General Information


Composting Steer Manure

Composting has an ecosystem all its own. When conditions are favorable, a complex world of microorganisms feed on organic material for energy to produce humus and nutrients that are valuable to plants and their environment.

Imperial Compost strives to create the ideal conditions for this natural decay process to occur efficiently by applying moderm manufacturing techniques. Composting requires organic waste, microorganisms, water, and air. These requirements must be balanced for productive composting. During the composting process, microorganisms digest organic (carbon containing) waste and break it down into its simplest parts.

In aerobic decomposition, living organisms that use oxygen feed on the organic matter. They require nitrogen, phosphorus, some carbon, and other necessary nutrients released by the composting process to sustain their activity. Much of the carbon serves as a source of energy for the organisms and is burned up and respired as carbon dioxide. Since carbon serves both as a source of energy and as an element in the cell protoplasm, much more carbon than nitrogen is needed.

Different communities of microorganisms thriving at different temperatues and on different materials participate in the composting process. Mesophilic microbes (those active at low temperatures) rapidly break down the soluble, readily degradable compounds to initiate decomposition. The heat they produce causes the compost temperature to rapidly rise.

As the temperature rises above 104 degrees Fahrenheit, the mesophilic microorganisms become less competitive and are replaced by others that are thermophilic (heat loving). At temperatures of 131 degrees Fahrenheit and above, many human or plant pathogens and weed seeds are destroyed. Temperatures higher than 149 degrees Fahrenheight are detrimental to the on-going process. Many forms of microbes are killed at these temperatures which slow the rate of decomposition.

During the thermophilic phase, high temperatures accelerate the breakdown of the major structural molecules of the organic matter. As the supply of these high-energy compounds becomes exhausted, the compost temperature gradually decreases and mesophilic microbes once again take over for the final phase of "curing" or maturation of the remaining organic matter.

Bacteria and fungi are the primary organisms that break down the organic matter. These microorganisms are not added to the organic matter. They are present in sufficient numbers in the soil and manure removed from the cattle pens during cleaning to begin the decaying process. In aerobic composting, actinomycetes bacteria and fungi are the most active.

  • Bacteria are the most numerous in composting; they make up 80-90% of the microbes typically found in compost. Bacteria are responsible for most of the decomposition and heat generation in composting. They are the most nutritionally diverse group of compost organisms, using a broad range of enzymes to chemically break down a variety of organic materials.

  • Actinomycetes (filamentous bacteria) play an important role in degrading complex organic compounds such as cellulose, lignin, chitin, and proteins. Their enzymes enable them to chemically break down tough debris such as woody stems. Some species are active during the termophilic phase, others become important during the cooler, curing phase when only the most resistant compounds remain in the last stages of the formation of humus.

  • Fungi include molds and yeasts. They are responsible for the decomposition of many complex plant polymers in composting. Fungi are important because they break down tough debris, enabling bacteria to continue the decomposition process once most of the cellulose has been exhausted. Fungal species are numerous during both mesophilic and thermophilic phases of composting. When temperatures are high, most fungi live in the cooler, outer layer of the composting material.

  • Soil Microorganisms and Organic Matter

    One of the greatest challenges to Imperial Valley crop production is managing its fine-textured soils, particularly the clay soils. The limitations of clay soils arise from a lack of large pore spaces restricting both water and air movement.

    The best management practice for clay soils is routine applications of organic matter, such as Imperial Compost brand, and attention to fostering the activity of soil microorganisms. As soil microorganisms decompose the organic matter, the soil particles bind together into large aggregates increasing pore space. As the organic content increases, soil microbes become more active resulting in imporived soil structure.

    Soil organic matter is the storehouse for the energy and nutrients used by plants and other organisms. An incredible diversity of organisms makes up the soil biological community. Bacteria, fungi, and other soil dwellers transform and release nutrients from organic matter. As individual plants and soil organisms work to survive, they depend on interactions with each other. By-products from growing roots and plant residue feed soil organisms. In turn, soil organisms support plant health as they decompose organic matter, cycle nutrients, enhance soil structure, and control the populations of soil organisms including crop pests.

