How Compost Is Produced

How Compost Is Produced

The road from raw organic material to finished compost is a complex one, because both chemical and microbial processes are responsible for the gradual change from one to the other.

Decomposition of compost is accomplished by enzymatic digestion of plant and animal material by soil microorganisms. Simultaneously, the chemical processes of oxidation, reduction, and hydrolysis are going on in the pile, and their products at various stages are usedby microorganisms for further breakdown.

Bacteria use these products for two purposes: (1) to provide en­ ergy to carry on their life processes and (2) to obtain the nutrients they need to grow and reproduce. The energy is obtained by oxidation of the products, especially the carbon fraction. The heat in a compost pile is the result of this biological “burning,” or oxidation. Some materials can be broken down and oxidized more rapidly than others. This explains why a pile heats up fairly rapidly at the start. It is because the readily decomposed material is being attacked and bacterial activity is at its peak. If all goes well, this material is soon used up, and so bacterial activity slows down—and the pile begins to cool. Of course,  if the mass of the material is big enough, it acts as an insulator to prevent heat loss, and the high temperature may thus persist for some time after the active period is over, especially if the pile is not turned.

Persistent high temperatures are the result of uneven breakdown.

The raw materials that you add to your compost heap will have to be of biological origin in order to decompose down to finished com­ post. Wood, paper, kitchen trimmings, crop leavings, weeds, and manure can all be included in the heap. As compost is broken down from these raw materials to simpler forms of proteins and carbohydrates, it becomes more available to a wider array of bacterial species that will carry it to a further stage of decomposition.

Carbohydrates (starches and sugars) break down in a fairly rapid process to simple sugars, organic acids, and carbon dioxide that are released in the soil. When proteins decompose, they readily break down into peptides and amino acids, and then to available ammonium compounds and atmospheric nitrogen. Finally, species of “nitrifying” bacteria change the ammonium compounds to nitrates, in which form they are available to plants.

At this stage of decomposition, the heap is near to becoming finished compost, with the exception of a few substances that still resist breakdown. Through complex, biochemical processes, these substances and the rest of the decomposed material form humus. There is some evidence that humus is largely the remains of microbial bodies.

The microorganisms of the compost heap, like any other living things, need both carbon from the carbohydrates, and forms of nitrogen from the proteins in the compost substrate. In order to thrive and reproduce, all microbes must have access to a supply of the elements of which their cells are made. They also need an energy source and a source of the chemicals they use to make their enzymes. The principal nutrients for bacteria, actinomycetes, and fungi are carbon (C), nitrogen (N), phosphorus (P), and potassium (K). Minor elements are needed in minute quantities.

These chemicals in the compost pile are not in their pure form, and certainly not all in the same form at the same time. For example, at any given moment, nitrogen may be found in the heap in the form of nitrates and nitrites, in ammonium compounds, in the complex molecules of undigested or partly digested cellulose, and in the complex protein of microorganism protoplasm. There are many stages of breakdown and many combinations of elements. What’s more, microorganisms can make use of nitrogen and other elements only when they occur in specific forms and ratios to one another.  The carbon cycle. Green plants use carbon dioxide gas, water, and sunlight to make sugars and other carbon-containing compounds that animals use as food. Carbon compounds in plant and animal wastes provide food for decomposers in the compost pile. Materials that have passed through the decomposers’ bodies and the microbial bodies themselves contain nutrients used by plants to continue the carbon cycle.

Nutrients must be present in the correct ratio in your compost heap. The ideal C/N ratio for most compost microorganisms is about 25:1, though it varies from one compost pile to another. When too little carbon is present, making the C/N ratio too low, nitrogen may be lost to the microorganisms because they are not given enough carbon to use with it. It may float into the atmosphere as ammonia and be lost  to the plants that would benefit by its presence in humus. Unpleasant odors from the compost heap are most often caused by nitrogen being released as ammonia. Materials too high in carbon for the amount of nitrogen present (C/N too high) make composting inefficient, so more time is needed to complete the process. When added to the soil, high-carbon compost uses nitrogen from the soil to continue decomposition, making it unavailable to growing plants. See chapter 6 for more

on balancing the C/N ratio.

Affecting the interwoven chemical and microbial breakdown of the compost heap are environmental factors that need to be mentioned here.

