Thesis completed by Mr. Randy Tidwell in partial fulfillment of the requirements for the Master of Science Degree.

Major Advisor: Dr. Donald L. Cawthon
 
 

Regulations for the disposal of confined animal waste products have reached critical proportions for the poultry and dairy farmers of East and Northeast Texas. New state and EPA standards have increased the need to establish better means of waste disposal. The concentrated animal feeding operations consist primarily of dairy and poultry enterprises in this region of the state. Large amounts of waste are produced daily. According to Sweeten (1991) the average 500-cow dairy produces about 10,290 lbs./day of dry manure and about 71,400 lbs/day of wet manure. The amount of manure produced contributes to the potential for underground and watershed pollution.

A non-renewable resource, peat moss, is the primary ingredient used as a growing media in the horticulture industry. As demands for the product increases the cost and availability becomes of utmost importance. A possible shortage of the product with the next century is anticipated and a study to explore the feasibility of using composted cattle manure and poultry litter as a partial or complete substitute was researched.
 
 

The enforcement of Title 31 of the Texas Administration Code Section 321.31-321.41 has positioned waste management as a critical issue for the Texas dairy and poultry farmers. This regulation indicates that no discharge of waste and/or waste waters from a concentration and confined area can be deposited into the waters of the state of Texas. Waste water is defined as water containing waste or water contaminated by contact with waste, including water containing any production process or contaminated rainfall runoff. Also, because of an ever increasing demand and rising cost for peat as a growing medium in horticulture, a high-quality, low-cost substitute has been pursued, i.e., composts derived from organic waste material (Chen et al., 1988).

Waste products are amplified when people, animals, or plants are concentrated into small confined areas (Hansel and Mancl, 1988). The disposal of said waste is costly, time consuming, and a constant reoccurring problem.

All organic waste has a natural population of microorganisms including bacteria, actinomycetes, and fungi. Under satisfactory conditions which includes nutrient balance, moisture content, temperature and aeration; the microbes multiply and grow. This growth of microorganisms is called decomposition (Hansen and Mancl, 1988).

Composting is a method of solid waste management whereby the organic component of the solid waste stream is biologically decomposed under controlled conditions to a state in which it is stable and can be handled, stored, and/or applied to the land without adversely affecting the environment (Golueke, 1977). Before the existence of bacteria was known, primitive agriculturists made rough piles of weeds, garbage, manure, and other wastes. They observed the piles becoming smaller and smaller as the original volume of materials changed into compost, a dark fluffy material that conditions and enriches the soil into which it is mixed. Today composting is a popular activity of numerous organic gardeners and farmers. Many community ordinances prevent the burning of leaves and refuse, and space for waste disposal is becoming scarce; therefore, numerous cities have turned to composting, which produces both a useful and an ecologically compatible product (Hansen and Mancl, 1988).

Four criteria that must be considered for composting to be achieved include C/N ratio, moisture, temperature, and aeration. Balancing nutrient requirements in composting is very similar to balancing feed nutrients in livestock production. In composting, the carbon to nitrogen ratio or C/N ratio is very important. Carbon stimulates the growth in bacteria, actinomycetes and fungi, while nitrogen provides for the formation of proteins and enzymes. The optimum C/N ratio for these microbes is 30 parts carbon to 1 part nitrogen. Under normal conditions, a C/N ratio above 30 causes the composting process to decrease. When the C/Nreaches 25:1 or lower, nitrogen is converted to ammonia and is released into the atmosphere as an undesirable odor (Hansel and Mancl, 1988).

Maturity of composts critically affects their successful utilization in agriculture. This is especially important when composts are applied immediately before planting or when they are used in container media (Y. Inbar et al., 1990). Zucconi (1981) states that all immature composts induce high microbial activity in soil for some time after incorporation, creating the potential for oxygen deficiency and a variety of indirect toxicity problems for plant roots. Also, plant and animal health aspects and disease suppressive properties of composts are affected by maturity (Hoitink and Fahy, 1986). Chanyasak et al. (1983) proposes that the organic-carbon to organic-nitrogen ratio in water extract could serve as a reliable indicator of compost maturity. The C/N ratio is often used as an index of compost maturity despite many pitfalls associated with this approach. A decrease from an initial C/N value of 35-40 or higher for wood wastes to a final level of 18-20 implies an advanced degree of stabilization (Zucconi and de Bertoldi, 1987).

