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Basic Soils. Is it alive? Is it fragile? Should we consider soil a fragile resource?

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Presentation on theme: "Basic Soils. Is it alive? Is it fragile? Should we consider soil a fragile resource?"— Presentation transcript:

1 Basic Soils

2 Is it alive?

3 Is it fragile? Should we consider soil a fragile resource?










13 Soil loss through plowing

14 Soils A medium for plant growth 1,000 years to form 1 ” of topsoil Deplete 1 ” of topsoil in 100 years or less

15 Soils Composition Soil is composed of three “fractions” An organic fraction A mineral fraction A water and gas fraction

16 Soils Composition An organic fraction organic materials provide a reservoir of plant nutrients nutrients are continually recycled as organic materials Living organisms including plant parts, bacteria, fungi, worms, insects, etc.; dead/decomposing organisms

17 Soils Composition The mineral fraction Sand, silt and clay Sand and silt – primary minerals decomposition of various rock materials referred to as “ parent material ” Clays – secondary minerals dissolved minerals in solution precipitate out to form clays crystalline

18 Soils Composition Gasses and water Ex. Oxygen (O), carbon dioxide (CO 2 ), nitrogen (N), etc.; H 2 O Fills in all of the pore spaces between the soil particles Larger pore spaces tend to contain more gasses Smaller pore spaces tend to contain more water

19 The Mineral Fraction So what’s a rock? Consolidated mass of minerals Then what’s a mineral? Unique, repeatable combination of elements And what’s an element? Found on the periodic table, unique combination of protons, neutrons in a nucleus and electrons

20 Soils Composition Rocks can be divided into three categories Igneous rock Sedimentary rock Metamorphic rock

21 Soils Composition Igneous rock – molten, liquid magma or lava Divided into two sub-categories Intrusive igneous rock Extrusive igneous rock

22 Soils Composition Intrusive igneous rock “magma” cools and hardens slowly within the crust forms distinct crystals from slow cooling often referred to as plutonic rock ex. granite, quartz

23 Soils Composition Extrusive igneous rock “lava” is extruded out of the Earth’s crust cools and hardens quickly outside the crust in contact with air or water forms small to no crystals from rapid cooling ex. basalt, obsidian

24 Soils Composition Sedimentary rock formed from layers of deposited sediments – sands, silts or clays deposited by wind or water ex. sandstone

25 Soils Composition Metamorphic rock rock changed from one form to another over time changed deep in the earth by heat and pressure ex. marble changed from limestone and slate changed from shale

26 Soils Composition Sand and silt soils “primary” minerals direct product of erosion Clays “secondary” minerals result of chemical weathering breaking down primary minerals minerals leached in solution deposited out as clays

27 Soils Composition Soils are the uppermost layers of tectonic plates Formed from weathered and eroded rock or “parent materials”

28 Weathering Chemical action of air and rainwater and the biological action of plants and animals Rock and minerals disintegrate, decompose and synthesize new compounds and clay minerals

29 Erosion Wearing away of land surfaces by wind, water, ice and rock-on-rock

30 Soils Combination of sand, silt and clay and organic material Sand  2.0 mm to 0.05 mm in diameter Silt  0.05 mm to mm in diameter Clay  less than mm in diameter

31 Soil Particle Sizes

32 As the surface area for a given mass (or volume) of particles decrease in size, the total surface area increases geometrically In other words—in a given volume, there is more surface area on smaller sized particles than larger sized particles Sand particles are larger than clay particles So a given volume of clay particles will have more surface area than sand

33 Soil Particle Sizes Imagine 2 identical pencils One broken in half Which has the greatest amount of surface area?


35 Bulk Density Refers to weight per a given volume We talk about: "Light" soils having a higher sand content "Heavy" soils having a higher clay content In reality—a given volume of clay weighs more than the same volume of sand

36 Soil Texture Percentages of sand, silt and clay per volume of soil Loam soils contain a blend of sand, silt and clay Loam soils make some of the better gardening soils Soil texture determined by a "settling" test

37 Soil Settling Test 100 grams oven dried, cleaned, screened soil into a blender with: 5 ml 8% Calgon® (sodium hexametaphosphate) solution 100 ml water Blend 5 minutes Pour and rinse blender contents completely into 1000 ml graduated cylinder

38 Soil Settling Test Fill graduated cylinder to 1000 ml with water Cover graduated cylinder with palm of hand, invert several times getting soil into suspension Set cylinder on flat surface Wait 40 sec., insert Bouyoucos hydrometer into solution

39 Soil Settling Test Take hydrometer reading Repeat three times and average readings Adjust for temperatures Take another reading at 2 hours Adjust for temperatures Preform calculations

40 Soil Settling Test The Bouyoucos hydrometer measures density of solution After the 40 sec. reading what soil particles remain in solution—sand, silt or clay? Silt and clay What has settled out first? Sand Why? Sand is heaviest—it settles first

41 Soil Settling Test After the 2 hour reading what soil particles remain in solution—sand, silt or clay? Clay What has settled out? Silt Why? Silt is heavier than clay—it settles next

42 Soil Settling Test Assuming we started with 100 grams soil The 40 sec. reading indicated 72 grams in solution How many grams have settled out? 100g – 72g = 28g 28g of what? Sand

43 Soil Settling Test The 2 hour reading indicated 15 grams remaining in solution How much has settled out of solution? 72g – 15g = 57g 57g of what? Silt

44 Soil Settling Test What is left in solution? 15g clay 100g soil – (28g sand + 57g silt) = 15g clay Why is the clay still in solution? Clay is the lightest—it stays in solution

45 Soil Settling Test How much sand, silt and clay is there? 28g sand = 28% sand +57g silt = 57% silt +15g clay = 15% clay =100g soil = 100% soil It checks Refer to soil texture chart to determine soil texture What soil texture do we have?

