On-farm composting systems for regenerative agriculture. A review

Composting wastes is a common organic farming practice that has recently generated interest among regenerative farmers. A range of composting methods are used, but there is a lack of evidence on the relative agronomic, soil and environmental impacts of these methods. Here we review the academic literature on windrow, hot composting, biodynamic, aerated static pile, lactic acid (Bokashi) fermentation, vermicomposting, extracts, and teas. While previous reviews have considered regenerative management practices in general, the increasing interest, diversity of composting practices, and variability of outcomes necessitates this focussed review for the first time. It is well known that regular, high application rates of organic inputs can improve soil health and maintain crop yields. Rates of application that reflect the land’s production potential (1-2 t ha -1 y -1 ), improve soil health in the long term but require additional inputs of synthetic fertilisers to maintain yields. Biodynamic methods can build soil health and stable carbon; however, in most cases biodynamic compost has been tested within biodynamically managed systems, making it impossible to separate the effects of the composting method from the production system. Lactic acid fermentation reduces carbon loss during composting, providing more carbon to “feed the soil” from the same volume of initial feedstock. Vermicompost has higher levels of available nutrients than other aerobic methods. Compost teas and extracts offer the most potential when used as foliar applications for disease suppression and plant growth promotion. Future studies should focus on comparing composts made with the same feedstocks using different production methods. Application rates should reflect the production potential of the land to demonstrate how composting methods can be scaled up across the agricultural sector.