Abstract
During biogas production anaerobic digestion of plant material produces a nutrient-rich residue called digestate. The application of the nutrients present in the digestate should improve soil fertility, particularly in nutrient poor soils, and thus crop yield, promoting the closure of the nutrient cycle. This study evaluated the effect of digestate application on the germination and early stages of plant development since these are the first steps to be considered when studying the benefits on plant growth in low fertility substrates. A greenhouse experiment was conducted to evaluate the effects of three substrates of different texture and fertility (field loam, field sand, sand), as well as type and amount of fertilizer (pure maize digestate vs. inorganic nitrogen/phosphorus/potassium (NPK) fertilizer) on both germination and early plant performance of maize (Zea mays L. subsp. mays). While digestate and NPK fertilizer applications had no significant effect on germination in the two field soils, digestate applications significantly decreased the germination rate in sand (36–82% reduction) due to an increase of surface water repellency. In contrast, for aboveground biomass yield, the most positive fertilization effects of digestate application were found on sand (up to 3.5 times the biomass of the unamended control) followed by field sand (1.5 times), compared to no effect for field loam. Our findings suggest that digestate application have positive fertilization effects in low-fertility substrates, similar to NPK, even though digestate application may have a negative impact on the permeability in sandy substrates that could interfere with germination.
Highlights
To promote a sustainable biomass production within a growing bio-based economy, the use of organic residues warrants consideration as fertilizers and soil conditioners
We hypothesized that adding pure maize digestate from biogas production would have a fertilizing effect on plant performance broadly comparable to that of NPK fertilizer addition and that the effect would be modulated by the original fertility of the substrate used, observing in the lower fertility substrates the more significant effect of the digestate
The differences in the SPAD readings between digestate-treated plants and NPK-treated plants decreased as the fertility of the substrates decreased, which we found for aboveground biomass, indicating that the digestate increased the fertility of soils with low nutrient content
Summary
To promote a sustainable biomass production within a growing bio-based economy, the use of organic residues warrants consideration as fertilizers and soil conditioners. The use of residues from biogas production as bio-fertilizers should be seen as a highly valuable resource [1]. Besides providing a viable option for disposal, digestate represents a strategy to sustain or increase soil fertility and to foster plant biomass yields within the long-term goal to substitute mineral fertilizers [2,3]. The amount of digestates resulting from biogas production has increased rapidly in the last 10 years due to the growing number of biogas facilities. In Germany, the number of biogas plants increased from 1600 in 2002 to more than 7000 in 2011 [4] due to the German Act launched in 2002 that made renewable energy sources a high priority. Dry matter is partially degraded, resulting in a volume reduction and concentration of Agronomy 2019, 9, 473; doi:10.3390/agronomy9080473 www.mdpi.com/journal/agronomy
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