SUITABILITY OF COMPOSTED GREEN WASTE FOR HORTICULTURAL USES

The study was undertaken to determine the physiochemical properties an d nutrient supply characteristics of composted green yard and landscap e waste (CGW) and to document its performance as a field soil amendmen t or constituent of potting media. Three CGW samples were collected fr om each of two composting operations in California from Nov. 1993 to A pr. 1994. Macronutrient content varied widely between operations, and among samples from the same operation, with mean total N, P, and K lev els averaging 1.1%, 0.26%, and 0.67%, respectively. Controlled-environ ment 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 lo w 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 yie ld was increased by soil amendment with CGW (17 or 34 t . ha(-1)) unde r a low N fertilizer regime (168 kg . ha(-1)), but was unaffected wher e sufficient fertilizer N (280 kg . ha(-1)) was applied. CGW was compa red 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 varyin g 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 growt h; CGW did contribute to crop macronutrient nutrition, but the highest fertigation rate was required for optimum growth.