Classics
The following article has been selected because it is deemed very important to the arboricultural profession and deserves special recognition. It has appeared in a previous Seminar and because of this it is not eligible for earning certification credits; there is no test at the end of this article.
Compost Improves Soil Structure
Edited by Len Phillips
Prehistoric farmers discovered that if they mixed manure with other organic waste, the mixture would change into a fertile soil-like material excellent for growing crops. Arborist's can benefit from using this age-old technique, today.
Uses of Compost
In today's cities, autumn leaves are a major concern and their collection is a big budget item. Many cities that have suitable space and means, have adopted a program to compost autumn leaves to create leaf mold compost that is an excellent amendment to soil as well as being a product that can be sold to local nurseries, landscape companies, and home gardeners.
Compost is the best amendment to any existing soil for optimizing tree growth. In certain situations, such as growing small or short-lived trees in a container or the tree pit in a sidewalk, there is a need to amend the planting pit soil. When compost is applied as a soil amendment, it should be evenly and deeply mixed into the soil. The final amended soil should contain at least 20% to as much as 40% leaf mold compost. Compost amendment is not recommended for sites where the tree roots are expected to venture out into poorer quality urban and the tree is expected to live for many years.
Benefits of Compost
Compost improves low-quality soil by adding:
Organic Matter Content
High-quality organic soil amendments usually contain at least 20% – 40% organic matter. Concentrations of organic matter as low as 25% are often adequate for mulches. Soil typically makes up the remainder of the compost dry matter. A moderate amount of inorganic content is desirable as foundation material for compost blankets, filter berms and similar installations.
Particle Size Distribution
Particle size is determined by passing the compost through a set of sieves and determining respective weight fractions retained on each sieve size. Different distributions serve different purposes. For example, at least 90% of a compost to be used as a turf or landscape soil amendment should pass through a 5/8-inch screen. Conversely, composts with larger particle sizes serve as excellent mulches.
Compost Regulations
The U.S. Composting Council (USCC) has developed a complete nationwide compost testing system. Composts that have been tested using the approved methods can be purchased and used with confidence. Nonetheless, some characteristics of acceptable quality compost can be evaluated with little or no special equipment. Arborists should obtain compost from a reputable source that guarantees high quality and provides comprehensive data on the product's origin, processing, and characteristics. Due to the diverse nature of compost material, composting processes, and maturation standards, compost quality can vary significantly. Following the composting council's guidelines helps make certain that the appropriate compost for your specific need is chosen.
Making Compost
The following items are the required components for making good quality compost:
Temperature – is a key indicator to gauge how far along the decomposition has progressed. The optimum temperature is 140°F (60°C). This is not difficult to obtain in summer but composting over-winter requires special insulation with hay or uncomposted leaves, which will also protect the compost from winter rains. This generally takes at least one month to achieve and will occur more quickly when the compost product is chipped to one inch or less and the pile is small. Larger piles take longer to complete the process and should be turned in approximately 30 days. When the internal temperature of the compost has cooled to 100°F (38°C), the compost is ready to be turned. Turning requires that the outside edges of the pile, which have not experienced much decomposition, are moved into the center of the pile and the center of the pile can be moved to the outside. When all the compost in the pile has stabilized at 100°F (38°C), it should be sent to the curing pile. Make sure to use a temperature probe that reaches at least one yard or one meter deep into the compost pile. Leave the probe in place long enough for the reading to stabilize and then turn it or move it to a new location. Take readings in several locations, including at various depths from the top and sides. Although long thermometers are available, it is often more practical to use a conventional thermometer tied to a string and slipped down a small pipe pushed into the center of the pile. Compost may have hot and cold pockets depending on the moisture content and chemical composition of ingredients.
Cured – When the internal temperature of the entire compost pile has cooled to 100°F (38°C), the compost action is finished. Cured compost is stable, well decomposed, consumes little oxygen, and generates little carbon dioxide or heat. Unstable compost heats up significantly if wet and stirred, and should not be used.
Carbon-to-nitrogen (C:N) ratio – Nitrogen release rates from composts are difficult to predict with accuracy, but the C:N ratio is a good starting place. At high C:N ratios (approximately 30:1 or greater) nitrogen may be temporarily immobilized by microbes needed during the decomposition process. Because this deprives plants of needed nitrogen, additional fertilizer is required. Products with C:N ratios below 15:1 are likely to supply at least some soil nitrogen. However, once the composting action is completed and the compost is cured, immobilized nitrogen is ready to be released in plant-available forms.
Contaminants – Compost materials used for landscape applications should be free of measurable levels of inert contaminants, such as glass, metal, and plastic. Contaminants should make up less than one percent by weight of the final product, and should not be detectible to the naked eye.
Moisture Content – Compost should have a moisture level that ranges between 40 – 55% of full saturation. Rainfall is generally sufficient, but a sprinkler may be necessary to supplement natural rainfall and maintain the moisture content at a wet but not dripping condition. Compost that is too dry is dusty, while compost that is too wet is heavy, and in both cases it can be hard to apply evenly.
