Compost, Soil Health And Climate Change
How much do you know about the connections between compost, soil health, and climate change? What role can compost play in mitigating and/or adapting to climate change? Where does soil health fit into this picture? What unique benefits does compost bring to the table in taking on these challenges? Take this quiz and see how your knowledge matches up with the latest science and most innovative thinking on these subjects.
Questions and Answers
- 1.
Compost (and composting) can be important tools in fighting climate change. Which of the following are proven, well-documented climate-change benefits of composting and compost applications to soil?
- A.
Composting keeps organics out of landfills, reducing methane emissions to the atmosphere.
- B.
Adding compost to soil can increase the rate at which the soil sequesters carbon.
- C.
Adding compost to soil decreases the rate at which carbon dioxide is released into the atmosphere.
- D.
Compost helps soil become more resilient and less vulnerable to climate extremes.
- E.
Composting does not generate any greenhouse gasses.
- F.
Compost can reduce the need for nitrogen fertilizer, thereby reducing the risk of N2O emissions from soil.
Correct Answer(s)
A. Composting keeps organics out of landfills, reducing methane emissions to the atmosphere.
B. Adding compost to soil can increase the rate at which the soil sequesters carbon.
D. Compost helps soil become more resilient and less vulnerable to climate extremes.
F. Compost can reduce the need for nitrogen fertilizer, thereby reducing the risk of N2O emissions from soil.Explanation
- True. Methane emissions are the result of organic wastes decomposing in anaerobic (low oxygen) conditions; methane (CH4) is 25 times as potent a GHG as CO2 - True. Compost adds organic matter to soil, and it also stimulates the soil food web, which encourages more plant growth and thus even more organic matter added to the soil (as organic wastes and plant root secretions, or exudates); to find out more about how this works, check out the work of the Carbon Cycle Institute in California. Better yet, come to the CCC Annual Conference in Montreal in September and hear the Institute'sTorri Estrada and Dr. Phil Creque talk about how important compost can be in fighting climate change. - False. Adding compost can actually increase the rate at which CO2 is released from soil, because of the stimulatory effects of compost on the soil microbiota. However, as discussed in the previous point, these soils still retain more carbon after compost addition, simply because of the greatly increased amounts of carbon added to the soil. Retained carbon = carbon in - carbon out. In the case of compost, the carbon coming in increases by more than the carbon going out, resulting in a net gain. - True. Because compost stimulates the soil food web, soils with added carbon end up with better structure (more stable soil aggregates). This means more pore space, which in turn means better rainfall infiltration rates and better water holding capacity. This capacity to allow more infiltration reduces flooding during heavy rainfalls; the higher water holding capacity increases drought resistance. - False. The composting process releases a number of greenhouse gases. However, if the process is done properly, the majority of these gases are CO2. Although CO2 is a GHG, its release in composting is not considered to be an addition to the GHGs in the atmosphere, because it is just part of the natural carbon cycle. On the other hand, if the composting process is not managed well, it can release methane and nitrous oxide as well as CO2. Overall, however, most scientists consider the composting process to be fairly close to neutral in terms of net emissions (however, this does not count equipment use, transportation, etc.). - True. Nitrogen fertilizers can create nitrous oxide emissions if not taken up by the crop. By using compost along with fertilizer, the risk of these emissions can be reduced.Rate this question:
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- 2.
Soil health is dependent on the number, diversity, and general state of health of the organisms of the "soil food web". True, or False?
- A.
True
- B.
False
Correct Answer
A. TrueExplanation
The "soil food web" is a term scientists use to describe the sum total of the organisms living in any given soil, and the relationships between them. Soil is in fact a living ecosystem and it is the health of that ecosystem (i.e., number or organisms, diversity of types of organisms, their access to energy, air, water, etc.) that dictates the health of the soil itself.Rate this question:
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- 3.
Compost provides many benefits to soil organisms. Which of the following is NOT a benefit supplied by compost?
- A.
Food energy
- B.
Shelter
- C.
Protection from predators
- D.