Moisture is an important factor in the success of composting. Ideally, a 60% moisture content should be obtained after the mixture of organic waste has been administered. When the 60% moisture content is exceeded, oxygen movement is somewhat restricted, creating a deterioration of structural strength. This allows the process to become anaerobic and putrid. Moisture contents that reach below 50% rapidly decrease decomposition (Hansen and Mancl, 1988).

While composting is in progress, the temperature will increase due to the breakdown of organic material by bacteria. Temperature can range from near O⁰ C to 71⁰ C according to the classification of microorganisms involved in the composting (Hansen and Mancl, 1988).

The final condition which is essential to the success of composting is aeration. Oxygen in sufficient amounts must be available to stimulate vitality of aerobic types of microorganisms. When the right conditions are met, bacteria can decompose nearly anything. They can produce enzymes which will digest most materials in their individual environment (Hansen and Mancl, 1988).

Three categories in composting which have a practical significance are degree of aeration, temperature, and technology. The resulting classes are aerobic vs. anaerobic; mesophlic vs. thermophilic; and mechanized vs. nonmechanized. Aerobic composting is the process of decomposition in the presence of air (i.e., oxygen). Conversely, anaerobic composting is the process of decomposition in the absence of air. Anaerobic composting is similar to the anaerobic digestion processes used in treatment of sewage sludges. The two processes are very similar, but a technological difference does exist between anaerobic composting and anaerobic digestion. In composting, wastes are maintained in a "solid state" whereas in anaerobic digestion the wastes are in a slurry form (Gouleke, 1977).

Most modern compost systems take advantage of aerobic decomposition for many reasons. One of the main reasons for preferring aerobic decomposition is the absence of objectionable odors. The second, and possibly the most important, reason for aerobic decomposition pertains to public health and crop production. Public health and crop safety is obtained from the high temperatures that are common in a properly constructed aerobic compost operation. The temperature in an aerobic pile reaches levels above the thermal death point of most plant and animal pathogens and parasites. These extreme temperatures are also lethal for weed seeds. Another advantage of aerobic composting over anaerobic is the speed in which aerobic decomposition occurs. In recent years, through careful design of equipment and operational procedures, much progress has been made in accelerating anaerobic composting. Many organisms that are involved in composting thatrapidly breakdown refractory compounds are obligate aerobes which cannot survive in an anaerobic environment (Golueke, 1977).

According to Golueke (1977) the next classification in composting is mesophilic vs. thermophilic. Mesophilic organisms are organisms, which have an optimum temperature range of 8-10⁰C to 45-50⁰C. Organisms having an optimum temperature range of 45-50⁰C and higher are known as thermophilic. The cut-off point between the various ranges is not sharp, and one blends into the next. Temperatures in an aerobic mass of material can begin in a range below 4-5⁰C called psychrophiles and will increase into mesophilic followed by thermophilic. This process will occur unless measures are taken to prevent it from doing so. If prepared properly, compost reaches 71⁰C or more. Obtaining this temperature is important in the destruction of most weed seeds, insect eggs, and disease organisms. Thus, a relatively pest-free product to mix with other soils and growing media is produced. According to Christopher and Asher 1994, composting may be accomplished by using materialssuch as chicken feathers, beet and felt waste, leather dust, dryer lint, vacuum cleaner dust, straw and spoiled hay, tobacco stems, sawdust, and various types of animal manures.

The last major classification, mechanical vs. nonmechanical/windrow, deals with the technology involved in the compost operation (Golueke, 1977). Mechanical composting involves the use of mechanized, or enclosed units, equipped to provide control of the environmental factors. Open, or windrow, implies stacking the raw material in elongated piles, thus allowing the composting process to occur within.

Compost is usually categorized into three broad areas according to use: compost used as a fertilizer, compost used as a soil conditioner, and compost used to reclaim land. The nitrogen, phosphorus, and potassium (N,P,K) content of compost from refuse in the United States has been low. Therefore, compost by itself will not be sufficient to meet the legal specifications for fertilizer. If compost is to be used as a fertilizer, it must be enhanced with inorganic N,P,K (Golueke, 1977). A commercial fertilizer blend 5-10-5 is a true 5% nitrogen, 10% phosphorus, and 5% potassium; while some synthetic fertilizers, such as urea, are even more concentrated. By comparison, compost provides a very modest amount of N,P,K-approximately 3.5-1-2.