Nutrient Content – Composts are not normally considered fertilizers because their nutrient content is often lower than conventional fertilizer and is highly dependent on the type of compost, as well as its rate of the nutrient release. Because nutrient concentrations and moisture content varies, nutrient contents cannot be guaranteed with the same precision as fertilizers. Compost derived from manures or bio-solids often have higher levels of nitrogen and other nutrients than compost derived from leaves.
pH – measures the soil's acidity or alkalinity. As the composting action proceeds, the pH value fluctuates from acidic in the beginning to neutral at completion, regardless of the product being composted. When compost is used as a soil amendment, it is generally desirable to have the final soil and compost mixture fall between a pH of 6.5 and 7.5.
Phytotoxicity – describes a compound's degree of toxicity on plant growth. Mature plants are less likely to succumb to phytotoxicity than younger ones. The threat of phytotoxicity is also reduced when compost is allowed to cure in the soil or a stock pile for several weeks before using.
Soluble salts (salinity) – Many plants are intolerant of high-soluble salts. The salinity of a soil is measured by Ece (Electrical Conductivity of a saturated soil Extract). After it is amended it should be less than 2.5 dS/m (deciSiemens per meter). It is important to note that most plants prefer a soil Ece of less than 1.0 dS/m. If a compost's Ece value is measured higher than 1.0 dS/m by a soil test, the ultimate level can be reduced through leaching (a slow, deep application of water to move excess salts down through the soil to beneath the root zone).
Trace elements (micro-nutrients) – The presence of trace elements in compost is directly attributable to the compost's origin. Many trace elements, such as copper, zinc, manganese, iron, boron, molybdenum and chlorine are micro-nutrients required by plants for normal growth. However, many other trace elements (particularly heavy metals) often raise concerns when found in high concentrations. Commercial compost producers routinely test for heavy metals as part of their quality-control process, and reputable compost producers will provide this data.
Weeds and disease organisms – Proper composting destroys insects and disease-causing organisms, as well as most weed seeds. Most pathogens and weed seeds are killed when the compost temperature reaches 140°F (60°C).
When the compost process is completed, the compost may be screened to remove any contaminates or uncomposted product. The material is then piled in a curing pile until needed in the landscape. Curing allows the compost to stabilize so nutrients are released when applied to the landscape instead of being consumed by bacteria and continued decomposition.
Sources
The following article has been selected because it is deemed very important to the arboricultural profession and deserves special recognition. It has appeared in a previous Seminar and because of this it is not eligible for earning certification credits; there is no test at the end of this article.
Compost Improves Soil Structure
Edited by Len Phillips
Prehistoric farmers discovered that if they mixed manure with other organic waste, the mixture would change into a fertile soil-like material excellent for growing crops. Arborist's can benefit from using this age-old technique, today.
Uses of Compost
In today's cities, autumn leaves are a major concern and their collection is a big budget item. Many cities that have suitable space and means, have adopted a program to compost autumn leaves to create leaf mold compost that is an excellent amendment to soil as well as being a product that can be sold to local nurseries, landscape companies, and home gardeners.
Compost is the best amendment to any existing soil for optimizing tree growth. In certain situations, such as growing small or short-lived trees in a container or the tree pit in a sidewalk, there is a need to amend the planting pit soil. When compost is applied as a soil amendment, it should be evenly and deeply mixed into the soil. The final amended soil should contain at least 20% to as much as 40% leaf mold compost. Compost amendment is not recommended for sites where the tree roots are expected to venture out into poorer quality urban and the tree is expected to live for many years.
Benefits of Compost
Compost improves low-quality soil by adding:
- stable organic matter,
- beneficial soil microbes that out-compete soil diseases for nutrients,
- water-holding capacity,
- nutrient-holding capacity.
- a soil amendment,
- a turf top-dressing,
- a mulch,
- an erosion-control agent,
- a water-quality enhancer.
- promoting plant establishment,
- improving moisture retention,
- improving structure,
- improving infiltration and drainage capacity.
Organic Matter Content
High-quality organic soil amendments usually contain at least 20% – 40% organic matter. Concentrations of organic matter as low as 25% are often adequate for mulches. Soil typically makes up the remainder of the compost dry matter. A moderate amount of inorganic content is desirable as foundation material for compost blankets, filter berms and similar installations.
Particle Size Distribution
Particle size is determined by passing the compost through a set of sieves and determining respective weight fractions retained on each sieve size. Different distributions serve different purposes. For example, at least 90% of a compost to be used as a turf or landscape soil amendment should pass through a 5/8-inch screen. Conversely, composts with larger particle sizes serve as excellent mulches.
Compost Regulations
The U.S. Composting Council (USCC) has developed a complete nationwide compost testing system. Composts that have been tested using the approved methods can be purchased and used with confidence. Nonetheless, some characteristics of acceptable quality compost can be evaluated with little or no special equipment. Arborists should obtain compost from a reputable source that guarantees high quality and provides comprehensive data on the product's origin, processing, and characteristics. Due to the diverse nature of compost material, composting processes, and maturation standards, compost quality can vary significantly. Following the composting council's guidelines helps make certain that the appropriate compost for your specific need is chosen.
