creeks and watersheds. This project developed the technology to stabilize and convert solid animal waste into a peat moss substitute marketable to the horticultural industry; thereby converting a watershed liability (animal waste) into an income generating source of revenue for a CAFO operator, and providing a competitive option for imported peat moss. Enhanced sustainability of both confined animal feeding operations and horticultural industries should result.

Following preliminary feasibility studies initiated in 1993 by the investigators, this project was initiated in June, 1995 to 1) identify and implement the composting technology necessary to convert solid animal waste and municipal sewage sludge into an organic product for use in the horticultural industry, 2) determine the feasibility of co-composting animal wastes and sewage sludge with other waste biomass, 3) develop the production practices necessary to utilize the composted products as a substitute for peat moss in the plant nursery industry, 4) document microbial and enzymatic parameters of decomposition and develop means for reducing heavy metal availability, and 5) document the economics of production, marketing, and utilization of the product.

Sewage sludge and CAFO wastes from dairy, cattle feedlot and poultry operations were composted with and without use of bulking agent biomass for textural modification and moisture regulation. Composting was by windrow (Israel) and in-vessel aerobic techniques (Texas). The microbial parameters were monitored throughout the composting process, and the chemical and physical properties were documented at compost completion. Microbial, chemical, and physical properties of the composts and subsequent growing media blends were related to plant growth, dry weight accumulation, general appearance, and tissue nutrient content.

Dairy cattle solid waste collected by hydraulic flush and dry-scrape techniques, poultry litter from broiler operations, and sewage sludge from the belt-press facility in Sulphur Springs, Texas have all been evaluated for suitability as a peat moss substitute in soilless growing media used for marigold bedding plant production. Additionally, use of bulking agents (fine and coarse textured sawdust and hay) as a carbon source during composting and for moisture absorption have been evaluated. Studies determining the need for supplemental nitrogen to aid in the composting process have also been completed.

Properly composted dairy cattle manure, whether collected by hydraulic flush or dry-scrape techniques, can be substituted for peat moss in a soilless growing media for marigold production without a loss of plant quality. Due to the texture of composted dairy manure collected by hydraulic flush techniques, plants were successfully grown in 100% compost without the addition of more expensive vermiculite and/or perlite typically used in a peat-lite blend when peat moss is used. Composted poultry litter may have limited utility as a peat moss substitute for bedding plant production due to high nitrogen and high total salt concentration. However, use of a compost blend containing between 12.5 or 25% poultry litter may be acceptable for some applications. Addition of 12.5 to 25% poultry litter with dairy manure increased the rate of composting as indicated by composting temperature. Sewage sludge did not generate the temperatures experienced during composting of either dairy or poultry waste, but appears (data not yet analyzed) to produce excellent quality plants in a greenhouse situation.

Fresh dairy manure collected by hydraulic flush techniques from a confined animal facility averages between 70 and 75% moisture. This moisture level was found to be too high to achieve aerobic composting due to a lack of porosity and oxygen availability. Either partial drying of the animal waste prior to composting or use of bulking agents to absorb excess moisture and improve porosity were necessary to achieve adequate composting. The use of bulking agents with wet dairy manure was detrimental to subsequent plant growth. However, supplemental nitrogen applied at the rate of 0.37% actual N (dry wt. basis) overcame the detrimental effects of bulking agent addition. Use of a bulking agent of high carbon content such as sawdust or hay in conjunction with a low nitrogen containing manure from a hydraulic flush collection system probably restricts nitrogen availability to plants. Co-composting of a high-carbon bulking agent with poultry litter was beneficial to plant growth due to the high nitrogen content of poultry litter.

A 24 cubic yard in-vessel aerobic composter modeled from the prototype composters used in this project has been manufactured and installed on a 400-cow dairy near Como, Texas. The economics of operating this composting facility has been estimated using actual installation costs and estimated annual fixed and variable costs. Annual fixed costs include depreciation, insurance, taxes and land value which is used for the composting site. Variable costs include electricity, fuel, labor, repairs, and maintenance. Details of the annual and fixed costs are outlined in Table 27 in the data appendix of this report.

The composter currently in operation at the Vellenga Dairy is a model 0824 composter which can be purchased for $73,625.00. Installation of a separator which separates the liquid waste from the solid waste is valued at $15,000.00. Cement slabs and structures to support the composter are estimated at $1,200.00. Additional concrete pad valued at $1,250.00 is required for product storage and handling. Approximately 1 acre of land valued at $550.00 is needed to house this composting system. In this operation a $30,000.00, 90 horsepower tractor equipped with a 2.5 yd³ front end loader is used approximately 25% of the time for composter loading and unloading.

A 400 cow freestall dairy barn produces approximately 6 yd³ of solid waste material per day to be composted. A market price of $20.00 per cubic yard for composted material has been offered to the Vellenga Dairy. Total income from compost sales (6 yd³/day x 365 days/yr x $20.00/yd³) is estimated at $43,800.00, providing and estimated net income of $14,972.54 (see Table 27).

