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University of Kentucky College of , AGR-204 and Environment Cooperative Extension Service and Fertility Kentucky Master Gardener Manual Chapter 4

By Craig Cogger, extenstion scientist, Washington State University. Adapted for Kentucky by Edwin Ritchey, extension soils specialist, and Brad Lee, extension quality specialist, University of Kentucky.

oil is a mixture of weathered rock fragments () and In this chapter: organic matter at the ’s surface. It is biologically active—a home to countless , invertebrates, and Soil and Water...... 51 Sroots. It varies in depth from a few inches to 5 feet or more. Soil Organisms...... 55 is roughly 50% pore space (50% voids between soil particles). This space forms a complex network of pores of varying sizes, much Nutrients ...... 57 like those in a sponge. Soil provides nutrients, water, and physical Understanding ...... 60 support for as well as air for plant roots. Soil organisms are How Much to Use...... 65 nature’s primary recyclers, turning dead cells and tissue into nutri- ents, , carbon dioxide, and water to fuel new . Cooperative Extension Publications...... 66 Estimating Rates ...... 66 Soil and Water When to Fertilize...... 67 A productive soil is permeable to water and is able to supply Adding Organic Matter...... 68 water to plants. A soil’s permeability and water-holding capacity Soil pH...... 70 depend on its network of two types of pores: Soils and Fertilizer Terminology...... 72 • Large pores (macropores) control a soil’s permeability and aera- tion. Macropores include and root channels. Because For More Information...... 74 they are large, water moves through them rapidly by gravity so that rainfall and infiltrate into the soil, and excess water drains through it. • Micropores are fine soil pores, typically a fraction of a millime- ter in diameter. They are responsible for a soil’s water-holding capacity. Like the fine pores in a sponge or towel, micropores hold water against the force of gravity. Much of the water held in micropores is available to plants, but some is held so tightly that plant roots cannot use it.

Soil that has a balance of macropores and micropores provides adequate permeability and water-holding capacity for good plant growth. Soils that contain mostly macropores drain readily but are droughty and need more frequent irrigation. Soils that contain mostly micropores have good water-holding capacity but take longer to dry out and warm up in the spring. Runoff of rainfall and irrigation water also is more likely on micropore-dominant soils. , structure, organic matter, and activity affect porosity. You can evaluate your garden soil in terms of these proper- ties to understand their impact. The only tools you need are your eyes, fingers, and a shovel.

Cooperative Extension Service | Agriculture and Natural | Family and Consumer Sciences | 4-H Youth Development | Community and Economic Development 52 • Soils and Fertility Chapter 4

Texture Particle size also affects the surface area in soil. Surface area is important because Texture describes the relative abundance surfaces are the most active part of the soil. of sand, silt, and clay-sized materials. The Surfaces hold plant nutrients, bind contam- coarsest soil particles are sand. They are inants, and provide a home for microorgan- visible to the eye and give soil a gritty feel. isms. Clay particles have a large surface area Silt particles are smaller than sand—about relative to their volume, so a small amount the size of individual particles of white flour. of clay makes a large contribution to a soil’s They give soil a smooth, floury feel. On surface area. close inspection, sand and silt particles look Nearly all soils have a mixture of particle like miniature rocks (Figure 1). sizes and a both types of pore sizes (Figure Clay particles are the smallest—about 2). A soil with roughly equal influence from the size of bacteria and viruses—and can be sand, silt, and clay particles is called a loam. seen only with a microscope. They typically Loams usually make good agricultural and have a flat shape, similar to a sheet of mica. garden soils. They have a balance of mac- Soils high in clay feel very hard when dry ropores and micropores, so they usually but are easily shaped and molded when have both good water-holding capacity and moist. moderate permeability. A sandy loam is similar to a loam, but it Figure 1. Shapes of soil particles. contains more sand. It feels gritty, yet has enough silt and clay to hold together in your hand. Sandy loams usually have low to moderate water-holding capacity and good silt permeability. (0.002 - 0.05 mm dia.) Silt loams are richer in silt and feel smooth rather than gritty. They are pliable when moist but not very sticky. Silt loams usually have high water-holding capacity sand clay and low to moderate permeability. (0.05 - 2 mm dia.) (<0.002 mm dia.) Clays and clay loams are very hard when dry, sticky when wet, and can be molded into wires and ribbons when moist. They Although all of these particles seem generally have high water-holding capacity small, the relative difference in their sizes is and low permeability. quite large. If a typical clay particle were the Almost any texture of soil can be suitable size of a penny, a sand particle would be as for gardening as long as you are aware of the large as a house. soil’s limitations and adjust your manage- Soil texture directly affects porosity. ment to compensate. Clay soils hold a lot of Pores between sand particles tend to be water but are hard to dig and dry slowly in large, while those between silt and clay the spring. Sandy soils need more frequent particles tend to be small. That means sandy watering and lighter, more frequent fertil- soils contain mostly macropores and usually ization, but you can plant them earlier in have rapid permeability but limited water- the spring. All soils can benefit from addi- holding capacity. In soils containing mostly tions of organic matter, as described later in silt and clay, micropores predominate, this chapter under “Adding Organic Matter.” creating high water-holding capacity but reducing permeability. Chapter 4 Soils and Fertility • 53

Many soils contain coarse fragments— Aggregation is a natural process caused gravel and rocks. Coarse fragments do not largely by biological activity such as contribute to a soil’s productivity and can be earthworm burrowing, root growth, and a nuisance when you are digging. Don’t feel microbial action. is an compelled to remove all of them from your important binding agent that stabilizes and garden, however. Coarse fragments aren’t strengthens peds. harmful, and your time is better spent on The spaces between peds are a soil’s other gardening tasks. The only time rocks macropores, which improve permeability, are a problem is when you have nothing , and recharging of air into the soil but rocks on your . Then, water- and profile. The pores within peds are predomi- nutrient-holding capacities are so low that it nantly micropores, contributing to the soil’s is difficult to grow healthy plants. water-holding capacity. A well-structured soil is like a sponge, allowing water to enter Structure and soak into the micropores and let- ting excess water drain down through the Individual particles of sand, silt, and clay macropores. Good structure is especially tend to cluster and bind together, form- important in medium- to fine-textured soils ing aggregates called peds, which provide (soils with appreciable amounts of clay), structure to a soil. Dig up a piece of grass because it increases the soil’s macroporosity, sod and examine the soil around the roots. improving permeability and drainage. The granules of soil clinging to the roots are examples of peds. They contain sand, silt, clay, and organic matter. Human Activity is fragile and can be dam- aged or destroyed by compaction, excessive Figure 2. Percentages of clay, 100 tillage, or tilling when the soil is too wet. silt, and sand in the basic soil Loss of organic matter, typically a result of textural classes. 90 10 tillage, also weakens structure. Compaction squeezes macropores into 80 20 micropores and creates horizontal aggre- gates that resist root penetration and water movement (Figure 3). Compaction often 70 30 occurs during site preparation or house clay construction, creating a difficult environ- 60 40 ment for establishing plants. Protect your

SILT % soil from compaction by avoiding unneces- 50 50 silty sary foot or machine traffic. CLAY % clay Tilling when soil is too wet also damages 40 sandy 60 soil structure. If you can mold a piece of soil clay into a wire or worm in your hand, it is too clay silty clay loam 30 loam 70 wet to till. If the soil crumbles when you try sandy clay to mold it, it is dry enough to till. loam 20 loam 80 sandy loam silt loam 10 loamy sand 90 silt sand 100 100 90 80 70 60 50 40 30 20 10

