Soil Science for Master Gardeners

Soil Science for Master Gardeners
Presented by: Jeff Schalau Agent, Agriculture & Natural Resources The University of Arizona Cooperative Extension Adapted from: Dr. James Walworth, Arizona Cooperative Extension Soil Specialist This slide set is designed to accompany the “Soils and Fertilizers” section of the Arizona Master Gardener Manual, although it also can be used as an independent, stand alone presentation. Questions regarding this set can be directed to: Dr. James Walworth Department of Soil, Water and Environmental Sciences 429 Shantz Bldg. #38 University of Arizona Tucson, AZ 85721 (520)

Soil Information Sources
Soil Surveys are available for most of the United States. They are produced by the Natural Resource Conservation Service (NRCS) and are available from their offices. Soil Surveys include, among other things, soil maps, descriptions, use limitations, agricultural and engineering properties. They are an extremely useful resource and available to the public.

Soil Components Mineral Particles Open Spaces (pores)
sand silt clay Open Spaces (pores) air water Organic Materials carbon-based Soils are comprised of 1) mineral particles 2) pores, and 3) organic particles. Mineral particles are described by their size. In this slide sand is green, silt is red, clay is yellow. Pores can be filled with either air (white) or water (light blue). Organic materials are from plants or animals (light brown).

Composition of Soil by Volume
Pores can be filled with either air or water The soil spaces or pores usually occupy about half a soil’s volume. They can be filled almost entirely with air, entirely with water, or (usually) a combination of both. In a well-drained, but moist soil, pores will be about half filled with water (so about one fourth of the volume is air and about one fourth of the volume is water). Organic matter (plant, animal, and microbial remains) makes up anywhere from 0 to 25% or more of a soil’s volume, but in Arizona 0 to 2% is the norm. The rest (~50%) is mineral particles.

Parent Materials Residual Transported rock weathered in place
organic deposits at soil surface Transported gravity: colluvial water: alluvial, marine, lacustrine wind: eolian (loess) ice: glacial Parent materials, or the materials from which soils are formed, can be divided into two general types: residual (formed in place) or transported (formed elsewhere and moved to the current site). Residual parent materials can be either mineral, consisting of rocks weathered in place, or organic materials deposited from living sources. Transported parent materials are classified by their mode of movement: colluvial: moved down hill by gravity alluvial, marine, and lacustrine: moved by water eolian: moved by wind (loess or wind-blown silt is an example) glacial: moved by ice

Factors of Soil Formation
Parent materials (geological or organic soil precursors) Climate (especially rainfall and temperature) Biota (living organisms - vegetation, microbes, soil animals, human beings) Topography (configuration of soil surface) Time parent materials are subjected to soil formation processes Soils vary in their physical and chemical properties due to a combination of factors known as the soil forming factors. These five factors – parent material, climate, biota, topography, and time – determine the characteristics of a given soil.

Weathering Physical weathering (disintegration)
heating/cooling water, ice, wind abrasion plants and animals Chemical weathering (chemical alteration) hydrolysis (splitting by water) hydration (combining with water) acid weathering oxidation Parent materials are transformed through weathering processes into soil constituents. These processes are either physical or chemical. Physical weathering reduces the size of particles, but not their chemical nature. Physical weathering is caused by forces that cause expansion and contraction, like wetting/drying, heating/cooling, root penetration, animal activity, and by abrasion. Chemical weathering alters the fundamental nature of parent materials, and includes hydrolysis: water splits into H+ and OH-, which combine with parent material constituents hydration: water combines with something directly acid weathering: acid from sources such as rainfall (carbonic acid) causes transformations oxidation: oxygen combines with parent material constituents

Soil Formation in Moist Environments
Water Water transports clay particles, organic matter, salts Soils are formed from various types of parent material - sediments, decayed rocks, glacial deposits, etc. Parent material changes as things are added to the soil, moved within the soil, or washed out of the soil. Water, nutrients, and mineral particles are added as rainfall, dust, and organic materials are deposited on the surface. Water moves through the soil, carrying dissolved salts, organic materials (dissolved and particles), and clay particles with it. These can be redistributed within the soil, or removed be washing out of the soil entirely. These processes of addition, redistribution, and removal are instrumental in the formation of horizontal soil layers or horizons. A soil is made up of a set of horizons which is also called a soil profile. Note that soil layers can also be formed when parent material is deposited by wind or water, and that these layers can look very much like the soil horizons described here and in the next few slides. Water, Salts

Soil Formation in Arid Environments
Water Water transports salts In most parts of the United States, net water movement is downward. Even though short-term water movement may be upward (from the soil to the atmosphere) as water evaporates from the soil and as plants transpire, precipitation is great enough that, in the long run, water moves down through the soil profile. This water carries dissolved salts deeper into the profile or washes them from the soil. In arid regions like Arizona, however, net water movement is upward because rainfall is limited and high temperatures increase evaporation. Water moving up through the soil profile carries dissolved salts with it, and when the water evaporates from the soil surface, the salts are left behind. Thus over time, arid region soils tend to become saltier and saltier because salts added from precipitation, ground or surface waters, and parent materials do not get washed out of the soil profile. Here we see a layer of sodium chloride at the soil surface. Depending on the types of dissolved salts, saline or sodic soils can form. This is also one of the mechanisms responsible for caliche formation. Water, Salts

Soil Horizons Soils develop horizontal layers, or horizons, as materials move through the soil profile Here are a couple of horizon photographs with horizon designations. There’s nothing special about them; they just provide an idea of what horizons actually look like.

Soil Horizons A horizon E horizon B horizon C horizon
dark layer, high in organic matter E horizon layer of leaching depletion of organic matter, clays, iron & aluminum oxides B horizon zone of accumulation enrichment of organic matter, clays, iron & aluminum oxides C horizon parent material Horizons are given letter designations. The main horizons are: A horizon - a surface horizon formed by a buildup of organic matter at or near the soil surface. E horizon - E for eluviation (leaching or washing out of). These horizons are depleted of organic matter, clays, iron and aluminum oxides which have been moved out or the E horizon and deposited below. B horizon - this is a horizon of accumulation, rich in organic matter, clays, iron and aluminum oxides. The material that washed out of the E horizon ended up in the B horizon. C horizon - this is the unweathered parent material. Note: The soil profile horizons were initially labeled A, B, C going from the surface down. The E horizon used to be called A2, but was later changed to E. This is why the sequence is screwed up. Horizons can have many sub-designations to further describe them. Soils need not have all horizons, and some can have more than one of a given horizon.

