SOILS Sam Angima OSU Extension Agent Lincoln County, Oregon
Soils Introduction Definition & Function Soil Physical Properties Soil Chemical Properties Soil Biological Properties Soil Organic Matter
Soil is composed of : 1. Water and air 2. Water, air, and solids 3. Solids, organic matter 4. Organic matter 5. Air, water, organic matter, and solids 0% 0% 5% 0% 95% 1 2 3 4 5
Soils Defined An ecological system consisting of inorganic minerals, organic matter, living organisms & Plant roots, water & air Ideal ratio by volume: ½ Soil particles (5% OM by weight) ½ Pore spaces (½ water, ½ air)
Soil Composition By Volume Solids Mineral 45% Water 25% Soil gases 25% Pore Space Organic 5% % by volume (but % weight for OM) Ideally, a volume of soil should be ½ solid material and ½ pore space. Ron Smith, 2005
Pore Space & Particle Space - Magnified
Gross Anatomy of a Soil University of Minnesota adapted from The Last Billion Years
Benefits Functions of Soil Regulates water in the environment Cycles nutrients between plants and animals Filters and detoxifies pollutants
Which soil pores are responsible for pulling water from deep depths? 1. Macropores 2. Micropores 3. Megapores 4. Organic matter 5. Do not know 38% 29% 5% 19% 10% 1 2 3 4 5
Micropores Filter & detoxify pollutants Macropores = earthworms & root channels (drainage) Micropores = water holding capacity, minerals
Soil Physics Soil Physical Properties
The Mineral Part of Soil Clay Less than 0.002 mm (0.000078 ) in diameter Feels smooth when dry, slick & sticky when wet Silt Betwn 0.002 and 0.05mm (0.002 ) in diameter Feels floury when dry, smooth when wet Sand Between 0.05 and 2.0 mm (0.078 ) in diameter Feels rough
Soil Separates Sand (see with naked eye) Silt (size of flour ) Clay (Electron Microscope)
Soil Texture
Surface Area in One Acre* Plow Layer Coarse sand Fine sand 500 acres 5,000 acres Silts 50,000 acres Clays 25,000,000 acres (Oregon is 60,000,000 acres) *One acre = 43,560 ft 2
What is soil texture? 1. Shapes of soil particles 2. Proportion of sand, silt, and clay particles 3. Proportion of sand and clay 4. Proportion of silt and clay 5. Percentage of plant nutrients in the soil 95% 5% 0% 0% 0% 1 2 3 4 5
Soil Texture Texture is the proportional amount of each of these groups (using size of particles only) Loam soil has about 40% sand and silt and 20% clay Good soils are Loam => 40% sand, 40% silt & 20% Clay sandy loam => 60% sand, 30% silt & 10% Clay silt loam => 20% sand, 60% silt & 20% Clay clay loam => 30% sand, 30% silt & 40% Clay Use textural triangle
Soil Texture Triangle There are 12 texture classes A texture class is determined by the relative proportions of sand, silt, and clay in a soil body
What is the best soil texture? 1. Any soil texture 2. Loam soil 3. Clay soil 4. Sandy soil 5. Silt soil 82% 9% 0% 5% 5% 1 2 3 4 5
Water Infiltration Any soil texture is good for gardening if you know what its limitations are Redrawn from Cooney & Peterson)
Notes Sandy soils drain faster and warm up fast Clay soils remain cold and wet late into the spring Due to their large surface area, clay soils take more lime to raise ph Clays soils may require drainage Clay-loam soils hold enough water for good plant growth
Determine Soil Texture at Home Fill a quart jar filled about half way with a sample of your soil and then topped off with water If you have it, add a teaspoon of Calgon or activated carbon Cover & shake it (min 2 min) energetically until everything is swirling around Set it aside and let it settle until the water clears
Determine Soil Texture at Home The sand particles are the heaviest and they will settle to the bottom within a few minutes Within an hour or two, the silt will have formed the next layer The fine clay particles will finally settle in a day or two OM may remain floating around on the top Measure layer heights and convert to percentage ratios If the clay layer makes up half or more of your sample, you have a heavy clay soil
Soil Texture 52% sand, 17% silt, & 32% clay
Soil Structure Arrangement of soil particles into secondary units (peds) = given name
Soil Structure Allows for movement of air and water Lets roots penetrate Compaction squeezes macropores to micropores Less water movement Less root penetration If you can make a soil ribbon = too wet to till Excessive tillage by roto tiller destroys soil structure
What soil structure is this?
