Effects of biogas and raw slurries on grass growth and soil microbial indices

Abstract

Biogas slurry is increasingly used as fertilizer. Earlier research was focused on plant growth and soil chemical properties, with only little information available regarding the effects of biogas slurry on soil and root microbial indices. For this reason, a 70 d pot experiment was conducted in which biogas and raw slurries obtained from six biodynamic farms were added to a soil. Italian ryegrass (Lolium multiflorum Lam.) was cultivated to investigate the effects on plant yield, N uptake (two harvests), soil microbial biomass, soil fungi, and root-colonizing microorganisms. Biogas slurries increased the mean total above-ground plant biomass by 66% and raw slurries by 35% in comparison to the control. The mean plant N-uptake increased under biogas and raw slurry application by 166% and 65%, respectively, compared with the unfertilized pots. The effects of biogas and raw slurry application on soil microbial indices were similar except for the lower fungal biomass after biogas slurry amendment. In contrast to biogas slurries, the raw slurries significantly increased microbial biomass C and N by roughly 25% in comparison to the control. The application of biogas slurries significantly decreased the soil ergosterol content in comparison with raw slurry and control treatment, leading to a significantly lower ergosterol : microbial biomass C ratio. In the roots, biogas and raw slurry application significantly decreased the concentrations of the amino sugars galactosamine and glucosamine by 39 and 27%, respectively, but not that of ergosterol in comparison with the control. This was most likely due to a reduced colonization with arbuscular mycorrhizal fungi in the presence of highly available plant nutrients.

How do biogas solutions influence the sustainability of bio-based industrial systems?

“…After digestion, organic materials remain which have become a nutrient-rich slurry, often called digestate, or biofertiliser when applied as fertiliser (Wellinger et al, 2013). This nutrient-rich biofertiliser is considered to not only contribute with the nitrogen (N), potassium (K) and phosphorus (P) required by plants; biofertilisers, in addition, contain micronutrients and soil organic carbon which helps soils to become more resilient and resistant towards changes in the environment (Alburquerque et al, 2012;Barbosa et al, 2014;Wentzel and Joergensen, 2016). Biofertiliser, therefore, has the potential to replace mineral fertiliser (Tambone et al, 2010).…”

“…Lately, there has been an increase in researching circular systems and the fertilising abilities of the digestate. At the same time, knowledge about fertilising abilities are becoming more widespread ( Kouřimská et al, 2012;Barbosa et al, 2014;Wentzel and Joergensen, 2016;Risberg et al, 2017). This development is probably mirroring the development in society, but the question remains of if methods for assessing the new challenges are on the way.…”

Assessing the Effects of Digestates and Combinations of Digestates and Fertilizer on Yield and Nutrient Use of Brassica juncea (Kai Choy)

“…Roots are integral for plant growth and nutrient acquisition and changes in root morphology can, in turn, have significant effects on nutrient use efficiency (NUE) and yield. The limited research on the effects of digestates on root growth shows varying and somewhat contradictory effects on overall root biomass, with some studies showing increased root biomass under digestate treatment [13,14], some showing decreased root biomass with digestates [15,16] and another showing no difference in root biomass with digestate, as compared with mineral fertilizer [17]. However, digestate addition may induce important changes in root growth rate and root morphology that affect NUE.…”

Untargeted Metabolite Profiling for Screening Bioactive Compounds in Digestate of Manure under Anaerobic Digestion

“…Generally, the digestate is rich in macronutrients (e.g., N, P, K) and is traditionally used as fertilizers in agriculture. It has been well documented that the supplementary application of digestate to wheat, maize, grass, pasture, peanut, green pepper, eggplant, cabbage, cucumber, autumn lettuce, and sorghum can improve the plant growth, yield, and quality [3][4][5][6][7]. In addition to supplying nutrients to the plants, the application of digestate has been reported to play an essential role in the inhibition of plant pathogens (fungal and bacterial) and insects [8].…”