Confined animal feeding operations (CAFO’s) generate large volumes of animal wastes, which create disposal problems. Alternative utilization strategies for these waste products are desirable. This project was designed to evaluate raw and composted dairy cattle solid waste from a freestall CAFO as a partial or complete substitute for peatmoss in greenhouse growing media. To evaluate the suitability of raw waste, 'Bonanza Yellow' dwarf marigold (Tagetes patula) and mixed-color snapdragon (Antirrhinum majus) were greenhouse grown in 36-count trays using two commercial media and three media prepared as follows: 1) a peat-lite blend containing 50% No. 3 grade vermiculite and 50% Canadian peat moss by volume; 2) a blend containing 50% No. 3 grade vermiculite, 25% Canadian peat moss and 25% raw dairy cattle solid waste; and 3) a blend containing 50% No. 3 grade vermiculite and 50% raw waste. To compost waste and evaluate its effectiveness as a growing media component, an in-vessel prototype composter was constructed. Nine media formulations using three forms of dairy cattle solid waste (raw, composted alone, or composted with 50% sawdust) and three blends containing 50% vermiculite and either 50% waste, 25% waste and 25% peat moss, or 50% peat moss were prepared. 'Bonanza Yellow' dwarf marigold (Tagetes patula) were grown as outlined above. Raw dairy cattle solid waste was unsuitable as a substitute for peat moss in peat-lite growing blends due to poor plant growth and leaf color. However, composting the waste with or without sawdust allowed complete substitution for peat moss in the growing media without a sacrifice in plant height, dry weight accumulation, or leaf color. Media blends containing composted dairy cattle solid waste had acceptable physical and chemical properties for production of marigolds. Composting the animal waste increased media bulk density, reduced air space and total porosity, lowered media pH and increased measurable levels of N in both the media and plant tissue.

Confined animal feeding operations (CAFO's), including dairy, beef cattle feedlot, poultry and swine operations, generate large amounts of animal waste products. Agriculture has been identified as the largest contributor to nonpoint source pollution in the United States (U.S. Environmental Protection Agency, 1992) and one-third of all agricultural nonpoint source pollution impairments are attributed to waste from livestock CAFO's (Long and Painter, 1992).

Research has been conducted on animal and municipal wastes to stabilize organic compounds and reduce odors, particle size, volume and weight (Albin and Sherrod, 1974; Darmody et al., 1983; Epstein et al., 1976; Hileman, 1974; Kuhlman, 1990; Sweeten, 1990). Most composting is accomplished by aerobic microorganisms (Finstein and Morris, 1979) and on a large scale can be facilitated by use of either windrow or in-vessel techniques (Nordstedt et al., 1993). The decomposition process is accomplished by bacteria, actinomycetes and fungi (Keener et al., 1993). The composting process should be allowed to proceed to a stage so that end products can be handled and stored without adverse environmental effects (Golueke, 1977). Composted organic materials such as tree bark, leaf mold, yard trimmings, municipal waste, sewage sludge, sawdust, grape marc, spent mushroom compost and animal excreta have been used experimentally as substitutes for peat moss (Chen et al., 1988; Klock and Fitzpatrick, 1997).

Composting within a temperature range of 54°-66°C is characterized as thermophilic (Bollen, 1993) and is desirable for reduction of pathogenic microorganism populations. Pathogen reduction requires approximately 3 days in aerated in-vessel or static-pile composting processes and approximately 15 days when using windrow techniques (Bollen, 1993 and Sweeten, 1990).

The physical properties of plant growing media are important (Bungee and Frink, 1989), and the essential characteristics of soilless growing media and field soils are distinctly different (Warncke and Krauskopf, 1983). The physical characteristics of soilless growing media can be partially described through determination of bulk density, container capacity, air space and total porosity (Fonteno et al., 1981; Karlovich and Fonteno, 1986; Milks et al., 1989).

The purpose of this study was to evaluate the feasibility of in-vessel composting of dairy cattle solid waste for production of a partial or complete substitute for peat moss in greenhouse soilless growing media.

Solid animal waste was collected in August, 1993 from a 400-cow freestall dairy barn. The dairy utilized a hydraulic flush waste removal system that deposited solid and liquid waste along with flush water into an open-topped in-ground holding tank. Solid waste was removed from the tank using an auger encased in a perforated stainless steel screen allowing removal of excess water. The solid waste was dried on an asphalt surface by stirring twice daily with a tractor-mounted front-end loader for 7 days and placed in dry storage for later use.

Experiment A: Evaluation of raw dairy cattle solid waste.