Soil Horizons A E B C Here is photograph of a soil with the main horizons labeled. It has an A horizon, then an E horizon, which has been depleted of clay. This clay has been transported down to the B horizon, which is considerably darker and more clayey than the E horizon. Below this is the C horizon (parent material).

Arid Soil Horizons Sodium chloride Calcium carbonate (Caliche)
The upward movement of water In arid regions like Arizona, carries dissolved salt up through the soil, and salts accumulate in the profile. Over time, salt layers form. They are classified according to the type of salt that accumulates. The soil on the left has an accumulation of sodium chloride, forming a salic horizon. The one on the right has a hardened (petro) calcium carbonate layer. Caliche is a another term for a petrocalcic or cemented calcium carbonate layer. It can be relatively weak, or cemented into a rock-like layer . This cemented layer can impede water flow and root penetration. It is also fairly alkaline, which can cause additional problems that we’ll look at later.

Soil Physical Properties
Color Texture Structure Drainage Depth Surface features Soil physical properties can be described to help categorize or classify soils. We usually look at: 1. Soil color 2. Soil texture - describes the size of soil particles 3. Structure - arrangement of soil particles 4. Drainage - how freely water moves out of a soil 5. Depth - how thick the soil is 6. Surface features - topography, etc.

Soil Color Organic matter:
dark brown High organic matter content Drainage conditions and degree of oxidation (weathering): red-brown Good drainage yellow Moderate drainage gray Poor drainage Soil color can give a good indication of several properties. Dark brown colors usually come from organic materials. Typically, we see these colors near the soil surface where organic materials have been deposited, but we may find them in B horizons that have an accumulation of organic materials. Red, yellow, and gray colors are indicative of how well drained and how weathered soil mineral horizons are. Iron in soil is sensitive to weathering and to long-term soil moisture levels. It becomes bright red in highly weathered (old) soils - so we find red soils in warm, high rainfall areas where land disturbance in minimal - Hawaii, Puerto Rico, etc. Iron turns gray (called gleying) when it stays wet for long periods of time, so swamp soils often have gray mineral horizons. Yellow colors indicate moderate drainage. Soils that are alternately wet and dry often have splotchy red-yellow-gray patterns. This is called mottling.

Soil Color Soil color is described by with a coded color book (shown on the right) using the Munsell color system. Color is divided into three components: hue, chroma, and value. The first number and letter sequence (for example 10yr) is the color or hue (in this case the amount of yellow (y) and red (r). The second two (3/2 for the A horizon in the photo on the left) are the chroma (the intensity or brightness) and the value (the lightness or darkness). If you look in a county soil survey (an excellent source of local soils information) you will find that each horizon of each soil is described with this system.

Soil Color Highly weathered soil Organic soil Young soil
Here we see examples of varying soil colors. Left: a highly organic soil showing a typical rich, dark color. Center: a young soil (probably from a flood plain or other recent deposit) without much color development. Right: A well-drained, highly weathered soil with good red or orange color resulting from highly oxidized iron. Basically the iron in this soil has rusted and you will notice that this is, indeed, a reddish rusty color. Highly weathered soil Organic soil Young soil

Mineral Particles Mineral Particles Pore Spaces Organic Matter sand
silt clay Pore Spaces Organic Matter We divide the soil mineral particles into three groups - sand, silt, and clay - based on their size.

Soil Texture Soil texture is determined by the amount of sand, silt, and clay excludes organic matter large particles (larger than 2 mm) Size of mineral particles sand 2 to 0.05 mm silt to mm clay less than mm Sand is the largest, clay the smallest, and silt is in between. These designations are used to describe all mineral particles smaller than 2 mm in diameter (about 1/10 of an inch). Individual sand particles are visible with the naked eye and have a gritty feel. Silt particles are visible with a light microscope. Silt feels soft and smooth like flour. Silt particles are easily carried by the wind and are a major component of dust. Most clay particles are too small to be seen with a light microscope and are visible only with an electron microscope. The amounts of sand, silt, and clay in a soil determine the soil texture. Particles bigger than 2 mm are given other names (gravels, cobbles, etc.), but do not affect soil texture. Organic matter is also excluded from soil texture characterization.

Relative Size of Soil Particles
Clay less than mm Silt 0.05 to mm Here we can see the relative sizes of sand, silt, and clay. Note that sand and silt look like little boulders, and that’s basically what they are. In fact they come from boulders that have been physically broken into small pieces by weathering processes. The clay, which we had to magnify to fit into the same scale as the sand particle, is fundamentally different. It is made of layers, and the clay particle looks like a stack of pancakes. Clays are formed through chemical reactions that reform constituents from silt and sand particles. Sand 2.0 to 0.05 mm (1 inch = 25.4 mm)

Structure of Clay Particles
This is a photograph of a clay particle (or a group of particles) taken through an electron microscope. The individual layers are clearly visible. It looks like a piece of mica. These layered minerals are called layer silicate minerals and they can actually occur in various sized pieces (not just clay-sized). Mica is a layer silicate and that’s why a piece of mica looks like a huge clay particle.

Structure of Clay Particles
Montmorillonite Kaolinite Layered clay minerals come in many forms. We are familiar with some such as montmorillonite, vermiculite, and mica (also called muscovite or biotite). We use many of them without realizing it; for example Kaopectate is made of the clay mineral kaolinite. The layers of some of the clay minerals are held together weakly so that water and charged molecules can get in. Some, like montmorillonite, expand greatly when they get wet because water moves between the layers. Sometimes molecules get stuck between the layers as is shown in the e mica diagram. (Kitty litter is made of a clay mineral that has the ability to trap ammonia between its layers - thus eliminating odor.) Mica water and charged molecules

Area per weight (square meters per gram)
Specific Surface Area Area per weight (square meters per gram) 1 gram sand ~ square meter 1 gram silt ~ 1 square meter 1 gram clay ~ 10 to 1,000 square meters One reason soil texture is an important property is because of the relative surface areas of sand, silt, and clay particles. One gram (a bit less than  of a teaspoon) of sand has a surface area of 0.1 square meters or a 1 ft x 1 ft square. The same amount of silt has a surface area of 1 square meter or a 3 ft x 3 ft square. But clay can have a surface area of up to 1,000 square meters or 100 ft x 100 ft ! (This is partly because of the very small size of the clay particles and partly because the clay has surfaces between layers as well as outside surfaces.)