SAND % 54 • Soils and Fertility Chapter 4

Increasing soil organic matter is the best way to improve the plant environment in nearly all soils, because it helps build and stabilize soil structure in fine-textured and compacted soils, improving permeability and aeration and reducing the risk of runoff and erosion. In addition, when organic material decomposes, it forms , which acts as a natural glue to bind and strengthen soil aggregates. Organic mat- ter also helps soils, particularly sandy soils, hold water and nutrients and is a reservoir of energy for soil microbes. See “Adding Organic Matter” later in this chapter for more information. Figure 3. Compacted soil resists root penetration and water movement. tire track Water Management in Your Garden Slope, aspect, and soil depth compaction layer Slope, aspect (direction of exposure), and soil depth affect availability of water and its use in a soil. Choose plants that are best suited to your property’s conditions. Structural damage caused by human Ridgetops and side slopes tend to shed activity usually is most severe within the top water, while soils at the bottoms of slopes foot of soil and can be overcome by proper and in low areas collect it (Figure 4). Soils . that collect water often have high winter water tables, which can affect the health of Organic Materials, Organic some plants. Soils on ridgetops are more Matter, and Humus likely to be droughty. Site aspect also is important. Exposures Organic materials (called organic resi- facing south or southwest collect the most dues), such as plant and animal residues of heat and use the most water. recognizable origin, are the building blocks Soil depth also affects water availability of organic matter, or humus. Soil organic by determining the rooting zone. Soil depth matter and humus (terms often used syn- is limited by compacted, cemented, or onymously) contain decomposed plant and gravelly layers or by bedrock. A shallow soil animals remains of unrecognizable origin, has less available water simply because the their partial decomposition products, and volume of soil available to roots is smaller. the wastes from soil . Dig below the in your garden. The deeper you can dig before hitting a restric- tive layer, the greater the soil volume for Figure 4. Ridgetops ridgetop holding water. and slopes tend to shed water, while soils at the bottom of slopes and in slope low areas collect water.

bottomland Chapter 4 Soils and Fertility • 55

See the Cooperative Extension pub- Sometimes, simple practices can reduce lication Improving the Productivity of problems with wet soil, including the with Little or No Topsoil following: (AGR-203) for more information. • Divert runoff from roof drains away from your garden. Irrigation • Avoid plants that perform poorly in wet Most gardens in Kentucky require conditions. summer irrigation. The need for irrigation • Use raised beds for perennials that varies, depending on -holding require well-drained soil and for early- capacity, weather, site aspect, the plants season vegetables. grown, and the plants’ growth stage. • Investigate whether a drain on a slope In most cases, the goal of irrigation is to will remove excess water on your prop- recharge the available water in the top foot erty. Installing drainage can be expensive, or so of soil. For sandy soil, 1 inch of irriga- however. When considering drainage, tion water is all you need. Any more will make sure there is a place to drain the leach (move downward) through the root water. Check with local regulatory agen- zone, carrying nutrients with it. A silt loam cies about any restrictions on the project. or clay soil can hold more than 2 inches of water, but you may need to irrigate more slowly to prevent runoff. Organisms Wet soils Soil abounds with life. Besides the plant roots, , insects, and other crea- If your soil stays wet in the spring, you tures you can see, soil is home to an abun- will have to delay tilling and planting. dant and diverse population of microorgan- Working wet soil can damage its structure, isms. Soils with more organic matter tend to and seeds are less likely to germinate in have more organisms. cold, wet soil. The more microorganisms the better. Some plants don’t grow well in wet soil. The important thing is to make the environ- Raspberries, for example, often become ment favorable for activity, infected by root diseases in wet soil and lose which includes well aerated soils, warm, vigor and productivity. moist, near-neutral pH and good levels of A soil’s color gives clues to its tendency organic matter. Other factors must also be to stay wet. If a subsoil is brown or reddish, considered; for example, if trying to grow the soil probably is well drained and is rarely blueberries, which like more acidic condi- too wet. Gray subsoils, especially those tions, this constraint for plant growth would with brightly colored mottles, often are be more important than a near-neutral pH wet. If your soil is gray and mottled directly for microbial growth. You must first satisfy beneath the topsoil, it will be saturated in the needs of the plant. some part of the year. A single gram of topsoil (about 1⁄4 teaspoon) can contain as many as a billion microorganisms (Table 1). Microorganisms Table 1. Approximate abundance of are most abundant in the rhizosphere—the microorganisms in agricultural topsoil. thin layer of soil surrounding plant roots. Number/gram The main function of soil organisms is to Organism (dry-weight basis) break down the remains of plants and other Bacteria 100 million to 1 billion organisms. This process releases energy, Actinomycetes 10 million to 100 million nutrients, and carbon dioxide and creates Fungi 100,000 to 1 million soil organic matter. Algae 10,000 to 100,000 Protozoa 10,000 to 100,000 Nematodes 10 to 100 56 • Soils and Fertility Chapter 4

macropredators mesopredators

micropredators

detrivores microbial feeders fungivores herbivores

dead plants bacteria fungi plant roots

Figure 5. The .

Organisms ranging from tiny bacteria Figure 6. Earthworm channels create macro- to insects and earthworms take part in a pores, which improve a soil’s permeability and aeration. complex soil food web (Figure 5). Mammals such as moles and voles also are part of the food web, feeding on insects and earthworms and mixing organic matter throughout the soil profile. This mixing also improves soil structure. Some soil organisms play other benefi- cial roles. Mycorrhizae are fungi that infect plant roots and increase their ability to take up nutrients from the soil. Rhizobia bacteria are responsible for converting atmospheric nitrogen to plant-available forms, a process known as nitrogen fixation. Earthworms mix large volumes of soil and create mac- ropore channels that improve permeability and aeration (Figure 6). “” is often judged by the numbers of earthworms in the soil—the more earthworms, the better. Chapter 4 Soils and Fertility • 57

Not all soil organisms are beneficial. of molybdenum, which is involved in the Some are pathogens, which cause diseases functioning of only a few plant enzymes. such as root rot of raspberries and scab Molybdenum nonetheless is essential, and on potatoes. Moles can damage crops and plant growth is disrupted if it is deficient. lawns, and slugs are a serious pest in many Plants also require carbon, hydrogen, and Kentucky gardens. oxygen, which they derive from water and The activity of soil organisms depends air. on and temperature as well A soil nutrient is classified as a primary as on the soil’s organic matter content. nutrient (macronutrient), secondary nutri- Microorganisms are most active between ent, or micronutrient, based on the amount 70° and 100°F, while earthworms are most of the nutrient needed by plants (Table 2). If active and abundant at about 50°F. Most a soil’s nutrient supply is deficient, fertilizers organisms prefer moist soil. The rela- can provide the additional nutrients needed tionships between gardening practices, for healthy plant growth. microbial populations, and are complex and often poorly understood. Deficiencies Almost all gardening activities—including tillage; the use of fertilizers, , and The most common nutrient deficien- pesticides; and the choice of crop rota- cies are for the primary nutrients—nitro- tions—affect the population and diversity gen (N) , phosphorus (P), and potassium of soil organisms. For example, amending (K)—which are in largest demand by plants. soils with organic matter, returning crop Nearly all soils lack enough available N for residues to the soil, and rotating plantings ideal plant growth. tend to increase the number and diversity Secondary nutrients also are deficient of beneficial organisms. in some Kentucky soils, but not very often. The secondary nutrients are calcium (Ca), magnesium (Mg), and sulfur (S). Nutrients Micronutrient deficiencies do occur in Kentucky, but to a limited extent. Soil supplies 13 essential plant nutrients. Except for boron and zinc, micronutri- Each nutrient plays one or more specific ents are rarely deficient. Boron deficiencies roles in plants. Nitrogen, for example, is a occur most often in root crops, brassica component of chlorophyll, amino acids, crops (e.g., broccoli), and caneberries (e.g., proteins, DNA, and many plant hormones. raspberries). Zinc deficiency usually is asso- It plays a vital role in nearly all aspects of ciated with high P levels and high pH soils plant growth and development, and plants and most often affects tree fruits and corn. need a lot of nitrogen to grow well. In Each nutrient deficiency causes char- contrast, plants need only a tiny amount acteristic symptoms. In addition, deficient plants grow more slowly, yield less, and Table 2. Essential plant nutrients. are less healthy than plants with adequate nutrient levels. Primary nutrients Micronutrients Because most soil in the Central and (macronutrients) Secondary nutrients (trace nutrients) Outer Bluegrass region of Kentucky have Chemical Chemical Chemical been formed from limestone that is natu- Name symbol Name symbol Name symbol rally high in phosphorous, plant-available Nitrogen N Sulfur S Zinc Zn phosphorus is very high (exceeding 200 Phosphorus P Calcium Ca Iron Fe lb/acre), and these fields may never need Potassium K Magnesium Mg Copper Cu phosphorus fertilization. Adding fertilizer Manganese Mn phosphorus in this region simply increases Boron B the chances for eutrophication (algal Molybdenum Mo Chlorine Cl 58 • Soils and Fertility Chapter 4

