Soil Science Fundamentals

• Students will be able to define soil in different terms
• Students will be able to explain the two approaches to learning soils
• Students will be able to discuss the various components of soils
• Students will be able to outline the difference between the organic and inorganic components of soils

The Composition of Soil

• Soil is a loose material forming a thin layer covering the earth's surface

• Soil is a medium for plant growth in crop production that supplies nutrients, water, air, and support

• Soil forms as a result of weathering rocks and minerals

• Soil consists of organic and inorganic materials on the Earth's surface that provides the medium for plant growth

• Soil develops slowly over time and is composed of different materials

• Inorganic materials include weathered rocks and minerals

• Weathering is the mechanical or chemical process by which the rocks are broken down into smaller pieces

• Saprolite is when underlying rocks are weathered in place to the point where its loose enough to dig with a spade

• Rocks, when broken down, mix with organic materials that originate from living organisms

• Nutrients are released back into the soil when plants and animals decompose

• Whitney (1982), Hilgard (1892), Dokuchaiev (1900), and Joffe (1936) defined soil as a natural body of mineral and organic constituents

• Soil is differentiated into unconsolidated horizons of variable depth, which differs among themselves and the parent material

• Regolith is a unconsolidated layer that varies in thickness

• Saprolite is when the underlying rock has weathered in place to the point where its loose enough to dig with a spade

• Soil supports the growth of plants by providing a medium for plant roots and supplying nutrient elements

• Soil properties control the fate of water in the hydrologic system

• Soil functions as a recycling system, within the soil, waste products and dead bodies are assimilated, making elements available for reuse

• Soil provides habitats for various living organisms

• Soil plays a role as an engineering medium in human-built ecosystems

• All life depends on the soil

• Human food is obtained from crops grown on soil

• Livestock and herbivores graze on plants that grow in the soil

• Most fibers used in clothing are grown in soil

• Building materials such as brick, adobe, aluminum, and glass come from soil materials

• Timber used for construction and furnishings is grown in soil

Nature and Uses of soil

• Soil mechanically supports plant roots, helps tall trees stand against strong winds
• Soil supports structures like houses, buildings, sidewalks, streets, and highways
• Soil is involved in several ways in the hydrologic cycle, water moves into the soil or evaporates
• Soil is an air-storage facility, plant roots and organisms need oxygen

Soil as a Natural Body

• "Soil" can refer to "the soil", "a soil," or "soils”, two concepts- soil as a material or natural bodies
• Soil is composed of minerals, gas, water, organic substances, and microorganisms

Approaches To Studying Soil

• Two approaches to studying soil, one treats it as a natural body, the other treats it as a medium for plant growth
• Pedological Approach is examining the origin, classification, of soil in Pedology, which is the study of soil as a natural body
• Edaphological Approach is studying soil from the viewpoint of higher plants, and considers soil properties concerning plant production

Components of Soil

• Four components of soil are inorganic minerals, organic matter, water, and air
• Inorganic mineral matter about 40 to 45% of soil volume
• Organic matter about 5% of soil volume
• Water about 25% of soil volume
• Air about 25% of soil volume
• Amount of each major components depends on vegetation, soil compaction, and water
• Healthy soil has sufficient air, water, minerals, and organic material to promote plant life
• Humus is organic material comprised of microorganisms, dead animals and plants in decay, improving soil structure
• Inorganic material of soil is composed of rock that breaks down into smaller particles varying in size
• Soil particles that are 0.1 to 2 mm in diameter are sand
• Soil particles between 0.002 and 0.1 mm are called silt
• Soil particles less than 0.002 mm in diameter are called clay
• Soils with no dominant particle size, containing a mixture of sand, silt, and humus, are called loams
• Solid phase of soil consists of mineral particles and pieces of rock, the inorganic component that forms framework of soil

Inorganic component of soil

• Soil normally consists of rock pieces and mineral particles of varying sizes
• Rock particles are the remains of rocks transformed by erosion into loose material called regolith
• Mineral particles in soil vary greatly in size
• Size Fraction determines cross-section
  • Stone: Greater than 75mm
  • Gravel: 2-75mm
  • Sand: 0.05-2.0 mm
  • Silt: 0.002-0.05mm
  • Clay: Less than 0.002mm
• Primary minerals did not undergo chemical change in weathering processes, quartz is priamry
• Minerals formed by chemical changes during the weathering of parent rock are secondary minerals
• The organic materials are compounds consist of carbon compounds

The Organic Component of Soil

• Organic materials are compounds usually found in the following forms in soils -Decaying Materials: dead plant material in which the original material is still identifiable -Non-humus Substances: forms of plant and animal material that have decomposed to the point original material cannot be identified -Humus: part of organic material remaining after the decomposition of original decaying material
• The organic content of South African soils is relatively low due to favorable temperature conditions which promotes microbiological breakdown of dead plant material
• Organic matter is almost the only source of nitrogen to help plant growth
• Organic matter improves the mineral component structure, soil rich in humus has crumbly consistency
• The only source of energy-rich nutrients are required by the microorganisms, who breakdown organic matter
• Humus colloids play role in preventing the leaching of nutrients by large cation adsorption capabilities

The Liquid Phase (Soil Water)

• Soil water is important for higher plants
• Soil water is an essential plant growth factor
• Water accessibility is determined by water and clay contents
• Soil water with dissolved sats forms the soil which serves as a medium for providing nutrients to plants

The Gas Phase (Soil Air)