Diversity
Correct Answer
C. Protection from predatorsExplanation
Compost is comprised largely of organic matter, in the form of substances that are more stable chemically than you would find in uncomposted organics, manure, etc. Microbes are able to use many of these substances as food sources. They also attach themselves to clumps of organic matter, helping build soil aggregates. These aggregates give soil its good structure, which in turn provides the microbes with beneficial habitat, or shelter. Another important benefit of compost is its impact on diversity. Compost made from food wastes, for instance, is chock full of thousands of species of beneficial microbes, many of which may be new to the soil where the compost is added. Finally, compost does not directly provide any protection from predators, but that is a good thing, because predation is the basis for soil fertility -- larger microbes eat the smaller ones, then "poop" out the nutrients in plant-available form.Rate this question:
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- 4.
Healthy soil has a sponge-like structure, able to infiltrate and hold water. This is due to "clumps" of soil, held together by a combination of electrical charges, biological glues secreted by microbes, fungal hyphae (filaments) and root hairs. Scientists call these clumps "stable soil ________".
Correct Answer
aggregatesExplanation
Compost can speed up or enhance the formation of stable soil aggregates, largely by providing food and habitat for the microbes that secrete the glues and grow the filaments that hold aggregates together. Some of the organic matter in compost becomes enclosed within the aggregate. This slows down the rate at which the organic matter decomposes, because the conditions inside the aggregate are less conducive to the the activity of decomposing microbes. As a result, the rate of carbon loss from soil is reduced and carbon levels rise (one of the main mechanisms of soil carbon sequestration).Rate this question:
- 5.
Which of the following statements about compost is entirely accurate (as opposed to partially accurate, or unproven)?
- A.
Compost is an equivalent replacement for synthetic fertilizer, as long as soil testing is used to calculate nutrient content.
- B.
When added to soil, compost supports and/or stimulates natural biological processes beneficial to plants, such as nutrient cycling and disease supression.
- C.
Compost eliminates nutrient run-off from farm fields.
- D.
Compost has little to no effect on a soil's ability to adapt to climate change.
Correct Answer
B. When added to soil, compost supports and/or stimulates natural biological processes beneficial to plants, such as nutrient cycling and disease supression.Explanation
- Although compost can reduce the need for synthetic fertilizer, it should not be viewed as an equivalent replacement, even when soil testing is used to calculate the amount of nutrients supplied by the compost. This is not only because compost can provide additional benefits, such as better soil structure. It is also due to the fact that compost releases its nutrients slowly, over decades. Compost has many nutrients beyond what the soil tests show (they simply show what is available to the plant). These nutrients are tied up in various forms of organic matter. How much of that extra nutrition will be made available will depend on many factors, including the health of the soil. - When compost is added, the soil food web is stimulated. This can enhance the natural nutrient cycling taking place in the soil. One farmer in the United States, who has been practicing soil health for decades, says that he can stop adding fertilizer, with no yield penalty, when his fields reach a soil organic matter (SOM) level of 8 per cent. Most fields are well below that. Compost can help to bring up levels of SOM, but it takes many years if the starting level is low. - Similarly, compost cannot completely eliminate nutrient run-off, and can even contribute to it. However, a healthy soil, with a high SOM level, can greatly reduce nutrient loss. This is because the higher number of soil micobes in healthy soil will ensure that the soil has good structure (aggregation) and therefore lots of storage capacity (SOM also has a very high cation exchange capacity (CEC), which means that the soil will hold on to nutrients better). The nutrients that end up in solution in the soil water don't leave the field because they are held in the pore spaces created by the soil food web. - Finally, compost has been shown to have the potential for major impacts on the adaptability and resilience of soils. Again, this is due to the stimulation of the soil food web and the beneficial soil structure that is the inevitable result of healthy soil best management practices. We should note here that tillage, in particular, can have detrimental effects on soil structure. Compost can perhaps ameliorate this damage, but the best results come from the application of compost to land managed with no or minimum tillage.Rate this question:
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- 6.
Carbon farming is a term that is used to describe farmers or ranchers that adopt soil-health best management practices (including the application of compost). The goal of all carbon farmers is to maximize the capture of ________ ________ through photosynthesis, in order to feed BOTH the crop and the soil food web.
Correct Answer
solar, sun's
energyExplanation
By having the soil surface covered with green plants as much as possible, the amount of solar energy captured and converted into biochemical energy is maximized. Up to half of this energy is transferred to the creatures of the soil food web, fueling their beneficial activities. Some of this energy is transferred when plants and animal die, or eliminate waste. However, much is directly transferred by plants to the soil via root exudates -- energy-rich substances secreted through the roots to feed microbes (in return for the nutrients microbes bring to plants). This is the original carbon trading system.Rate this question:
- 7.