Making Compost
The following items are the required components for making good quality compost:
Temperature – is a key indicator to gauge how far along the decomposition has progressed. The optimum temperature is 140°F (60°C). This is not difficult to obtain in summer but composting over-winter requires special insulation with hay or uncomposted leaves, which will also protect the compost from winter rains. This generally takes at least one month to achieve and will occur more quickly when the compost product is chipped to one inch or less and the pile is small. Larger piles take longer to complete the process and should be turned in approximately 30 days. When the internal temperature of the compost has cooled to 100°F (38°C), the compost is ready to be turned. Turning requires that the outside edges of the pile, which have not experienced much decomposition, are moved into the center of the pile and the center of the pile can be moved to the outside. When all the compost in the pile has stabilized at 100°F (38°C), it should be sent to the curing pile. Make sure to use a temperature probe that reaches at least one yard or one meter deep into the compost pile. Leave the probe in place long enough for the reading to stabilize and then turn it or move it to a new location. Take readings in several locations, including at various depths from the top and sides. Although long thermometers are available, it is often more practical to use a conventional thermometer tied to a string and slipped down a small pipe pushed into the center of the pile. Compost may have hot and cold pockets depending on the moisture content and chemical composition of ingredients.
Cured – When the internal temperature of the entire compost pile has cooled to 100°F (38°C), the compost action is finished. Cured compost is stable, well decomposed, consumes little oxygen, and generates little carbon dioxide or heat. Unstable compost heats up significantly if wet and stirred, and should not be used.
Carbon-to-nitrogen (C:N) ratio – Nitrogen release rates from composts are difficult to predict with accuracy, but the C:N ratio is a good starting place. At high C:N ratios (approximately 30:1 or greater) nitrogen may be temporarily immobilized by microbes needed during the decomposition process. Because this deprives plants of needed nitrogen, additional fertilizer is required. Products with C:N ratios below 15:1 are likely to supply at least some soil nitrogen. However, once the composting action is completed and the compost is cured, immobilized nitrogen is ready to be released in plant-available forms.
Contaminants – Compost materials used for landscape applications should be free of measurable levels of inert contaminants, such as glass, metal, and plastic. Contaminants should make up less than one percent by weight of the final product, and should not be detectible to the naked eye.
Moisture Content – Compost should have a moisture level that ranges between 40 – 55% of full saturation. Rainfall is generally sufficient, but a sprinkler may be necessary to supplement natural rainfall and maintain the moisture content at a wet but not dripping condition. Compost that is too dry is dusty, while compost that is too wet is heavy, and in both cases it can be hard to apply evenly.
Nutrient Content – Composts are not normally considered fertilizers because their nutrient content is often lower than conventional fertilizer and is highly dependent on the type of compost, as well as its rate of the nutrient release. Because nutrient concentrations and moisture content varies, nutrient contents cannot be guaranteed with the same precision as fertilizers. Compost derived from manures or bio-solids often have higher levels of nitrogen and other nutrients than compost derived from leaves.
pH – measures the soil's acidity or alkalinity. As the composting action proceeds, the pH value fluctuates from acidic in the beginning to neutral at completion, regardless of the product being composted. When compost is used as a soil amendment, it is generally desirable to have the final soil and compost mixture fall between a pH of 6.5 and 7.5.
Phytotoxicity – describes a compound's degree of toxicity on plant growth. Mature plants are less likely to succumb to phytotoxicity than younger ones. The threat of phytotoxicity is also reduced when compost is allowed to cure in the soil or a stock pile for several weeks before using.
Soluble salts (salinity) – Many plants are intolerant of high-soluble salts. The salinity of a soil is measured by Ece (Electrical Conductivity of a saturated soil Extract). After it is amended it should be less than 2.5 dS/m (deciSiemens per meter). It is important to note that most plants prefer a soil Ece of less than 1.0 dS/m. If a compost's Ece value is measured higher than 1.0 dS/m by a soil test, the ultimate level can be reduced through leaching (a slow, deep application of water to move excess salts down through the soil to beneath the root zone).
Trace elements (micro-nutrients) – The presence of trace elements in compost is directly attributable to the compost's origin. Many trace elements, such as copper, zinc, manganese, iron, boron, molybdenum and chlorine are micro-nutrients required by plants for normal growth. However, many other trace elements (particularly heavy metals) often raise concerns when found in high concentrations. Commercial compost producers routinely test for heavy metals as part of their quality-control process, and reputable compost producers will provide this data.
Weeds and disease organisms – Proper composting destroys insects and disease-causing organisms, as well as most weed seeds. Most pathogens and weed seeds are killed when the compost temperature reaches 140°F (60°C).
When the compost process is completed, the compost may be screened to remove any contaminates or uncomposted product. The material is then piled in a curing pile until needed in the landscape. Curing allows the compost to stabilize so nutrients are released when applied to the landscape instead of being consumed by bacteria and continued decomposition.
Sources
- Martin, Janet, "Compost Improves Soil Structure and Plant Growth", LCN, July 2010.
- Phillips, Leonard, "Composting", Online Seminars Archive #29, November/December 2009.