Abstract
On-farm composting offers the potential to significantly reduce problems associated with manure management including odors, pathogens, ground water pollution, and utilization costs. Three controllable variables that directly affect the efficiency of on-farm composting are weather, windrow size and windrow turning frequency. In temperate climates, low ambient temperatures and winter precipitation may lower composting temperatures and increase 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 affecting composting rate. Windrow turning reduces moisture and temperature gradients within the compost windrows, but the benefits of frequent turning on composting rate have not been well documented. The objectives of this study were to understand the effects of these variables on composting rate, weight loss, volatile solids loss, moisture content, oxygen and temperature gradients, bulk density and particle size of unseparated dairy manure composted with hardwood sawdust (DM+S). Two composting windrow 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) were evaluated. Results showed that the seasonal differences were primarily associated with compost moisture content, which varied as a function of ambient air temperature and humidity. Windrow size affected oxygen and temperatures in windrows. Before turning, the temperature averages (different depths) were significantly higher (p < 0.05) and oxygen concentrations averages were lower in the larger windrows (p > 0.1) than those observed in the smaller windrows. Turning frequency was positively correlated (r > 0.7) with bulk density, moisture and wet weight loss but not with volatile solid loss, particle size or oxygen and temperatures. Overall, the final compost properties (day 120) were very similar regardless of turning frequency, season or windrow size. In conclusion, dairy manure composted in larger windrows turned 3 times per month resulted in composts not significantly different than those made in smaller windrows turned 10 times per month.
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