Plant growers are responsible for providing 12 essential plant nutrients: six macronutrients and six micronutrients. Ten nutrients can be supplied in the substrate prior to planting in quantities that will last for the whole crop period. This makes a postplant fertilization program much easier (Nelson, 1994). Trace or microelements are required by plants in small amounts usually presented in parts per million of plant dry weight (Janik, 1986). Micronutrients include iron, manganese, zinc, copper, boron, and chlorine. Macronutrients include nitrogen, phosphorus, potassium, calcium, sulfur, and magnesium. High nitrogen content results in succulent vegetation which may delay flowering and reproductive growth. Symptoms of nitrogen deficiency are reduced growth and pale green to yellow leaves (Janick, 1986).

Janick (1986) states that phosphorus is never found free in nature. Weathering rocks that contain mineral apatite, Ca₅F(PO₄)₃ released into the soils is the source of phosphorus. Nucleoproteins, phospholipids, and the high-energy phosphate bonds of ADP and ATP utilize phosphorus. Seeds contain high amounts of phosphorus. Deficiency symptoms are found in older plant tissues which seem to lose their sheen and appear dull and dark.

Potassium becomes extremely volatile when exposed to oxygen. Normally only 1 or 2 percent of total potassium is readily available to plants. Potassium is involved in the activation of enzymes that regulate photosynthesis, rate of respiration, carbohydrate metabolism, and translocation. Leaf tissue should contain about 3.5 to 4.5 percent of this element. Early deficiency symptoms include chlorosis, scorched older leaves, poorly developed root systems, and retarded plant growth (Janick,1986).

Calcium has a strong influence on ion absorption by soil particles and on the availability of other elements. Calcium containing compounds are added to the soil in an attempt to lower the pH of the soil. Calcium is important in the formation of plant cell walls and in the layers between cells called the middle lamella. Deficiency symptoms include stunted growth and curled, distorted leaves. Fruit symptoms include cracking, pits in the skin, and blossom-end rot (Janick, 1986).

Sulfur is a component of several amino acids including methionine and cysteine which are essential to human nutrition. Deficiency symptoms are very similar to nitrogen. Foliage tends to be light green, because sulfur is essential for chlorophyll synthesis (Janick, 1986).

Magnesium is closely related to calcium and is absorbed in the soil as an ion. It is involved in energy transfer and phosphorus metabolism. Seeds are extremely high in magnesium. Magnesium deficiency appears as intervienal chlorosis, and because it is mobile in the plant, the deficiencies appear in the older leaves and move upward (Janick, 1986).

Research was conducted to evaluate the use of composted dairy manure, poultry litter, and sawdust as a complete substitute for peat moss in plant 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.

Poultry litter, a mixture of bedding, excreta, feathers, and spilled feed, was collected from a 15,000-capacity broiler facility that uses hardwood sawdust as bedding. The litter had been used for production of six flocks of birds before removal from the production facility and stored under dry conditions until composting.

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 3 revolutions per hour by a 0.5-hp motor and a ratchet drive mechanism. 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.

Seven treatments were used for production of ‘Bonanza’ Yellow Dwarf Marigolds (Tagetes patula) and they were replicated three times. The seven media consisted of a peat moss control and the following composts containing dairy cattle solid waste/poultry litter/hardwood sawdust expressed on a percentage basis by volume: 0/50/50, 25/25/50, 25/50/25, 50/25/25, 50/50/0, and 50/0/50. Each of the completed composts and peat moss was blended with 0, 25, or 50% no. 1 grade vermiculite prior to use. Aqua-Gro 2000 surfactant was added to each blend at the rate of 0.6 kg per m³. Lime was added to the 100% peat moss control at a rate of 336g/cf. A rate of 168g/cf was added to the blends containing 50% peat moss and vermiculite. While a rate of 84g/cf was added to the blends containing 25% peat moss. Lime was added to blends containing peat moss to raise pH to the approximate range of the other blends.

Marigolds were germinated in Metro Mix 350 seedling trays. With the emergence of true leaves, the uniform seedlings were transplanted into ten by twenty-inch (25.4 by 50.8 cm) flats containing 36 cells filled with the growing media.

