Properties of Raw and Composted Green Wastes and Cotton Gin Trash -Report of Progress

Stuart Pettygrove

UC Davis

The physical and chemical properties of urban yard trimmings and landscape prunings in California are not well documented. These materials are referred to as "green wastes" by the California Integrated Waste Management Board and consist of grass clippings, leaves, pine needles, twigs, and branches from trees and shrubs. Other constituents include discarded soil, potting mixes, gravel, and various contaminants such as plastic, wood, and pet wastes.

Much of this material is collected separately from municipal solid waste and is processed at privately operated facilities into mulch or compost. Average chemical and physical properties of non-composted, semi-mature or partially composted , and fully composted green wastes are shown in Table 1. Properties of an agriculturally-derived compost, cotton gin trash compost, are also shown.

Samples of these materials were provided by participants in the California Integrated Waste Management Board's compost demonstration projects, 1994-96. Participants include Will Gehr (City of San Jose Agriculture in Partnership project), Jesus Valencia (Stanislaus Co.), Marc Buchanan and Richard Smith (UC Santa Cruz/San Benito Co.), Harry Andris (Fresno Co.), and Carol Frate (Tulare Co.). Additional samples of yard trimmings were provided by Ron Ganiatts, Valleys Pride. John Texiera and Rick Wegis provided cotton gin trash compost samples.

Table 1. Properties of organic amendments, 1994-1996.

	Non-composted yard trimmings	Semi-mature composted yard trimmings	Mature composted yard trimmings	Composted cotton gin trash
n =	8	8	18	3
Organic matter*	68	59	40	49
C	33	29	19	24
C:N	25	20	14	10
C:OM	0.48	0.48	0.48	0.48
N	1.38	1.43	1.42	2.40
P	0.20	0.20	0.27	0.30
K	0.85	0.84	1.00	1.58
NO3-N,mg/kg	18	11	98	618
NH4-N,mg/kg	158	140	62	8
EC,dS/m (5:1)	4.2	4.0	3.9	8.2
Bulk density, lb/yd3	186	381	1061	998
Particles >3/8 inch	43	27	5	2
*All values are percent dry weight basis except where noted. Organic matter content=100-%ash.