blooms which may cause fish kills) and can Nutrient release from soil organic diminish the uptake of other essential plant matter is fastest in warm, moist soil and nutrients like zinc. Since fertilizer analysis is nearly nonexistent in cold or dry soil. Thus, given in percent of N, P205, and K20, make the seasonal pattern of nutrient release is certain that the center number in a fertilizer similar to the pattern of nutrient uptake by product is 0 (example 23-0-30) when soils plants. About 1 to 4% of the nutrients in soil are already high in phosphorus . organic matter are released in soluble form Long-term use of complete fertilizers or each year. animal manures can also increase P concen- Soluble, available nutrients are in ionic trations to levels so that no additional P is form, meaning they have either positive or required, which is another reason to negative charges. Positively charged ions when applying nutrients—so you will know are cations, of which potassium, calcium, what nutrients are needed and the correct and magnesium are examples. Negatively amount to add. charged ions are anions. Chlorine is an example of an anion. Excess Nutrients Clay particles and soil organic matter have negative charges on their surfaces Excess nutrients can be a problem for and can attract cations. They hold nutrient plants and the environment. Excesses usu- cations in ready reserve for rapid release ally occur because too much of a nutrient is into soil solution to replace nutrients taken applied or it is applied at the wrong time. up by plant roots. This reserve supply of Too much boron is toxic to plants. Too nutrients contributes to a soil’s fertility. A much nitrogen can lead to excessive foliage soil’s capacity to hold cations is called its production, increasing the risk of disease; cation exchange capacity, or CEC. wind damage; and delayed flowering, fruit- ing, and dormancy. Available nitrogen left in the soil at the end of the growing season The Nitrogen Cycle can leach into and threaten Managing nitrogen is a key part of drinking . growing a productive and environmentally The key to applying fertilizers is to meet friendly garden. Nitrogen is the nutrient plant needs without creating excesses that needed in the largest amount by plants, can harm plants or the environment. but excess nitrogen can harm plants and degrade water quality. Understanding how Nutrient Availability to Plants the nitrogen cycle affects nitrogen availabil- ity can help you become a better nutrient Plants can take up only nutrients that are manager (Figure 7). in solution (dissolved in soil water). Most Nitrogen is found in four different soil nutrients are not in solution but instead forms in the soil (Table 3). Only two of are tied up in soil and organic them, ammonium and nitrate, can be used matter in insoluble forms. These nutrients directly by plants. become available to plants only after they Most nitrogen in soil is tied up in organic are converted to soluble forms and dissolve matter and plant, animal, and microbial in the soil solution. biomass. This organic nitrogen is not avail- This process occurs through weathering able to plants. As soil warms in the spring, of mineral matter and biological decom- soil microbes begin breaking down organic position of organic matter. Weathering of matter, releasing some of the nitrogen as mineral matter is a very slow process that ammonium (NH4+). Any nitrogen source releases small amounts of nutrients each that contains ammonium or has an ammo- year. The rate of nutrient release from soil nium intermediary is acid forming. Urea organic matter is somewhat faster and (NH2)2CO will form NH4+ when applied depends on the amount of biological activ- to the soil. When the soil is warm, a group ity in the soil. of microbes called nitrifiers convert the Chapter 4 Soils and Fertility • 59

Figure 7. Nitrogen cycle: a. Legumes, soil organic mat- Organic additions ter, crop residues, and organic (, , etc.) additions (manures, , etc.) are sources of organic N. (a) b. Organic N is mineralized into ammonium (NH4+) by soil microbes. N- xation (a) soil (a) c. Commercial fertilizer sup- (legumes) organic Crop residues plies N as ammonium or nitrate nitrogen (NO3-). d. Microbes nitrify ammonium to nitrite and then nitrate. mineralization e. Plants, microorganisms, (microbes) below the root zone, and release of gaseous N to the (b) atmosphere remove N from the root zone soil solution. + NH4 f. Crop removes N (ammonium) (g) stored in plants. g. Nitrogen present in both (c) crop residues and soil microor- nitri cation (e) ganisms becomes a part of the (microbes) soil organic N content. (d) (Note: An alternate schematic - of the nitrogen cycle is illus- Commercial NO2 trated in Chapter 11, Your Yard fertilizer (nitrite) Plants and soil and Water Quality.) microorganisms

(f) (c) - (e) NO3 (nitrate) Harvest removal (e) (e) Gaseous leaching nitrogen loss

- ammonium to nitrate (NO3 ). When the retained by the soil due to its positive - nitrifiers convert the NH4+ to NO3 , they charge, is a soluble ion that is available to release H+ (acidity), which will lower soil plants and soil microbes. Nitrate is also pH. On the other hand, nitrate forms soluble and available to plants. The ammo- (NO3-) are not acid forming. Ammonium, nium and nitrate ions released from soil organic matter are the same as the ammo- Table 3. Common forms of nitrogen in soil. nium and nitrate contained in processed fertilizers. Form of nitrogen Characteristics Because nitrate has a negative charge, it Organic N Primary form of N in soil. Found in proteins, lignin, is not held to the surface of clay or organic amino acids, humus, etc. Not available to plants. Mineralized to ammonium by soil microorganisms. matter, so it can be lost readily by leaching. Nitrate remaining in the soil at the end of Ammonium N (NH4+) Inorganic, soluble form. Available to plants. Converted to nitrate by soil microorganisms. the growing season will leach during the Nitrate (NO3-) Inorganic, soluble form. Available to plants. Can be fall and winter and may reach ground- lost by leaching. Converted to gases in wet soils. water, where it becomes a contaminant. Atmospheric N (N2) Makes up about 80% of the soil atmosphere. In soils that are saturated during the wet Source of N for N-fixing plants. Not available to other plants. season, soil microbes convert nitrate to nitrogen gases, which diffuse back into the Note: Any nitrogen source that contains ammonium or has an ammonium intermedi- ary is acid forming atmosphere. 60 • Soils and Fertility Chapter 4

Ammonium and nitrate taken up by one source of nutrients over another, but plants are converted back to organic forms the nutrients’ behavior in the soil often dif- in plant tissue. When plant residues are fers (Table 4). returned to the soil, they decompose, slowly Processed fertilizers are manufactured releasing nitrogen back into available forms. or refined from natural ingredients to make The nitrogen cycle is a leaky one, with them more concentrated and more avail- losses to leaching and the atmosphere. able to plants. Typically, they are processed Harvesting crops also removes nitrogen. into soluble, ionic forms that are immedi- To maintain an adequate nitrogen supply, ately available to plants. nitrogen must be added back into the sys- Organic fertilizers are natural materials tem through fixation or fertilization. that have undergone little or no process- Nitrogen fixation is a natural process ing. They include both biological (plant and involving certain plants and Rhizobia bacte- animal) materials and mineral materials. ria. The Rhizobia form nodules in the plant Once in the soil, organic fertilizers release roots, and through these nodules they are nutrients through natural processes, includ- able to take atmospheric nitrogen (N2 gas) ing chemical weathering of mineral materials from the soil air and convert it to available and biological breakdown of organic matter. N within the plant. Legumes (plants that The released nutrients are available to plants produce seeds in pods) such as peas, beans, in water-soluble forms. These soluble forms alfalfa, and clover are common nitrogen of nutrients are the same as those supplied by fixers. The Kentucky coffeetree, the honey processed fertilizers. locust, redbuds, and Alder trees also fix When compared with processed fertil- nitrogen. Growing legumes as a izers, organic fertilizers usually have a lower will supply nitrogen to future crops. concentration of nutrients and release nutrients more slowly. That means larger amounts of organic fertilizers are needed, Understanding Fertilizers but their effects last longer. Fertilizers supplement a soil’s native Using organic fertilizers recycles materi- nutrient supply. They are essential to good als that otherwise would be discarded as plant growth when the soil nutrient supply wastes. Production of processed fertilizers, is inadequate. Rapidly growing plants such on the other hand, can create wastes and as annual vegetable crops generally need use substantial amounts of energy. more nutrients than slowly growing plants Choosing organic fertilizers involves such as established perennials. trade-offs in cost or convenience. You can use processed fertilizers, organic Farmyard manure usually is inexpensive fertilizers, or a combination of the two to or free, but can be inconvenient to apply. supply soil nutrients. Plants do not prefer Packaged organic blends, on the other hand, are convenient but often expensive.

