Environmental Technology, Vol. 21. pp 1037-1046 @ Selper Ltd, 2000 EFFECT OF WINDROW TURNING AND SEASONAL TEMPERATURES ON COMPO STING OF HOG MANURE FROM HOOP STRUCTURES S.M. TIQUIA", T.L. RlCHARD2 AND M.s. HONEYMAN3 'Department of Food, Agricultural, and Biological Engineering, The Ohio State University- Ohio Agricultural Research and Development Center (OARDe), Wooster OH 44691, USA 2Department of Agricultural and Biosystems Engineering, Iowa State University, Ames, IA 50011, USA 3Department of Animal Science, Iowa State University, Ames, IA 50011, USA (Received 14 December 1999; Accepted 18 April 2000) ABSTRACT A studywas undertaken to investigate the effect of windrow turning on composting of hoop manure (a mixture of partially decomposed hog manure and cornstalk). wee series of experiments were conducted: one during summer, one during winter, and one during spring. In all three series of experiments, windrows were either turned (once a week) or left unturned during the composting process, which lasted for 42 days. The effects of windrow turning were evaluated by measuring the physicochemical properties (temperature, oxygen concentration water content, pH, organic matter, and nutrients) of the hoop manure during composting. Turning affected a number of important physical and chemical parameters such as temperature, oxygen concentrations, and C and mass loss. The temperature of the unturned windrows took longer to drop to ambient temperature, had lower oxygen concentration, and C and mass loss than the turned windrows. These results suggest that the decomposition rate in turned windrows is much faster than the unturned ones. However, the final product from the two composting treatments (turned and unturned windrows) was similar in terms of the organic matter, nutrient contents, and C:N ratios. N loss was a major problem during composting of hoop manure. As much as 60% of the N in the hoop manure (both in turned and unturned windrows) was lost during composting, indicating that composting has significantly reduced the value of hoop manure as N fertilizer. These losses could be attributed to ammonia volatilization, leaching, and run-off. Overall, composting was similar in all three seasons (summer, winter, and spring). This study demonstrated that hoop manure could be successfully composted during winter. Keywords: Composting, open-air windrows, compost turning, nitrogen loss, deep litter system INTRODUCTION r Swine producers in the United States who are looking for lower cost structures to raise hogs have recently shown a great deal of interest in the so called hoop structures as swine 'production facilities [1]. The unit set-up cost is low compared to confinement facilities, as the internal infrastructure is less sophisticated (absence of slatted floors, scraper systems, and manure pits). These facilities rely upon the use of large amounts of bedding material (usually cornstalks) to absorb the hog feces and urine, similar to the deep litter system being practiced by hog farmers in Hong Kong, Japan, New Zealand and The Netherlands [2]. Hoop structures are somewhat different from conventional pig housing facilities as the animals in these structures are kept on f{ thick layer of bedding material. The environmental benefit of hoop structures is that no effluent needs to be discharged- the hog manure is decomposed in-situ and the hoop manure (a I mixture of partially decomposed hog manure and cornstalk) can be used as soil amendment. The hoop manure is normally cleaned out after each group of pigs is sold (2-3 times a year), and either stored or composted in windrows. Composting of agricultural waste is used increasingly to reduce its weight and volume, and to improve the properties for its use [3-5]: Subsequent windrow composting studies also demonstrated a higher degree of homogeneity achieved in the composted material [5, 6]. Windrow turning is one of the composting strategies that affect the degree of decomposition, and quality of the composted product [4, 7, 8]. It is often cited as the primary aeration and temperature control during composting [9, 10]. However, the advantages and disadvantages of windrow turning during composting are heavily disputed. Some agriculturists advocate a slow composting process that involves little disturbance (Le. infrequent turning) [11], while others are in favor of frequent turning to hasten aerobic 1037