Effects of Substrate and Processing Conditions on Nematode Suppressiveness of Anaerobic Biogas Digestates

Biogas digestates produced from anaerobically processed food or dairy manure had demonstrated some potential to suppress different pathogens and pests. In this study, digestates from these two substrates processed mesophilically (20-40 ºC) or thermophilically (>40 ºC) were compared for their nematode-suppressive potential. In bioassays, their suppressive potential of Heterodera schachtii or Meloidogyne incognita was tested at different amendment rates. Testing was expanded to field microplot experiments with M. incognita and greenhouse tests with Pratylenchus vulnus. In the bioassay with H. schachtii, fewer nematodes penetrated radish roots after amendment with thermophilic than with mesophilic digestates. Root penetration was lowest after treatment with food waste and thermophilic dairy manure at the highest rate. In a watermelon bioassay with M. incognita, nematode-induced galling and egg mass production were reduced after amendment with food waste digestates compared to manure digestates, and after thermophilic compared to mesophilic digestates in the case of egg masses. In a greenhouse experiment with peach rootstock ‘Nemaguard’, the numbers of P. vulnus in roots were diminished after amendment with digestates at the highest rate. In microplot experiments with bell peppers, plants initially were more vigorous after amendment with thermophilic digestates than after mesophilic digestates additions. This effect was transient and was no longer measurable at harvest. In summary, food waste digestates, especially thermophilically produced had nematode suppressive and plant growth improving properties. These effects were not long-lasting and probably need additional mitigation for practical utility.