Table 4. Comparing organic and processed fertilizers. Organic fertilizers Processed fertilizers Source Natural materials; little or no processing Manufactured or extracted from natural materials; often undergo extensive processing Examples Manure, cottonseed meal, rock Ammonium sulfate, processed urea, phosphate, fish by-products, ground potassium chloride limestone Nutrient availability Usually slow-release; nutrients are Nutrients usually are almost immedi- released by biological and chemical ately available to plants processes in soil Nutrient content Usually low Usually high Chapter 4 Soils and Fertility • 61

Nutrient Release Fertilizer Labels Nutrients in most processed fertilizers The labels on fertilizer packages tell the are available almost immediately. Processed amount of each of the three primary nutri- fertilizers can furnish nutrients to plants in ents in the fertilizer, expressed as a percent the spring before the soil is warm. However, of total fertilizer weight. Nitrogen (N) nitrogen in these fertilizers is vulnerable to always is listed first, phosphorus (P) second, leaching loss from heavy rainfall or irriga- and potassium (K) third. tion. Once nitrogen moves below the root Historically, the amount of phosphorus zone, plants no longer can use it, and it may in fertilizer has been expressed not as P, leach into groundwater. but as units of the oxide form P2O5 (phos- Organic fertilizers are slow-release fertil- phate). Similarly, fertilizer potassium is izers because their nutrients become avail- expressed as K2O (potash). This practice able to plants over the course of the grow- still is used for fertilizer labels and recom- ing season. The rate of nutrient release from mendations, even though there is no practi- organic materials depends on the activity cal reason for the system except that people of soil microorganisms, just as it does for are accustomed to it. (If you need to convert nutrient release from soil organic matter. from P to P2O5, the conversion is: Temperature and moisture conditions that favor plant growth also favor the release of 1 lb P = 2.29 lb P2O5. nutrients from organic matter. Some organic fertilizers contain imme- For potassium, the conversion is: diately available nutrients as well as slow- 1 lb K = 1.2 lb K O. release nutrients. These fertilizers can 2 supply nutrients to plants both early in the season and later. Fresh manure, biosolids, Thus, a bag of fertilizer labeled 5-10-10 and fish emulsion are examples of organic contains 5% nitrogen, 10% phosphorus fertilizers containing available nutrients. expressed as P2O5, and 10% potassium We assume that in manures, 100% of expressed as K2O. This information is called postassium (potash) is available the first a fertilizer analysis. year, 80% of phosphorus, and about 50% of The analysis for processed fertilizers the nitrogen. Remember that nitrogen val- guarantees the amount of available nutri- ues vary depending on the type of manure, ents in the fertilizer. The analysis for organic the environmental conditions during the fertilizers represents the total amount of growing season, and when during the sea- nutrients rather than available nutrients. son the manure was applied. Because nutrients in most organic fertilizers As manure ages, the most readily avail- are released slowly, the amount of immedi- able nutrients are lost into the air or leached ately available nutrients is less than the total. into the soil, leaving slow-release material in the aged manure. Common Processed Fertilizers Some material in organic fertilizers Nitrogen breaks down so slowly that it is not available The raw material for processed nitrogen the first season after application. Repeated fertilizer is nitrogen gas from the atmo- application of organic fertilizers builds up sphere. The manufacturing process is the a pool of material that releases nutrients chemical equivalent of biological nitrogen very slowly. In the long run, this nutrient fixation and requires a substantial amount supply decreases the need for supplemental of energy. Examples of processed fertilizer. nitrogen fertilizers available for home gar- den use include those listed in Table 5. 62 • Soils and Fertility Chapter 4

Phosphorus and potassium Common Organic Fertilizers Processed phosphorus fertilizers come Farmyard manure can be an inexpensive from phosphate rock. The rock is treated source of nutrients. If you or your neighbors with acid to release phosphorus into plant- have livestock, it makes environmental and available forms. economic sense to recycle the manure as The most common raw material for fertilizer. Packaged manure products cost potassium fertilizers is sylvinite, a mixture more than manure off the farm, but they of sodium chloride and potassium chloride usually are more uniform and convenient to salts. The potassium in sylvinite is already in handle. soluble form, but the sylvinite is treated to Animal manures vary widely in nutrient remove the sodium salts to make it suitable content and nutrient availability, depend- for use as a fertilizer. Some other potassium ing on the type of animal that produced the fertilizers are made from potassium sulfate manure and the manure’s age and handling. salts, which supply sulfur as well as potas- For example: sium. Table 6 lists examples of processed • Fresh manure has higher nutrient levels phosphorus and potassium fertilizers. than aged manure. Mixed, or complete, fertilizers • Manure diluted with large amounts of bedding has fewer nutrients than undi- Mixed, or complete, fertilizers contain all luted manure. three primary nutrients. The ratios can vary. • Exposure to leaches nutrients. Fertilizers for annual gardens typically have • Composting under cover retains N:P O :K O ratios in the range of 1:1:1 or 2 5 2 more nutrients but reduces nutrient 1:2:2. Examples include 8-8-8 and 10-20- availability. 20 blends. Fertilizer blends for starting plants usually have a higher proportion of phosphorus. Lawn fertilizers are higher in nitrogen; an example is a 12-4-8 blend.

Table 5. Examples of processed nitrogen fertilizer materials. Material Analysis Comments Urea 46-0-0 Rapidly converted to ammonium in soil. Ammonium sulfate 21-0-0 Also contains 24 % available sulfur. Used with acid-loving plants. Diammonium 18-46-0 Used in mixed fertilizers as a source of nitrogen and phosphate phosphorus. Sulfur-coated urea 35-0-0 Sulfur coating slows release of available N, making this a slow- (SCU) release fertilizer.

Table 6. Examples of processed phosphorus and potassium fertilizer materials. Material Analysis Comments Triple 0-46-0 — superphosphate Monoammonium 11-52-0 Used in mixed fertilizers as a source of nitrogen and phosphate phosphorus. Diammonium 18-46-0 Used in mixed fertilizers as a source of nitrogen and phosphate phosphorus. Potassium chloride 0-0-60 High salt index. Potassium magne- 0-0-22 Also contains 11% magnesium and 18% sulfur. sium sulfate Potassium sulfate 0-0-50 Also contains 18% sulfur. Chapter 4 Soils and Fertility • 63

Table 7 compares average nutrient con- To use manure, simply spread it over the tents of typical manure products. soil and turn it in if you wish. It doesn’t take much fresh manure to fer- The best time to apply manure is in the tilize a garden. One 5-gallon bucket of fresh spring before planting. You also can apply cow manure is enough for about 50 square manure in the fall, but environmental risks feet of garden. The same amount of fresh of leaching and runoff increase in winter. poultry manure covers 100-150 square feet. If you do apply manure in the fall, apply it Larger amounts can harm crops and leach early and plant a cover crop to help capture nitrogen into groundwater. nutrients and prevent runoff. See “Green Fresh manure can carry disease-causing Manure (Cover Crops)” later in this chapter pathogens. Be sure to refer to the informa- for more information. tion on manure safety below before using fresh manure. Using Manure Safely It takes larger amounts of aged, diluted, or leached manure to provide the same Fresh manure sometimes contains amount of nutrients as fresh manure. If disease-causing pathogens that can contam- you’re using it, increase the amount applied inate garden produce. Salmonella bacteria based on how much it is aged, diluted, and/ are among the most serious pathogens or leached. Composted manure solids from found in animal manure. Pathogenic strains dairy farms also have low nutrient avail- of E. coli bacteria also can be present in ability, so you can apply them at higher rates cattle manure. Manure from swine, dogs, than fresh manure. Use these manures as cats, and other carnivores can contain hel- much for the organic matter they supply as minths, which are parasitic worms. for nutrients. You can add as much as 1 to These pathogens are not taken up into 2 inches of manure and still have very low plant tissue, but they can adhere to soil on nutrient availability. plant roots or to the leaves or fruit of low- To fine-tune your application rate, growing crops. The risk is greatest for root experiment with the amount you apply and crops (for example, carrots and radishes) or observe your crops’ performance. It’s better leaf crops (such as lettuce), where the edible to be conservative and add more nutrients part touches the soil. The risk is negligible later if crops seem deficient than to risk for crops such as sweet corn, which do not overfertilizing. contact the soil, or for any crop that is thor- oughly cooked. Avoid using fresh manure where you grow high-risk crops. Table 7. Typical nitrogen, phosphate, and potash content Cooking destroys pathogens, but raw (%) of some manures and tobacco stalks. food carries a risk. Washing and peeling raw produce removes most pathogens, but Animal % nutrients some may remain. 1 2 Manures Water (%) N P2O5 K2O Composting manure at high tempera- Dairy Cattle 80 0.55 0.45 0.60 tures kills pathogens, but it is very hard to Swine 80 0.45 0.45 0.40 maintain rigorous composting conditions Beef 80 0.55 0.35 0.50 in a backyard pile. Commercial manure Broiler litter 20 2.75 2.75 2.25 composts are composted under controlled Broiler layers 40 1.75 2.75 1.50 Broiler pullets 30 2.00 2.25 2.00 conditions to destroy pathogens. Goat 70 1.10 0.25 0.75 Bacterial pathogens die naturally over Horse 80 0.60 0.30 0.60 a period of weeks or months, so well- Tobacco Stalks 20 1.50 0.50 3.50 aged manure should not contain them. 1 Animal manures contain chloride, which can reduce the quality of some crops. Helminths in dog, cat, or pig manure can 2 Plant-available N can range from 20 to 80% of the total N in the year of application. persist for years, however, so do not add See UK Cooperative Extension publication Using Animal Manures as Nutrient Sources (AGR-146) for more details. these manures to your garden or compost This table was taken from UK Cooperative Extension publication Lime and Fertilizer pile. Recommendations (AGR-1). 64 • Soils and Fertility Chapter 4

