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