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Anaerobic digestion (AD) has the potential to enhance the availability of nitrogen (N) from green manures; however, part of the sulfur (S) is lost with the biogas. In this study, the N and S availabilities from untreated and digested cover crop (CC) and straw mixtures were measured after application to soil in the laboratory. In addition, a microplot experiment was carried out to assess the N availability in a spring barley crop. A CC consisting of red clover (Trifolium pratense L.) and chicory (Cichorium intybus L.) was harvested and ensiled with barley straw (Hordeum vulgare L.) at different ratios (1:0, 10:1 and 3:1). The silages were either digested alone or co-digested with cattle manure (CM) in continuously fed anaerobic reactors. Six months after soil application, the net inorganic N release was − 7%, 15% and 25% of total N for untreated CC:straw ratios of 3:1, 10:1 and 1:0, respectively. AD significantly increased the net inorganic N release of these plant materials to 5%, 26% and 38% (mono-digestion) and 40%, 41% and 43% (co-digestion with CM). Results from the laboratory experiment corroborated the field experiment in which AD significantly increased the nitrogen fertiliser replacement value (NFRV) of the CC:straw from 19 to 41% of total N applied. Gaseous loss of S up to 30% was observed during AD while the total N content remained unchanged. Sulfate from untreated CC:straw and digestates was immobilised soon after application to soil, resulting in low availability of inorganic S. Digestion of CC and straw significantly reduced N immobilisation but clearly did not contribute to inorganic S supply.

Bangladesh is in the midst of a severe and worsening energy crisis. The continuous depletion of fossil fuels is sticking the concern into the search for new energy sources which are renewable as well as sustainable. Among the renewable energy sources, biogas from the poultry and dairy industries is an increasingly growing and promising sector. A survey was conducted to understand the present status of biogas technology in Bangladesh. Data were collected by interviewing farm owners and major stakeholders. The problems and barriers to the implementation and dissemination of biogas plants in Bangladesh were also identified through SWOT analysis. A total of sixteen farms were selected to collect data regarding current operational conditions. The economic viability was also evaluated. Most of the selected farms were found to be under-fed in spite of having huge potential. Though the H2S concentration of biogas produced from different plants was high, most of them had no purification unit. The results of the economic analysis showed that the biogas plants operating in Bangladesh are at a loss as currently no subsidies are provided. The outcome of the SWOT analysis identified high initial investment, lack of technical knowledge, lack of local technology, poor management, and proper bio-slurry handling technology as the main barriers to disseminating biogas technology in Bangladesh.