Compost is treated as a waste product by many regulatory agencies, monitored and assessed only for its potential to harm humans or to harm the environment. However, horticulture practitioners are the number one consumer of compost, whether in nursery production, vegetable production, or home landscaping and gardening. In Arkansas, no state regulations require reporting chemical or physical characteristics of compost such as plant nutrient content, pH, bulk density, or organic matter content. Therefore, a statewide survey of participating Arkansas Department of Energy and Environment permitted composting facilities was conducted to characterize the availability of compost throughout the calendar year, the variability in plant nutrient content and physical characteristics. A total of 11 compost sites were sampled from nine compost production operations in Arkansas, including water treatment facilities, commercial depackaging companies, and municipal compost facilities. Yard waste (YW) was a component of all compost feedstocks, but some facilities could further handle food waste (FW) or biosolids (BS). Dry matter analysis found that composts from YW alone contained 1.31% to 1.92% N; composts from YW plus FW contained 2.57% to 3.70% N; and composts from YW BS contained 1.25% to 2.80% N. Major disparities were observed dry matter Na content when FW was included in compost. Composts including FW contained 2,185 to 7,672 mg/kg Na while composts from YW or YW BS contained 167 to 402 mg/kg Na. Present findings indicate that compost feedstocks affect the resulting nutrient content, particularly when introducing FW. Substrate testing beyond the standard testing for pathogens and trace metals will be critical for effective use of composts as a substrate or soil amendment in horticulture systems.
