Effect of nitrogen fertilization on the production of biogas from sweet sorghum and maize biomass.

The aim of the study was to determine the biogas productivity from selected cultivars of sorghum (Sorghum bicolor Moench) and maize (Zea mays L.) depending on the dose of mineral fertilization with nitrogen. The topic is novelty in the northern Poland area due to the fact that this crop is not very widespread here. The silage samples were derived from two experiments: 1) two factors experiment with sorghum varieties (Arbatax, KWS Maja, Herkules) and two doses of mineral nitrogen fertilization (0 and 150 kg·ha-1 N) in split-plot design. 2) one-factor experiment with fodder maize, variety NK Magitop, and two doses of mineral nitrogen fertilization (0 and 150 kg·ha-1 N) in a randomized complete block design. The experiment was performed in four replications in the split-plot design. Methane fermentation was carried out under mesophilic conditions. The temperature of the process was 37°C ± 1°C, while pH 7 ± 0.1. The content of total solids in the bioreactor was 7.0%. The composition of the gas produced was measured once a day with the use of an automatic biogas analyser (GFM 416, GasData). The trial was run in triplicate until the daily yield was less than 1% of the cumulative biogas yield (DIN 38 414-S8). Sorghum was characterized by higher average biogas productivity (about 12%), higher methane content in biogas (about 10%), and higher methane productivity (about 43%). It can, therefore, be stated that sorghum represents as an alternative plant to maize for the purpose of biogas production.