The Effect of Anaerobic Digestate on the Soil Organic Carbon and Humified Carbon Fractions in Different Land-Use Systems in Lithuania

Abstract

The most important component of agricultural system are soils as the basis for the growth of plants, accumulation of water, plant nutrients and organic matter. The main task of our research was to ascertain changes in soil organic carbon (SOC) and mobile humified carbon fractions in digestate-treated soils. We have performed three field experiments using the same design on two soil types in 2019–2020. We studied the fertilization effects of different phases of digestate on Retisol and Fluvisol. Fertilization treatments: control; separated liquid digestate 85 kg ha−1 N; and 170 kg ha−1 170 N; separated solid digestate 85 kg ha−1 N; and 170 kg ha−1 N. We have found a greater positive effect on the increase in SOC because of the use of the maximum recommended fertilization rate of the solid digestate. The content of mobile humic substances (MHS) tended to increase in grassland and crop rotation field in digestate-treated soil. In our experiment, maximum concentration of SOC was found in 0–10 cm soil layer, while in the deeper layers the amount of SOC, MHS and mobile humic acids proportionally decreased. We concluded, that long-term factors as soil type and land use strongly affected the humification level expressed as HD (%) in the soil and the highest HD was determined in the grassland soil in Fluvisol.

Matured Manure and Compost from the Organic Fraction of Solid Waste Digestate Application in Intensive Apple Orchards

“…The composting of digestate requires the proper adjustment of the C/N ratio by the addition of lignocellulosic waste which has the function of bulking agent, which also increases the aromatic-C in the final compost [ 19 ]. Moreover, the organic matter fraction of digestate contains a more recalcitrant fraction of OM from the OFMSW, due to the mineralization occurring during the anaerobic process, which leads to a higher fraction of easily degradable compounds consumption [ 35 , 36 ]. For both the previous reasons, the compost from digestate may be considered different from the compost from raw OFMSW.…”

Deciphering the Effectiveness of Humic Substances and Biochar Modified Digestates on Soil Quality and Plant Biomass Accumulation

“…Since AD was developed for energy production, the potential use of digestate as exogenous organic matter (EOM) to enhance soil carbon sequestration is still being evaluated. However, the importance of the role of carbon mitigation in current and future EU policies on agricultural systems increases the significance of digestate as a potential contributor to SOC formation (and carbon dynamics) [8,9]. Several studies have concluded that digested EOM shows higher stability than undigested EOM in SOM [10][11][12].…”

“…The use of liquid digestate fraction, generally richer in LOC, was strongly encouraged by some authors [22,27]. On the other hand, its contribution to SOC stock is still weak compared to solid fraction digestate, due to low carbon input [9,22]. Because digestate based on food waste has properties close to those of the liquid fraction of digestate from agricultural waste, e.g., raw material with lower C:N ratio and low dry biomass of the final product, we had to assume lower recalcitrance of the digestate fertilizer.…”

Digestate Potential to Substitute Mineral Fertilizers: Engineering Approaches

“…Biogas reactors (BRs) are designed to produce methane from organic waste by anaerobic digestion (AD). BR produce leftovers, also known as digestate that has been successfully used as biofertilizer due to their high contents of mineralized Nitrogen (N), Phosphorus (P), Potassium (K), and organic materials [1]. Recycling organic materials to land is considered the best practicable environmental option in most circumstances, completing both natural nutrient and carbon cycles.…”