Quantifying non-marketed compost benefits for application in horticulture.

Knowledge of the true social benefits of pro-environmental activities is limited due to the difficulty of evaluating and quantifying the non-market benefits of such actions. Valuing non-marketed compost benefits and impacts is difficult because they do not have market prices, as they are not bought and sold (i.e. traded) in markets. This article fills this gap by quantifying the non-market benefits of compost use in agriculture. As an initial contribution, this study applied revealed preference methods to quantify the economic values of important non-marketed compost benefits to plant and soil systems in tree and shrub nursery production. The estimated benefits were compared for compost produced using two windrow composting methods, namely: aerobic or thermophilic composting and fermentative or static pile inoculated composting. Specific compost benefits considered included: (i) medium in potting soil mix; (ii) Nitrogen Phosphorus and Potassim (NPK) nutrient supply; (iii) improved nursery plant yield/performance; (iv) disease, pest and weed control and (v) reduced branch pruning. Total economic value, aggregated for the compost benefit types considered, was lower for thermophilic compost applied (CAD$192 per tonne per year) than for fermentative compost (CAD$385 per tonne per year), due to lower fermentative compost production cost. Among the compost benefit types considered, improved nursery plant yield and performance accounted for the highest proportion of quantified benefits; 75% of total economic value for thermophilic compost and 93% for fermentative compost. Further studies considering all important compost benefits beyond those considered in this study, and compost use in other agricultural production systems will be useful.