The effect of field application of food‐based anaerobic digestate on earthworm populations. (7th October 2020) - Rollett, Alison J.
Abstract: In general, farming systems that provide the greatest organic matter returns to the soil support the highest earthworm populations and typically the application of organic materials will increase earthworm numbers because of an abundance of food. There has been limited work on the effects of digestate applications on earthworm populations with most focus on the short‐term effects of digestate from manure or crop‐based feedstocks, not from food wastes. To address this gap in current knowledge, the objective of this study was to assess the impact of repeated food‐based digestate applications on earthworm populations/biomass in both the short term ( c. 6 months after digestate application) and longer term (2 years later) in comparison with other commonly used inputs (manufactured nitrogen‐N fertilizer, compost and livestock manures). This multi‐site field experiment has shown that the application of food‐based digestate at application rates above current good practice can have a short‐term, negative impact on earthworm numbers under certain conditions. Six months after the final digestate addition, earthworm numbers were 32%–60% lower than following the additions of other organic materials at four of the seven sites investigated. A combination of high ammonium/low organic matter loadings and soil compaction most likely explained the observed effects.