Composting can be defined in the terms of availability of oxygen. Aerobic decomposition means that the active microbes in the heap require oxygen, while in anaerobic decomposition, the active microbes do not require oxygen to live and grow. When compost heaps are located in the open air, as most are, oxygen is available and the biological processes progress under aerobic conditions. Temperature, mois­ ture content, the size of bacterial populations, and availability of nutrients limit and determine how much oxygen your heap uses.

The amount of moisture in your heap should be as high as possible, while still allowing air to filter into the pore spaces for the benefit of aerobic bacteria. Individual materials hold various percentages of moisture in compost and determine the amount of water that can be added. For example, woody and fibrous materials, such as bark, saw­ dust, wood chips, hay, and straw, can hold moisture equal to 75 to 85 percent of their dry weight. “Green manures,” such as lawn clippings and vegetable trimmings, can absorb moisture equaling 50 to 60 per­ cent of their weight. According to longtime composting advocate and researcher Dr. Clarence Golueke in Composting, “The minimum content at which bacterial activity takes place is from 12 to 15 percent.

Obviously, the closer the moisture content of a composting mass approaches these low levels, the slower will be the compost process. As a rule of thumb, the moisture content becomes a limiting factor when it drops below 45 or 50 percent.”

Temperature is an important factor in the biology of a compost heap. Low outside temperatures during the winter months slow the decomposition process, while warmer temperatures speed it up. During the warmer months of the year, intense microbial activity inside the heap causes composting to proceed at extremely high temperatures.

The microbes that decompose the raw materials fall into basically two categories: mesophilic, those that live and grow in temperatures of 50° to 113°F (10° to 45°C), and thermophilic, those that thrive in tempera­ tures of 113° to 158°F (45° to 70°C). Most garden compost begins at mesophilic temperatures, then increases to the thermophilic range for the remainder of the decomposition period. These high temperatures are beneficial to the gardener because they kill weed seeds and diseases  that could be detrimental to a planted garden.

The nitrogen cycle. Shortage of available nitrogen is often a limiting factor in plant growth, since plants can’t make use of abundant atmospheric nitrogen gas. (So-called nitrogen-fixing plants rely on symbiotic bacteria.) Composting plant and animal wastes exposes the nitrogen they contain to nitrogen-fixing microorganisms and decomposers that break it down into forms available to plants

The bacterial decomposers in compost prefer a pH range of be­ tween 6.0 and 7.5, and the fungal decomposers between 5.5 and 8.0. Compost must be within these ranges if it is to decompose. Levels of pH are a function of the number of hydrogen ions present. (High pH levels indicate alkalinity; low levels, acidity.) In finished compost, a neutral (7.0) or slightly acid (slightly below 7.0) pH is best, though slight alkalinity (slightly above 7.0) can be tolerated.

Lime is often used to raise the pH if the heap becomes too acid. However, ammonia forms readily with the addition of lime, and nitrogen can be lost.

How to compost your kitchen waste at home

Compost from kitchen waste at home is one of the best methods to utilize kitchen waste for gardening.

You can also just make a pile in a sunny location and layer the scraps with leaf litter, grass clippings and soil. Turn the compost material every week and mist with water when composting kitchen waste.

This video briefly explains the method of compost from kitchen waste at home.

The Benefits of Using Compost in Your Garden

Many of us approach composting as a way to control household waste. And while minimizing waste is one significant benefit of composting, gardeners can delight in scores of other perks by utilizing nutrient-rich compost to improve soil composition. Read on to learn about the many ways compost can help you create a flourishing garden and healthier soil in the long-term.

1. Improve soil structure
According to the University of Illinois Extension, soil structure refers to the way inorganic particles, such as sand, silt and clay, combine with decayed organic particles, like humus and compost. Soil with a healthy structure is crumbly to the touch, allowing plenty of room for air, water and energy to move freely.

Adding compost to your garden also helps to neutralize pH and improve the cation exchange capacity (CEC) of soils, increasing their ability to hold nutrients for plant use.

So, why does all of this matter? If you’ve had trouble getting certain fruits, vegetables or decorative plants to grow in your garden, poor soil structure may be to blame. Think of it this way: If the soil in your garden is hard and clay-like, young roots have to struggle to get through and obtain the nutrients they need for healthy growth. If the soil is sandy, it may be lacking nutrients plants need to thrive.

When used in sufficient quantities, adding compost has both immediate and long-term positive impacts on soil structure by adding humus proteins, according to the U.S. Composting Council. These proteins bind soil particles together, allowing the soil to resist compaction and increasing its ability to hold moisture and nutrients.

