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Created by Diana Shell, SMHS 2012
Rich, dark humus
Soil Properties: Soil Particles:
Soil particles have a negative ionic charge, they attract positively charged ions from nutrients & minerals.
Nutrients may leach from the soil (where water carries the nutrients away). o Solution: add inorganic fertilizer (increase N, P, & K); add dried
blood (raises N), add bone meal (raises P), burn crop residue (raises K)
Pore space (aka Soil Porosity): the amount of space in between each soil particle.
Larger soil particles have larger pore space, but less total pore space than smaller soil particles.
Water holding capacity depends on porosity (how much water a soil sample can hold)
Clay particles are very small and have a large amount of pore space – water gets stuck in the small pore spaces and does not allow more water to seep down if rain falls quickly (causes flooding). Holds water for a long time.
Sand particles are larger allowing much water to flow – often results in leaching of nutrients – greatest soil porosity. o Solutions to poor drainage: add sand to the soil o Solutions to too much leaching of nutrients: add clay
Permeability: the ability of water or other minerals to move through soil particles. pH: the amount of H
+ ions in the soil. High pH (7-14) = alkaline (base); low pH (1-7) = acidic
pH is lowered when fertilizer is added. Solution: add lime to raise pH.
pH is raised when certain types of rocks (CO3 -rich) are present. Solution: add sulfur
Soil Texture: Important because different types of plants need different soil textures
in order to grow. o Cactus require large amounts of sandy soil o Plants in our region grow best in clay-based soils
Tests used to determine soil texture: o Soil Texture Determination by Fractionation
Put a sample of soil in a graduated cylinder Add enough water to cover the soil + extra Shake up the cylinder containing the water &
soil sample. Allow the soil to settle (takes a few hours) The soil will settle into layers based on density – clay is the most dense, sand is the least dense. Determine how many “mL” each layer is. Determine the amount per layer as a percentage of the whole. Use the USDA Soil Texture chart to determine the soil texture.
SOIL
2 major components of soil (also air & water) Humus – dark colored, dead organic stuff (on
top)
Similar water retention to & binds to nutrients like clay, but is much more porous
some nutrients (slow release)
many microorganisms live in it, help plants absorb nutrients (bacteria produce nitrates (N))
Solutions for low humus
add compost or manure
Rock Particles
Main source of MINERAL NUTRIENTS (N, P, K, etc.)
3 Main components of soil: a. Clay – bad porosity/good water retention b. Silt – med. Porosity/med. water retention c. Sand – good porosity/bad water
retention
LOAM = 40% sand, 40% silt, 20% clay (best)
Determine the soil texture for the following: Clay = 20%; Sand=10%: Silt=70% Clay = 50%; Sand=30%: Silt=20% Clay = 30%; Sand=10%: Silt=___%
Created by Diana Shell, SMHS 2012
A Horizon
Parent Rock
B Horizon
A Horizon
B Horizon
Types of Soils & their horizons
Not enough rain to leach A, best farm soil. B High in nutrients
Dead plants decompose quickly in moist, hot environment & assimilate into plants, little nutrients in soil
Soil Composition 45% Minerals 5% Organic matter 25% Air 25% Water iron-rich soil on Lanai, Hawaii
Factors affect Soil Formation
1. Climate – precipitation & temperature affect how quickly organic matter decomposes
2. Living Organisms – aerate soil, decompose (themselves or other organic matter) – plant roots break up rock
3. Parent Material – the foundation of the earth 4. Topography – slope of the land causes more erosion (greater slope = more soil
at base) 5. Time – older = more soil
Soil Profile: Cross section of the earth
Soil Horizons = different layers of soil in profile
soil forms in separate layers, old soils have 4 layers, younger soils have 3 or 2 layers
Layers form because of o different types of materials that decompose (i.e. leaves, organic
material), o amount of decomposers (i.e. bacteria, microorganisms, worms, etc) o different amounts of water present (i.e. rainfall) o temperature (higher temps = more decomposition
O Horizon - On top of the ground
Organic leaf litter, lots of bugs A Horizon (topsoil)
soil that is mixture of 3 rock particles (loam) + humus (dark-colored)
nutrient poor because clay & nutrients are leached out by rain to the next lower horizon (B)
lots of bugs & bacteria live here because plant roots create air spaces
E Horizon (Zone of Leaching)
Not all soil horizon diagrams show this.
