1、COMPOSTING Improve Your Soil Recycle Kitchen and Yard Wastes Grow Healthier Plants Create an Earth-Safe Garden Easy Methods for Every Gardener The two most important aspects of a compost pile are the chemi cal makeup of its components and the population of organisms in it. Compost piles are intricat
2、e and complex communities of animal, vege table, and mineral matter, all of which are interrelated, and all of which play a part in the breakdown of organic matter into humus. Compost ing is the result of the activities of a succession of organisms, each group paving the way for the next group by br
3、eaking down or convert ing a complex biodegradable material into a simpler or more usable material that can be utilized by its successor in the chain of breakdown. Generally speaking, the more “simple“ the molecular structure of the material, the more resistant it becomes to bacterial attack and, he
4、nce, the more biologically stable it becomes. Whether the decomposition process takes place on the forest floor or in a gardeners compost heap, the biochemical systems at work are the same, and humus is always the result. Humus Humus, the relatively stable end product of composting, is rich in nutri
5、ents and organic matter and highly beneficial to both the soil and crops grown in the soil. As we saw in chapter 2, the advantages of humus are twofold. First, when it is mixed with the soil, the resulting combination becomes a heterogeneous, loosely structured soil mixture allowing air and water to
6、 penetrate to soil organisms and growing plants. Because of its loose texture, humus-rich soil soaks up water in its pores so that less runoff occurs. Second, humus contains a number of chemical elements that enrich the soil with which it is mixed, providing nutrients for growing plants. The major e
7、lements found in humus are nitrogen, phosphorus, potassium, sulfur, iron, and calcium, varying in amounts according to the original composition of the raw organic matter thrown on the heap. Minor elements are also present, again in varying amounts depending on the type of compost. The N-P-K percenta
8、ges of finished compost are relatively low, but their benefit lies in the release of nitrogen and phosphorus in the soil at a slow enough rate that plants can use them and they arent lost through leaching. Soil mixed with humus becomes a rich, dark color that absorbs far more heat than nonorganic so
9、ils, making it a more favorable environ ment in which to grow crops and ornamental plants. How Compost Is Produced The road from raw organic material to finished compost is a complex one, because both chemical and microbial processes are re sponsible for the gradual change from one to the other. Dec
10、omposition of compost is accomplished by enzymatic diges tion of plant and animal material by soil microorganisms. Simulta neously, the chemical processes of oxidation, reduction, and hydroly sis are going on in the pile, and their products at various stages are used by microorganisms for further br
11、eakdown. 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 resul
12、t 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 wel
13、l, this material is soon used up, and so bacterial activity slows downand 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 i
14、f 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 ma nure can a
15、ll 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 f
16、airly 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 t
17、he 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 sub stances and the rest of
18、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 nitro gen from the proteins in the compost substrate. In order
19、 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), nitro gen (N
20、), 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 a
21、nd nitrites, in ammonium compounds, in the complex molecules of undigested or partly digested cellulose, and in the com plex protein of microorganism protoplasm. There are many stages of breakdown and many combinations of elements. Whats more, mi croorganisms can make use of nitrogen and other eleme
22、nts 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
23、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 a
24、bout 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 tha
25、t 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. Wh
26、en added to the soil, high-carbon compost uses nitrogen from the soil to continue decompo sition, 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 n
27、eed 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
28、 the open air, as most are, oxygen is available and the biologi cal processes progress under aerobic conditions. Temperature, mois ture content, the size of bacterial populations, and availability of nutri ents limit and determine how much oxygen your heap uses. The amount of moisture in your heap s
29、hould be as high as possi ble, 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
30、, 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. Clare
31、nce Golueke in Composting, “The minimum con tent 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 l
32、imiting 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. Dur ing the warmer months of the year, intense microbial
33、 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 The nitrogen cycle. Shortage of available nitrogen is often a limiting f
34、actor in plant growth, since plants cant 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
35、available to plants. to 113F (10 to 45C), and thermophilic, those that thrive in tempera tures of 113 to 158F (45 to 70C). Most garden compost begins at mesophilic temperatures, then increases to the thermophilic range for the remainder of the decomposition period. These high temperatures are benefi
36、cial to the gardener because they kill weed seeds and diseases that could be detrimental to a planted garden. 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. Lev
37、els 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 rai
38、se the pH if the heap becomes too acid. However, ammonia forms readily with the addition of lime, and nitro gen can be lost. Compost Organisms Since decomposition is the crux of the composting process, lets take a look at the various organisms involved in this vital function of the working compost h
39、eap. Most are microscopic, some are large enough to be observed with the unaided eye, but nearly all are benefi cial, each having a role in breaking down raw organic matter into finished compost. They are known as decomposers. You can gauge the progress of your compost by regularly checking the temp
40、erature inside the heap. Mesophilic decomposers work best at temperatures of 50 to 113F (10 to 45C); as decomposition progresses, temperatures increase to 113 to 158F (45 to 70C) and thermophilic microorganisms continue the breakdown process. Microscopic Decomposers By far the most important microsc
41、opic decomposers are bacteria, which do the lions share of decomposition in the compost heap. But there are other microscopic creatures, such as actinomycetes, proto zoa, and fungi, that also play important roles. Together, these micro scopic decomposers change the chemistry of the organic wastes; t
42、hey carry the name of chemical decomposers. The larger fauna in the heap include mites, millipedes, centipedes, sow bugs, snails, slugs, spiders, springtails, beetles, ants, flies, nema todes, flatworms, rotifers, and most important, earthworms. Collec tively, these are called the physical decompose
43、rs since they bite, grind, suck, tear, and chew the materials into smaller pieces, making them more suitable for the chemical work of the microscopic decomposers. Bacteria. The bacteria likely to be found in a compost heap are those that specialize in breaking down organic compounds, those that thri
44、ve in temperatures ranging up to 170F (77C) in the thermophilic range, and those that are aerobic, needing air to survive. Bacterial populations differ from pile to pile, depending upon the raw materials of the compost, degree of heat, amount of air present, moisture level, geographic location of th
45、e pile, and other considerations. Bacteria are single-celled and can be shaped like spheres, rods, or spiral twists. They are so small that it would take 25,000 bacteria laid end to end to take up 1 inch on a ruler, and an amount of garden soil the size of a pea may contain up to a billion bacteria.
46、 Most bacteria are colorless and cannot make carbohydrates from sunshine, water, and carbon dioxide the way green plants can. Some bacteria produce colo nies; others are free-living. All reproduce by means of binary fission. Bacteria are the most nutritionally diverse of all organisms, which is to s
47、ay, as a group, they can eat nearly anything. Most compost bacteria, similar to fungi and animals, can use living or dead organic materials. Some are so adaptable they can use more than 100 different organic compounds as their source of carbon because of their ability to produce a variety of enzymes
48、. Usually, they can produce the appro priate enzyme to digest whatever material they find themselves on. In addition, respiratory enzymes in the cell membrane make aerobic res piration possible. Since bacteria are smaller, less mobile, and less complexly orga nized than most organisms, they are less
49、 able to escape an environment that becomes unfavorable. A decrease in the temperature of the pile or a sharp change in its acidity can render bacteria inactive or kill them. When the environment of a heap begins to change, bacteria that for merly dominated may be decimated by another species. At the beginning of the composting process, mesophilic (medium-temperature) bacteria and fungi predominate. They gradually give way to thermophilic (high-temperature) bacteria as the pile becomes hotter; the more thermophilic bacteria that are present, breaking down com pounds a
