Decomposition of Fresh and Anaerobically Digested Plant Biomass in Soil

Abstract

Abstract Using water hyacinth [ Eichhornia crassipes (Mart.) Solms] for wastewater renovation produces biomass that must be disposed of. This biomass may be anaerobically digested to produce CH 4 or added to soil directly as an amendment. In this study, fresh and anaerobically digested water hyacinth biomass, with either low or high N tissue content, were added to soil to evaluate C and N mineralization characteristics. The plant biomass was labeled with 15 N before digestion. The fresh plant biomass and digested biomass sludge were freeze‐dried and ground to pass a 0.84‐mm sieve. The materials were thoroughly mixed with a Kindrick fine sand (Arenic Paleudults) at a rate of 5 g kg −1 soil and incubated for 90 d at 27 °C at a moisture content adjusted to 0.01 MPa. Decomposition was evaluated by CO 2 evolution and 15 N mineralization. After 90 d, approximately 20% of the added C of the digested sludges had evolved as CO 2 compared to 39 and 50% of the added C of the fresh plant biomass with a low and high N content, respectively. First‐order kinetics were used to describe decomposition stages. Mineralization of organic 15 N to 15 NO ™ 3 ‐N accounted for 8% of applied N for both digested sludges at 90 d. Nitrogen mineralization accounted for 3 and 33% of the applied organic N for fresh plant biomass with a low and high N content, respectively.