Landscape Waste Research Articles

Duration of Composting Affects Compost Characteristics of Importance to Agriculture

A recently enacted state law requiring California cities to reduce their solid waste flow to landfills has greatly increased the composting of yard and landscape wastes. Currently, much of this material is being composted for less than 16 weeks, some for as little as 4 weeks, before agricultural use. A study was conducted to document the effects of composting method and duration on the physiochemical and biological characteristics of green waste compost. At each of four commercial composting facilities, two windrows of municipal green waste were sampled at 3-week intervals over a 15-week composting period. Each sample was analyzed for pH, NH4-N, NO3-N, and total N and C. Phytotoxicity was measured by a tomato seed bioassay. N mineralization/immobilization behavior was evaluated in a 2-week aerobic incubation of a 10% compost/90% soil blend at 30°C. The growth of vinca plugs (Vinca minor cv. `Pink Cooler') in a 50% compost/50% perlite mix was also evaluated. At all sites, the initial green waste was similar, with 1.1–1.5% N and C/N ratio of 20–28. Rapid mineralization of carbon in the first 6- to 9-weeks reduced C/N ratios to 14–18, with little change thereafter. Phytotoxicity decreased through 9 to 12 weeks, then stabilized. Net N immobilization was observed throughout the compost period, but decreased with increased composting time. Vinca growth increased with increasing compost age, up to 9 to 12 weeks. In summary, at least 12 weeks of composting was required to produce material of sufficient quality for typical agricultural uses.

Suitability of Composted Green Waste for Horticultural Uses

The study was undertaken to determine the physiochemical properties and nutrient supply characteristics of composted green yard and landscape waste (CGW) and to document its performance as a field soil amendment or constituent of potting media. Three CGW samples were collected from each of two composting operations in California from Nov. 1993 to Apr. 1994. Macronutrient content varied widely between operations, and among samples from the same operation, with mean total N, P, and K levels averaging 1.1%, 0.26%, and 0.67%, respectively. Controlled-environment incubation of a moist 1 CGW: 9 soil blend (2 weeks at 30 °C) was conducted to determine net N mineralization from CGW. Despite low C: N ratios (<12), five of six CGW samples showed net immobilization, a characteristic of immature compost. An in-field incubation of soil amended with 1% or 2% CGW (w/w) showed no net N release from CGW over 4 months. In a field trial, bell pepper (Capsicum annuum L.) fruit yield was increased by soil amendment with CGW (17 or 34 t·ha–1) under a low N fertilizer regime (168 kg·ha–1), but was unaffected where sufficient fertilizer N (280 kg·ha–1) was applied. CGW was compared with peat as a constituent of potting media; both were blended 1:1 (v/v) with perlite and used in the production of tomato (Lycopersicon esculentum Mill.) and marigold (Tagetes erecta L.) plants under varying fertigation regimes (constant feed of N at 0, 50, or 100 mg·L–1 as 15N–13P–12K). CGW was equivalent or superior to peat in plant growth; CGW did contribute to crop macronutrient nutrition, but the highest fertigation rate was required for optimum growth.

EDUCATIONAL PROGRAMS FOR HANDLING LANDSCAPE WASTES: A PARTNERSHIP BETWEEN THE ILLINOIS DEPARTMENT OF ENERGY AND NATURAL RESOURCES AND THE UNIVERSITY OF ILLINOIS

The State Of Illinois passed legislation banning landscape wastes deposition in land fills. Approximately 18% of all solid wastes going into Illinois landfills were landscape wastes including grass clippings, branch prunings, leaves and wood. A cooperative program between the Horticulture Department, the Cooperative Extension Service and the Illinois Department of Energy and Natural Resources was initiated to train county extension advisers, municipalities, and the consuming public on methods for landscape waste reduction and recycling. Workshops, video tapes, Master Composters, mobile displays, fact sheets and a model municipal composting facility were developed. Publications and other educational materials will be displayed.

Composting Landscape Waste

In the fall of 1985, our Yard Waste Reclamation Site was established to divert landscape waste from the Urbana, Illinois landfill. It has been our experience that significant portions of the waste stream can be diverted to a facility of this type and yard waste materials can be recycled into useable products. Three basic operations are conducted at this reclamation facility: 1) grinding brush eight inches or less in diameter, 2) composting of leaves and grass, and 3) cutting and splitting bulk wood (largerthan eight inches in diameter) into firewood. The site primarily serves the urbanized area of Urbana/Champaign (population 125,000); however, the site is available to all Champaign County residents. A schedule of volumes that have been received at the site since September of 1985 are found in Table 1. Gate volumes both loose and compacted have ranged from 20,000 to 27,000 cubic yards received. It has been our experience that approximately 50 percent of this volume is comprised of brush, with the remainder being leaves and grass. It is estimated that up to 60,000 cubic yards of material can be processed annually. The site is in operation from 8:00 a.m. to 3:30 p.m. (Monday through Saturday) except for holidays throughout the year. During these times, the site will be open to receive yard waste materials for processing and will also disperse processed materials to the general public and private companies.