Fermentation of cow dung and sawdust: Begin by selecting undisturbed sawdust, sift it, and expose it to sunlight for 2–3 days. Ensure even spreading during drying and allow it to dry completely before storing for later use. Similarly, dry the cow dung thoroughly and break it into smaller pieces for better mixing. In addition to these main materials, you will need auxiliary ingredients such as ammonium bicarbonate, potassium dihydrogen phosphate, quicklime, and light calcium carbonate.
Mix cow dung and sawdust in a 1:1 volume ratio. The total weight of the mixture should include 0.3% ammonium bicarbonate, 2% potassium dihydrogen phosphate, approximately 2% quicklime (the exact amount depends on the quality and the desired pH after mixing, which should be between 7.5 and 8), and 2% light calcium carbonate. After mixing all components, add water to achieve a moisture content of 68–70%.
Once the mixture is ready, form a pile that is 1 meter high and 1.2 meters wide, with an unlimited length. Insert a thermometer into the pile to monitor temperature. When the internal temperature reaches around 75°C, perform the first turning, typically after about 10 days. Before each turning, lightly spray the surface of the pile with lime water. During the fermentation process, if the middle or lower parts of the pile begin to darken or emit an unusual odor—indicating poor aeration—use wooden sticks to poke and ventilate the pile.
The turning process usually takes 4–5 times, with intervals of 10, 9, 8, and 7 days respectively. If time is limited, you can reduce the number of turns to 3. After completing the fermentation, dry the material thoroughly. Below are some common issues that may occur during the process and their solutions:
1. **Slow or no temperature rise**: Sawdust tends to ferment more slowly than straw. If the temperature increases too slowly, consider adding a small amount of ammonium bicarbonate to adjust the carbon-to-nitrogen ratio and promote faster heating. If the temperature eventually rises above 60°C, no further adjustment is needed.
2. **Dark brown color and strange smell at the base of the pile**: This is a sign of insufficient oxygen, often due to overly large or compacted piles. To resolve this, turn the pile more frequently and ensure proper aeration after each turn.
After fermentation, prepare the culture medium. Cook wheat grains thoroughly, then mix them with the fermented sawdust material in a ratio of approximately 1/4 of the grain volume. Add lime and adjust the pH to 7.5–8. Based on the weight of the dry wheat, add 1–2% light calcium carbonate, mix well, and bottle the mixture. Ensure that the sawdust material is finely crushed and free of large chunks to avoid blockage during sterilization or incomplete digestion. When bottling, place the bottles upright and avoid tilting them too much, as improper positioning can cause the wheat and sawdust to separate, leading to uneven bacterial distribution.
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