You can never add too much compost. True, or False?
- A.
True
- B.
False
Correct Answer
B. FalseExplanation
Although compost is great for soil health, too much added at one time can result in several different problems. For example, it can create a nutrient overload, with subsequent run-off causing pollution of surface waters; also, some types of compost (e.g., C:N ratio below 11) can have detrimental effects on the diversity of some later-successional ecosystems (e.g., grasslands), as the available nutrient levels are too high, encouraging invasion by earlier successional species. Compost has the potential to be a major tool in both the soil-health and climate-change endeavours, but it should always be used within the proper nutrient and ecological context.Rate this question:
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- 8.
.Indicate which of the following statements you believe to be correct.
- A.
There is at least one jurisdiction where farmers are paid for applying compost, based on the greenhouse gas reduction benefit.
- B.
In general, as compost matures, the type of microbes that dominate changes from bacteria to fungus.
- C.
Immature compost has lower nutrient levels.
- D.
Compost and manure help soil sequester carbon at about the same rate.
- E.
On average, about 5 per cent of the nitrogen in compost is released in the first year, 2.5 per cent in year 2, and around 2 per cent each year for subsequent years, until all the original N has been released.
- F.
Compost contains many more nutrients than show up in standard lab tests.
- G.
As soils increase in organic matter, their ability to absorb more carbon decreases.
Correct Answer(s)
A. There is at least one jurisdiction where farmers are paid for applying compost, based on the greenhouse gas reduction benefit.
B. In general, as compost matures, the type of microbes that dominate changes from bacteria to fungus.
E. On average, about 5 per cent of the nitrogen in compost is released in the first year, 2.5 per cent in year 2, and around 2 per cent each year for subsequent years, until all the original N has been released.
F. Compost contains many more nutrients than show up in standard lab tests.Explanation
1 True. Come to the Council's Annual Conference in Montreal and hear how California has made compost application an important part of their fight against climate change, including carbon-offset payments for application of compost to croplands and rangelands. 2 True. As compost matures, its nutrients get tied up in more complex molecules. This is why mature compost is more stable. Fungi are better able to feed on these complex humic molecules than are bacteria, so the microbial composition changes to become fungal dominated over time. This has implications for how the compost should be used. At the Montreal Conference, Vivian Kaloxylos of DocTerre labs will explain the importance of the ratio of fungi to bacteria in compost and in soils. 3 False. Immature compost has more plant-available nutrients, because it has not yet been fully stabilized. Many farmers prefer immature compost for the quick nutrient hit it provides. However, more mature compost has many extra benefits, including long-term slow release of nutrients and higher levels of carbon sequestration (this is due to the higher fungal populations, which are vital to good soil aggregation). 4 False. Studies have shown that adding compost sequesters carbon in soils at a faster rate than does adding raw manure. 5 True. Although these numbers can vary, depending on the type and age of the compost. These figures would be representative of a mature compost with a C:N ratio higher than 11. Composts with a lower C:N ratio than 11 would release N at about double that rate, on average. 6 True. Standard soil lab tests only tell you what is either plant available, (that is, in solution), or in an "exchangeable" state (that is, easily released into solution). Many nutrients are more permanently tied up in organic molecules or in minerals. An active soil food web can release these nutrients over time. 7 False. Up to a point, the opposite is true. As carbon levels rise in soil, the soil food web increases in number and diversity. Since it is the food web that creates the ideal conditions for carbon to be sequestered, higher populations of microbes usually results in greater sequestration. However, that does not mean that this increased ability to absorb carbon will last forever. There is some evidence that it gets harder to sequester carbon after the level in soil reaches 4 per cent. In addition, at some point a soil will reach an equilibrium point, where C is respired as fast as it is sequestered, and no further increase in C will occur. This level will be different for differnt soil types, with clay soils having the highest capacity to sequester carbon, and sandy soils the lowest capacity. However, most agricultural soils worldwide have lost so much carbon since the introduction of the plough, some 10,000 years ago, that they could gain carbon at a substantial rate for many decades before reaching their equilibrium point.Rate this question:
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