Particle Surfaces are Important
Coated with water Electrically charged Sites for microbial growth Sites of chemical reactions weathering adsorption of chemicals retention of nutrients soil aggregate formation Why do we care about particle surfaces? 1. Most soil particle surfaces are also electrically charged. 2. Water sticks to particle surfaces. 3. They are the sites of microbial growth. 4. Surfaces are where reactions take place: a. Chemicals adsorb or stick to surfaces b. Nutrients are retained by surfaces c. Surfaces provide the ability for particles to stick together or aggregate d. Weathering takes place at particle surfaces (We have all experienced surface reactions. When we want to start a fire, we begin with twigs or small pieces of wood. They burn more easily because of their large amount of surface area.)

Clay Particles have Electrical Charge
Most clay particles are negatively charged Ions (charged molecules) cations are positively charged ions anions are negatively charged ions Cations are attracted to negatively charged clays these cations are loosely held or exchangeable this process is called cation exchange Clay particles carry an electrical charge, in most cases a positive charge. Many of the molecules dissolved in soil water are also charged. These are called ions. Positively charged ions are cations (examples: calcium Ca++, sodium Na+, potassium K+, magnesium Mg++, aluminum Al+++ , hydrogen H+, NH4+ ). Negatively charged ions are anions (examples: phosphate PO43-, sulfate SO42-, nitrate NO3-). Negatively charged clay particles attract and hold positively charged cations. These cations can be removed in a process called cation exchange. (Some are easily exchanged (sodium, for example), and some are held more tightly (aluminum is one). In general, the more highly charged cations are held most tightly.

Cation Exchange Cation Clay particle
Here is a schematic diagram of a negatively charged clay particle surrounded by cations. The soil liquid (soil solution) contains dissolved cations and anions. The concentration of cations is much greater close to the particle surface than in the bulk soil solution. The cations are not bonded to the clay, but just attracted to the surface. Conversely anions are repelled by negatively charged clays, so the concentration of anions is greater in the bulk soil solution than close to a clay particle.

Cation Exchange Exchangeable soil cations include
calcium, magnesium, potassium, ammonium, sodium hydrogen, aluminum in acid soils Exchangeable cations can replace one another Exchangeable cations are available to plants, microbes, etc. The amount of exchange in a soil is called the Cation Exchange Capacity (CEC) Soil cations are exchangeable. The most common ones are calcium, magnesium, potassium, ammonium , sodium, aluminum, and hydrogen. Aluminum and hydrogen are found in large quantities only in acid soils. One cation can replace another. Exchangeable cations are really just floating close to the clay particle (much as the atmosphere floats close to the earth’s surface, attracted by the force of gravity, but free to move around). Exchangeable cations can therefore be used by soil organisms (plants, bacteria, fungi, etc.). The quantity of exchangeable cations a soil can hold is called the cation exchange capacity (abbreviated CEC). This is an important property because it tells us about the level of nutrient a soil can hold - the higher the CEC, the greater the ability to hold nutrients. (Units of CEC are milliequivalents/100g (meq/100g - the old units) or centimoles of charge/kg (cmol/kg - the new units) - they are equivalent. A low CEC soil may have about 5 cmol/kg and a high CEC soil over 100 cmo/kg.

Percent clay Percent clay Percent silt Percent silt Percent sand
Percent clay Percent clay Percent silt Percent silt Clay Clay Silty Silty Sandy Sandy clay clay clay clay Silty clay Silty clay Clay loam Clay loam loam loam Sandy Sandy clay loam clay loam Soil texture is determined by the relative proportions (percentages) of sand, silt, and clay particles. If we know the percentages of each (measured in the laboratory), we can use the textural triangle shown above to figure out the textural class. The percentage of silt is shown on the right-hand side, going from 0 to 100% as we move from the top to the bottom. Sand is on the bottom; 0% on the right and 100% on the left. And clay is on the left with 0% on the bottom and 100% at the top. To determine the textural class of a soil with 20% clay, 30% silt, and 50% sand, for example, find the 20% clay line and follow it horizontally; locate the 30% silt line and follow it diagonally to the lower left; these two lines will intersect at the 50% sand line (they must because the sum of the three percentages must be 100%). The textural class of this soil is loam. (Loams are soils that exhibit the properties of sand, silt, and clay in roughly equal proportions - they do not contain equal percentages of sand, silt, and clay.) Soil texture is a pretty much a permanent property. It can not be changed by adding organic materials, cultivation, etc, but only by adding or losing sand, silt, or clay. Loam Loam Silt loam Silt loam Sandy Sandy Loamy Loamy loam loam sand sand Silt Silt Sand Sand 70 40 10 Percent sand Percent sand

Soil Structure Soil particles are grouped in aggregates Aggregates
vary in size, shape, and strength are promoted by organic matter calcium and other ‘flocculating’ cations can be destroyed by tillage and traffic allow movement of air, water, roots Soil structure describes the arrangement of soil particles in groups or aggregates. Aggregates come in several general shapes. They also vary in size and strength (how difficult it is to break them). Aggregation is favored by organic matter, and also by certain cations - basically the most highly charged ones such as Ca2+ and Al2+. The process of bringing soil particles together is called flocculation. Certain forces, such as wetting/drying and freezing/thawing cycles help soil particles to group into aggregates. Tillage and traffic (particularly when soils are wet) can break aggregates and destroy soil structure. Aggregates are important because they allow air, water, and roots to penetrate the soil.

Soil Aggregates Single Grain Individual grains not held together
Some soils, such as sands, contain particles in an un-aggregated state or as single grains. (This is because sand particles do not have enough surface area to be attracted to each other enough to form aggregates.) Individual grains not held together - common in sands

Soil Aggregates Granular
In A horizons, where organic matter levels are high and there is a lot of biological activity (earthworms, ants, termites, microbes, etc.) particles tend to be arranged in small, round aggregates or granules. Porous granules held together by organic matter and clay - common in A horizons

Soil Aggregates Platy Flat aggregates
Compacted layers and E horizons often have flat or platy aggregates. These may form naturally, or may be formed by compaction or tillage. These aggregates often impede water flow and root penetration. Flat aggregates - found in compacted layers and E horizons

Soil Aggregates Blocky Roughly equidimensional aggregates
Blocky aggregates are usually found in lower soil horizons where clays have accumulated. This can be a desirable type of structure, but in some soils blocky aggregates can become extremely hard when dry. Roughly equidimensional aggregates - found in clayey B horizons

Soil Aggregates Columnar and Prismatic Vertical aggregates
Soil aggregates can take the form of columns, particularly in arid-region soils. If the columns are polygonal, they are called prisms. Columns form in soils that shrink and swell as they wet and dry. Particular clays (as we saw earlier) exhibit this property. Vertical aggregates - found in some B horizons

Soil Pores Mineral Particles Pore Spaces Organic Matter water air
Soil pores make up roughly one half of the soil volume. They can be filled with either air or water. In well-drained soils, they will be about half filled with air and about half filled with water when the soil is moist. Of course there will be more air and less water when the soil is drier. In poorly-drained soils, the pores may be nearly completely filled with water for long periods of time.