Biosolids Biosolids contain small amounts of trace elements. Some trace elements are micro- Biosolids are a by-product of wastewater nutrients, which can be beneficial to crops. treatment. Most of the biosolids produced However, large amounts can be toxic to in Kentucky are used to fertilize agricultural crops, animals, or . When you apply and crops. Biosolids also are available biosolids at proper rates to provide nutri- to gardeners from some wastewater treat- ents, the risk of applying harmful amounts ment plants. of trace elements is negligible. A common form of biosolids is a spongy, Because biosolids come from the black substance called “cake.” Biosolids cake wastewater treatment process, they con- is about 20% to 25% dry matter and 75% to tain synthetic materials that were present 80% water. It typically contains about 3% to in the wastewater or added during treat- 6% nitrogen and 2% to 3% phosphorus on a ment. Biosolids are not certified as organic dry-weight basis as well as small amounts of fertilizers. potassium and trace elements. Some of the Biosolids do have two important charac- nitrogen in biosolids is immediately avail- teristics common to organic fertilizers: able to plants. The rest is released slowly. A • Their nutrients are released slowly from 5-gallon bucket of biosolids cake is enough the organic form by natural processes in to fertilize 50 square feet of garden. Apply the soil. biosolids as you would apply manure. • They are a product of the waste stream Biosolids also are an ingredient in some that can benefit crop growth. commercial composts. Like other com- posts, biosolid compost releases nutrients very slowly (other than the immediately- Salts from irrigation water, fertil- released nitrogen). It is a good source of izer, compost, and manure applications organic matter and provides small amounts can accumulate to the point where they of nutrients to plants. harm plant growth. In areas where rain- Use only biosolids that are free of fall exceeds evaportranspiration, salts are disease-causing pathogens (Class A biosol- leached from the soil and do not accumu- ids). Examples include biosolids compost late in the root zone. and some heat-treated biosolids. Class B A salinity test measures the total soluble biosolids have not been treated to the same salts in a soil. Table 8 shows how to inter- extent and may contain pathogens, includ- pret a salinity test. problems are ing some that are long-lived in the soil. rare in Kentucky. Check with the wastewater treatment plant You can leach salts from soil by applying offering biosolids to find out whether its irrigation water in excess of the water-hold- biosolids meet Class A requirements and ing capacity of the soil. The excess water are available for home use. must drain down through the soil to carry away excess salts. When leaching, apply Table 8. Soil salinity measured in conductivity units water slowly enough so that it drains freely (millimhos/cm) and potential effects on plants. through the subsoil. Three inches of excess water removes about half of the soluble salts Conductivity (mmho/cm) Interpretation in a soil. Five inches of water removes about 4 or above Severe accumulation of salts. May restrict growth of 90%. many vegetables and ornamental plants. Reduce salt by leaching. 2 to 4 Moderate accumulation of salts. Will not restrict plant growth but may require more frequent irrigation to prevent wilting. Less than 2 Low salt accumulation. Will not affect plants. Chapter 4 Soils and Fertility • 65

Commercial Organic Fertilizers How Much Fertilizer to Use Many organic by-products and some The goal of applying fertilizer is to sup- unprocessed minerals are sold as organic ply enough nutrients to meet plant needs fertilizers. Table 9 shows approximate nutri- without accumulating excess nutrients in ent contents of some of these materials. The the soil that could leach into groundwater numbers represent total nutrient content. or run off into . Soil tests and Because most are slow-release fertilizers, use of Cooperative Extension publications not all of the nutrients are available the year can help you estimate fertilizer needs. they are applied. Table 9 shows that most organic fertil- izer materials contain one main nutrient. Soil Tests The other nutrients are present in smaller A soil test gives information on the levels amounts, which means that although of nutrients in your soil and recommends organic fertilizers contain a variety of how much fertilizer to add each year based nutrients, they may not be present in the on the test results and the crops you grow. proportions needed by plants. Several com- You don’t need to test your soil every year; panies produce balanced organic fertilizers every three to five years is enough. by blending these materials into a single A garden soil test typically includes the product that provides all of the primary nutrients phosphorus, potassium, calcium, nutrients in balanced proportions. magnesium, and zinc. The test also includes Commercial organic fertilizers tend to soil pH and recommends lime if it’s needed be more expensive per pound of nutrients to raise pH. In areas with historically high than either processed fertilizers or manures. manure applications, a test for soluble salts Sometimes the difference in price is sub- can be worthwhile. stantial. Nevertheless, many gardeners use Soil test labs don’t routinely test for these products because of convenience. nitrogen because there is no simple way to They are most economical for small gardens predict nitrogen availability. The lab will where little fertilizer is needed. give a general nitrogen recommendation, The cost per pound of nutrients in however, based on the plants you are grow- organic fertilizers varies widely, depending ing and on information you provide about on the type of material, the concentration the soil (such as whether there is a history of of nutrients, and the package size. Compare manure applications, which would increase costs and nutrient availability when shop- soil-available nitrogen). ping for organic fertilizers. To take a soil sample, first collect sub- samples from at least 10 different spots in your garden. Avoid any unusual areas, such Table 9. Total nitrogen, phosphate, and potash as the site of an old trash dump, burn pile, content of selected organic fertilizers. or rabbit hutch. Sample the top 6 inches of soil (0 to 6 inches) if the soil has been Material Nitrogen (%) P2O5 (%) K2O (%) Cottonseed meal 6–7 2 1 tilled and 0 to 4 inches for non-tilled soil Blood meal1 12–15 1 1 and lawns. Air-dry the samples and mix Alfalfa 2 0.5 2 them together well. Send about a pint of the Bat guano1 10 3 1 mixed sample to the lab. Fish meal1 10 4 0 If you’re planting different crops but the Fish emulsion1 3–5 1 1 area has had similar previous fertilizer addi- Bone meal 1–4 12–24 0 tions, it’s probably not necessary to submit Rock phosphate2 0 25–30 0 more than one soil sample. Instead, use the Greensand 0 0 3–7 fertilizer recommendations for the various Kelp meal 1 0.1 2–5 crops. 1 Contains a substantial amount of quickly available nitrogen that plants can use early in the season. 2 Very low P availability (only 2–3%). Useful only in acid soils. 66 • Soils and Fertility Chapter 4

