Chapter 12Chapter 12Soil ResourcesSoil Resources

Overview of Chapter 15Overview of Chapter 15

o What is soil?What is soil?o Soil PropertiesSoil Propertieso Major Soil OrdersMajor Soil Orderso Soil ProblemsSoil Problemso Soil Conservation Soil Conservation o Soil ReclamationSoil Reclamation

SoilSoil

o Uppermost layer of earth’s crust that Uppermost layer of earth’s crust that supports plants, animals and microbessupports plants, animals and microbes

o Soil Forming FactorsSoil Forming Factors• Parent MaterialParent Material• ClimateClimate• Organisms – N- fixing bacteria, fungi, Organisms – N- fixing bacteria, fungi,

insects, worms, snails…insects, worms, snails…• Topography – slope, elevation, wind Topography – slope, elevation, wind

exposureexposure

Soil CompositionSoil Composition

o Mineral Particles (45%)Mineral Particles (45%)• Weathered rockWeathered rock• Provides essential nutrients for plantsProvides essential nutrients for plants

o Organic Material (5%)Organic Material (5%)• Litter, animal dung, dead remains of plants Litter, animal dung, dead remains of plants

and animals, humus (picture)and animals, humus (picture)

o Water (25%)Water (25%)o Air (25%)Air (25%)

Soil CompositionSoil Composition

o Pore space Pore space • 50% of soil50% of soil• Soil air- good for Soil air- good for

aerationaeration• Soil water- Soil water-

provides water to provides water to rootsroots

Soil HorizonsSoil Horizonso O-horizonO-horizon• Rich in organic materialRich in organic material

o A-horizonA-horizon• TopsoilTopsoil

o E-horizon – (eluviated) E-horizon – (eluviated) heavily leached heavily leached

o B-horizon (subsoil- B-horizon (subsoil- illuviation)illuviation)• Lighter colored subsoil – Lighter colored subsoil –

can be rich in nutrientscan be rich in nutrients

o C-horizon (regolith)C-horizon (regolith)• Weathered parent Weathered parent

materialmaterial

Soil OrganismsSoil Organismso There are millions of microorganisms in There are millions of microorganisms in

1 tsp of fertile agricultural soil1 tsp of fertile agricultural soil

Soil OrganismsSoil Organisms

o Soil organisms provide Soil organisms provide ecosystem ecosystem servicesservices• Def: Important environmental benefits that Def: Important environmental benefits that

ecosystems provide ecosystems provide

o ExamplesExamples• Decaying and cycling organic materialDecaying and cycling organic material• Breaking down toxic materialsBreaking down toxic materials• Cleansing waterCleansing water• Soil aeration (especially done by Soil aeration (especially done by

earthworms)earthworms)

Nutrient Nutrient CyclingCycling

o Nutrients are cycled Nutrients are cycled between plants, between plants, organisms and soilorganisms and soil

o ExampleExample• Bacteria and fungi Bacteria and fungi

decompose plant decompose plant and animal wastesand animal wastes

• They are They are transformed into transformed into COCO22, soil nutrients , soil nutrients and waterand water

Soil PropertiesSoil Propertieso Soil TextureSoil Texture

• Relative proportion of sand, silt and clayRelative proportion of sand, silt and clay• Sand: 2mm-0.05mmSand: 2mm-0.05mm• Silt: 0.05mm-0.002mmSilt: 0.05mm-0.002mm• Clay: >0.002mmClay: >0.002mm

Soil PropertiesSoil Properties

o Soil texture affects soil propertiesSoil texture affects soil propertieso Coarse textured soil (sandy)Coarse textured soil (sandy)

• Will not hold water well- flows through Will not hold water well- flows through easilyeasily

o Fine textured soil (high in clay)Fine textured soil (high in clay)• Poor drainagePoor drainage• Low oxygen levels in soilLow oxygen levels in soil• Due to negatively charged surface, able to Due to negatively charged surface, able to

hold onto important plant nutrients (Khold onto important plant nutrients (K++, , CaCa2+2+, NO, NO22

--))

Soil PropertiesSoil Properties

Soil PropertiesSoil Properties

o Soil AciditySoil Acidity• Measured using pH scaleMeasured using pH scale

• 0-7 = acidic0-7 = acidic• 7 = neutral7 = neutral• 7-14 = basic7-14 = basic

• pH of most soils range from 4-8pH of most soils range from 4-8• Affects solubility of certain plant nutrientsAffects solubility of certain plant nutrients• Optimum soil pH is 6-7Optimum soil pH is 6-7

