Agronomic and economic benefits of green-waste compost for peri-urban vegetable production: implications for food security

A long-term field experiment in western Sydney evaluated the effect of source-separated green-waste (garden organics) compost on peri-urban vegetable crop yields and economic returns, compared to farmer practice. Comparisons were made over 10 vegetable crops between a compost (COMP) treatment (one off application of 125 dry t ha(-1) of green waste compost at the start and then every five crops, supplemented with urea when required), a mixed (MIX) treatment (one-off compost application of 62.5 dry t ha(-1) at start and then every five crops, but with inorganic NPK fertiliser inputs for each crop) and a conventional farmer practice (FP). Both COMP and MIX treatments consistently achieved similar or higher yields than FP, but the yield gains were more pronounced for COMP. COMP and MIX treatments delivered benefit-cost ratios of 3.3 and 2.6 respectively compared to FP over the 10 crops, indicating that this system could deliver economic benefits to growers as well as improve soil quality and the environment. Follow up large applications of compost generated more substantial yield increases in responsive vegetable crops and economic benefits. The substantial capsicum crop yield response provided a classic example of closing a crops 'yield gap' through improvements to soil quality with organic inputs, with implications for food security. The COMP treatment lifted the capsicum yield to similar to 60 t ha(-1), 50% above its perceived maximum potential crop yield for Eastern Australia. The value of larger applications of compost for soil quality, fertiliser savings, crop yield and farm income was apparent.