Before choosing a lab, call to make sure Estimating Organic it tests and make recommendations for garden soils. Ask a lab representative the Fertilizer Rates following questions: Estimating how much organic fertilizer • Do you routinely test garden soils for to use can be a challenge because you must plant nutrients and pH? estimate the availability of nutrients in the • Do you use Kentucky test methods and fertilizer. Here are some tips: fertilizer guides? • Organic fertilizers with large proportions • Do you give recommendations for gar- of available nutrients (such as bat guano den fertilizer applications? and fish emulsion) can be substituted • Are there forms to fill out? What infor- for processed fertilizers on a one-to-one mation do you need? basis. Use the same quantity called for in • How much does a test cost? the processed fertilizer recommendation. • How quickly will you send results? • Apply other packaged fertilizers according to their nutrient availability. Cooperative Extension Composts, rock phosphate, and plant residues generally have lower nutrient Publications availability than more concentrated Soil testing is highly recommended, but animal products (for example, blood if you are unable to submit a sample for meal, bone meal, and chicken manure). testing, you can use Cooperative Extension The recommended application rates on publications to estimate your needed fertil- packaged organic fertilizers are a good izer additions. These publications usually guideline. Check these recommenda- give recommendations for processed fertil- tions against other products to make sure izers, but some give guidelines for organic they seem reasonable. fertilizers as well. Kentucky has published • Nutrient concentration and availabil- fertilizer recommendations for a variety of ity in farmyard manures vary widely, crops. See “For More Information” at the depending on the type of manure and end of this chapter. Also see other chapters its age and handling. Application rates in this series for information on specific range from 5 gallons per 100-150 square crops. feet for high-nitrogen chicken manure to A typical extension recommendations 1-2 inches deep for cow or horse manure is for 2 lb of nitrogen per 1,000 square composted with bedding. Estimate appli- feet of garden, usually applied in a mixed cation rates based on the type of manure. fertilizer with a 1:1:1 ratio. Gardens with a • Observe your crops carefully. Lush history of fertilizer application may need plant growth and delayed flowering less phosphorus and potassium than this and fruiting are signs of high amounts rate supplies—you won’t know if you don’t of available nitrogen and may indicate test. (Fast-growing crops such as sweet corn overfertilization. need more nitrogen.) The best way to know • Experiment with different fertilizer what your garden or lawn needs is to soil rates in different parts of a row, and see test. whether you notice differences in crop performance. Plan your experiment care- fully so you are confident that differences are the result of different fertilizer rates rather than differences in soil, water, , or management practices. • Soil testing is valuable in understanding your soil’s nutrient status. Many estab- lished gardens have high levels of soil fertility, so that crops grow well with little fertilizer. Chapter 4 Soils and Fertility • 67

How to Calibrate a Fertilizer Example: With a 10-ft spread width and 50-ft length, total Spreader by the Volume Method area = 500 ft2 1. Based on the fertilizer analysis, determine For this area, we want 1.5 lbs N/1,000ft2, or 15 lb the amount of actual fertilizer that needs to of 10-10-10. be spread per 1,000 ft2. (1.5 lbs N/1,000 ft2 needs 30 lb of 5-5-5 to get this rate of nutri- • After spreading 50 ft of fertilizer at a 10-foot width, pour the remaining fertilizer back into the ent, or 15 lb of 10-10-10). bucket and measure and assume you measure 7 2. Start with a known amount of fertilizer inches. (for example, a 50-lb bag) and a known • Based on the previous determination of a fertil- volume (for example, two 5-gal buckets of izer weight of 1.6 lb/inch, 7 inches x 1.6 lb/inch = 11.2 lb of fertilizer. same size). • Because calibration is on 500 ft2 and the recom- 3. Pour the fertilizer into the buckets and mendation is for 1,000 ft2, multiply by 2, which = measure the total height, leveled. If the 22.4 lb fertilizer/1,000ft2. measurement is in inches, there will be a • Amount of 10-10-10 to achieve the 1.5 lb of N/ acre is 15 lb and our calculations show that 22.4 known amount of fertilizer (50 lb) per so lb was applied; therefore, we are applying too many inches. For example, if 50 lb measures much and need to reduce the amount coming 31 inches total in the two buckets, 50 lb/31 out of the spreader and calibrate again. inches = 1.6 lb/inch of bucket height. This • Continue using this procedure until you have standard calculation will allow determina- the desired rate. tion of a weight if scales are not available. 4. Determine the width of the fertilizer When to Fertilize spread pattern, then the total area. In most cases, the best time to apply (Known width x distance = total area) fertilizer is close to the time when plants need the nutrients. This timing reduces the 5. Set the spreader’s gate to manufacturer’s potential for nutrients to be lost before they recommendation. Most fertilizers will are taken up by plants. Not only is nutrient have a different flow pattern and density, loss inefficient, it may contaminate ground- so one factory setting will not work for all water or surface water. fertilizers. Plants need the largest amount of nutri- 6. Measure a known distance—for example, ents when they are growing most rapidly. 50 feet. Apply the fertilizer to the 50-ft line. Rapid growth occurs in midsummer for Do not collect the fertilizer. Pour fertilizer corn and squash, earlier for spring plantings remaining fertilizer in the spreader back of lettuce and other greens. Plants also need into the bucket, and measure the height. available nutrients (especially phosphorus) (Remember that for this example, 1 inch in shortly after seeding or transplanting. the bucket weighs 1.6 lb.) For a long-season crop such as corn, many gardeners apply a small amount of fertilizer as a starter at the time of seeding and then add a larger amount in early sum- mer just before the period of rapid growth. When using organic fertilizers, a single application usually is adequate, because nutrient release usually is fastest just before plant demand is greatest. 68 • Soils and Fertility Chapter 4

For perennial plants, timing depends Compost on the plant’s growth cycle. Blueberries, for example, benefit most from fertilizer Compost is an excellent source of applied early in the season at bud break, organic matter for garden soils. Composting while June-bearing strawberries are fertil- also closes the recycling loop by turning ized after harvest. Refer to other chapters in waste materials into a soil amendment. You this manual and to other extension publica- can make compost at home or buy com- tions for information on timing fertilizer mercially prepared compost. applications for specific crops. Making compost The key to composting is to supply a bal- Adding Organic Matter ance of air, water, energy materials (mate- rials with a low C:N ratio, such as grass Organic matter builds and stabilizes clippings, green garden trimmings, or fresh soil structure, thus reducing erosion and manure), and bulking agents (materials with improving soil porosity, infiltration, and a high C:N ratio, such as corn stalks, straw, drainage. It holds water and nutrients for and woody materials). You don’t need addi- plants and soil organisms. It also is a long- tives to stimulate your compost pile. You term, slow-release storehouse of nitrogen, just need to provide conditions favorable phosphorus, and sulfur, which continuously for natural composting organisms. become available as soil microorganisms You can compost in the following ways: break down the organic matter. • Hot (fast) composting produces high- The value of organic materials varies, quality, finished compost in six to eight depending on their nitrogen content (more weeks. To maintain a hot compost pile, specifically, their carbon to nitrogen, or mix together balanced volumes of energy C:N, ratio). Organic materials with a low materials and bulking agents, keep the C:N ratio, such as undiluted manure or pile moist, and turn it frequently to keep blood meal, are rich in nitrogen. They are a it aerated. good source of nutrients but must be used • Cold (slow) composting requires less sparingly to avoid over-fertilization. work than hot composting. Build the Materials with an intermediate C:N ratio pile and leave it until it decomposes. This (including many composts, leaf , process may take months or longer. Cold and cover crop residues) have lower nutri- composting does not kill weed seeds or ent availability. They are the best materials pathogens. Rats and other pests can be to replenish soil organic matter. Because attracted to edible wastes in cold com- they are relatively low in available nutri- post piles. ents, you can add them to the soil in large • You can compost fruit and vegetable amounts. scraps in a worm bin. This method works Materials with a high C:N ratio (such as well for urban gardeners who have little straw, bark, and sawdust) contain so little space. nitrogen that they reduce levels of avail- • You can bury fruit and vegetable scraps able nitrogen when mixed into the soil. Soil and allow them to decompose in the soil. microorganisms use available nitrogen when they break down these materials, leaving Commercial compost little nitrogen for plants. This process is called Yard debris is the major raw mate- “immobilization” and results in nitrogen rial in most commercial compost sold in deficiency. If you use materials with a high Kentucky. Commercial compost also may C:N ratio in your garden, add extra nitrogen contain animal manure, biosolids, food fertilizer to compensate for immobilization. waste, or waste. Commercial com- The best use for these materials is for mulches post is made on a large scale, with frequent around perennial crops or in walkways. They aeration and/or turning to create condi- do not cause nitrogen immobilization until tions that kill weed seeds, plant pathogens, you mix them into the soil. and human pathogens. Chapter 4 Soils and Fertility • 69

