a complete guide to on-farm animal manure composting

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    On-Farm Manure Composting Summary:

    Composting manure is an effective manure management tool, composting converts manure into a stable humus like product that improves the soil and is a fertilizer as well.

    Composting manure could reduces manure volumes, kills pathogens and weed seeds, which in turn improve farm operation profit.

    Proper management is needed when doing on-farm manure composting (moisture, C:N ratio, aerobic conditions,  temperature).

    Composting Definition and advantages:

    Composting is a controlled biological process that converts organic wastes (like manure, carcasses, and plant materials) into organic fertilizer. Organic residues are mixed, piled and moistened to undergo thermophilic decomposition, the decomposition occurs until organic materials have been substantially decomposed. By composting, we are actually speeding up the decomposition process.

    manure composting to make fertilizer
    Composting Definition

    Manure Composting can greatly reduce the raw material volume and weight (about 2/3), correspondingly reduce hauling cost, make composting an economic advantage when compared to hauling raw manure.

    The high temperature in the compost pile sterilizes weed seeds and kills pathogens, and no weeds would growing on the compost, it is another advantage over manure.

    However, compost pile need turning, which stimulates the microbes that raise temperature and does the composting.

    Managing Microorganisms in Manure Pile:

    Bacteria and fungi in the compost are indigenous to the pile, they will start composting manure almost immediately. It is composter’s job to make the pile habitable for the decomposing microbes, to achieve that, we need a carbon to nitrogen ration (C/N ratio) to range from 20 to 40. That is, 20 parts on carbon for every part of nitrogen, and 40 parts of carbon to every part of nitrogen.

    There are pore space in the compost pile, the pore space needs to have approximately 40 to 60 percent water and 35 to 60 percent air. By managing the C/N ratio, water and air properly, the pile should heat in a day or two after initial piling.

    Managing C/N Ratio Properly:

    If the C/N ratio is too low, means there’s excessive nitrogen, nitrogen can be lost due to ammonia volatilization. The pile may smell ammonia and temperature can exceed 150 degrees Fahrenheit and kill beneficial microbes. Adding a carbon source like straw or wood chips can help remediate this.

    If the C/N ratio is too high, means there is excessive carbon, the microbes lack sufficient nitrogen, the pile may not heat or compost slowly. Adding more manure can alleviate this issue. Below is typical C/N ratio of composting materials.

    CN Ration of different composting materials
    CN Ratio of Different Materials

    Per above table, you may compost 90% manure and 10% wheat straw to get right C/N ratio.

    Control moist level of manure compost pile:

    40-65% of pore space needs to have water, summer rainfall and moisture in the composting materials can serve as a water source. However, during long dry periods, you need to add water. You may use hose attached to a mobile tank, or spray system on compost turner to add water when turning.

    Squeeze test compost pile moisture control
    Compost Material Squeeze Test

    Testing for adequate moisture can be easily done using squeeze test. The right water content should be damp to touch but not dripping water. If compost doesn’t feel moist, water need to be added, If it is dripping by squeeze, the pile should be turned to increase evaporation or add further dry compost material.

    Guarantee Optimum Oxygen Level of Compost pile:

    Microbes doing the composting need oxygen to breathe, 35-60% of the pore space needs to have air, which is known as aerobic conditions. If there isn’t sufficient oxygen, anaerobic decomposition will occur, anaerobic condition produces little heat, compost slowly and produces methane and other odorous compound.

    Monitor pile temperatures is a way to monitor oxygen, turning the pile is a way to introduce oxygen into the system and homogenize the compost. For on-farm manure composting, tractor tow behind compost turner is most common type of turner.

    YYK Barn Compost Turner

    Compost Temperature:

    Temperature probe of 18-24 inches works fine, they can be found on internet or hardware stores and cost roughly 30 dollars. Several location in a pile should be checked and averaged out, this gives you an idea of entire pile temperature. The temperature should be checked every 3-5 days.  Checking temperature gives you an indication of pile turning frequency and if pathogens or weed seeds will die.

    If temperature reaches 131 degree Fahrenheit for a few days, it will kill most pathogens. Many weed seeds will sterilize at the temperature too. However, some weeds require higher temperature to sterilize, e.g. buckwheat requires 145 degree Fahrenheit for a few days to become sterile. Over 150 degree Fahrenheit may kill beneficial microbes.

    For efficient composting, the pile should be turned when temperature drop below 110 degrees, when a pile is turned, it should heat back up after a day or two.

    compost pile temperature control
    Windrow Tuning Points and Temperature Tontrol

    Above chart shows the compost was first piled on May 8, and thermophilic condition remained until May27, high temperature maintained for nearly 3 weeks, the pile was turned on May30, the temperature rose almost immediate.

    This time the pile didn’t heat as much and high temperature duration was shorter. The pile was again turned on June 13, and required water. The pile didn’t heat as much as 2nd turn, but did maintain high temperature for a longer time.

    The pile was turned for a third time on July3rd, and temperature barely rose, this indicates the pile almost done composting.

    On July25, the pile was turned one last time, the temperature rose slightly and slowly. This indicates the pile is essentially composted and the majority of manure and bedding are decomposed.

    The pile should be allowed to sit a month or so to complete the hot phase of composting, this is known as curing. They compost cn ten be applied on field.

    Please take note, application of immature compost on field can cause crop issues.   

    Manure Compost Nutrient Values:

    Compost can improve many soil properties, include lower soil bulk density, increase soil water holding capacity increase the cation exchange capacity. Cation exchange capacity allow the soil to release positively charged plant nutrient slowly throughout the growing season and prevent those nutrients being lost.

    Compost Nutrient Values
    Compost Nutrient Values

    Not only compost improve soil characteristics, but it is also a fertilizer. Above are the averages from 10 compost nutrient tests, these values come from the NDSU soil testing lab. The average was 16.6 pounds of nitrogen per ton of compost, 13 pounds of phosphorus per ton and 14.3 pounds of potassium per ton.

    These values do have a wide range, so sample testing it for nutrients are important to make sure the nutrients aren’t over or under applied. It is important to follow soil test trends when determining compost applications.  

    In many cases, the compost should be used as a phosphorus source and be supplemented with a conventional nitrogen source. If compost is applied to meet nitrogen requirement, phosphorus may be greatly over-applied. Over-application can lead to nutrient running off the compost applied field, resulting in water quality issues.

    Manure Compost Utilization:

    Not all the nutrients in compost is plant available, most of the nutrients are in an organic form, plants use inorganic forms of nitrogen, phosphorus and potassium. Microbes in the soil utilize the organic nutrients found in the compost and transform or mineralize them in plant available nutrients.

    animal manure compost land application
    Compost Land Application

    On the first year of compost application, 15% of total nitrogen can be expected to be plant available in conventional tillage. If the compost is applied in a no-till system, approximately 20% of total nitrogen will be plant available.

    30% and 70% of phosphorus is mineralized in the 1st and 2nd growing seasons.

    31% of total potassium is mineralized the 1st year.

    Use soil test, compost test and a calibrated manure spreader will help ensure the crop yield goals are met.

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