Oxygen use in compost storage as influenced by moisture, temperature and degradability

Abstract

Storing organic rooting media may result in microbial degradation of the media during storage. Related problems are anaerobia, production of phytotoxic substances, loss and fixation of nitrogen and excessive heat production. In the potting soil industry, protocols for storing peat as well as for other organic growing media are widely used. A growing interest in peat alternatives, notably composts, resulted in more frequent problems during the storage of the alternative rooting media. Our goal was to deliver a protocol that allows the storage of composts for up to 8 weeks. An experiment was designed using small oversized gas tight bags with a known volume of air and oxygen as well as compost samples of known moisture content. A stable and less stable compost were used. The composts were set to moisture contents ranging from 14 to 75% v/v. The storage temperatures used were 5 and 20°C. In the bags the oxygen content was monitored over time and nitrogen forms as well as degradability were measured before and after storage. Results showed a temperature of 5°C reduced the oxygen use compared to a storage temperature of 20°C with a factor 3 for stable compost and with a factor 5 for less stable compost. Oxygen consumption showed a maximum for intermediate water contents of 30-40% v/v. Calculations based on the data found showed that the goal, undisturbed storage for up to 8 weeks, could only be reached by storing stable compost and; pre-cooling prior to bagging and; storing at low temperature and; storing at low moisture content.