EFFECTS OF TURNING FREQUENCY, LEAVES TO GRASS MIX RATIO AND WINDROW VS PILE CONFIGURATION ON THE COMPOSTING OF YARD TRIMMINGS

Because of proposed bans on the landfilling and incineration of leaves , grass and brush, large-scale composting is fast becoming the primary disposal option for yard trimmings in many states. Few systematic stu dies have been done to compare the effects of turning regime, feedstoc k mix ratio, or windrow vs. pile configuration on composting and the c haracteristics of finished compost. In this study, various ratios of l eaves, grass and brush were mixed and composted in two series of windr ows; and one set of static piles. One windrow series (#1) was turned s even times every four weeks, while the other windrow series (#2), and the piles, were turned once every four weeks. The effects of the diffe rent treatments were examined by measuring compost temperature, oxygen concentration, pH, organic matter and moisture content, volatile fatt y acid content, bulk density, stability, humification and seed germina tion indices, total and available nutrient levels, and particle size d istribution. Results showed that turning frequency had little impact o n oxygen concentrations, VFA content and temperatures during the compo sting of yard trimmings in windrows, however, in piles temperatures we re substantially higher and oxygen concentrations fluctuated greatly. The composts from all the treatments were stable, (oxygen uptake rates < 0.1 mg O-2/g OM/hr) after 60 days of composting regardless of the t urning frequency, mix ratio or configuration. Thee bulk density increa sed much more rapidly in frequently turned windrows than in the other treatments and particle sizes were smaller in these windrows. In most respects however, the final composts (day 136) were remarkably similar and none inhibited Cress seed germination or root elongation. The pH of all the composts, and the soluble salts and nitrate levels in compo sts made with high levels of grass, exceeded guidelines for greenhouse growth media.