BASIC SOIL SCIENCE MARYLAND MASTER GARDENERS FEBRUARY 24, 2016 RICHARD A. WEISMILLER PROFESSOR EMERITUS, UMCP DEPARTMENT OF ENVIRONMENTAL SCIENCE AND TECHNOLOGY
SOIL OR DIRT WHATEVER!!!!
SOIL SAY WHAT? Earth Loam Dirt Mud Topsoil Dust Clay Muck
WHAT WILL BE COVERED Why soils are important What are soils Soils and how they are formed Soil physical properties and importance Soil chemical properties (nominal) and significance Soil microorganisms, amount and value A fertility ditty (soil that is)
Biosphere Atmosphere Pedosphere Hydrosphere Lithosphere
FIELDS OF STUDY IN SOIL SCIENCE Physics Chemistry Genesis Classification Mineralogy Fertility Management
Why are soils important? Medium of crop production Producer and absorber of gases Great integrator Snapshot of geologic, climatic, biological, and human history Waste decomposer Medium for plant growth Home to organisms (plants, animals and others) Essential natural resource Source material for construction, medicine, art, etc. Filter of water and wastes
SOME INTERESTING FACTS We know less about life in the earth under our feet than we do about the far side of the moon. Yet every plant and animal you can think of depends on this vast hidden ecosystem. Each shovel of soil holds more living things than all the human beings ever born. Lots of species are still waiting for scientists to identify and name them. This is a world where fungi lay traps for thread-like worms. Bacteria dine on toxic chemicals. The smaller the creature, the stranger are its habits. A teaspoon of good farm soil contains up to 1 billion bacteria in more than 4,000 species. L. Clarke/Corbis
A SOIL UNIT
Average Soil Composition 25% Water 45% Inorganic mineral materials Pore space 50% { } 25% Air 5% Organic Matter Solids 50%
SOIL DEVELOPMENT Soil Forming Factors Parent Material Organisms Topography Climate Time Soil Forming Processes Additions Losses Transformations Translocations
SOIL PHYSICAL PROPERTIES Texture Surface Area Color Organic Matter Bulk Density Structure Hydrology Temperature Pore space
Two Meanings for Clay Clay can represent a particle size, e.g., less than 0.002 millimeters in diameter Clay can also represent a type of mineral, the phyllosilicates e.g., kaolinite, illite, smectite, etc. These are sometimes called colloids.
SOIL TEXTURE Texture relative proportion of the various grain sizes in a soil. To describe soil texture, names, such as loamy sand, silt loam, clay loam and silty clay are used. The best soils are generally those which contain 10 to 20% clay, with silt and sand in approximately equal amounts, and a fair amount of organic matter.
RELATIVE SIZE COMPARISON OF SOIL PARTICLES barrel plate coin Sand - feels gritty (2.00-0.05 mm) Silt - feels floury (0.05-0.002 mm) Clay - feels sticky (< 0.002 mm) USDA system for determining soil separates
STRUCTURE OF SOIL CLAY MINERALS
SURFACE AREA In comparing clay with sand and silt, it is important to be aware of the relative amount of surface area of these particle size groups, because it is on the surface that many chemical and physical processes take place. Smaller = more surface area (clay is tiny!)
SOIL PARTICLE SURFACE AREAS Surface Area Charge Sand 50 cm 2 /g none Silt 500 cm 2 /g none Clay 5,000,000 cm 2 /g negative
PARAMETERS OF SOIL PARTICLES Kind of Particle Diameter of Particle # of Particles in 1 gram Surface area of 1 gram Sand 2 mm 90 11 cm 2 Silt 0.02 mm 90,000,00 0 Clay 0.0002 mm (9x10 7 ) 1130 cm 2 9x10 13 113,000 cm 2
SOIL COLOR Color of soils tells us much about some of its other properties. The color of a surface soil horizon depends mainly on its organic matter content the darker the soil, the more organic matter it contains. This organic matter imparts favorable properties to the soil, such as better aggregation and a high water-holding capacity. Also, dark soils absorb more radiation during the day, and radiate more heat during the night. In subsoil horizons, soil color indicates the wetness and aeration conditions of the soil.
