Agricultural use of anaerobically digested wetland biomass

Abstract

Along with the development of anaerobic digestion processes, digestate, a by-product of biogas production has emerged as a new organic soil amendment. One of the substrates in anaerobic digestion is biomass of plants mown in wetlands as a part of extensive conservation measures. However, this biomass can be used also as fodder in animal production. Feed value of wetland plants varies and the system of numerical values (Lwu) can be used to compare the nutritional values of individual plant species. The aim of the research was to evaluate suitability of studied wetland plants for energy production and further for fertilization and feeding purposes. The examined digestates were obtained in the laboratory experiment on the bio-methane potential of five plant species. The degree of transformation of fermented organic matter was determined based on the results of the earlier experiment concerning CO2 emissions from soils enriched with the studied digestates. Among tested plants, reed canary grass (R-C) with Lwu = 7 had the highest feed value, while one of the worst was for common reed (C-R) with Lwu = 1. This classification looks interesting, when we compare it with the results of the CO2 emissions and degree of mineralization of OM supplied to soils with individual plant digestates. Among the studied wetland plants, the highest emission and the largest amount of potentially mineralized carbon had reed canary grass, while the lowest emission and lowest amount of mineralized carbon in the case of common reed was observed. As a result, C-R turned out to be the plant that used for biogas production was enriching soil with the largest amount of carbon delivered with the material remaining after anaerobic digestion. At the same time, C-R is one of the worst fodder plants, while R-C is the best one. Therefore, despite the fact that reed canary grass is characterized by high yield potential and belongs to plants with very good energy properties, it should be first of all used for animals feeding.