Fc. Michel et al., EFFECTS OF TURNING FREQUENCY, LEAVES TO GRASS MIX RATIO AND WINDROW VS PILE CONFIGURATION ON THE COMPOSTING OF YARD TRIMMINGS, Compost science & utilization, 4(1), 1996, pp. 26-43
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.