Using compost (Cover Crops) Adding 1 to 2 inches of compost each Green manures are cover crops grown year helps build a productive garden soil. specifically to be tilled or dug into the soil. You can till or dig compost directly into Planting green manure is a way to grow your garden or use it as a before your own organic matter. The value of cover turning it into the soil. One cubic yard of crops goes beyond their contribution of compost covers about 300 square feet to 1 organic matter, however. They also can do inch deep. In the first year after application, the following: partially decomposed woody compost may • Capture and recycle nutrients that oth- immobilize some soil nitrogen, resulting erwise would be lost by leaching during in for plants. If plants winter show signs of nitrogen deficiency (poor • Protect the soil surface from rainfall growth or yellow leaves), add extra nitrogen impact fertilizer (either organic or inorganic). In • Reduce runoff and erosion subsequent years, most compost contrib- • Suppress weeds utes small amounts of available nitrogen to • Supply nitrogen (legumes only ) the soil. It is important to know the source of Roots from cover crops, especially crops composted materials derived from grass that produce taproots, can penetrate a clippings or animal manure used as fer- moderately compacted zone and help dis- tilizer amendments on your garden or tribute nutrients deeper into the soil profile. plants. Herbicide residues could No one cover crop provides all of these be present that can cause injury to sensi- benefits. Deciding which cover crop or tive garden plants such as tomatoes and combination to grow depends on which other broadleaf plants. Active ingredients benefits are most important to you and in certain herbicide products applied to which cover crops best fit into your garden lawns can be retained in grass clippings, or plan (Table 10). With the exception of buck- animals consuming herbicide-treated pas- wheat, all of the cover crops listed in Table tures and hay can pass the material through 10 are suitable for fall planting and spring the digestive system, so that the herbicide tillage. in the manure persists at concentrations Gardeners usually plant cover crops in that will cause injury to sensitive crops. the fall and till them into the soil before Furthermore, the composting process may planting in the spring. The earlier cover not fully degrade these herbicide com- crops are planted, the more benefits they pounds. To be safe, make sure that com- provide. posted grass clippings and manure used on your garden or landscape areas have not been indirectly exposed to herbicides.

Table 10. Examples of cover crops for Kentucky. Cover Crop Characteristics Annual ryegrass Hardy, tolerates wet soils, can be difficult to control if seeds Austrian winter peas Legume, does not compete well with winter weeds, must establish early fall Buckwheat Rapid germination and growth, frost sensitive, drought tolerant Cereal rye Hardy, rapid growth, matures rapidly in spring Crimson clover Legume, grows more slowly than vetch Hairy vetch Legume, slow initial growth, grows quickly in the spring, can be difficult to kill Winter triticale Produces more vegetation than cereal rye or winter wheat Winter wheat Most common cover crop, covers soil well, matures slowly Turnip/Mustard greens Grow well in fall, strong taproots to break compacted layers, edible Note: All legumes fix nitrogen. 70 • Soils and Fertility Chapter 4

Legumes such as vetch and crimson Soil pH clover need an early start to achieve enough growth to cover the soil before cold weather Soil pH measures the acidity or alkalinity arrives. of a soil. At a pH of 7 (neutral), acidity and If your garden contains crops into alkalinity are balanced. Acidity increases by November or December, it will not be a factor of 10 with each 1-unit drop in pH possible to plant early cover crops over the below 7. For example, a pH of 5.5 is 10 times entire area. In this case, plant cover crops as acidic as a pH of 6.5. Alkalinity increases in areas you harvest early and use mulch in by a factor of 10 with each 1-unit change in those you harvest later. For example, plant a pH above 7. cover crop in a sweet corn bed immediately Native soil pH depends on the minerals following harvest in September, and mulch present in the soil and on rainfall. Soils in a bed of fall greens after you remove the arid areas tend to be alkaline, and those in crop in November. You also can start cover rainy areas tend to be acid. Gardening and crops between rows of late crops if space farming also affect soil pH; for example, allows. many nitrogen fertilizers tend to reduce pH, Till or dig cover crops into the soil before while liming increases pH. they flower. After flowering, plants become Soil pH influences plant growth in three woody and decline in quality. Also, digging ways, affecting the following: plants into the soil becomes quite difficult • availability of plant nutrients (Figure 8) if they grow too large. If you cannot till a • availability of toxic metals cover crop before it blooms, cut it off and • activity of soil microorganisms, which in compost it for later use. You will still get the turn affects nutrient cycling and disease short-term benefit of organic matter from risk the crowns and roots when you till your garden. The availability of phosphorus decreases The organic matter benefits of cover in acid soils, while the availability of iron crops last only about one year, so make increases. In alkaline soils, the availability of cover crops an annual part of your garden iron and zinc can be quite low. rotation. If they do not fit into your gar- Aluminum availability increases in acid den plan, you can use winter mulches as a soils. Aluminum is one of the most common substitute. elements in soil, but it is not a plant nutri- ent and is toxic to plants in high concentra- tions. Very little aluminum is in solution in Figure 8. Effect of soil pH on the availability of soils above pH 6, and what is present causes plant nutrients. no problems for plants. As pH declines and aluminum availability increases, aluminum Acid pH Neutral pH Alkaline pH toxicity can become a problem. 4.0 5.0 6.0 7.0 8.0 9.0 10.0 Microbes also are affected by soil pH. The most numerous and diverse micro- nitrogen bial populations exist in the middle of the phosphorus pH range. Fewer organisms are adapted potassium, sulfur to strongly acid or strongly alkaline soils. calcium Nutrient cycling is slower in acid and magnesium alkaline soils because of reduced microbial iron, copper, zinc, manganese, cobalt populations. molybdenum Many garden crops perform best in soil boron with pH of 5.5 to 7.5, but some (such as blueberries and rhododendrons) are adapted to more strongly acid soils. Before amending soil to adjust pH, it is important to know the preferred pH ranges of your plants. Chapter 4 Soils and Fertility • 71

Table 11. Materials required to lower soil pH Increasing Soil pH to specific levels. Use the following table for The most common way to increase soil each 100 sq ft.1 Multiply by 436 for lb/A. pH is to add lime, which is ground lime- Add stone, a rock containing calcium carbonate. To Change Wettable Aluminum3 It is an organic (natural) amendment, suit- pH from: Sulfur (lb) or Sulfate (lb) able for use by organic gardeners. 8.0 to 7.0 2 3.0 Lime raises the pH of acid soils and 8.0 to 6.5 3 4.5 supplies calcium, an essential nutrient. 8.0 to 6.0 4 6.02 Dolomitic lime contains magnesium as well 8.0 to 5.5 5 7.52 as calcium. 8.0 to 5.0 6 9.02 The best way to determine whether 7.5 to 7.0 1 1.5 your soil needs lime is to have it tested. Do 7.5 to 6.5 2 3.0 not lime areas where you grow acid-loving 7.5 to 6.0 3 4.5 plants, because they are adapted to acid 7.5 to 5.5 4 6.02 soils. 7.5 to 5.0 5 7.52 Lime is a slow-release material. Apply it 7.5 to 4.5 6 9.02 in the fall to benefit spring crops. 7.0 to 6.5 1 1.5 Wood ashes are a readily available source 7.0 to 6.0 2 3.0 of potassium, calcium, and magnesium. 7.0 to 5.5 3 4.5 2 Like lime, they also raise soil pH. High rates 7.0 to 5.0 4 6.0 7.0 to 4.5 5 7.52 of wood ashes may cause short-term salt 6.5 to 6.0 1 1.5 injury, so apply less than 15 to 25 pounds 6.5 to 5.5 2 3.0 per 1,000 square feet. We do not recom- 6.5 to 5.0 3 4.5 mend using wood ashes in alkaline soils. 6.5 to 4.5 4 6.02 Gypsum (calcium sulfate) is not a substi- 6.0 to 5.5 1 1.5 tute for lime. It supplies calcium and sulfur, 6.0 to 5.0 2 3.0 but has little effect on soil pH. Gypsum has 6.0 to 4.5 3 4.5 been promoted as a soil amendment to 5.5 to 5.0 1 1.5 improve soil structure. In the vast major- 5.5 to 4.5 2 3.0 ity of cases, it does not work. Gypsum 5.0 to 4.5 1 1.5 improves structure only when poor struc- 1 Aluminum sulfate is faster in reaction than sulfur. The two materials may be applied together (half of each). ture results from excess sodium in the soil, Incorporate into the top 6 inches of the soil. a rare condition in Kentucky. Use organic 2 Rates higher than 4.5 lb. per 100 sq ft can cause excess soluble salt problems. Split the amount in half and amendments to improve soil structure, as apply in the spring and fall. described earlier under “Adding Organic 3 Aluminum sulfate is much less effective in reducing pH than wettable sulfur but is quicker acting than Matter.” flowers of sulfate and is usually available. More fre- Some composts can increase soil pH, as quent applications may be necessary. Prepared by Kathy Keeney, McCracken County exten- can poultry litter, due to diet and amend- sion agent for horticulture. ments added to bedding material. Decreasing Soil pH You may need to decrease soil pH if you Ammonium sulfate fertilizer also lowers wish to grow acid-loving plants. Elemental pH, but it takes longer than sulfur to have sulfur lowers soil pH. Soil testing is the best an effect. All nitrogen fertilizers that con- way to determine whether sulfur is needed tain ammonium (NH4+) also reduces pH and, if so, how much. Refer to Table 11 to slowly, as do some organic fertilizers. determine the amount of sulfur needed when lowering soil pH. 72 • Soils and Fertility Chapter 4