GRASSLAND SOIL VS FOREST SOIL Mollisol Alfisol
WEA SOIL OVER GLACIAL OUTWASH
DIFFERENT COLORS OF SURFACE SOILS
SOIL COLOR, SOIL AERATION OR DRAINAGE, AND THE OXIDATION STATE OF IRON POOR AERATION 1. Iron is reduced 2. Fe ++ 3. dull colors (grays, blue) 4. poorly drained GOOD AERATION 1. Iron is oxidized 2. Fe +++ 3. bright colors (yellows, browns) 4. well drained
COMPONENTS OF SOIL ORGANIC MATTER Living organisms <5% Fresh residue <10% Stabilized organic matter (humus) 33% - 50% Decomposing organic matter (active fraction) 33% - 50%
IMPORTANCE OF SOIL ORGANIC MATTER PHYSICAL PROPERTIES Improves physical condition Allows for good aggregation of soil particles because of the plant and animal residues in the surface Increased water infiltration Allows water saturation by acting as an absorbent Improves Soil Tilth Allows for more uniformity of the soil aggregates in proportion to the plant, animal and mineral residues present
SOIL STRUCTURE Soil structure is the combination or arrangement of primary soil particles into secondary units The way soil particles are arranged to form stable aggregates Aggregates may be bound together with other aggregates in larger masses called peds. Compaction results from implement traffic, stable soil aggregates are broken down
COMMON TYPES OF SOIL STRUCTURE A E B Granular Platy Blocky C Massive
BULK DENSITY Soil is made of solids and pore spaces { } 1.33 grams For our example, let s assume we have 1 cubic centimeter of soil that weighs 1.33 grams To calculate Bulk Density: Volume = 1 cm 3 Weight = 1.33 grams Bulk Density = 1.33 1 Bulk Density = Weight of Soil Volume of Soil Bulk Density = 1.33 grams/cm 3
BULK DENSITY AND COMPACTION Depth 0 inches Bulk Density (g/cm 3 ) 7 inches 8 inches 9 inches 10 inches 1.43 1.90 1.87 1.84 1.80 1.60 Plow layer Compacted zone Uncompacted subsoil Data from Camp and Lund
INFLUENCES OF SOIL TEXTURE, STRUCTURE AND DENSITY Water movement Water retention Soil temperature Gas exchange Erosion potential Fertility
PORE SPACE Large pores are readily drained of water and filled by air after a heavy rain. They are valuable as an aeration system. Small pores hold water against gravity and pull water up from a water table by capillary action. They are necessary for the water supply of plants.
PORE SPACE, WATER, AND AIR
PORE SPACE, WATER, AND AIR
PORE SPACE, WATER, AND AIR
ORGANIC MATTER VS WATER CONTENT
WATER CONTENT AT VARIOUS TENSIONS
Inches water/ft. soil PLANT AVAILABLE WATER 4 3 2 1 Sand Sandy loam Silt loam Clay loam Clay
SOIL TEXTURE VS WATER CONTENT
SOIL TEXTURE VS WATER CONTENT
SOIL SOLUTION AND NUTRIENT MOVEMENT Soil solution is the water held within the soil that contains dissolved essential elements. Soil ph, CEC, and soil moisture determine nutrient supply available. Concentration of nutrients in soil solution often very small portion of total amount.
SOIL TEMPERATURE Just as important to plant growth as air temperature. The temperature of the surface soil fluctuates greatly both during a 24 hr period and with the seasons. Soil temperature has a direct effect on plant growth and also influences microbial activity.
MICROORGANISMS * IN THE SOIL Microbes live in small clumps In fact, less than 1% of the soil surface will support the growth of microbes Do not migrate much Their goal: maintain species 7,000 different species in one gram of soil! 4.5 x 10 16 bacteria/acre, 3 inches deep Microbes are hungry, immobile and ready to reproduce * Excludes nonarthropod and arthropod animals, as well as vertebrates
NITROGEN-FIXING BACTERIA Nodules formed where Rhizobium bacteria infected soybean roots.
RHIZOSPHERE
MICROBIAL BIOMASS WITH DEPTH
SEASONAL MICROBIAL ACTIVITY
CARBON NITROGEN RATIO
CHEMICAL PROPERTIES Cation exchange capacity Anion exchange capacity ph the master variable Buffering capacity Oxidation/reduction reactions Surface Chemistry Mineralogy
ORGANIC MATTER ph dependent charges, particularly the carboxylic acid components of the molecules. (C-OH and C-H) A large contributor to chemical ion exchange
CLAY MINERALS Clay is a negatively charged colloid. This negative charge is the reason that positively charged cations surround each clay particle. The individual cations can be exchanged for each other.
WHAT WAS COVERED Why soils are important What are soils Soils and how they are formed Soil physical properties and importance Soil chemical properties (nominal) and significance Soil microorganisms, amount and value A fertility ditty (soil that is)
Sixteen Essential Elements for Plant Growth A Helpful Mnemonic
C. Hopkins Café Managed by mine cousin Mo, Clean C HOPKNS CaFe, Mg B Mn CuZn Mo, Cl
C HOPKNS CaFe, Mg B Mn CuZn Mo, Cl C Carbon, O Oxygen, K Potassium, S Sulfur, Fe Iron, B Boron, Cu Copper, Mo Molybdenum, H Hydrogen, P Phosphorus, N Nitrogen, Ca Calcium, Mg Magnesium, Mn Manganese, Zn Zinc, Cl Chlorine
Macronutrients C HOPKNS CaFe, Micronutrients Mg B Mn CuZn Mo, Cl