Plants were grown for 45 days from March 1 to April 14, 1994 in a greenhouse. 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 by placing a ruler in the middle of each flat and measuring the average foliage height. General appearance was rated by four evaluators on a scale of 1-5 with 1 = poorest and 5 = best, and number of blossoms was counted. Dry weight was determined by cutting each plant at the media level and placing all aboveground plant parts from each flat into paper bags for subsequent drying at 60⁰C for 48 hours.

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.

Experimental design was a 7x3 randomized complete block with four replications. Data were analyzed by analysis of variance and LSD at 0.05 was used to separate means.
 
 

Replications did not have a significant effect on any of the plant growth or visual appearance parameters as indicated by probabilities of significance (Table 1). However, the main effect of organic matter (OM) was significant for all the attributes measured whereas the main effect of vermiculite (V) was significant for plant dry weight, plant height and appearance. The interaction of OM*V was significant for all attributes except the number of blossoms.

Main effects of organic matter source and vermiculite on plant growth and visual appearance of marigolds (Table 2) shows that the peat moss control and the 50/00/50 (dairy manure/poultry litter/sawdust) blend experienced less mortality than other blends. The interactive effects of organic matter source and vermiculite on number of live plants (Figure 1), shows that even though blends containing poultry litter suffered high mortality rates, use of 50% vermiculite reduced mortality rates in blends containing 25% poultry litter.

The peat moss control produced the largest dry weight accumulation with the 50/00/50 blend having significantly lower dry weight (Table 2). The high mortality rates in blends containing poultry litter contributed to the extremely low dry weights in those blends.

Interactive effects of organic matter source and vermiculite on plant dry weight (Figure 2) shows that the incorporation of higher rates of vermiculite into the growing media containing 25% poultry litter tended to increase dry weight accumulation. This trend was also true in the peat moss control and the 50/00/50 blend but only when 25% vermiculite was used. Increasing the percentage of vermiculite in the growing media blend to 50% was not advantageous if poultry litter was not used.

Plant height follows the same trends as the number of live plants and plant dry weight (Table 2) with peat moss control having the greatest height which averaged 11.6 cm. As expected, the blend without poultry litter (50/00/50) produced taller plants than any of the blends that contained poultry litter. Use of the higher rate of vermiculite (50%) also resulted in taller plants.

Peat moss with 0 and 25% vermiculite showed the greatest growth potential according to the interactive effects of organic matter source and vermiculite on plant height (Figure 3). The 50/00/50 blend and 25/25/50 with 50% vermiculite were comparable to the peat moss control. All other blends were below the acceptable range for the industry.

Appearance ratings (Table 2) shows that the peat moss control was superior to all other blends, and met the minimum level of acceptability established at 3.0 for this study. Two other blends (25/25/50 and 50/00/50) were close in ratings, but were below the quality needed for the horticulture industry. Visual appearance tended to increase as the % vermiculite increased. The visual appearance of dwarf marigolds grown in peat moss based media was considerably better than all other blends except the 25/25/50 containing 50% vermiculite (Figure 4). All other blends were below the needed quality.

Number of blossoms was greatest in the peat moss control (Table 2). The 50/00/50 blend had the next greatest amount of blossoms. Plants grown in all other blends produced very few blossoms. The increase of vermiculite in the various blends had little or no effect on the number of blossoms produced.

Probabilities of significance of treatment effects on pH, nutrient content, and salinity indicate that the main effects of OM and V affected all nutrients tested (Table 3). A significant OM*V interaction occurred for each nutrient.

The 00/50/50 blend had a pH of 8.1, which was the highest pH of a media used in this study (Table 4). All other blends were slightly lower in pH but yet above the ideal range of 6.5 to 7.0 for greenhouse crops. The high pH’s are due to the alkaline nature of poultry litter and dairy cattle solid waste, and the amount of lime added to the peat moss control. Vermiculite had little effect on media pH.

The main effects of organic matter and vermiculite on media P content (Table 4) indicate the peat moss control and the 50/00/50 blend had lower phosphorus content than the other blends. The largest difference was between the 25/25/50 with 2100 ppm and the 00/50/50 blend with 3623 ppm. As the vermiculite increased the phosphorus content decreased.

Poultry litter was the primary contributor of phosphorus to the growing media blends as indicated by the fact that the peat moss control and the 50/00/50 blend (Figure 5) had minimal levels of phosphorus. The phosphorus content of other blends was proportional to the poultry litter content.