Transition area between A & B Horizons where water carries nutrients downward
B Horizon (subsoil)
takes a long time to form in new soils
light-colored subsoil that has nutrients from Horizon A carried down by water.
clay + cations accumulate here (illuviation = accumulation of nutrients that are leached out of layer above)
little humus C Horizon (Weathered Parent Material)
parent rocks and pebbles mixed with some clay
below most roots & often saturated with water
R Horizon (Parent Rock)
solid rock beneath soil
particles break off forming the foundation of the soil
Usually granite or bedrock
Impermeable layer
C Horizon
Bad farmland - too acidic, nutrients leached
Enough rain to leach nutrients from A, must add fert. to farm
Created by Diana Shell, SMHS 2012
1. Deforestation 2. Steep land being cultivated down the slope 3. Monocrops grown over large areas 4. Landslide blocks road
5. Fish catch reduced in shallow waters 6. Siltation cuts hydroelectric plant's lifespan 7. Gully erosion eats into crop land 8. Mud banks reduce navigability of rivers
9. Urban slums grow as rural population migrates to the city 10. Bridge destroyed by floods 11. Crops grown on large unprotected fields 12. Wind erosion affects badly managed pasture 13. Frequently flooded village is deserted
Impacts of Soil Erosion
Soil Types Thousands of different types of soil based on nutrients present
Soil Degradation 1. SOIL EROSION:
a. Movement of soil from one area to another b. Types:
i. Wind erosion is more of a problem [than water erosion] in areas where soil is loose & dry.
1. Dust Bowl Why did it happen??? <”Just the Facts” clip on Discovery Education>
ii. Water erosion (sheet – entire layers of soil is removed & rill – rivulets of soil are removed) occurs most in hilly areas. = #1 cause erosion
c. Physical, natural process…but farming & construction accelerates it and leads to DESERTIFICATION (process where areas that were semi-desert environments become desert environments because
i. Large farm animals compact the soil ii. Water cannot soak into the ground
iii. Water runoff takes nutrients away iv. Plants are stomped by the animals & die v. Roots are missing
vi. Without water in the soil to evaporate, rainfall won’t occur
d. Chemical Erosion – when acids come in contact with the rocks causing them to break. (Ex: lichens, acid rain)
e. Causes of soil erosion: i. Conventional Tillage: turn over all soil in field &
remove all vegetation 1. nothing to hold soil down from wind & rain
= increase erosion 2. Solution: Conservation tillage – leave
remnants of last year’s crop to provide roots to hold soil & help w/ water retention (do need more pesticides to control bugs though)
ii. Construction sites 1. Ground is torn up to build infrastructure 2. Solution: barriers around construction sites; only cut as little vegetation as possible; plant more trees,
shrubs and grass as soon as possible; lay down straw over exposed soil iii. growing on steep land increases erosion
1. if natural vegetation removed from slope, nothing to hold soil 2. Solutions: less plowing & leave some weeds, do not plant rows vertically down hill… do contour farming
(follow flow of land) & terracing (planting on “ledges” on hills). 2. Deforestation w/o reforestation
a. Trees are cut exposing land; as roots come up soil becomes broken up resulting in more erosion
b. Construction Sites = worst of all for soil loss c. Solutions: plant trees around farms as windbreaks (shelterbelts), runoff
retention ponds 3. Overgrazing
a. grass eaten faster than it can grow. No plant roots to hold soil down. b. weight of animals may decrease porosity of soil (pushing the particles
together decrease air space) c. Solutions: alternate pastures, get rid of animals, re-fertilize
Kualoa Ranch, Hawaii
Created by Diana Shell, SMHS 2012
4. Mineral Depletion of Soil a. Nutrients run off into waterways
5. Overcultivation a. Overgrowing same crops in one area causes loss of specific nutrients b. Solution: give land time to recover by rotating crops & using fertilizer c. After corn depletes (N) from soil, rotate the crop & grow SOYBEAN or ALFALFA (both have bacteria in roots that add (N)
back to soil). Then grow corn again after them. 6. Salinization
a. irrigated water in ARID regions picks up nutrient salts as it passes thru soil channels (in primitive irrigation), evaporates, leaves salt behind (eventually toxic).
b. Solutions: flush soil w/ excess water (can waterlog though which kills roots) & don’t use soil for 2-5 years
Soil Degradation by Region
Major Causes of Soil Degradation
Soil Quality Testing Physical Tests:
1. Porosity / Water Holding Capacity – measure how much water will flow through the soil. 2. Density – how “heavy” one soil is compared to another 3. Color – brown color = humus; red color = clay; light brown = sand 4. Smell – decomposition will give a foul smell. 5. Soil Texture by fractionation / Soil Texture by Feel – determines the percentages of sand, silt & clay
Chemical Tests: 1. pH – measures the acidity of soil 1. Nitrogen 2. Phosphorus 3. Potassium