Soil Water Water is attracted to particle surfaces Dry soil Wet soil
Oven-dry Air-dry Field capacity Draining Soil particles are pretty much always coated with water. When the soil is dry, the coating is thin. As the soil gets wetter, the coatings get thicker and coalesce becoming continuous, and filling pores. When the largest pores are filled, the attraction of water for soil surfaces is not enough to overcome the force of gravity pulling the water downwards, and water drains out of the soil. The soil is basically like a sponge. If you take a submerged sponge from water, it immediately begins to drain, with the largest pores emptying most quickly. After a while it stops draining, but there’s still lots of water in the sponge. And no matter how hard you squeeze the sponge, the surfaces inside the sponge are always coated with water.

Available Soil Water Water is held too tightly for plants
Available Water for plant use Water drains from soil So, just like the sponge, a wet soil will lose water by drainage. In a dry soil, the water is held so tightly that even plant roots can’t pull it out (just like the sponge). The water that drains out of a wet soil, and the water held very tightly in a dry soil is not available to growing plants. The other soil water is, and it’s appropriately called available water. Dried soil Wilting point (plants die) Field capacity Saturated soil

Soil Water Field capacity Too wet Available water Wilting point
Field capacity is the amount of water held after a wet soil drains. Wilting point is the amount of water held too tightly for plants to get it. As we said, the amount in between is available water. The amount of available water depends on soil texture. Small soil pores hold water more tightly than big pores. Soils with just big pores (sands) lose water through drainage and, as the slide above shows, have little available water. Soils with small pores (such as clays) hold lots of water, but hold it very tightly, so they also may not large amounts of available water. The best soils from the standpoint of available water are the medium textured soils - the loams and silt loams. Too dry Sand Sandy Loam Silt Clay Clay loam loam loam

Organic Matter Organic Matter biological remains
Mineral Particles Pore Spaces Organic Matter biological remains less than1% to over 20% most AZ soils have < 2% energy-rich material broken down by organisms to form humus (improves structure and water-holding capacity) soluble nutrients Organic matter consists of remains and by-products of biological origin. Soil organic matter content ranges from nearly 0 to more than 20 or 30% by volume. Most Arizona soils have very little organic matter - 0 to 2% or so. Organic matter is energy-rich. Green plants capture energy from the sun through the photosynthetic process and convert it to sugars, starches, and other carbon compounds. This energy moves through the food chain as other organisms consume plants, and are then themselves consumed. Ultimately, much of this stored energy ends up in the soil when dead plant or animal tissues fall on the ground, from animal wastes, or directly from by-products released into the soil (root exudates, for example). Soil organic material serves as a source of carbon and energy for many soil microorganisms. As primary organic material is broken down, humus, a stable organic by-product is formed. Nutrients contained in the organic matter are also released.

Organic Matter (OM) Soil structure
aggregate formation promoted by OM OM increases water infiltration & water holding capacity OM increases cation exchange capacity OM can increase microbial activity Nutrients OM provides a nutrient source OM helps keep some nutrients available OM can retain pesticides Organic matter improves soil structure, and all the things that go along with good structure: good water infiltration properties, high water holding capacity and cation exchange capacity, good aeration, etc. It also provides a source of nutrients. On the downside, organic matter retains chemicals such as pesticides, and high organic matter soils often require higher rates of pesticide applications than do soils with little organic matter.

Organic Matter Content
slow plant growth in arid climate Low High rapid decomposition in warm soils organic organic matter soils matter soils The amount of organic matter in a soil depends on several factors: 1. The rate of organic matter addition to the soil. This is largely a result of the amount of plant growth that occurs. 2. The rate of microbial decomposition of organic materials added to the soil. A) decomposition is faster in warm than in cold soils. B) microbes need moisture, but decomposition is also slowed by waterlogged conditions. C) tillage increases decomposition by mixing organic materials with the soil and improving soil to organic contact. It’s easy to see why Arizona soils tend to have little organic matter - desert conditions do not favor plant growth, but decomposition is favored by the warm, well-drained soils. rapid decomposition in well-drained soils rapid decomposition in tilled soils

Aerobic Respiration C6H12O6 + 6 O2  6 H2O + 6 CO2 Soil microbes
Carbon dioxide (gas) Oxygen (gas) C6H12O6 + 6 O2  6 H2O + 6 CO2 Here is an illustration of the process of aerobic (in the presence of air) respiration or decomposition of organic matter. Soil bacteria combine the reduced carbon in sugars, starches, cellulose and other organic substances with oxygen to form water and carbon dioxide. This can also be described as an oxidation reaction. Energy (electrons) is transferred from the carbon to the oxygen, and the bacteria utilize some of the energy. This respiration process is the same one we (and other animals) use to transfer energy from food to our bodies. Different organisms and processes operate in waterlogged or anaerobic conditions. Water Organic material

Organic Materials in Soil
Organic materials are decomposed by soil microbes carbon (C) in organics used for substrate and energy nitrogen is also required about 1/10 as much N as C is needed C:N ratio of 10:1 Organics with C:N ratios greater than about 10:1 require additional N During decomposition of organic materials, microbes use carbon as a substrate for making various compounds, many of which also contain nitrogen. As a general rule-of-thumb, soil microorganisms need about 1/10 as much nitrogen as carbon. To put it another way, they need carbon and nitrogen in a 10:1 ratio - or a C:N ratio of 10:1. If organics with a C:N ratio much greater than 10:1 are added to soil, additional nitrogen may have to be added to help these materials decompose, and to make sure enough nitrogen remains available for other things - like plant growth.

C:N of Some Organic Materials
This table shows the C:N ratios of some common organic materials. Note that when carbon-rich materials such as straw, bark, wood chips, or sawdust are added to a soil, nitrogen should also be added. If it is not, microorganisms trying to decompose the organics will scavenge any available nitrogen, not leaving enough for growing plants.