The main (Table 4) and interactive (Figure 6) effects of organic matter and vermiculite on media content of potassium are similar to those of phosphorus. The 50/00/50 blend and the peat moss control were comparatively very low in potassium with 500 ppm and 62 ppm respectively. Again, this suggests that poultry litter was the primary contributor of potassium to the growing media blends.

The main effects of organic matter and vermiculite on the media content of calcium (Table 4) show that most blends were similar in calcium content. However, the largest quantity of 5108 ppm was found in the 0/50/50 blend. As the percent of vermiculite increased (Table 4) the amount of calcium in the media increased.

The interactive effects of organic matter and vermiculite on calcium media content (Figure 7) shows similar calcium content between blends and vermiculite rates except for the 00/50/50 blend without vermiculite. This treatment was approximately 3000 ppm higher than the other media. As vermiculite increased in the blends, calcium decreased.

The main effects of organic matter and vermiculite (Table 4) on media magnesium content showed that those blends containing poultry litter had elevated magnesium levels with the 00/50/50 and 50/50/00 blends containing the highest amounts of 1284 and 1263, respectively. As expected, vermiculite diluted the levels of magnesium in the growing media.

Interactive effects of organic matter and vermiculite on media magnesium levels (Figure 8) shows that poultry litter significantly contributed to the amount of magnesium in the media. Once again, as percent vermiculite increased, the amount of the nutrient increased.

Main effects of organic matter and vermiculite on media sodium and sulfur content (Table 4) follows the same trends as magnesium. The peat moss control contained the lowest levels of both sodium and sulfur. The 50/00/50 blend contained approximately three times as much sodium and twice as much sulfur as the peat moss control. The concentration of both sodium and in growing media appeared to be directly related to the quantity of poultry litter that was included.

Interactive effects of organic matter source and vermiculite on media sodium (Figure 9) and content (Figure 10) again shows that all blends containing poultry litter were high in nutrient content and that vermiculite reduced the nutrient concentration.

The peat moss control had the lowest level of salinity with only 687-ppm concentration. The 50/50/00 blend resulted in the greatest level of salinity with 6375 ppm followed by the 00/50/50 blend containing 6017 ppm. The media salinity levels appear closely related to the quantity of poultry litter used, and vermiculite is effective in reducing the levels in growing media containing high salinity levels as evidenced in Figure 11.
 
 
 
 
 

Figure 1. Interactive effects of organic matter source and vermiculite on number of live plants at project completion. (PM = peat moss; DM = dairy manure; PL = poultry litter; SD = sawdust).
 

Figure 2. Interactive effects of organic matter source and vermiculite on (g) of dry weight accumulated per flat. (PM = peat moss; DM = dairy manure; PL = poultry litter; SD = sawdust).
 

Figure 3. Interactive effects of organic matter source and vermiculite on plant height of Dwarf Marigolds. (PM = peat moss; DM = dairy manure; PL = poultry litter; SD = sawdust).
 
 
 
 
 

Figure 4. Interactive effects of organic matter source and vermiculite on visual appearance of Dwarf Marigolds. (PM = peat moss; DM = dairy manure; PL = poultry litter; SD = sawdust).
 
 
 

Figure 5. Interactive effects of organic matter source and vermiculite on media phosphorus content. (PM = peat moss; DM = dairy manure; PL = poultry litter; SD = sawdust).
 
 
 
 
 

Figure 6. Interactive effects of organic matter source and vermiculite on media potassium content. PM = peat moss; DM = dairy manure; PL = poultry litter; SD = sawdust).
 
 

Figure 7. Interactive effects of organic matter source and vermiculite on media calcium content. PM = peat moss; DM = dairy manure; PL = poultry litter; SD = sawdust).
 
 
 

Figure 8. Interactive effects of organic matter source and vermiculite on media magnesium content. (PM = peat moss; DM = dairy manure; PL = poultry litter; SD = sawdust).
 
 
 

Figure 9. Interactive effects of organic matter source and vermiculite on media sodium content. (PM = peat moss; DM = dairy manure; PL = poultry litter; SD = sawdust).
 
 
 

Figure10. Interactive effects of organic matter source and vermiculite on media sulfur content. PM = peat moss; DM = dairy manure; PL = poultry litter; SD = sawdust).
 
 
 
 

Figure 11. Interactive effects of organic matter source and vermiculite on media salinity content. (PM peat moss; DM = dairy manure; PL = poultry litter; SD = sawdust).