2. Increase nutrient content
When organic material is broken down in a compost pile, the decomposition process produces the best fertilizer you’ll ever find, the soil food web.

So, what is the soil food web? To put it simply: It’s a community of organisms that live their lives in the soil, from microorganisms like bacteria and fungi to macroorganisms like earthworms and beetles. While creepy critters crawling around in your garden may not sound too appealing, all of these organisms are essential to healthy soil and will only improve crop yields.

In addition to a thriving soil food web, the organic matter found in compost introduces vital nutrients to your garden, including macronutrients like nitrogen, phosphorous and potassium and micronutrients such as manganese, copper, iron and zinc.

3. Use less water
Improving soil structure and boosting nutrient content is about more than producing healthier crops. Fertile soil also has far greater moisture retention, allowing you to use less water in your garden.

With the introduction of organic matter, heavy soils are better equipped to hold water and resist compaction – reducing erosion and runoff. Recent research also suggests that adding compost to sandy soils can increase moisture dispersion by allowing water to move laterally from its point of application.

4. Ward off plant diseases
“Research is showing us that soil treated with compost tends to produce plants with fewer pest problems,” the University of Illinois Extension says in its Composting for the Homeowner guide. “Compost helps to control diseases and insects that might otherwise overrun a more sterile soil lacking natural checks against their spread.”

The macro- and microscopic critters that call the soil food web home also decompose organic compounds, such as manure, plant residue and pesticides, preventing them from entering water and becoming pollutants – meaning the addition of compost is beneficial for both your garden and the surrounding environment.


Moisture required for composting

Moisture is a parameter closely related to microorganisms, because, like all living beings, they use water to transport nutrients and energy elements through the cell membrane. The ideal moisture of the compost is around 55%, although it varies depending on physical condition, size of the particles and the composting system. If moisture drops below 45%, microbial activity decreases, the degradation phases cannot be completed and hence, the resulting product is biologically unstable. If the moisture is too high (> 60%), water will saturate the pores and interfere oxygenation through the material. In processes in which the main components are substrates such as sawdust, wood chips, straw and dry leaves, the need for irrigation during composting is greater than in wetter materials such as kitchen waste, vegetable, fruit and grass clippings. The optimal moisture content for composting is 45% to 60% water by weight of the base material.

Benefits of organic matter

• Improves physical properties:

– Facilitating soil management for ploughing or seeding

– Increasing moisture retention capacity of soil.

– Reducing the risk of erosion.

– Helping to regulate soil temperature (edaphic temperature).

– Reducing water evaporation and regulating moisture.

• Improves chemical properties:

– Supplying macronutrients such as N, P, K and micronutrients.

– Improving cations exchange capacity.

• Improves biological activity:

– Providing organisms (such as bacteria and fungi) capable to transform insoluble matter into plant nutrients and degrade harmful substances.

– Improving soil conditions and providing carbon to keep biodiversity of micro and macro fauna (earthworms).

Other additional benefit of composting is the reduction of bad odour from rotting and elimination of vectors such as insects and rats. It also has a very important role in the elimination of human pathogens, food contaminating bacteria, and also weed seeds and other unwanted plants

What is organic matter

The most important part of a good soil is organic matter. Most of the peoples consider organic matter is a single thing or compound in the soil but it is a diverse nature of composition that results due to the decomposition process of plants, animals and other organisms. When decomposition process of animals and plants started many diverse compounds produce that make organic matter helpful to improve soil structure, texture and fertility.

Animals and plants are made-up of basic elements like carbon, nitrogen etc, decomposition is the process of return all these minerals/elements to the soil that involved helped of micro and macro organisms. Common materials that used in composting are; leaves, roots, stem, animal manure, animal urine, birds feathers and hairs and microorganisms like bacteria, fungi and nematodes that decompose all organic materials into organic matter.

Organic matter formation stared from decomposition by macro and micro organisms lead to mineralization, in simple words we can say organic matter formation is the process of conversion of organic or living beings into its fundamental inorganic form like minerals, soluble or insoluble. These minerals are flowing through the water soluble and used by living plants and other organisms or if not used by living plants or organisms organic matter change into stable called HUMUS by the process of humification.

