Soil chemical and microbial responses to biogas slurry amendment and its effect on Fusarium wilt suppression

The rapid development of biogas production will result in increased use of biogas slurry (BS) as organic fertilizer. However, side effects such as suppression of soilborne diseases are not yet well investigated and understood. Therefore, the objectives of the study were to evaluate the effects of biogas slurry application on suppression of Fusarium wilt disease of watermelon and its relationship with soil chemical and microbiological properties. Pot and field experiments were conducted to compare effects of biogas slurry application on Fusarium wilt disease suppression of watermelon in soil with a moisture content of 60% water holding capacity (WHC) or flooded continuously. Fusarium wilt was significantly suppressed in soil from biogas slurry amended plots. Biogas slurry flooding enhanced the degree of suppression in the pot experiment. Moreover, the biogas slurry treatment also significantly suppressed Fusarium wilt in the field with a disease index of 33.2% compared with 69.6% in water treatment. Biogas slurry strongly reduced the pathogen population in rhizosphere soil. The populations were decreased by 43.1% and 95.9% in the biogas slurry moist and flooding treatments, respectively. Biolog data indicated that average well color development (AWCD) and Shannon-weaver index were increased significantly in biogas flooding treatment. Principal component analysis showed that Fusarium wilt was negatively correlated with NH4+-N, available K (AK), water-soluble carbon (DOC), water soluble nitrogen (DON) and phenolic acid (PA) contents in soil and positively correlated to soil pH and soil redox potential (Eh). Microbial communities, in general, did not significantly correlate with disease suppression.