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Current Research Projects

Compost Science & Utilization, (2008), Vol. 16, No. 4, 218

Materials And Methods

Effects on Turning Frequency, Pile Size and Seasonal Variability on the Production of Dairy Manure/Sawdust Composts
Investigators: Tirado, Sandra M. and Frederick C. Michel Jr., Department of Food Agricultural and Biological Engineering, The Ohio State University/OARDC, Wooster, Ohio

Objectives: To evaluate the effects of turning frequency, season and pile size in on-farm composting of dairy manure with hardwood sawdust (DM+S) on physical and chemical parameters as well as composting costs. Relatively few studies have focused on the effects of turning frequency, pile size or season on compost production on or mass losses, bulk density, volume and moisture content. In temperate climates, low ambient temperatures and winter precipitation may lower composting temperatures and effect compost moisture contents, making composting rates harder to maintain. Windrow size directly impacts the depth of penetration of oxygen and the amount of compost exposed to high temperatures, potentially reducing composting rate. Windrow turning reduces moisture and temperature gradients within the compost pile or windrow, but the benefits of frequent turning on composting rate have not been well documented. To better understand the effects of these variables on composting, weight loss, volatile solids loss, moisture content, oxygen and temperature gradients, bulk density, particle size and the costs associated with the composting of unseparated dairy manure with hardwood sawdust (DM+S) were evaluated for two pile sizes (surface area to volume ratios of 0.9-1.1m2/m3 and 1.7-2.1m2/m3) and two turning frequencies (every three days and every ten days) in two different seasons (winter and summer).

Bio-Contained Mortality Compost Using Liquid Manure
Investigators: K. Stanford, Alberta Agriculture and Food, Lethbridge Alberta, Canada; McAllister, T.A., T. Reuter, J. R. Moyer and F. J. Larney, Agriculture and Agri-Food Canada, Research Centre, Lethbridge, Alberta, Canada; W. Xu, Dalian University of Technology, Dalian, China
Objectives: To develop a simple on-farm protocol for static composting large animal mortalities in a simulated disease outbreak using liquid manure. During disease outbreaks, composting has been used to safely dispose of carcasses and infectious solid manure. However, optimized methods have not been established to use liquid manure (> 80% water content, WC) from dairies as the substrate for mortality composting. In April of 2007, a 3x2 factorial study was conducted in wooden compost bins (240 x 240 x 140 cm) lined with 0.5 mm plastic to a height of 50 cm. Three levels (LO, 95 kg; MED, 236 kg; HI, 606 kg wet wt.) of liquid manure (91% WC) were applied to barley straw containing a single calf mortality (avg. wt 130 kg). Compost temperature and carcass degradation were evaluated in each bin over 52 d. As an indication of compost efficiency, viability of four types of weed seeds (wild buckwheat, Polygonium convolvulus L, BW; dandelion, Taraxacum officinale, DL; stinkweed, Thlaspi arvense L., SW; and wild oat, Avena fatua, WO) was determined from seeds retained at the laboratory (Control) or from those placed in sealed nylon bags (50 µm pore size) embedded at 3 locations in each bin. Initial C: N ratios ranged from 58:1 to 68:1, while initial WC was 64, 52 and 42% for the HI, MED and LO treatments, respectively. Rate of compost heating and peak temperature (58.6 vs. 46.5o C) was increased (P < 0.05) for HI as compared to LO. Rate of temperature decline was lower (P < 0.05) and calf decomposition was visibly superior for HI as compared to LO. Viability of WO was eliminated by all compost treatments, but that of BW increased (P < 0.05) in MED and LO as compared to Control. Consequently, methodology used in the present study would not be suitable for elimination of resilient organisms such as Campylobacter jejuni, although HI, with 64% initial WC, showed the most promise for using liquid manure as a substrate in contained mortality compost.

Soil Improvement

Effect of Municipal Solid Waste Compost on Mine Soils as Evaluated by Plant Growth, Trace Element Leachability, Ecotoxicity of Leachates, and Biological and Biochemical Properties of Soils
Investiagators: C. Cunha-Queda, A. Nobre and A. de Varennes; Department of Agricultural and Environmental Chemistry, Instituto Superior de Agronomia, Technical University of Lisbon (TULisbon), Lisboa, Portugal; P. Alvarenga, Department of Environmental Sciences, Beja, Portugal
Objectives: To determine whether compost from mixed municipal solid waste (MSW) could be used to remediate two soils from a mine contaminated with trace elements. One of the soils was less acidic and had a greater content of Cu and Zn while the other had more Pb and a lower pH. The effect of MSW was evaluated by plant growth, trace element leachability, ecotoxicity of soil leachates, and biological and biochemical properties of soils. Growth of perennial ryegrass (Lolium perenne L. cv. Victorian) was stimulated in the MSW compost-amended soils compared with respective controls or with acidic soil when limed. After ryegrass had been growing for 119 days, the amount of water-extractable Zn was lower in MSW compost-amended soils, while the opposite was true for water-extractable Cu. Water-extractable Pb increased following MSW compost application to one soil and decreased in the other. The greatest dehydrogenase activity was obtained in amended limed soil, while the number of culturable bacteria and fungi and the activities of cellulase and b-glucosidase were similar in soil that was limed or following MSW compost application. In contrast, urease activity was repressed in limed or MSW compost-amended soils. Leachates from unamended soils were toxic towards Daphnia magna. Liming the very acidic soil led to a decrease in the toxicity of the leachate, but it was only in MSW compost-amended soils that ecotoxicity was no longer detected.