Managing Organic Amendments
High C:N ratio organics add adequate N during soil application compost to reduce C:N ratio to eliminate weed seeds Low C:N ratio organics add directly to soil watch for “burning” by high N organics High O2 consumption anaerobic conditions in poorly aerated soils Organic materials with high C:N ratios require careful management. One either needs to add supplemental nitrogen when these materials are added to a soil, or else the C:N ratio needs to be reduced through composting. Composting has the additional advantage of reducing numbers of viable weed seeds. Low C:N ratio organic materials can be added directly to soil. If nitrogen levels are very high, as in some poultry manures, plant “burning” can occur. Remember that the respiration process uses up oxygen. If very easily decomposed organic materials are added to soil, oxygen depletion can cause anaerobic conditions. This can be seen if one digs in a pile of grass clippings that have been allowed to decompose. The clippings become slimy when oxygen depletion occurs.

Plant Nutrients What’s in a plant?
Carbon (C) 45% Hydrogen (H) 6% Oxygen (O) 43% Nitrogen (N) to 6% Phosphorus (P) 0.1 to 1% Potassium (K) to 6% Calcium (Ca) to 4% Magnesium (Mg) to 2% Sulfur (S) to 1.5% One way to look at what elements or nutrients must be provided for healthy plant growth is to look at plant composition. This slide and the next indicate the elements that are contained in all higher plants, along with the general amounts (as a fraction of weight) of each. Carbon, hydrogen, and nitrogen make up the bulk of the plant - as water and various carbohydrates. The rest of the elements on this slide are called macronutrients because they are needed in relatively large (percent level) amounts. These are called Macronutrients because plants need relatively large amounts of them

Plant Nutrients Micronutrients (measured in parts per million or ppm)
Iron (Fe) to 1000 Manganese (Mn) to 1000 Molybdenum (Mo) to 10 Chlorine (Cl) to 30,000 Copper (Cu) to 50 Boron (B) to 75 Zinc (Zn) to 100 Nickel (Ni) to 1 The other nutrients are called micronutrients because they are needed in much smaller amounts (parts per million or ppm levels).

Sources of Plant Nutrients
H O N O N S C This slide shows sources of the various nutrients. Nitrogen, oxygen, and carbon can be obtained by plants directly from the atmosphere. The rest must be taken from the soil through the root system. Hydrogen and oxygen are provided by water. Rain water also adds nitrogen and sulfur to the soil. The others come from soil parent materials and decomposing organic matter. Ca Mo B Fe Ni Cl Mg Zn P Mn K S Cu

Primary Nutrients The three nutrients that most often limit plant growth nitrogen (N) phosphorus (P) potassium (K) Nitrogen, phosphorus, and potassium are macronutrients (needed in relatively large quantities) and are the nutrients that are most often lacking in cropped soils.

Nitrogen Nitrogen deficiency symptoms yellow or reddish leaves
leaf tips & margins yellow and die starting with oldest leaves stunted plants Nitrogen deficiency begins in the oldest leaves of a plant. The affected leaves become yellow. In grasses, the yellowing begins at the leaf tip and progresses back along the mid-rib. In other plants the whole leaf may become yellow, but deficiency symptoms can vary considerable in different plant species. Cabbage leaves (upper right), for example, become orange or red when nitrogen deficient. Corn (lower left) shows the typical symptoms of a grass that doesn’t have enough nitrogen - yellowing beginning at the leaf tip and progressing back along the mid-rib. Plant nitrogen deficiencies tend to show up on the oldest leaves because nitrogen is mobile within the plant. The plant will take nitrogen from the old leaves and move it into the newer growth when supplies are inadequate for normal growth. The same is true for phosphorus and potassium.

Nitrogen is an interesting element because it cycles between the atmosphere and the soil. Earth’s atmosphere is 78% nitrogen, although that nitrogen is available only to certain plants (such as legumes) that fix atmospheric nitrogen. Soil nitrogen takes several forms. It can be bound in organic matter, or it can be present as nitrate (NO3-) an anion, or ammonium (NH4+) which is a cation. Nitrate is easily leached from soil and can cause problems by contaminating ground water. Plants can absorb and utilize either nitrate or ammonium. Desert soils have little organic matter and therefore tend to have very low levels of nitrogen. Organic nitrogen must be converted to nitrate or ammonium before it can be used by plants, so organic fertilizers can be good nitrogen sources, but the nitrogen used by the plant is identical. Nitrogen rapidly cycles between the various forms, so levels of individual kinds of nitrogen can change rapidly.

Phosphorus Phosphorus deficiency symptoms
purplish foliage - oldest leaves first slow growth, stunted plants dark green coloration delayed maturity Phosphorus tends to be insoluble at very high or very low pH levels. In alkaline desert soils, phosphorus is tied up by soil calcium and is therefore not available to plants. Phosphorus deficiencies are common in these soils unless phosphorus-containing fertilizers are used. Phosphorus deficiencies also appear on the oldest leaves of affected plants. The affected leaves are often purplish. The whole plant may appear unusually dark green - sometimes almost bluish.

Potassium Potassium deficiency symptoms
leaf tips and margins ‘burn’ - oldest leaves first plants have weak stalks small fruit or shriveled seeds slow growth Potassium deficiency also affects the older leaves of the plant. These leaves turn yellow, then brown, beginning with the leaf margins. As with all deficiency symptoms, they vary in different types of plants. This slide shows potassium-deficient potatoes at the lower left. The older leaves are browning, beginning at the leaf edges, but the newer foliage still looks fine. Potassium-deficient alfalfa is in the upper right. You can see that the margins of the older leaves are showing deficiency symptoms. In the case of alfalfa, a spotted or speckled appearance is typical.

Acidity H+ (Acid) OH- (Base) H O H
Soil acidity is a basic soil property, and one that is very important in soil management. First let’s look at what acidity is. Water is comprised of two elements: hydrogen and oxygen, as illustrated above. Water is pretty stable, but it does come apart to some extent, forming hydrogen ions (H+) and hydroxide ions (OH-). Hydrogen ions are considered acidic, and hydroxide ions are basic or alkaline (alkaline and basic are the same thing). A water solution that has more hydrogen ions is acidic; one that has more hydroxide ions is basic. OH- (Base)

Each pH unit is 10 times more acid or alkaline
The pH scale Each pH unit is 10 times more acid or alkaline than the next unit Range of Alkalinity Range of Acidity Neutral We express acidity or alkalinity in pH units. The pH scale runs from 0 to 14. A solution with a pH of 0 is extremely acidic, whereas one with a pH of 14 is extremely basic. One with a pH of 7 is neutral. Each pH unit is ten times more acidic or basic than the next pH unit (pH 5 is ten times more acid than pH 6, for example). Plant growth will occur over a relatively wide range of soil pH’s - anywhere from 3.5 to 4 all the way up to 9 or 10, although most plants are happiest in a narrower range. 2 4 6 8 10 12 14 Plant Growth

Optimum for most plants
Soil pH Optimum for most plants 2 4 6 8 10 12 14 Here we can see the optimum range for most plants - about 5.5 to 7.0 and also the pH range of most Arizona soils - pH 7.0 to This presents a problem for those of us trying to grow many plant species. Most plants are adapted to the soils of their place of origin. Native Arizona plants are well-adapted to the high pH desert soils. But many ornamentals (and crop plants) we bring in from other parts of the world are not. For example, many tropical soils are quite acidic, so tropical plants tend to prefer acidic soils, and do poorly under alkaline conditions. Most Arizona soils

Soil pH Alters nutrient availability Affects microbial activity
Can affect disease susceptibility These are some of the things that are affected by soil pH.