Technical and economic content: In-vessel, on-farm composting of solid animal wastes from CAFO's (including dairy, poultry, and feedlot operations) offers several advantages to the Texas agricultural community and the general citizenry of the state. Animal wastes become a liability when over-supply must be applied to limited land area, resulting in high soil accumulation of nutrients, runoff carrying nutrients and microbial contaminants into surface waterways, and leaching of nutrients and fecal microorganisms into underground water resources.

CAFO operators can convert solid animal waste from a potential liability into a large-scale marketable product, thereby removing the waste from a potentially endangered watershed. Prevention of excessive nutrient loading and pollution improves the sustainability of agricultural operations and helps protect the environment for all citizens. Marketing of composted animal waste as a peat moss substitute will provide an additional source of income for a CAFO while being a good steward of Texas' natural resources and its environment.

The horticultural industry in Texas, including greenhouse and outdoor containerized plant production as well as landscape operations, is a major user of peat moss. Basically all peat moss used in the state is imported from Canada. To achieve marketshare and become competitive with Canadian peat moss, composted animal waste/peat moss substitutes must be produced using suitable quality control guidelines and should be consistent, reproducible, and of high quality. On-farm, in-vessel composting technology offers the advantage of control over the complete production process including control of aeration, temperature, and moisture, which comprise the key criteria for producing a consistently high quality compost product.

To successfully mass market composted animal waste/peat moss substitutes to either the wholesale user or the retail trade, cooperative approaches between producers may be advantageous to generate increased volume as well as allow blending to improve quality and reduce variation.

Key personnel:

Future plans: As a result of research conducted in part by this TIE project, a three-year implementation and demonstration grant (not a research grant) has been obtained from EPA and the Texas State Soil and Water Conservation Board to install a commercial sized on-farm in-vessel composter to compost the animal waste generated on a 400-cow freestall dairy in Como, Texas. This project will document and monitor NPS nutrient loading reductions in the Lake Fork Creek Watershed from the Como dairy and will generate sufficient quantity of composted dairy cattle solid waste to be adequately tested on commercial scale by the Texas greenhouse bedding plant industry.

The following projects have been proposed in the recently submitted grant proposal to the 1996-97 TIE Program:

1. In-vessel, mechanical composting of poultry mortality as an environmentally appropriate disposal alternative to burial, incineration, or static-bin composting.
1. Expand animal waste compost utilization research into other plant production industries including:

• woody ornamentals (landscape shrub and tree production)
• hanging baskets, and
• other bedding plant species

1. Evaluate the utilization of composted animal waste as a soil amendment (in place of peat moss) in landscape installation activities.

Project to evaluate the use of dairy cattle solid waste collected by hydraulic flush and dry scrape collection techniques and poultry litter when composted alone or with sawdust as a bulking agent.
 

Figure 1. Interactive effects of organic matter source and vermiculite on height of Marigold bedding plants.

• Peat=peat moss
• 100% HF=dairy waste collected by hydraulic flush technique and composted without sawdust as a bulking agent
• 50% HF=dairy waste collected by hydraulic flush technique and composted with 50% sawdust as a bulking agent
• 50% DS= dairy waste collected by dry scrape technique and composted with 50% sawdust as a bulking agent
• 50% PL=poultry litter composted with 50% sawdust as a bulking agent
 
 

Figure 2. Interactive effects of organic matter source and vermiculite on nitrogen content of soilless growing used for Marigold bedding plant production.

• Peat=peat moss
• 100% HF=dairy waste collected by hydraulic flush technique and composted without sawdust as a bulking agent
• 50% HF=dairy waste collected by hydraulic flush technique and composted with 50% sawdust as a bulking agent
• 50% DS= dairy waste collected by dry scrape technique and composted with 50% sawdust as a bulking agent
• 50% PL=poultry litter composted with 50% sawdust as a bulking agent

Project to evaluate the use of dairy cattle solid waste collected by hydraulic flush techniques when composted with and without supplemental nitrogen fertilizer and with and without sawdust as a bulking agent.
 
 

Figure 3. Interactive effects of % sawdust and % nitrogen addition to composting dairy cattle solid waste on height of Marigold bedding plants.

Figure 4. Interactive effects of % sawdust and % nitrogen addition to composting dairy cattle solid waste on dry weight accumulation of Marigold bedding plants.
 
 

Figure 5. Interactive effects of % sawdust and % nitrogen addition to composting dairy cattle solid waste on visual leaf color of Marigold bedding plants.
 
 
 

Project to evaluate co-composting of dairy cattle solid waste collected by hydraulic flush techniques with coarse and fine textured sawdust and poultry litter used as bulking agents.
 
 
 

Figure 6. Interactive effects of organic matter source and blend formulation on media sodium content.

Figure 7. Interactive effects of organic matter source and blend formulation on media salinity.