Assessment of Two Solid Anaerobic Digestate Soil Amendments for Effects on Soil Quality and Biosolarization Efficacy

Abstract

Anaerobic digestion is an organic waste bioconversion process that produces biofuel and digestates. Digestates have potential to be applied as soil amendment to improve properties for crop production including phytonutrient content and pest load. Our objective was to assess the impact of solid anaerobic digestates on weed seed inactivation and soil quality upon soil biosolarization (a pest control technique that combines solar heating and amendment-induced microbial activity). Two solid digestates from thermophilic (TD) and mesophilic (MD) digesters were tested. The solarized TD-amended samples presented significantly higher mortality of Brassica nigra (71%, P = 0.032) than its equivalent incubated at room temperature. However, biosolarization with digestate amendment led to decreased weed seed mortality in certain treatments. The plant-available water, total C, and extractable P and K were significantly increased (P < 0.05) in the incubated amended soils. The results confirm the potential of digestates as beneficial soil amendments. Further studies are needed to elucidate the impacts of digestate stability on biosolarization efficacy and soil properties.

Effect of management of organic wastes on inactivation of Brassica nigra and Fusarium oxysporum f.sp. lactucae using soil biosolarization

“…In addition to these specific impacts, other studies also observed that organic amendments followed by solarization led to higher values of total N, total P, several enzyme activities, microbial biomass C, potentially mineralizable N, water‐soluble organic C and microbial functional diversity when compared with non‐amended soils . Biosolarization studies using thermophilic and mesophilic digestates showed a significant decrease in EC after solarization . In this study, the increase in EC may suggest a need for irrigation after SBS application to avoid negative effects on crops if EC levels are not naturally recovered after SBS.…”

“…In this study, the increase in EC may suggest a need for irrigation after SBS application to avoid negative effects on crops if EC levels are not naturally recovered after SBS. SBS also decreased the NO 3 ‐ concentration and this effect was also observed in prior studies . This may be a negative outcome as NO 3 ‐ is the preferred form of nitrogen for plants.…”

“…The release of these pesticidal compounds depends on how readily the organic matter (OM) amendments are bioconverted in the soil under SBS soil conditions. For example, application of organic amendment previously stabilized via anaerobic digestion (AD) did not release significant amounts of VFAs during SBS . Alternately, non‐stabilized amendments, such as tomato pomace or wheat bran, led to greater changes in soil temperature, soil acidification, and VFA accumulation .…”

“…In a previous study, SBS using labile tomato pomace and mature green waste compost as amendments increased BN inactivation from ∼25% in the non‐amended soil to 100% in the amended soil after 8 days of SBS . In another study, SBS of soil amended with stable digestates from thermophilic anaerobic digestion increased BN seed mortality from ∼40% in the non‐amended, solarized soil to ∼71% in the digestate‐amended, solarized soil . The fungal pathogen FOL causes a disease of lettuce known as Fusarium wilt or Fusarium root rot, and affects lettuce production throughout the world .…”

The initial soil microbiota impacts the potential for lignocellulose degradation during soil solarization

“…However, the same treatment using 1·5 wt% mesophilic digestate did not significantly increase B. nigra mortality compared to the control treatments (Fernandez‐Bayo et al . ). It is possible that differences in performance were due in part to compositional differences in the amended substrate and micro‐organisms involved in the biotransformation of substrates to biopesticidal compounds (Fernandez‐Bayo et al .…”