Alkalinity in Arid Soils
calcium magnesium sodium move up with water and accumulate HCO3- CO3= carbonates bicarbonates Ca++ H2O In arid regions net water movement is upward because rainfall is limited and high temperatures increase evaporation. Water moving up through the soil profile carries dissolved salt with it, and when the water evaporates from the soil surface, the salts are left behind. These salts usually include carbonates and bicarbonate, which are basic or alkaline. As carbonates and bicarbonates accumulate, the soil pH rises and eventually the soil becomes alkaline. H2O Mg++ Na+ H2O H2O H2O H2O

Alkalinity in Arid Soils
Calcium bicarbonate Ca++ HCO3- + H2O OH- (moderately strong base) CO2 High pH (8.3) Calcium bicarbonate is a common salt in arid region soils. It combines with water (hydrolyzes) to form carbon dioxide and calcium hydroxide, a moderately strong base. Soils with calcium bicarbonate can have pH’s as high as 8.3.

Alkalinity in Sodic Soils
Sodium bicarbonate Na+ HCO3- + H2O OH- (very strong base) Very high pH (>8.5) CO2 Sodium bicarbonate is a common salt in sodic soils. It combines with water, forming sodium hydroxide, a very strong base. Soils with sodium bicarbonate can have pH’s greater than 8.5.

Effects of pH on Nutrient Availability
The thicker the bar, the more available the nutrient 4.0 5.0 9.0 8.0 7.0 6.0 8.5 7.5 6.5 5.5 4.5 4.0 5.0 9.0 8.0 7.0 6.0 8.5 7.5 6.5 5.5 4.5 pH pH This diagram shows schematically how pH affects nutrient availability. Most notably, iron, copper, and zinc become less available to plants when soil pH rises above 7.5 or Manganese and phosphorus are also affected.

Iron Chlorosis Iron deficiency appears on youngest leaves of plants
growing in alkaline soils Here are some photographs of iron deficiency (also called iron chlorosis - chlorosis just means yellowing). Unlike nitrogen, phosphorus, or potassium deficiency, iron deficiency appears first on the youngest leaves. Usually the interveinal area, or the area between the veins, on these leaves becomes bleached or whitish.

Treating Soil Alkalinity
Acidify the soil sulfuric acid H2SO4 aluminum sulfate: Al2(SO4)3 + 6H2O  2Al(OH)3 + 3H2SO4 NOTE: gypsum (CaSO4) is NOT an acidifying compound and will not lower pH of most soils! sulfur (biological reaction) 2S + 3O2 + 2H2O  2H2SO4 Alkaline soils can be made more acidic by adding various amendments. 1. An acid can be added directly - the most common is sulfuric acid. 2. Elemental sulfur added to the soil is microbially oxidized to form sulfuric acid. This is an effective, but relatively slow process. 3. Other acid-forming compounds can be used, such as aluminum sulfate, which forms an acid when it dissolves. 4. Because many sulfur-containing compounds are used to acidify soils, a common misconception is that all sulfur compounds acidify. This is not true! Gypsum, for example, does not acidify soil.

Fertilizing Alkaline Soils
Apply nutrients to high pH soils Metal nutrients are insoluble in alkaline soils iron, manganese, zinc Use chelated forms more soluble than unchelated forms stay in solution longer more available to plants Rather than trying to alter the soil, nutrients that are unavailable in alkaline soils (iron, manganese, zinc) can be added. The reason these nutrients are unavailable in alkaline soils is that they become insoluble, so just adding more may not help. To keep these nutrients soluble, they are often added in a chelated form.

Chelates A chelate (pronounced key-late) is a cage-shaped molecule that traps the nutrient inside. Shown here is iron chelated by a man-made chelate called EDTA (there are also many natural chelates). The chelate-nutrient complex remains soluble and can supply growing plants for long periods of time, although eventually nutrients in this form also become unavailable, so it’s not a short-term fix.

Treating Plants in Alkaline Soils
Apply nutrients directly to plant foliage Iron, Copper, Zinc use sulfate salts iron sulfate copper sulfate zinc sulfate use chelated forms EDTA DTPA others The soil can be bypassed altogether, and the nutrients that are unavailable in alkaline soils (iron, copper, zinc) can be applied directly to plant foliage. Sulfate salts or chelated forms can be used. A note of caution: it is very easy to damage plants by applying too much fertilizer to the leaf tissue. Very dilute solutions must be used. Find reliable directions, and follow them closely!

Salts and Soil Desert soils are often salty, and this can provide additional challenges.

Salt-Affected Soils Salt-affected soils
Occur naturally in arid climates Can be formed by addition of salts in irrigation water The term “soluble salts” refers to any salts more soluble than gypsum (calcium sulfate). Soluble salts can accumulate naturally, or by addition of salts in irrigation water. Periodically leaching soil by over-watering will move soluble salts deeper into the soil profile, and away from plant roots.

Water Transports Salts
This is a nice illustration of the way that salts move with water. Water has moved from the furrow into the bed, eventually moving to the center of the bed and evaporating from the peak of the bed. The salts that were left behind when the water evaporated have accumulated on the bed peak.

Salt-Affected Soils Saline - excess salts Sodic - excess Na
good structure moderate pH Sodic - excess Na poor structure high pH (>8.5) Saline-sodic excess salts excess Na good structure high pH There are essentially three kinds of salt-affected soils. The first kind are called saline soils (saline just means salty). The second kind are sodic soils. Sodic refers to sodium, and these are soils with lots of sodium, but they are not saline. The third kind of soil are both saline and sodic - salty and with lots of sodium - and are called saline-sodic soils. Saline soils have excess non-sodium salts - usually calcium or magnesium carbonates, chlorides, or sulfates. They tend to have good structure, and a moderate pH (less than 8.5). The main problem is that plants may not tolerate the salts, and they may have to be leached or flushed from the soil be washing water through the profile. If they are too alkaline, the pH may also have to be reduced, as described earlier. Sodic soils usually have poor structure (because sodium does not hold particles in aggregates very well), and a very high pH (over 8.5). They are hard to manage. Sodium must be replaced (usually by adding gypsum CaSO4), then leached with fresh water. Saline-sodic soils have relatively good structure because, even though they have lots of sodium, the total salt level is high enough to keep particles aggregated. pH is generally less than Before salt levels are reduced by leaching, sodium must be replaced by calcium, usually through gypsum addition.

