During high summer temperatures and dry weather, proper maintenance of biogas digesters is essential to prevent damage and extend the lifespan of the system. To ensure optimal performance, several key maintenance practices should be followed:
First, avoid leaving the digester empty for long periods. In some regions, large amounts of residue are removed before using it as fertilizer for late rice. If feeding is not done in time, the digester can become empty and vulnerable to heat exposure. Therefore, it’s best to avoid large refueling during hot and dry seasons. If necessary, prepare new fermentation materials beforehand to minimize the time the digester remains empty. If there isn’t enough material, do not empty the digester at all—seal it properly and protect it from direct sunlight. Refueling is most effective in spring or fall. In the first half of the year, raw materials can be prepared in April to May (except in southern areas), while in the second half, preparation should start in September, with feeding done in October. Feed in the afternoon and complete the process on the same day, ensuring the digester is sealed promptly to reduce exposure.
Second, focus on moisture retention. Biogas digesters built with cement are porous and can lose moisture easily during dry weather. To prevent cracks and leaks, regular maintenance is crucial. Some regions cover the top of the digester with 25–30 cm of soil and plant crops on it to maintain moisture and prolong the structure's life. In summer, applying a layer of triadic soil (lime, yellow mud, and sand) on the top, followed by tar, coarse sand, or coal ash, can help reduce evaporation. Alternatively, placing a plastic sheet on the top can also protect against moisture loss.
Third, perform regular maintenance checks. After years of use, parts of the masonry or stucco may deteriorate, leading to leaks. At this stage, cleaning the walls and applying sealing materials like cement slurry can improve the seal. However, always open the movable cover and remove gas pipes to ventilate the digester. Workers inside should wear safety ropes, and someone should monitor from outside to ensure safety.
Fourth, use mulching techniques to improve crop growth. Corn cultivation using mulch film can begin 10–15 days earlier than traditional methods. Choose high-quality, non-diseased seeds, and plant two to three per hole with spacing of 50–60 cm between rows and 25–30 cm between plants. After sowing, apply herbicides like butachlor evenly, then lay the plastic film flat and secure it with fine soil to retain heat, nutrients, and suppress weeds.
Fifth, manage the field effectively. After seedlings emerge, make small holes in the plastic film to allow them to grow through, then cover the holes with soil. Regularly check for missing plants and fill gaps with seedlings from a nursery. Thin the plants at the right time—early thinning at the 3-leaf stage, leaving two per hole, and later thinning at the 5-leaf stage, keeping one per hole. Apply fertilizer between rows, especially during tasseling, and consider foliar sprays of 0.2% potassium dihydrogen phosphate twice or thrice for better nutrition.
Ensure proper irrigation and drainage. During droughts, water the fields after loosening the soil, and clear ditches during rain to prevent waterlogging. Corn requires consistent moisture, especially during tasseling and flowering, when soil moisture should be maintained at 70–80% for high yields.
Pest control is also important. Use appropriate insecticides to manage corn borers, aphids, and leaf spot. For example, sprinkle 3% Miro 750–1000 g mixed with soil in the whorl stage to control borers, and spray 40% dimethoate to manage aphids. For fungal diseases, use 90% mancozeb at 1000 times dilution. Avoid using long-residual pesticides after tasseling to ensure food safety.
Finally, harvest on time and remove leftover plastic film. Sweet corn should be harvested 20–25 days after pollination, while normal corn is ready when the kernels harden and the husks turn white. After harvesting, collect any remaining plastic film to minimize environmental impact and protect future crops.
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