Gray mottles indicate soil stays too wet e.g. soil around septic systems
Soil Chemistry Soil Chemical Properties
Water In its simplest form, H 2 O dissociates H 2 O H + + OH - H + (positive) ions are responsible for acidity OH - (negative) ions are responsible for alkaline conditions) That is why: CaCO 3 Ca 2+ + CO 3 2- Then Ca 2+ replaces two H + from the soil surface to increase ph
Soil ph Measure of hydrogen ion activity ph range of 0-14 Less than 7: => acidic 7: => neutral Greater than 7: => alkaline One unit change in ph represents 10 fold change in H + ion concentration ph of 5 is 10 times acidic than ph of 6 Optimal plant growth betwn 5.5-7.5
What is the ph of stomach acid? 1. 7 2. 8 3. 5 4. 1 5. 4 26% 42% 16% 11% 5% 1 2 3 4 5
The ph Scale The diagram below indicates the ph values of some body fluids and household liquids. neutral acids bases
Optimal ph range Nitrate Potassium Aluminum Iron Calcium Phosphorus Magnesium Sulfur Manganese Molybdenum Zinc 4.5 5.0 5.5 6.0 6.5 7.0 7.5 8.0
Soil ph & Plants Affects availability of nutrients Affects microorganism populations Affects availability of toxic metals in soil solution e.g. aluminum is toxic in low ph and Fe is unavailable in higher ph At low ph, Aluminum complexes with phosphorus making it unavailable to plants
What causes soil acidity? 1. Rain and leaching 52% 2. Fertilizers 3. Parent rocks 30% 4. Decomposition 5. All of the above 13% 0% 4% 1 2 3 4 5
Causes of Soil Acidity Acidic parent material Leaching or plant nutrients with removal of basic cations Decomposing organic matter Acids formed in decomposition process Certain nitrogen fertilizers Conversion of ammonium to nitrate generates H + Acid rain ph of rainwater is 5.6, becomes more acidic with dissolved nitrous oxide or sulfur dioxide
How can you adjust soil ph? 1. Dolomite 2. Sulfur 3. Wood ash 4. Lime 5. All of the above 0% 0% 0% 52% 48% QUESTION 4 1 2 3 4 5
Adjusting Soil ph Adjust low soil ph Lime calcium carbonate (CaCO 3 ) Use 50lb per 1000 square feet of garden Dolomitic lime lime w. magnesium (CaMg(CO 3 ) 2 ) Quicklime (Ca(OH) 2 ) Wood ash (CaO) Use 20-25 lb/ 1000 sq ft of garden High rates may cause salt injury Lower ph Use 50 lb/1000 sq ft of elemental sulfur (S)
Calcium Carbonate Equivalents Material Calcium Carbonate Equivalent Limestone (CaCO 3 ) 100% Dolomitic lime (CaO MgO) 109% Quicklime (CaO) 179% Hydrated lime Ca(OH) 2 135% Wood ash 50%
At what ph do you get most of plant nutrients available to the plant? 1. 8 2. 7 3. 6 4. 5.5 5. 8.5 0% 29% 24% 47% 0% QUESTION 4 1 2 3 4. 5.
Additional Tips Availability of nutrients at different phs Lime before you fertilize ph N P K 5.0 53% 34% 52% 6.0 89% 52% 100% 7.0 100% 100% 100%
H + - Clay Then CaCO 3 and CaSO 4 (Gypsum) not the Same + CaCO 3 (Limesto ne) H 2 C O 3 > H 2 O (Wat er) > Ca ++ - Clay + CO 2 (Carb on Dioxi de) + H 2 CO 3 (Carbo nic Acid)
Plant Nutrients Soil supplies 13 essential plant nutrients Primary: N, P, K Secondary: S, Mg Ca Micronutrients: B, Mo, Cu, Zn, Fe, Mn, Cl We re deficient in N, S, Ca, Mg, B, Zn OM supplies 1-4% of its nutrients annually
Plant Nutrients Soil nutrients are in form of cations and anions cations e.g. NH +, Mg 2+, Ca 2+, = +ve Anions e.g. Cl -, H 2 PO 4- and HPO 4-2 = -ve Clay & OM particles are negatively charged So cations are adsorbed to these particles A soils capacity to hold cations is CEC
Cation Exchange Capacity Soil particles are negatively charged, attract positively charged ions (cations) CEC measure of the number of adsorption sites in a soil to adsorb and release cations A soil with a CEC of one (1) has 600,000,000,000,000,000,000 adsorption sites in 100 grams (about 8 TSP) of soil. Low CEC soils leach & store less nutrients K + Negativel y charged Soil particle K + Mg ++ Ca ++ Ca ++ Mg ++ H + Ca ++
Class CEC Demonstration
Cation Exchange Capacity Measured in milli-equivalents per 100 grams Varies with soil texture & OM content Soil Texture CEC (meq/100g) Sands 1 5 Fine sandy loams 5 10 Silt loams 5 15 Clay loams 15 30 Clays 30+
Organic Matter & Soil Biology the Living, the Dead, and the Very Dead Dr. Fred Magdoff Univ. of Vermont
Functions of Soil Organic Matter Source of plant nutrients Helps to keep nutrients available Improves soil structure and porosity Improves water holding capacity Improves CEC
The Living Larger soil organisms ( (fungi, algae, etc.) Plant roots Animals Earthworms, insects, mammals They aerate the soil Produce compounds for soil aggregates Important in nutrient cycling
Soil Microorganisms Break down Organic Matter to: Humus Energy Plant nutrients Good temp for microbes 60-100 o F
Bacteria & Fungi in ¼ tsp of soil (100 mg) Bacteria 80m-100m Fungi 100,000-1 million Abundant on rhizosphere (area around the roots)
Yeast & Protozoa (1/4 tsp of soil Yeasts 10,000-100,000 Protozoa 10,00-100,000
Actinomycetes & Nematodes Actinomycetes 10m-100million = bacteria that break down chitin & cellulose Nematodes 10-100
The Dead Fresh residues Recently added manures Recently deceased microorganisms, plants, or animals Source of food & energy for microbes
The Very Dead Well-decomposed organic matter humus or compost Provides chemical properties of organic matter Contributes to CEC Buffers the soil against changes in ph Helps form soil peds
OM Importance First, the organic matter coats soil particles, physically separating clay particles and aggregates from each other Second, and more important, microorganisms that degrade organic matter produce a by-product called glomalin that bind individual clay particles together into aggregates
SOM enhances water-holding capacity 25 yrs of conventional corn 20 yrs of bluegrass, then 5 yrs conventional corn Gruver, 2005
After adding water 25 yrs of conventional corn 20 yrs of bluegrass, then 5 yrs conventional corn Gruver, 2005
Bio-solids By-products of waste water treatment plants They can supply 3-6% Nitrogen 2-3% phosphorus Two classes Class A - heat & lime treated few pathogens Class B, not heat treated Bio-solids are not certified organic fertilizers
End!! At home, please check ph and texture of your soil