Salts Affect Soil Structure
A little sodium makes particles repel one another. - Na+ or a little calcium A lot of sodium Na+ - Large, low-valence cations such as sodium, are not very good at aggregating soil particles. At the other extreme, small, high-valence cations such as calcium and aluminum, are very effective aggregators. It takes a lot of sodium to aggregate particles, so a sodic soil with just a little sodium, but not a lot of other cations, will tend to disperse. If a soil contains high enough levels of sodium, as in a saline-sodic soil, the total level of sodium may be high enough to keep the soil from dispersing. In soils dominated by calcium, aluminum, etc., aggregates are stable even if the total salt level is quite low, because these cations are so effective at aggregating soil particles. Ca++ - make particles attract one another.

Salts Affect Soil Structure
Sodium level (SAR) Unstable soil Stable soil This is an illustration of the ability of sodium to destabilize soil. On the upper and left side of the graph, there is lots of sodium (measured by sodium adsorption ratio) but not enough total salts (represented by electrical conductivity) to keep soil particles aggregated. At the lower right, there are lower levels of sodium and more total salts, so soil structure is stable. Soil aggregates are stable if sodium levels are low and/or if total salt levels are high.

Tests for Soil Salts Measuring total soil salts
EC - electrical conductivity Measures of the amount of sodium SAR - sodium adsorption ratio ESP - exchangeable sodium percentage When a soil sample is sent to a laboratory for analysis, there are a couple of measurements that may be made that relate to saline and sodic soil conditions. Electrical conductivity - measures the amount of soluble salts in a soil and is a measure of salinity. Soils with an EC>4 dS/m are saline. Sodium adsorption ratio - this measures the amount of sodium relative to the other cations (calcium and magnesium). Soils with an SAR>13 are considered to be sodic. Exchangeable sodium percentage - the amount of the cation exchange capacity that is filled by sodium. This is roughly equivalent to SAR. Soils with ESP>15 are sodic.

Classifying Salt-Affected Soils
The system of classification we use in the United States divides soils into four categories based on salt levels and properties. Normal soil is non-saline (EC<4) and non-sodic (SAR<13). Saline soil is saline (EC>4), but non-sodic (SAR<13). Sodic soil is non-saline (EC<4) , but is sodic (SAR>13). Saline-sodic soil is both saline (EC>4) and sodic (SAR>13).

Electrical Conductivity (EC)
Here are some basic guidelines about how electrical conductivity affects the growth of plants. There is a huge range in the tolerance of plant species to soil salts. The Western Fertilizer Handbook is a good resource for information on salt tolerance of various plants.

Salt-Affected Soils Plant age affects tolerance to salts
Seedlings are most sensitive Mature plants are least sensitive Different plant parts may be variably affected Seeds Vegetation Plant species vary in salt tolerance The extent to which plants are affected by salts depends on plant age (seedlings are most sensitive), plant part (depending on the plant, one part or another may be more affected), and also on the species and variety of the plant.

Managing Non-Sodic Saline Soils
K+ SO4= Cl- H2O Na+ Non-sodic, saline soils can be converted to non-saline soils simple by leaching them with clean water. The water carries the salt out of the soil profile, leaving a non-saline, non-sodic soil.

Avoiding Salts Saline soils can also be managed by keeping salts away from seedlings. Here seeds are planted on the side of a peaked bed. Water in the furrows carries the salt past the seedling to the middle of the bed, where it accumulates.

Sodium-Affected Soils
Poor structure Poor drainage May have surface cracking when dry Very high pH (>8.5) Sodium-affected soils tend to have poor structure, poor drainage, and a very high pH. The soil surface often has a cracked or checked appearance when the soil dries.

*may be very difficult in soils with poor structure!
Managing Sodic Soils 1. Stabilize structure by adding gypsum (CaSO4) to replace Na+ with Ca2+ 2. Reduce salt level by flushing with water to wash out Na+ and excess gypsum* *may be very difficult in soils with poor structure! Sodic and sodic-saline soils must be stabilized by adding a flocculating cation such as calcium, usually in the form of gypsum. Excess salts can then be flushed by leaching clean water through the soil profile. This can be very difficult in a sodic soil, where structure is poor and water infiltration rates are very low. Formation of a sodic, non-saline soil should be avoided!

Managing Sodic Soils Ca++ SO4= Ca++ Ca++ - - - - - Ca++ - - - - - Na+
Here is a schematic representation of sodic soil reclamation. Na+ Na+ Na+ Na+ Na+ K+

Fertilizers Label must contain percent (by weight) of
total nitrogen (N) available phosphate (as P2O5 ) P2O5 times 0.43 = P soluble potash (as K2O ) K2O times 0.83 = K Other nutrients may be specified Fertilizers usually contain the three primary nutrients - nitrogen, phosphorus, and potassium. The label of a fertilizer container, by law, must include the amounts of these three elements expressed as follows: Nitrogen - the total amount of nitrogen in the fertilizer expressed as %N by weight. Phosphorus - the available phosphorus (determined by extraction with ammonium citrate) expressed as if it were P2O5. Fertilizers don’t actually contain P2O5, but usually some type of phosphates (PO43-). The P2O5 expression is left over from the early days of chemistry. To convert P2O5 to elemental P, just multiply by 0.43. Potassium - this is the water soluble potassium, expressed as if it were K2O (although, as with phosphorus, fertilizers don’t contain K2O). To convert K2O to elemental K, multiply by 0.83. Fertilizers may contain other nutrients, and they may or may not be listed on the label.

Types of Fertilizer Complete Incomplete
Complete contains all three primary nutrients (N, P and K) Incomplete is missing at least one of the primary nutrients 0-45-0 A complete fertilizer is one that contains nitrogen, phosphorus, and potassium. An incomplete fertilizer is one that does not have all three. Incomplete fertilizers are often used when only one nutrient needs to be applied (as when a lawn is fertilized with nitrogen fertilizer).

Common incomplete fertilizers
Here are some incomplete fertilizers that are commonly available.

