Chapter 12 Soil Resources

Overview of Chapter 15 o What is soil? o Soil Properties o Major Soil Orders o Soil Problems o Soil Conservation o Soil Reclamation

Soil o Uppermost layer of earth’s crust that supports plants, animals and microbes o Soil Forming Factors Parent Material Parent Material Climate Climate Organisms – N- fixing bacteria, fungi, insects, worms, snails… Organisms – N- fixing bacteria, fungi, insects, worms, snails… Topography – slope, elevation, wind exposure Topography – slope, elevation, wind exposure

Soil Composition o Mineral Particles (45%) Weathered rock Weathered rock Provides essential nutrients for plants Provides essential nutrients for plants o Organic Material (5%) Litter, animal dung, dead remains of plants and animals, humus (picture) Litter, animal dung, dead remains of plants and animals, humus (picture) o Water (25%) o Air (25%)

Soil Composition o Pore space 50% of soil 50% of soil Soil air- good for aeration Soil air- good for aeration Soil water- provides water to roots Soil water- provides water to roots

Soil Horizons o O-horizon Rich in organic material Rich in organic material o A-horizon Topsoil Topsoil o E-horizon – (eluviated) heavily leached o B-horizon (subsoil- illuviation) Lighter colored subsoil – can be rich in nutrients Lighter colored subsoil – can be rich in nutrients o C-horizon (regolith) Weathered parent material Weathered parent material

Soil Organisms o There are millions of microorganisms in 1 tsp of fertile agricultural soil

Soil Organisms o Soil organisms provide ecosystem services Def: Important environmental benefits that ecosystems provide Def: Important environmental benefits that ecosystems provide o Examples Decaying and cycling organic material Decaying and cycling organic material Breaking down toxic materials Breaking down toxic materials Cleansing water Cleansing water Soil aeration (especially done by earthworms) Soil aeration (especially done by earthworms)

Nutrient Cycling o Nutrients are cycled between plants, organisms and soil o Example Bacteria and fungi decompose plant and animal wastes Bacteria and fungi decompose plant and animal wastes They are transformed into CO 2, soil nutrients and water They are transformed into CO 2, soil nutrients and water

Soil Properties o Soil Texture Relative proportion of sand, silt and clay Relative proportion of sand, silt and clay Sand: 2mm-0.05mm Sand: 2mm-0.05mm Silt: 0.05mm-0.002mm Silt: 0.05mm-0.002mm Clay: >0.002mm Clay: >0.002mm

Soil Properties o Soil texture affects soil properties o Coarse textured soil (sandy) Will not hold water well- flows through easily Will not hold water well- flows through easily o Fine textured soil (high in clay) Poor drainage Poor drainage Low oxygen levels in soil Low oxygen levels in soil Due to negatively charged surface, able to hold onto important plant nutrients (K +, Ca 2+, NO 2 - ) Due to negatively charged surface, able to hold onto important plant nutrients (K +, Ca 2+, NO 2 - )

Soil Properties

o Soil Acidity Measured using pH scale Measured using pH scale 0-7 = acidic 0-7 = acidic 7 = neutral 7 = neutral 7-14 = basic 7-14 = basic pH of most soils range from 4-8 pH of most soils range from 4-8 Affects solubility of certain plant nutrients Affects solubility of certain plant nutrients Optimum soil pH is 6-7 Optimum soil pH is 6-7 This is the pH where plant nutrients are most available to plants This is the pH where plant nutrients are most available to plants Soil amendments (ex: lime) can be used to achieve this pH Soil amendments (ex: lime) can be used to achieve this pH

Essential Plant Nutrients o Nitrogen – stimulates above-ground growth and produces the rich green color of a healthy plant. Influences the quality of the plant’s fruit. Found in chlorophyll, amino acids, nucleic acids and enzymes. o Phosphorus – is abundant in the fruits and seeds and in parts of the root involved in uptake of water and nutrients. Increases resistance to disease. o Potassium – “the vigor and vitality” of the plant. Important in the root development, and in the synthesis of starch.

Nitrogen o Common sources of nitrogen are by o 1) nitrogen - fixing by legumes / Rhizobium bacteria and o 2) the decomposition of organic matter and application of commercial nitrogen fertilizers

Major Soil Groups o Variations in soil forming factors cause variation in soils around globe o Soil Taxonomy Separates soils into 12 orders Separates soils into 12 orders Subdivided into more than 19,000 soil series that vary by locality Subdivided into more than 19,000 soil series that vary by locality o Five common soil orders Spodosols, alfisols, mollisols, aridosols, oxisols Spodosols, alfisols, mollisols, aridosols, oxisols

Major Soil Groups o Spodosols- acidic soil Form under coniferous forests Form under coniferous forests O-horizon composed of needles O-horizon composed of needles Not good farmland- too acidic and few nutrients due to leaching Not good farmland- too acidic and few nutrients due to leaching

Major Soil Groups o Alfisols- temperate deciduous forests Brown to gray-brown A- horizon (color indicated high nutrients) Brown to gray-brown A- horizon (color indicated high nutrients) Precipitation high enough to leach most organics and nutrients out of O-, A- and B-horizons Precipitation high enough to leach most organics and nutrients out of O-, A- and B-horizons Soil fertility maintained by leaf litter Soil fertility maintained by leaf litter

Major Soil Groups o Mollisols - temperate, semi-arid grassland Very fertile soil Very fertile soil Thick, dark brown/ black A-horizon Thick, dark brown/ black A-horizon Soluble nutrients stay in A-horizon due to low leaching Soluble nutrients stay in A-horizon due to low leaching

Major Soil Groups o Aridosols – form in arid regions o Low precipitation preclude leaching and lack of organic matter means few nutrients Development of salic horizon possible Development of salic horizon possible

Major Soil Groups o Oxisols – forms in hot, wet areas Very little organic material accumulation due to fast decay rate Very little organic material accumulation due to fast decay rate B-horizon is highly leached and nutrient poor B-horizon is highly leached and nutrient poor

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