• This is the pH where plant nutrients are most This is the pH where plant nutrients are most available to plantsavailable to plants

• Soil amendments (ex: lime) can be used to Soil amendments (ex: lime) can be used to achieve this pHachieve this pH

Essential Plant NutrientsEssential Plant Nutrientso Nitrogen Nitrogen – stimulates above-ground growth – stimulates above-ground growth

and produces the rich green color of a and produces the rich green color of a healthy plant. Influences the quality of the healthy plant. Influences the quality of the plant’s fruit. Found in chlorophyll, amino plant’s fruit. Found in chlorophyll, amino acids, nucleic acids and enzymes. acids, nucleic acids and enzymes.

o PhosphorusPhosphorus – is abundant in the fruits and – is abundant in the fruits and seeds and in parts of the root involved in seeds and in parts of the root involved in uptake of water and nutrients. Increases uptake of water and nutrients. Increases resistance to disease.resistance to disease.

o PotassiumPotassium – “the vigor and vitality” of the – “the vigor and vitality” of the plant. Important in the root development, and plant. Important in the root development, and in the synthesis of starch.in the synthesis of starch.

NitrogenNitrogen

o Common sources of nitrogen are by Common sources of nitrogen are by o 1) nitrogen - fixing by legumes / 1) nitrogen - fixing by legumes /

Rhizobium bacteria and Rhizobium bacteria and o 2) the decomposition of organic matter 2) the decomposition of organic matter

and application of commercial nitrogen and application of commercial nitrogen fertilizersfertilizers

Major Soil GroupsMajor Soil Groups

o Variations in soil forming factors cause Variations in soil forming factors cause variation in soils around globevariation in soils around globe

o Soil TaxonomySoil Taxonomy• Separates soils into 12 ordersSeparates soils into 12 orders• Subdivided into more than 19,000 soil Subdivided into more than 19,000 soil

series that vary by localityseries that vary by locality

o Five common soil ordersFive common soil orders• Spodosols, alfisols, mollisols, aridosols, Spodosols, alfisols, mollisols, aridosols,

oxisolsoxisols

Major Soil GroupsMajor Soil Groups

o SpodosolsSpodosols- acidic - acidic soilsoil• Form under Form under

coniferous forestsconiferous forests• O-horizon composed O-horizon composed

of needlesof needles• Not good farmland- Not good farmland-

too acidic and few too acidic and few nutrients due to nutrients due to leachingleaching

Major Soil GroupsMajor Soil Groupso Alfisols- Alfisols- temperate temperate

deciduous forestsdeciduous forests• Brown to gray-brown A-Brown to gray-brown A-

horizon (color indicated horizon (color indicated high nutrients)high nutrients)

• Precipitation high Precipitation high enough to leach most enough to leach most organics and nutrients organics and nutrients out of O-, A- and B-out of O-, A- and B-horizonshorizons

• Soil fertility maintained Soil fertility maintained by leaf litterby leaf litter

Major Soil GroupsMajor Soil Groups

o MollisolsMollisols - - temperate, semi-temperate, semi-arid grasslandarid grassland• Very fertile soilVery fertile soil• Thick, dark brown/ Thick, dark brown/

black A-horizonblack A-horizon• Soluble nutrients Soluble nutrients

stay in A-horizon stay in A-horizon due to low leachingdue to low leaching

Major Soil GroupsMajor Soil Groups

o Aridosols Aridosols – form in – form in arid regions arid regions

o Low precipitation Low precipitation preclude leaching preclude leaching and lack of organic and lack of organic matter means few matter means few nutrientsnutrients• Development of Development of

salic horizon salic horizon possiblepossible

Major Soil GroupsMajor Soil Groups

o Oxisols Oxisols – forms in – forms in hot, wet areashot, wet areas• Very little organic Very little organic

material material accumulation due to accumulation due to fast decay ratefast decay rate

• B-horizon is highly B-horizon is highly leached and nutrient leached and nutrient poorpoor

o Mollisols and alfisols are the 2 best soils Mollisols and alfisols are the 2 best soils for growing crops. They comprise 15% for growing crops. They comprise 15% of the land area and are mostly found in of the land area and are mostly found in the middle latitudes of the Northern the middle latitudes of the Northern hemisphere and in South America.hemisphere and in South America.