Biogas digestates affect crop P uptake and soil microbial community composition.

Area of Science:

• Agricultural Science
• Soil Microbiology
• Environmental Science

Background:

• Fermentation residues from biogas production, known as digestates, are valuable organic fertilizers.
• Understanding their impact on soil microbiota is crucial for sustainable agriculture.
• Pre-treatment methods like solid-liquid separation can influence digestate properties.

Purpose of the Study:

• To investigate the effects of different organic fertilizers (cattle slurry, co-digested slurry, energy crop digestate) and mineral fertilizers on soil microbial activity and composition.
• To evaluate the impact of solid-liquid separation of digestate on soil microbiota.
• To assess the effects on two crop species: Amaranthus cruentus and Sorghum bicolor.

Main Methods:

• An 8-week pot experiment was conducted on loamy sand soil.
• Treatments included cattle slurry, co-digested cattle slurry, co-digested energy crops, mineral fertilizers, and their solid-liquid separated variants.
• Soil microbial activity was assessed via basal respiration and metabolic quotient.
• Community-level physiological profiles (CLPP) using MicroResp and molecular analysis (PCR-DGGE) were employed.
• Alkaline phosphatase gene expression was analyzed.

Main Results:

• Amaranthus cruentus, with high phosphorus uptake, induced microbial stress and reduced microbial biomass carbon.
• Digestates generally increased microbial basal respiration and metabolic quotient compared to untreated slurry or mineral fertilizers.
• Solid-liquid separation of digestate significantly altered microbial community structure and function.
• PCR-DGGE and CLPP revealed distinct microbial community profiles across treatments.
• Alkaline phosphatase gene expression was highly sensitive to the different fertilization regimes.

Conclusions:

• Organic fertilizers, particularly digestates, significantly influence soil microbial activity and community composition.
• Solid-liquid separation is a critical factor affecting the biological impact of digestates.
• Crop-specific responses (e.g., P uptake by Amaranth) interact with fertilization effects on soil microbes.
• These findings highlight the need for tailored application of organic fertilizers to optimize soil health and microbial function.