'Bonanza Yellow' dwarf marigold (Tagetes patula) and mixed-color snapdragon (Antirrhinum majus) were germinated in seedling trays containing Metro-Mix 350 for transplanting into five growing media blends. The two commercial media used were Metro-Mix 350 (Canadian peat moss, sphagnum peat, vermiculite, sand and processed bark ash), and Nature’s Little Garden (ground pine bark, composted hardwood sawdust, animal waste, brewery by-product, Canadian peat moss, sand and perlite). Three additional media, each containing 0.6 kg Aqua-Gro 2000 surfactant and 6.0 kg hydrated lime per m³, were prepared on-site with the following specifications: 1) a peat-lite blend containing 50% No. 3 grade vermiculite and 50% Canadian peat; 2) a peat-lite blend containing 50% No. 3 grade vermiculite, 25% Canadian peat moss and 25% dried raw dairy cattle solid waste; and 3) a peat-lite blend containing 50% No. 3 grade vermiculite and 50% raw dairy cattle solid waste.

Flats, 25 by 50 cm containing 36 cells, were filled with the growth media. Marigold and snapdragon seedlings were transplanted at the first true leaf stage. Each flat was equally divided with 18 marigolds and 18 snapdragons on opposite ends.

Plants were grown for 46 days from February 12 to March 30, 1994 in a climate controlled greenhouse. Daytime temperatures ranged from 24-34^oC. Plants were watered as needed to prevent moisture stress with a 300 ppm N solution using a 20-20-20 soluble fertilizer.

On day 46 of the project, plant height was measured and leaf color and degree of bloom were rated by two evaluators on a scale of 1-10 with 1 = poorest and 10 = best. Ratings of the two evaluators were averaged. The above ground plant parts were harvested, dried at 60^oC for 72 hr and dry weight was recorded. The plant tissue was digested (Nelson and Sommers, 1980) and analyzed by ICP emission spectroscopy for N, P, K, Ca, Mg, Na, Zn, Fe, Cu and Mn. Growing media samples were analyzed for NO₃-N, P, K, Ca, Mg, Na, and S by the Texas A&M University Soil Testing Laboratory in College Station using procedures of Hons et al., 1990. Soil salinity was determined using a Beckman Sol-U-Bridge. The C/N ratio of growing media was analyzed using an NCHS-O EA-1108 Elemental Analyzer.

Wet and dry bulk density, container capacity, air space and total porosity were determined for each media using porometers with an internal volume of 350 cm³ (7.62 cm high by 7.62 cm dia) made from PVC pipe and miscellaneous fittings following the guidelines of Fonteno (1981).

Experimental design was a 5 by 2 randomized complete block using five growing media and two plant species with four replications. Data were analyzed by analysis of variance and means were separated by LSD at the 5% level of significance.

Experiment B: Evaluation of composted dairy cattle solid waste

To compost waste, an in-vessel prototype composter was constructed of an open-ended metal tank measuring 0.9 m diameter and 1.8 m long resting in a horizontal position on a set of 4 steel casters. The tank was rotated at the rate of 1 revolution per hour by a 0.5 hp motor equipped with a gear-reduction chain drive mechanism. The ends of the tank were enclosed by masonite doors with a 1 cm perimeter gap for ambient air exchange. The tank was fitted with a center partition creating two 0.9 m long by 0.9 m diameter chambers. Each chamber would hold 0.4 m³ of material when filled to approximately two-thirds capacity, allowing headspace in each chamber for air exchange.

Dried dairy cattle solid waste at the rate of 0.4 m³ was added to one chamber and 0.2 m³ dairy waste plus 0.2 m³ of softwood sawdust were added to the other chamber of the composter. Moisture content was adjusted to 50% using tap water. The compost reached temperatures of 56^oC after 48 hr and cooled to ambient within 9 days.

Nine media formulations using three types of dairy cattle solid waste (raw, composted alone, or composted with 50% sawdust) and blends containing 50% vermiculite and either 50% waste, 25% waste plus 25% peat moss, or 50% peat moss were used as outlined in Table 1.

Aqua-Gro 2000 surfactant was added to each blend at the rate of 0.6 kg per m³. Hydrated lime was added at the rate of 3.0 kg per m³ for blends containing 25% peat moss and 6.0 kg per m³ for blends containing 50% peat moss. No lime was added to blends using 50% waste.

'Bonanza Yellow' dwarf marigold (Tagetes patula) was used in Experiment B. Each flat contained 36 plants. Experimental design was a 3 by 3 randomized complete block with four replications. Growing procedures, data collection and analysis were as described in Experiment A.
 
 

Experiment A

The dry bulk density of Nature's Little Garden media (NLG) was notably higher than the other formulations probably due to the presence of sand and bark in the media (Table 2). Metro-Mix 350 (MM) and the Peat-lite (PL) blend, both containing approximately 50% peat moss, had the lowest dry bulk densities. Although the variation in wet bulk densities was small, NLG and the two blends containing 25% and 50% raw dairy waste (MPL and SPL) were highest.