• Soil air composition in the macro pores of soil differs considerably from that of the atmosphere
• Content and composition of soil air is determined by the ratio of micro to macro pores
• Soil air in macro pores and soil water is usually held up in the micro pores
• Micropores mean good water retention but poor aeration
• Macropores mean well-aerated but poor water retention capacity
• The speed of gaseous exchange is determined by macro/micropore ration
• The oxygen content of soil is important for root and microorganism activities
• Needed to replenish oxygen/diffuse carbon dioxide

Soil air Differs From Atmospheric Air

• Soil air does not occur evenly/continuously, foundonly in pore spaces
• Composition of soil air varies while atmospheric air does not vary as much
• Soil air contains much more moisture
• The percentage of carbon dioxide in soil air is higher/oxygen is much lower than the amount in atmospheric air
• Soil contains Oxygen: 20.5%, NItrogen: 79%, Carbon Dioxide: 0.5%

Soil as growth mediums for plants

• Growth is a permanent change that increases a plant's size, supports gaining nutrients from other places
• Plant growth is determined by the generic composition, and determined the degree a crop will develop
• Environmental factors cant increase any further than the generic potential

Influencing Plant Growth

• Some environmental factors that influence plant growth are -Temperature -Water provision -Radiant energy -Provision of nutrient elements -Gas content of the atmosphere and soil -pH -Biotic factors
• If an environmental factor is less than ideal it is a limiting factor in plant growth
• Limiting factors also responsible plant geography
• Plant problems caused by environmental stress/aspects affecting plant growth, like light, temp , water, nutrition

LIght

• Three characteristics affecting plant growth are quantity, quality, and duration
• Light quantity refers to intensity of sunlight varying with the season
• Better capacity to produce plant flood from photosynthesis with more sunlight
• Light quantity decreases photosynthesis
• Decreased by shade-cloth/paint or increased by surrounding plants with material or lights
• Light quality refers to color or wavelength Sunlight broken up by a prism into colors
• Red and blue light have greater effect on growth, greenlight is least effective
• Blue= Vegetative growth leaf
• Red+blue= flowering
• Fluorescent= High blue encourage leafy growth, excellent seedlings
• Incandescent light= High red/orange range/heat is not valuable
• Grows light = red + blue to imitate sunlight, costly no value

Light Duration

• Amount of time exposed to sunlight
• Not the length of light period but the length of dark periods that is critical to floral development controlled by photoperiod
• Temperature influences process: photosynthesis, transpiration, respiration, germination, + flowering
• Increases photosynthesis, transpiration, and respiration with temperature (up to a point)
• Affects vegetative to flowering growth, can speed up or slow down transition
• Temperature affects productivity depending on warm - cool season crop variety
• Cool high day season crops such as broccoli and spinach will bolt over flower
• Warm low high season will prevent fruit set, high season for tomato/pepper can cause pollen to become invisible an dnot pollinate
• Adverse temperatures cause stunted growth and poor quality, bitterness caused by temperatures
• Thermoperiod: daily temperature change, max growth is exposed around 5.5- 8C, allows plant to photosynthesis/respire during optimum and curtail during cooler night
• High temperatures= increased respiration, photosynthesis must be greater than respiration Low Temperatures= poor growth with slower photosynthesis/lower yields

Water (humidity)

• Primary component of photosynthesis
• Maintains turgor pressure transports nutrients
• Constituent of protoplasm of cell,regulate opening/closing of stomata
• Solvent for minerals, evaporation helps stabilize leaf temp
• Relative Humidity is the ratio of air % for temp pressure, warm= more water
• If amount stays the same and temperature increases= humidity decreases
• Vapor moves from high to low humidity
• Humidity the faster water will move
• Air space equals 100%, stomata open humidity is formed cools leaf
• Cloud away transpiration, increase keeping open and balance humidity

NUTRITION

• Nutrition needs and uses of elements plants, fertilization is materials supplied environment
• Plants needs 18 elements for growth: C,H,O in air and water, N,P,K,Mag,Ca,S in soil
• Large amounts= macronutrients
• Smaller amounts= micronutrients: Fe, Zn, Mo, Ni, Mn, B, Cu, Co, Cl, essential

Nutrient uptake processes

• Surrounded by pores, blocks by material and minerals
• Surfaces absorbinfg ions and molecules, microenvironment changes each cyccle by changing soil ecosystem
• In terms of soil fertility is physical soil ecosystem and criteria -In proer chemical form and pass -Must be at rot surface

Plant Nutrient Requirements

• Supplying an essential needs to be holistically, if not it wil lbe detrimental to the crop
• Limiting factors developed form Leibigs LaW of the Minimum, one nutrient ignored other nutrients and etc may be benfial
• From 1843 says Justus Von Leibig, is it hollistically not address the situation
• Nitrongen that applies more than the consumption is pollutant groundwater
• Organic soil amendment has benefits of synthetic ones with micronutrients
• Liebigs Barrel visual is deficiency, deficeint palnt gorwth esential mutruents
• Stave/barrel represents ditfeten essential nutrient-lenght=amount avalible to soil

Leibigs help to Understand

• LIimiting factors essential steo
• Number wont increase plan gorwth- limiting can help
• Protewt plentiful but no became limiting
• 4R helps to srtuch the barrel
• Growth controllwed or scarted limiting factor and not abundant factots
• Laws explicate limiting facturs leibilng, lackamans, shelors
• Minimum is the growth controlled by resources abundant
• L imutng factor tend depend on ate to a rate limted
• Tolernce survivak success is depened a set enfviromental tactors