Sharing Notes from a Microbial Fertilizer and Composting Course
Foreword: Thank you all for your support of the Biopesticide Notes. It is my honor to share with everyone on this platform. Following the previous class share, here I share with you the "Notes on Microbial Fertilizers and Composting." I also ask experts to point out any shortcomings. Thank you.
Microbial Fertilizers
All microorganisms in microbial fertilizers must be native to nature or artificially induced by mutation, and must not be genetically modified microorganisms. They can be classified into legume rhizobium fertilizers, free-living nitrogen-fixing bacteria fertilizers, phosphate-solubilizing bacteria fertilizers, potassium-solubilizing bacteria fertilizers, and compound microbial fertilizers. To be called a microbial fertilizer, besides the above requirements, it must go through a purification process; otherwise, it should be called compost.
From a cost perspective, microbial fertilizers are more expensive than chemical fertilizers, but the three components nitrogen, phosphorus, and potassium in soil produce antagonistic effects. Therefore, soil can be sent to local improvement stations for free analysis. If the phosphorus and potassium values are higher than the standard values, it is recommended to use phosphate-solubilizing and potassium-solubilizing fertilizers. Nitrogen-fixing bacteria are only suitable for leguminous plants. In fact, phosphorus values in general soil tend to be high, stored in soil in non-ionic form, while plants only absorb fertilizers in ionic form. Therefore, phosphate-solubilizing bacteria are the microbial fertilizer we are most likely to use.
Crushed forage grass plus nitrogen fertilizer will become very good compost over time (Photo: Xidiyao Learning Farm)
Basic Principles of Composting
1. Carbon-to-nitrogen ratio. The initial carbon-to-nitrogen ratio is recommended to be 25~35:1, and through the composting process
microorganisms will consume part of the carbon and nitrogen until the carbon-to-nitrogen ratio stabilizes at about 20:1. If the carbon-to-nitrogen ratio is too high, microbial reproduction will be too slow due to nitrogen deficiency, and the composting process will be too long. If the carbon-to-nitrogen ratio is too low, nitrogen will escape as ammonia gas and be lost. Materials with a high carbon-to-nitrogen ratio include leaves (need to be crushed), weeds, rice straw, and wood chips (be careful that there must be no preservatives). Materials with a low carbon-to-nitrogen ratio include poultry and livestock manure, rapeseed meal, rice bran, and soybean powder. The simplest method that requires no analysis is to take 4 parts of high carbon-to-nitrogen material and mix with 1 part of low carbon-to-nitrogen material to reach the optimal ratio of about 25~35:1. Composting generally takes 60 days.
2. Aeration. Compost needs to provide enough oxygen for microorganisms to use, so turning the pile is often needed to increase oxygen. With enough oxygen, microbial action will increase fermentation and raise the temperature. Oxygen can also be pumped into the compost. If aeration is poor, rice hulls, bark, sawdust, etc. can be added to increase aeration.
3. Moisture. There must be enough moisture to maintain microbial life and activity. The appropriate moisture content is 60%, about the humidity at which a handful is squeezed and five drops or fewer drip along the gaps between the fingers.
4. Temperature. The temperature rises quickly at first. The measurement position is the center of the upper layer, at a depth of about 30~50 cm, and the measurement time is about 10~20 minutes. If the temperature rises to 60°C and is maintained for 48~72 hours, it can kill 80% of insect eggs. If the temperature continues to rise to above 75°C, nutrients will be destroyed, so the compost height needs to be lowered and other methods used to cool it down (generally a height of about 1.5 m is recommended).
5. pH value. Composting can proceed between pH 3~11, but pH 5.5~8.0 is best. If the pH value is too high, nitrogen will escape, and wood chips or fine sand can be added to improve it. Adding lime will make it smell worse. After composting and complete decomposition, the pH value is neutral at about 7.
6. Microbial strains. One of Trichoderma or Bacillus subtilis can be added to increase the composting effect. Do not add both at the same time. If both are to be added at the same time, compatibility must be evaluated. Bacillus subtilis is generally first diluted 200 times and added to a weed pile. Trichoderma is effective on bagasse, wood chips, rice hulls, etc. Bacillus F can be added to pig manure and rice straw. Adding bacteria to compost can make composting easier to succeed and faster to complete.
7. Degree of decomposition. Identify it by appearance. It can be judged complete by looseness, dark brown color, no foul odor, and an earthy aroma. In addition, if the temperature does not rise after turning the pile and is about room temperature, it can be used.
Composting Precautions
1. A stacking site with a roof is better, as it can avoid sterilization by direct sunlight and avoid rain washing that affects moisture and the shape of the compost.
2. Large organic materials must first be cut to below 5~8 cm to facilitate microbial decomposition.
3. Materials with a high carbon-to-nitrogen ratio, such as rice hulls, wood chips, bagasse, and chopped branches, need to go through a pre-stacking process. First add water and stack them separately to soften the fibers, then mix with other materials.
4. The composting process is long. To prevent mosquitoes and insects from laying eggs, straw mats, rice straw, burlap, etc. can be spread on top.
5. In the final stage, the compost needs to be spread flat to evaporate excess moisture, which helps with storage.
6. Selection of organic materials: choose soybean powder for high nitrogen, bone meal for high phosphorus, fish meal or pig bone meal for high nitrogen and phosphorus, and whey powder (feed-grade milk powder) for high nitrogen and phosphorus in organic farming.