Nitrogen availability of various biogas residues applied to ryegrass

Abstract

Biogas plants in Germany are producing an increasing amount of biogas residues to be recycled via agricultural crop production. To test whether the wide range of various substrates used in the anaerobic digestion can affect the chemical composition and nutrient availability, seven biogas residues derived from different substrates were investigated with respect to their N supply to ryegrass. Both the short-term and the long-term N availability were studied in a 309-d pot experiment lasting for five successive growth cycles each starting with a fertilizer application. The organic fertilizers were applied based on an equal amount of ammonium-N (300 mg N per pot) and compared to mineral N from ammonium nitrate of equal dosage. Biogas residues varied greatly in their chemical composition (ammonium-N 0.20% to 0.51%, N total 0.36% to 0.75%, and C org 1.85% to 4.75% in fresh matter). After the first growth cycle, the N availability of the biogas residues applied based on ammonium-N was at least equal to that from ammonium nitrate. Differences in N offtake after one fertilizer application were negatively correlated to the C org : N org ratio of the organic fertilizers. After five successive fertilizer applications, the N utilization of most of the organic fertilizers was increased compared to that of the mineral fertilizer. It is concluded that biogas residues provide plant-available N at least corresponding to their ammonium content and that the accumulation of organic N in soil through repeated application of biogas residues contributes to N release.

Effects of anaerobic digestion on soil carbon and nitrogen turnover, N emissions, and soil biological activity. A review

“…The total carbon content of digestates varies between 28 and 47 % of the dry matter (Tambone et al 2010;Fouda 2011;Möller and Schultheiss 2014). Approximately 80-95 % of that C was organically bound with carbonate as the remaining inorganic C (Chantigny et al 2004;Fouda et al 2013).…”

“…Approximately 80-95 % of that C was organically bound with carbonate as the remaining inorganic C (Chantigny et al 2004;Fouda et al 2013). During anaerobic digestion, lignin is not degraded, whereas volatile fatty acids (>90 %), cellulose (>50 %), hemicellulose (>80 %), and raw protein are partially degraded (Asmus et al 1988;Molinuevo-Salces et al 2013).…”

“…Both fractions have, immediately after the separation process, a high NH 4 + to total N share (e.g., Möller et al 2010;Fouda et al 2013). The liquid fraction is stored in tanks (either uncovered or covered) and the solid fractions in open manure heaps.…”

“…A recently published study of Thomsen et al (2013) confirmed these findings and suggests that on a longer-term perspective, the retention of plant-derived C in soil is little affected by pretreatments such as passage through a ruminant and/or anaerobic digestion. Fouda (2011) carried out a pot experiment with different digestates and with undigested cattle slurry as a control treatment. Regardless of anaerobic digestion, soil C accumulation was similar, although the C org input in the undigested treatment was nearly twice as high as in the anaerobic digestion treatment.…”

“…The type of feedstock to biogas plants influences the properties of the by-product digestate and also the C and N dynamics after application of the digestates (Sänger et al 2014;Fouda 2011). Fouda (2011 compared the effects of digestates from different mixtures of feedstocks on soil C accumulation based on the application of equivalent NH 4 + amounts.…”