The Influence of Plant Cultivation Conditions on Biogas Production: Energy Efficiency

The influence of the fertilization level and soil type on the energy efficiency of the biogas production from maize, sorghum and reed canary grass silages were studied in this work. The plant material used to prepare silages was obtained from the experimental field with light, medium and good soil. High yields of biogas were obtained from maize silage with the lowest fertilization level of 80 kg N ha(-1) from 194.5 up to 315.33 m(3) t(-1) green mass (g.m.) depending on soil quality. The highest biogas yields of sorghum and reed canary grass were lower (about 120 m(3) t(-1) g.m.) than that for maize. Depending on the soil type, the Energy Return on Energy Investment index (ERoEI) and the Net Energy Value (NEV) values for maize ranged from 5.05 and 189 000 MJ ha(-1) (light soil), obtained at the level of 120 kg N ha(-1) to 9.76 obtained at the level of 80 kg N ha(-1) and 433 000 MJ ha(-1) at the level of 120 kg N ha(-1) (good soil). For sorghum (light soil) values of about 5.2 and 200 000 MJ ha(-1) were appropriately obtained at the level of 160 kg N ha(-1). In the case of reed canary grass the highest ERoEI and NEV values obtained at the level of 80 kg N ha(-1) amounted to 3.8 and 74 000 MJ ha(-1) (light soil), respectively. The investigations indicate that in general, the production technologies of crops where the low levels of nitrogen fertilization were applied proved to have the highest energy efficiency.