Container capacity of the two blends containing dairy waste (MPL and SPL) was similar to that of PL, suggesting that dairy cattle solid waste is as effective as peat moss in contributing to water holding capacity (Table 2). The NLG blend had the lowest container capacity probably due to the sand and bark incorporated into the blend. Air space was similar among blends, but MPL exhibited the highest total porosity.

The SPL media formulation (containing 50% dairy waste) had the highest pH (Table 3), possibly due to the effects of bicarbonates which are routinely added to dairy cattle rations. The pH of all other media formulations ranged from a low of 5.6 in PL to 6.9 in MM. NLG had the highest N, P, K, Ca, and Mg levels as well as the highest level of salinity. Blends containing 25% (MPL) and 50% (SPL) dairy cattle waste had the lowest salinity levels, and both were low in N. Salinity levels and N were low in these blends due to the hydraulic flush waste collection system used in freestall barns. Flushing of animal wastes from the containment facility would dissolve a portion of the total salts, thus removing them from the separated solid waste component used in this project.

Blends with incorporated animal waste contained lower salinity, and levels of P, K, Ca, Mg, and Na equal to or greater than the commercial formulation of Metro-Mix 350 (Table 3). The C/N ratios of media containing dairy cattle solid waste were lower than the Metro-Mix 350.

SPL produced the highest levels of Na in tissue compared to the other media formulations and use of both PL and SPL resulted in tissue with higher levels of Fe than MPL (Table 4). The higher Na and Fe in these plants was due primarily to accumulations in snapdragon tissue as indicated by a significant species by media interaction (data not shown).

The SPL blend, which substitutes dairy waste for all of the peat moss in a peat-lite formulation, had the lowest N content of all media tested (Table 3) and produced plants with the lowest accumulation of N in the tissue (Table 4).

The height of plants grown in MM, which was used as an industry standard for this experiment, was taller than plants grown in NLG and SPL (Table 5). SPL produced the more inferior plants in this experiment as indicated by reduced height, dry weight accumulation and leaf color values. This poor growth could be partly due to the low media N content (Table 3).

Plants in MM and PL produced the largest dry weight accumulation and best leaf color, whereas NLG and the MPL displayed similar, intermediate effects on these parameters. More blooms were present at project termination when plants were grown in MM or MPL, and the fewest were present when plants were grown in PL or SPL.

Experiment B

Media blends containing composted dairy waste without sawdust had the highest dry and wet bulk density (Table 6), possibly due to a reduction in particle size as a result of mechanical abrasion during the composting process. A reduction in particle size would cause tighter compaction and reduce air space, which occurred in both of the composted waste treatments. Blends containing animal waste (MPL and SPL) were higher in wet and dry bulk density than PL, and both blends exhibited lower container capacity, air space and total porosity.

Composting with or without sawdust reduced media pH by approximately 0.5 units compared to media containing raw waste (Table 7). Media containing raw waste contained less N, K, S, and salts than mixes with composts. C/N ratio did not significantly differ between any of the wastes used.

The SPL blend, which completely substituted dairy waste for peat moss had the highest pH, nutrient and salinity levels of all the blends (Table 7). The PL blend had the highest C/N ratio and, except for Mg, had the lowest levels of nutrients, pH, and salinity.

Composting with or without sawdust resulted in increased N levels in plant tissue (Table 8). Marigolds grown in media containing composted dairy waste with 50% sawdust accumulated the highest levels of Na, Zn, Fe, Cu, and Mn in the tissue, but had significantly lower levels of K. Although foliar N levels were similar, plants grown in PL accumulated higher levels of P, Mg, and Na, but lower K and Ca concentrations than when the other two blends were used.

Use of growing media containing composted dairy waste with or without sawdust resulted in plants which were superior in height, dry weight accumulation, leaf color and degree of bloom than did use of media containing raw dairy waste (Table 9). PL, MPL and SPL blends produced plants similar in height.

Raw solid waste from dairy cattle was unsuitable as a substitute for peat moss in peat-lite potting mix blends. However, composting the waste with or without sawdust allowed for complete substitution for peat moss without a sacrifice in plant height, dry weight accumulation, or leaf color. Media blends containing composted solid waste from dairy cattle had acceptable physical and chemical properties for production of marigolds. Composting lowered media pH and increased measurable levels of N in both the media and plant tissue. Incorporation of sawdust as a bulking agent for co-composting with dairy cattle waste was unnecessary for completion of the composting process or successful plant production. Additional work is needed to evaluate the use of different animal wastes as growth media components, different waste collection techniques, applicability to other plant species, long range product stability, and economics of utilization.

This project was supported in part by grants from the Graduate School, Texas A&M University-Commerce, the Houston Livestock Show and Rodeo, Houston, TX, and the Texas Department of Agriculture, Austin, TX. The authors wish to thank Dairyland Automation, Inc. and BW Organics, Sulphur Springs, TX for manufacture and donation of the prototype composter used in this project.

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