Author: Asad Manzoor  Email:    Submitted: 12-January-2018

Beginner’s Guide to Making Compost: Organic Gardening

By: Willi Evans Galloway

Nature creates compost all the time without human intervention. But gardeners can step in and speed up the composting process by creating the optimal conditions for decomposition: Air + Water + Carbon + Nitrogen = Compost

Air. Like most living things, the bacteria that decompose organic matter, and the other creatures that make up the compost ecosystem, need air. Compost scientists say compost piles need porosity—the ability for air to move into the pile. I like to think of porosity in terms of fluffiness. A fluffy pile has plenty of spaces—or pores—for air to move about. A flat, matted pile of, say, grass clippings does not. Even fluffy piles compress during the composting process. Occasionally turning your pile refluffs the material, moves new material into the center, and helps improve air flow into the pile, says Craig Cogger, Ph.D., extension soil scientist at Washington State University.Beginner’s Guide to Making Compost: Organic Gardening

Water. Compost microbes also need the right amount of water. Too much moisture reduces airflow, causes temperatures to fall, and can make the pile smell; too little water slows decomposition and prevents the pile from heating. Conventional wisdom says that compost should feel like a wrung-out sponge, says Abigail Maynard, Ph.D., agricultural scientist at the Connecticut Agriculture Experiment Station.

Carbon ingredients. The microbes that break down organic matter use carbon as an energy source. Ingredients with a high percentage of carbon are usually dry and brown or yellow in color. The most common high-carbon ingredients are leaves, straw, and corn stalks. Sometimes people call these ingredients browns.

Nitrogen ingredients. Microbes need nitrogen for the proteins that build their tiny bodies. Ingredients high in nitrogen are generally green, moist plant matter, such as leaves, or an animal by-product, such as manure. These ingredients are called greens, but in reality they can be green, brown, and all colors in between.

C/N ratio. In order for a compost pile to decompose efficiently, you need to create the right ratio of carbon (C) to nitrogen (N) (C/N). Piles with too much nitrogen tend to smell, because the excess nitrogen converts into an ammonia gas. Carbon-rich piles break down slowly because there’s not enough nitrogen for the microbe population to expand. An ideal compost pile should have a 30:1 C/N ratio. Grass clippings alone have about a 20:1 C/N ratio. Adding one part grass clippings, or other green, to two parts dead leaves, or other brown, will give you the right mix.

Building a Compost Pile
There are two main ways to make compost: cold compost (minimum effort) and hot compost (maximum effort).

Cold Black Gold
Nearly every expert I talked with admitted (sometimes sheepishly) that they do this type of composting in their own back yards because it’s easy. Here’s how to make cold compost: Mix together yard wastes, such as grass clippings, leaves, and weeds, place them in a pile, and wait 6 to 24 months for the microorganisms, earthworms, and insects to break down the material. Add new materials to the top of the pile. You can reduce the waiting period by occasionally turning the pile and monitoring and adjusting the pile’s moisture level. The compost will be ready when the original ingredients are unrecognizable. Generally, compost on the bottom of the pile “finishes” first. You may not want to include woody material, because it breaks down too slowly.

Pros: Takes little effort to build and maintain; can be built over time.
Cons: Takes up to 2 years to produce finished compost; doesn’t kill pathogens and weed seeds; undecomposed pieces may need to be screened out.

Some Like It Hot
Hot, or fast, composting takes more work and the right combination of ingredients, but you can get high-quality compost in under 2 months. Here’s how: Wait until you have enough material to create compost critical mass (27 cubic feet), which is the minimum volume for a pile to hold heat. Then mix one part green matter with two parts brown matter. Bury any vegetative food scraps in the center to avoid attracting animals. Check to make sure the mixture has the ideal moisture level. Continue adding mixed greens and browns and checking the moisture until you’ve built a pile that is 3 feet by 3 feet by 3 feet, or 5 feet wide at the base and 3 feet wide at the top. The microorganisms will immediately start decomposing, and their bodies will release heat. The pile will insulate the heat, and the temperature of the pile’s interior will reach 120°F to 150°F. Turn the pile weekly and regulate moisture levels. After about a month, the hot phase will be done, and the pile will finish decomposing at temperatures between 80°F and 110°F. The compost will be ready to use when it no longer heats and all of the original ingredients are unrecognizable.

Pros: Produces high-quality compost within 2 months (and sometimes as soon as a few weeks); can kill weed seeds and pathogens. (Organic Gardening does not recommend adding weed seeds or manures that contain human pathogens to compost—hot or cold—because uniform heating is difficult to achieve in home compost piles.)
Cons: Time-consuming; requires careful management of moisture, air, and C/N ratio.