Slow-release fertilizers
Release nutrients (usually nitrogen) over a long period of time slowly soluble materials urea formaldehyde granules coated with resins or sulfur sulfur-coated urea Osmocote® materials that must decompose to release nutrients organic fertilizers Some fertilizers, slow release fertilizers, provide nutrients over a much longer period of time than do conventional fertilizers. Some dissolve slowly (urea formaldehyde is an example), others must decompose or break down first (most organic materials), and others have coatings that slow down dissolution of soluble nutrients inside the fertilizer pellet (osmocote and sulfur-coated urea, for example).

Organic fertilizers Remains or by-products of plants or animals
cottonseed meal blood meal fish meal manures Relatively low nutrient contents Contain micronutrients Slow release Low burn potential Condition soil by adding organic matter Almost any plant or animal waste or by-product can be used as a fertilizer material - some are listed in this slide. In general, they have much lower nutrient concentrations than conventional fertilizers, although there’s a lot of variation. Some of the benefits of using organic fertilizers: 1. They usually contain micronutrients, often in a chelated form. 2. They release nutrients slowly, so the nutrients are less likely to be lost through leaching processes or tied up in the soil. 3. Because they release nutrients slowly, it is harder to overdo it and damage or‘burn’ plants. 4. They add organic matter to the soil, improving soil structure. Organic fertilizers are not magical - the nutrients they provide are exactly the same as those contained in conventional fertilizers and the plants grown with both types of fertilizers are identical in every respect.

Typical composition of organic fertilizers
Here are compositions of some commonly used organic fertilizer materials.

Fertilizer formulations
Fertilizers can be combined with herbicides common in turf formulations Fertilizers granular solids slow-release granules liquids/water soluble powders slow-release spikes/tablets Fertilizers can be mixed with pesticides. Several widely-used turf fertilizers contain herbicides to control broad-leaf weeds in lawns. Fertilizers also come in many physical forms. The most common are solid granules, which can be either conventional fertilizers or slow-release materials. Soluble powders or liquids are frequently sold for household use. These forms are also used for foliar application (application directly on the leaves). Other forms include slow-release spikes and tablets.

Fertilizers are salts Fertilizers are salts, and they have the potential to damage plants by increasing the salinity or saltiness of the soil. In general, nitrogen fertilizers pose the biggest salt hazard, partly because large amounts of nitrogen are often used, and partly because most nitrogen fertilizers are very soluble. Phosphorus fertilizers pose the least risk, because these tend to be relatively insoluble.

Avoiding fertilizer burn
Do not over-apply fertilizers particularly nitrogen fertilizers Make sure adequate moisture is present after applying fertilizer Periodically flush soluble salts from soil make sure adequate drainage is available irrigate 2 to 3 times as long as normal every 6 to 8 weeks to flush salts from soil To avoid burning plants with fertilizers: 1. Apply recommended amounts- do not over-apply (especially important for nitrogen fertilizers. 2. Make sure the soil remains moist after fertilizer application. This will, in effect, dilute the fertilizer in the soil. 3. Periodically, plants should be over-watered (enough so water drains through the soil) to flush excess salts from the soil. This is recommended no matter what kind of fertilizers are used because dissolved salts are added every time plants are irrigated, and soils will become saline over time unless these salts are removed by leaching.

Soil Testing Available nutrients Soil properties Phosphorus Potassium
Calcium Magnesium Nitrogen Sulfur Micronutrients Soil properties Texture pH Cation Exchange Capacity (CEC) Electrical Conductivity (EC) Sodium Adsorption Ratio (SAR) or Exchangeable Sodium Percentage (ESP) When a soil sample is submitted to a laboratory for analysis, there are several tests that are routinely run. Levels of available nutrients are usually analyzed, including phosphorus, potassium, calcium, and magnesium. Nitrogen is sometimes run, but it changes forms rapidly enough that evaluating results can be problematic. The same is true of sulfur. Micronutrients may also be analyzed, but they often cost extra, and they can be tricky to interpret. They would usually be run if a specific problem is suspected. Basic soil properties that are always determined include texture and pH. Cation exchange capacity is frequently run, and electrical conductivity, and sodium adsorption ration or exchangeable sodium percentage may be run if salinity problems are suspected.

Soil Sampling Obtaining a representative sample is the critical step in soil analysis A 1 cup sample from a 1,000 square foot field is 1/100,000 of the field! A good soil sample made up of 15 to 25 cores or subsamples never take less than 5 subsamples Taking a good soil sample is the single most important step in soil analysis. Soils are remarkably variable, and when sampling even a very small area (like a small garden) a sample made up of at least 15 subsamples is recommended. Individual subsamples should be combined in a clean container, and thoroughly mixed.

Soil Sampling Divide fields into uniform areas for sampling soil type
slope degree of erosion cropping/use history growth differences Upper end Middle A separate composite sample should be taken for each area of soil that will be individually managed. In a yard, this might mean that individual beds or gardens would be sampled separately. On a farm, individual fields are individually sampled. Sometimes areas might be divided if there are noticeable differences in soil type, slope, degree of erosion, or if the areas have been planted with different crops, or if differences in growth are noted. A problem area in a field is often sampled separately to help identify the problem. However, it may not make sense to sample an area individually unless it will be managed separately. Lower end

Soil Sampling Sample to the proper depth
usually eight inches Make sure soil cores represent sampled area mix individual cores thoroughly to make sample Time of sampling depends on analyses, field operations, etc. Sampling tools soil probe or sampling tube is best It is important that soils are sampled to a reasonable depth. For cropped fields or for gardens, the typical sampling depth is approximately 8 inches (roughly the rooting depth for many crops). Trees and other plants with deeper rooting systems may require correspondingly deep soil samples. Make sure individual cores that comprise a composite sample are thoroughly mixed to help ensure that the sample is representative. It doesn’t usually make a great deal of difference when a soil sample is collected. Convenience probably the most important factor. If one is planting trees or other long-lived perennials, samples should be collected well in advance of planting so soil problems can be addressed prior to planting. For an annual garden, it is less critical because corrections can be made annually. Any digging device can be used for sample collection, but a soil probe like the one illustrated above work best. If a shovel or trowel is used, be very careful to get representative material from the entire sampling depth.

This photograph shows typical symptoms of salinity - dead (or burned)areas around the leaf margin.
In northern areas, these symptoms are quite common in plantings along roadsides and sidewalks where salt used as a de-icer has leached into the soil.

Comments and/or suggestions for improving this slide set and notes are welcomed.

Soil Science for Master Gardeners

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