    Practices, such as regular additions of organic material, that build soil organic matter will raise the proportion of active organic matter long before increases in total organic matter can be measured.

    Soil Bacteria

    Bacteria are tiny, one-celled organisms. A teaspoon of productive soil generally contains between 100 million and 1 billion bacteria. That is as much mass as two cows per acre. Agricultural soils usually have bacteria-dominated food webs.

    Bacteria beneficial to agriculture:


  • Actinomycetes are a large group of bacterial that grow as hyphae. They are responsible for the characterically "earthy" smell of freshly turned, healthy soil. Actinomycetes decompose a wide array of substrates, but are especially important in degrading hard-to-decompose compounds, such as chitin and cellulose, and are active at high pH levels.

  • Nitrogen-fixing bacteria (Rhizobium species) form symbiotic associations with the roots of legumes like sesbania, clover and alfalfa. Visible nodules are created where bacteria infect a growing root hair. The plant supplies simple carbon compounds to the bacteria, and the bacteria convert nitrogen (N2) from air into a form the plant host can use. When leaves or roots from the host plant decompose, soil nitrogen increases in the surrounding area.

  • Nitrifying bacteria (Nitrosomonas, Nitrobacter species) change ammonium (NH4+) to nitrite (NO2-) then to nitrate (NO3-) -- a preferred form of nitrogen for grasses and most row crops. They use the energy from decaying organic matter in the soil to fuel soil processes, including nitrogen fixation. This seemingly simple process involves a complex series of reactions.

  • Soil Fungi

    Fungi are microscopic cells that usually grow as long threads or strands called hyphae that push their way between soil particles, roots, and rocks. A single hypae's length can span from a few cells to many yards. Hyphae sometimes group into masses called mycelium that look like roots.

    Fungi are important to water dynamics, nutrient cycling, and disease suppression. Along with bacteria, fungi are important as decomposers in the soil food web. They convert hard-to-digest organic material into forms that other organisms can use. Fungal hyphae physically bind soil particles together, creating stable aggregates that help increase water infiltration and soil water holding capacity.

    Fungi are aerobic organisms. Soil that becomes anaerobic for significant periods generally loses its fungal component. Anaerobic conditions often occur in waterlogged and compacted soils.

    Soil fungi beneficial to crop production:


  • Mycorrhizal fungi colonize plant roots. In exchange for carbon from the plant, mycorrhizal fungi help solubolize phosphorus and bring soil nutrients (phosphorus, nitrogen, and micronutrients) to the plant.

    Mycorrhizal fungi in agriculture are a symbiotic association between fungi and plant roots and is unlike either fungi or roots alone. Most agricultural crops depend on or benefit substantially from mycorrhizae. The exceptions are many members of the crucifer family (e.g., broccoli, mustard), and the chenopodium family (e.g. lambsquarters, spinach, beets), which do not form mycorrhizal associations. The level of dependency on mycorrhizae varies greatly among varieties of some crops including wheat and corn.

  • Saprophytic fungi convert dead organic material into fungal biomass, carbon dioxide (CO2), and small molecules such as organic acids. Like bacteria, fungi are important for immobilizing, or retaining, nutrients in the soil.


  • Fungal hyphae have advantages over bacteria in some soil environments. Under dry conditions, fungi can bridge gaps between pockets of moisture and continue to survive and grow even when soil moisture is too low for most bacteria to be active. Fungi are able to use nitrogen up from the soil allowing them to decompose surface residue that is often low in nitrogen.

    Refernces:
  • Soil Bacteria and Fungi: The Soil Biology Primer; Elaine R. Ingham; Chapters 3 and 4; USDA, Natural Resources Conservation Service, Soil Quality.
  • Managing Soil Tilth, Colorado State University Cooperative Extension, updated 12-20-04
  • Soil Microbiology and Biochemistry Slide Set. 1976. J.P. Martin, et al., eds. SSSA, Madison, WI
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