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 degrees 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 pat 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.