46 Soil Texture Settling Test Turn to the soil texture triangle and find the soil texture class. We have a “silt loam”

47 Ribbon Test “Quick and dirty” test for soil texture With a handful of moistened soil, attempt to squeeze out a ribbon of soil between your thumb and forefinger Clay and silt soils feel smooth Clay “ribbons” can be 2” long Sandy soils feel gritty Sandy soils won’t form ribbons See handouts at end of PowerPoint

48 Soil Structure Soil structure is determined by arrangement of soil particles Soil aggregates are soil particles (sand, silt and clay) held together by iron oxides, calcium carbonate, clays and/or silica as well as humus Texture and structure combined help determine soil pore sizes Texture and structure greatly determine water movement through soils

49 Soil Porosity Soil pore sizes determine how well water (and air) moves through soil Infiltration – downward movement water of into soils Percolation – downward movement water of through soils

50 Soil Porosity Sandy soils drain quickly – don’t hold water Sandy soils have mostly large pore spaces Clay soils don’t drain well – hold water Clay soils have mostly small pore spaces

51 Soil Porosity Micropores Small spaces between soil particles Hold water tightly – inhibits drainage Retain various nutrients in solution, making them available to plant roots Do not aid in circulation of gasses in soil

52 Soil Porosity Macropores L arger spaces between soil particles Hold water more loosely - essential to good drainage Do not retain nutrients in solution particularly well Aids in circulation of gasses in soil

53 Soil Structure

54 Soil Horizons Horizon layers and composition are a product of their surroundings.... O-Horizon – organic matter A-Horizon – darkened by organic matter E-Horizon – materials leached away downward B-Horizon – accumulates clays, salts and other fine materials C-Horizon – loose or cohesive materials, rests on bedrock R-Horizon – bedrock solid rock

55 Humus Residue formed after the decomposition of organic matter Acts to "glue" soil particles together Provides a source of carbon to soil Soils with a higher carbon content referred to as an organic soil (between 12% and 20% organic carbon by weight) Can change soil structure over time

56 Changing Texture Soil texture takes years to affect... Why? Sand, silt or clay must be added to change texture Large amounts of sand can be added to change texture and increase drainage to clay soils Not enough makes mortar! Expensive! Raises soil level – something must be removed

57 Changing Structure Soil structure can be changed through tillage Tillage can both loosen and compact soils Organic amendments can be added to soils to enhance the structure Provides humus through decomposition Organic materials slow drainage in sandy soils Organic materials increase drainage in clays

58 Changing Structure Peat moss helps water retention Never add peat moss to heavy clay soils Peat moss helps to reduce soil pH Use compost and soil sulfur in clay soils Addition of salts through fertilizers or irrigation water can eventually inhibit drainage

59 “Soil Drainage Test” Good drainage is a determining factor in successful landscapes Simple drainage test – dig a hole about 1’ deep Fill the hole with water Determine time required for hole to drain 1”/hour – adequate drainage Less than 1”/hour – problems - clay Faster than 1”/hour – problems - sand 24 hours or more – serious problems Puddles after irrigation or rain – indicators of problems

60 Soil Drainage Test

61 Soil Reaction Soil reaction refers to the relative amount of free hydrogen ions ( H + ) in the soil/water solution In other words how acidic or alkaline is the soil solution Soil reaction is important in that it determines the availability if different nutrients Also the susceptibility of plants to various plant disease

62 pH – Percent Hydrogen Soil reaction measured by pH on a scale of 1 through 14 pH of 7 represents a neutral soil Acidic soils — pH 1 to less than 7 Alkaline soils — pH greater than 7 to 14

63 pH Scale




67 Appendix: Home Soil Settling Test You can try this one at home

68 Soil Texture Settling Test Spread soil on a newspaper to dry; remove all rocks, trash, roots, etc.; crush lumps and clods Finely pulverize the soil Fill a tall, slender jar (like a quart jar) ¼ full of soil Add water until the jar is ¾ full. Add a teaspoon of powdered, non-foaming dishwasher detergent

69 Soil Texture Settling Test Put on a tight fitting lid and shake hard for 10 to 15 minutes. This shaking breaks apart the soil aggregates and separates the soil into individual mineral particles Set the jar where it will not be disturbed for 2 to 3 days Soil particles will settle out according to size; after 1 minute, mark on the jar the depth of the sand

70 Soil Texture Settling Test After 2 hours, mark on the jar the depth of the silt When the water clears mark on the jar the clay level. This typically takes 1 to 3 days, but with some soils it may take weeks Measure the thickness of the sand, silt, and clay layers. a. Thickness of sand deposit _____. b. Thickness of silt deposit _____. c. Thickness of clay deposit _____. d. Thickness of total deposit _____.

71 Soil Texture Settling Test 12. Calculate the percentage of sand, silt, and clay [clay thickness] ______________ = _____ percent clay [total thickness] [silt thickness] ______________ = _____ percent silt [total thickness] [sand thickness] ______________ = _____ percent sand [total thickness]


73 Ribbon Test

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