Hot composting—A fast composting process that Soils and Fertilizer Terminology produces finished compost in six to eight weeks. Aggregation—The process by which individual High temperatures are maintained by mixing particles of sand, silt, and clay cluster and bind balanced volumes of energy materials and bulk- together to form peds ing agents, keeping the pile moist, and turning it frequently to keep it aerated. Anion—A negatively charged ion. Plant nutri- ent examples include nitrate (NO-3), phosphate Humus—The stable end product of decomposed animal and plant remains of unrecognizable (H2PO4-), and sulfate (SO42-). origin, their partial decomposition products, Aspect—Direction of exposure to sunlight. and waste for soil biomass. Same as soil organic matter. Biosolids—A by-product of wastewater treatment sometimes used as a fertilizer. Immobilization—The process by which soil micro- organisms use available nitrogen as they break Capillary force—The action by which water mol- down materials with a high C:N ratio, thus reduc- ecules bind to the surfaces of soil particles and ing the amount of nitrogen available to plants. to each other, thus holding water in fine pores against the force of gravity. Infiltration—The movement of water into soil. Cation—A positively charged ion. Plant nutrient Ion—An atom or molecule with either positive or examples include calcium (Ca++) and potassium negative charges. (K+). Leaching—Movement of water and soluble nutri- Cation exchange capacity (CEC)—A soil’s capacity to hold ents down through the soil profile. cations as a storehouse of reserve nutrients. Loam—A soil with roughly equal influence from Clay—The smallest type of soil particle (less than sand, silt, and clay particles. 0.002 mm in diameter). Macropore—A large soil pore. Macropores control C:N ratio—The ratio of carbon to nitrogen in organic a soil’s permeability and aeration and include materials. Materials with a high C:N ratio are good earthworm and root channels. bulking agents in compost piles, while those with a low C:N ratio are good energy sources. Micronutrient—A nutrient used by plants in small amounts (iron, zinc, molybdenum, manganese, Cold composting—A slow composting process boron, copper, and chlorine). Also called a trace of simply building a pile and leaving it until it element. decomposes. This process may take months or longer. Cold composting does not kill weed seeds Micropore—A fine soil pore, typically a fraction of a or pathogens. millimeter in diameter. Micropores are responsible for a soil’s ability to hold water. Compaction—Pressure that squeezes soil into layers that resist root penetration and water movement. Mycorrhizae—Beneficial fungi that infect plant roots Often the result of foot or machine traffic. and increase the plants’ ability to take up nutri- ents from the soil, particularly phosphorus. Compost—The product created by the breakdown of organic materials under conditions manipu- Nitrifier—A microbe that converts ammonium to lated by humans. nitrate. Cover crop—A crop that is dug into the soil to return Nitrogen cycle—The sequence of biochemical organic matter and nitrogen to the soil. Also changes undergone by nitrogen as it moves from called green manure. It is planted to reduce soil living organisms, to decomposing organic matter, loss and capture nutrients not used during the to inorganic forms, and back to living organisms. growing season. Nitrogen fixation—The conversion of atmospheric Decomposition—The breakdown of organic materials nitrogen into plant-available forms by Rhizobia by microorganisms. bacteria. Fertilizer—A natural or synthetic product added to Organic fertilizer—A natural fertilizer material that the soil to supply plant nutrients. has undergone little or no processing. Can include plant, animal, and/or mineral materials. Fertilizer analysis—The amount of nitrogen, phos- Organic materials—Recognizable materials originat- phorus (as P2O5), and potassium (as K2O) in a fertilizer expressed as a percent of total fertilizer ing from living organisms, the precursors to soil weight. Nitrogen (N) always is listed first, phos- organic matter. phorus (P) second, and potassium (K) third. Organic matter—Plant remains of unrecognizable Green manure—Same as cover crop. origin, their partial decomposition products, and waste for soil biomass. See Humus. Chapter 4 Soils and Fertility • 73

Pathogen—A disease-causing organism. Sand—The coarsest type of soil particle (0.05 to 2 Pathogenic soil organisms include bacteria, mm in diameter). viruses, fungi, and nematodes. Secondary nutrient—A nutrient needed by plants Ped—A cluster of individual soil particles. in a moderate amount (sulfur, calcium, and magnesium). Permeability—The rate at which water moves through a soil. Silt—A type of soil particle that is intermediate in size between sand and clay (0.002 to 0.05 mm in pH—A measure of acidity or alkalinity. Values from diameter). 0 to 7 indicate acidity, a value of 7 is neutral, and values from 7 to 14 indicate alkalinity. Most soils Slow-release fertilizer—A fertilizer material that must have a pH between 4.5 and 9. be converted into a plant-available form by soil microorganisms. Phosphate—The form of phosphorus listed in most fertilizer analyses (P205). Soil—A natural, biologically active mixture of weathered rock fragments and organic matter at Potash—The form of potassium listed in most fertil- the earth’s surface. izer analyses (K20). Soil salinity—A measure of the total soluble salts in Primary nutrient—A nutrient required by plants in a soil. a relatively large amount (nitrogen, phosphorus, and potassium ). See Macronutrient. Soil solution—The solution of water and dissolved minerals found in soil pores. Processed fertilizer—A fertilizer that is manufactured or is refined from natural ingredients to be more Soil structure—The arrangement of aggregates concentrated and more available to plants. (peds) in a soil. Quick-release fertilizer—A fertilizer that contains nutri- Soil texture—How coarse or fine a soil is. Texture is ents in plant-available forms such as ammonium determined by the proportions of sand, silt, and and nitrate. clay in the soil. Rhizobia bacteria—Bacteria that live in association Soluble salt—A compound often remaining in with roots of legumes and convert atmospheric soil from irrigation water, fertilizer, compost, or nitrogen to plant-available forms, a process manure applications. known as nitrogen fixation. Water-holding capacity—The ability of a soil’s micro- Rhizosphere—The thin layer of soil immediately sur- pores to hold water for plant use. rounding plant roots. 74 • Soils and Fertility Chapter 4

For More Information Kentucky Cooperative Extension Service. Home Composting: A Guide to For more information, contact your Managing Home Yard Waste (HO-75). county extension agent. You may also refer http://www.ca.uky.edu/agc/pubs/ho/ to the following publications: ho75/ho75.pdf. Kentucky Cooperative Extension Service. ID-128 Home Vegetable Gardening Winter Cover Crops for Kentucky (http://www.ca.uky.edu/agc/pubs/id/ Gardens and Fields (ID-113). http:// id128/id128.pdf) www.ca.uky.edu/agc/pubs/id/id113/ Bohn, H.L., B.L. McNeal, and G.A. id113.htm O’Connor. , 3rd edition Kentucky Cooperative Extension Service. (John Wiley & Sons, New York, 2001). Organic Manures and Fertilizers for Brady, N.C., and R.R. Weil. The Nature and Vegetable Crop http://www.uky.edu/Ag/ Properties of Soils, 14th edition (Prentice- Horticulture/manures.htms. Hall., New York, 2007). Tisdale, S.L., and W.L. Nelson. Soil Fertility Craul, P.J. Urban Soil in Landscape Design and Fertilizers (Macmillan Publishing (John Wiley & Sons, New York, 1992). Co., Inc., New York, 1985). Donahue, R.L., R.W. Miller, and J.C. Shickluna. Soils: An Introduction to Soils and Plant Growth (Prentice-Hall, Inc., Englewood Cliffs, NJ, 1990).

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