Test 2 Flashcards
Hydrologic cycle
All life depends on and involves run off and excess water
Water balance
P=et+ss+d
Et=evapotranspiration
Ss=soil storage
D=discharge
Soil plant atmosphere continuum
Water moves from soil to plants to the atmosphere and back to soil
Water deficit
Potential water evaporation - evapotranspiration
Is considered a measure of plant stress
Conservation tillage
Leaving plant residues on surface to minimize both evaporation loses and erosion
Two ways water leaves the soil
Through percolation or drainage that carries with it plant nutrients, pesticides and other dissolved chemicals that can move into groundwater and nearby streams
Through runoff water that carries with it plant nutrients as well as the finer fractions of the soil itself through soil erosion
Preferential flow
Percolating water moving rapidly through very large macro pores such as those formed by root holes and earth worms
Vadose zone
The unsaturated zone above the water table
Capillary fringe
Zone of unsaturated material directly above groundwater table and part of vadose Zone
Problems with preferential flow
Brings chemicals and solubles down farther in the soil profile
Open ditches
Drainage method used to lower the water table in a poorly drained soil
Buried tile lines
Perforated plastic pipe that acts in the same way as an open ditch yet it is not visible and doesn’t provide an obstacle.
Footer drain
Used around foundation of the house to keep water level lower and prevent flooded basements. Topsoil is angled away and a drainage pipe is present.
Septic tank
Wastewater from homes is piped to a concrete box where the solids settle out and decompose. The liquid effluent overflows into a series of perforated pipes buried which operate in the opposite way of the drainage system
Perc test
Used to check for permeability for septic tank
Micro irrigation
Trickle or drip systems that apply very small quantities of water directly onto the plant and is the most efficient method
Soil aeration
Influences most chemical physical and biological processes in soils
Hydrophytic plants
Plants that can adapt to saturated conditions due to aerenchyma tissues that allow them to thrive in water saturated conditions by getting oxygen from the atmosphere
Gases in soil air
Nitrogen, oxygen and carbon dioxide
Nitrogen is about 78 percent
Oxygen is about 21
Co2 is definitely higher than that of atmosphere at .035
Aeration status of soil can be determined by:
The O2 content in the soil
The proportion of the pores pace filled with air
The oxidation reduction potential of the soil
Redox potential
Gives an indication of the tendency of the soil to accept or donate electrons which infuences the ionic species of several elements in the soils.
Measures in Millivolts
400-700 indicates oxidizing conditions
300 to -300 suggest reducing conditions
Colors of redox status
Red and brown colors indicate oxidized Fe and Mn compounds
The Blues and Grays predominating under reduced conditions
Factors influencing soil temperature
Soil radiation
The specific heat of a soil
Energy needed to evaporate soil water
Colloidal particles
Very small in size at less than 2 micrometers in diameter and are made up of clay and/or humus.
Carry negative or positive changes that attract particles
The absorbed ions are subject to exchange with plant roots thereby providing plants with most of their essential mineral elements
4 colloidal particles
Crystalline silicate clays
Allophane and associated non-crystalline silicate clays
Hydrous iron and aluminum oxide clays
Humus
Silicate clays
Found all over the world but most prominently in temperate regions
Allophane
Most prominent in volcanic regions
Oxide clays
Prominent in soils of the tropics
Humus
Found wherever organic residues are
Kaolinite
1:1 as in one tetra to octa
Non expanding and no swelling
.7nm
Little isomorphous substitution and therefore low cation exchange
Smectite
2:1 T/O/T
Expanding and max swelling
1-2 nm between groups
Vermiculite
2:1
Expanding and some swelling
1.0-1.5 nm
Expansive cation holding capabity
Fine grained mica
2:1
Non expanding
Minimum swelling
Has higher cation exchange is higher than 1:1 but lower than other 2:1 clays
Chlorite
2:1
Non expanding
Minimum swelling
1.4nm
Tetrahedral
Silica sheet called a tetra hedral sheet because of the four sides configuration and associated oxygen atoms.
4 SIDED
Octahedral
Aluminum and magnesium sheets comprise eight sided building blocks
Isomorphous substitution
Ions having nearly the same radius as a silicon atom can fit in the tetrahedral sheet.
Once this occurs the crystal is negatively charged attracting cations which then exchange with plant roots
Soil acidity or alkalinity
Expressed as soil ph, it determines which plants dominate natural landscape and which crops can be grown
Natural ph levels in different environments
Acidity in humid environments and alkalinity in arid environments.
pH scale
Natural rain and souls are 5.5 to 6 and pure water is 7
Battery acid is 1 and bleach is 12
Causes of alkalinity
Caused when hydroxyl ions from carbonates and biocarbonates react with water
Role of aluminum
Another principle acid cation besides hydrogen, it’s hydrolysis reactions produce H- ions and its toxicity comprise one of the main detrimental effects of soil acidity.
Active acidity
A measure of the H + ion activity in the soil solution. Quantity of H+ ions in this form is very small.
Salt replaceable acidity
Gives an indication of the exchangeable Al3- and H+ present on the exchange complex and is equivalent to 200-2000 kg CaCO3 per hectare furrow slice
Remaining acidity
Mostly associated with aluminum and hydrogen ions that are tightly bound by the organic matter and silicate clays. The amount of residual acidity is commonly much higher than even the salt replaceable form and may be as high as 5000-20000 kg CaCO3 per hectare
Total acidity
Must be overcome to raise soil ph to a desired value
Total acidity definition
Sum of active, exchangeable and residual pools of soil acidity (salt replaceable)
Acidifying agents
This can be done by applying quantities of organic material, sulfur
Liming
Used to balance the loss of calcium and magnesium in the soil to decrease soil acidity
Saline soils
pH value of 8,5 or less
Sodic soils
Have the sodium levels of Saline-sonic soils without the moderating influences of the neutral salts. PH greater than 8.5
Flocculation
Ability for colloids to form and stick together
Primary producers
Higher plants and algae
Nematodes
Highly diverse tiny roundworms. A few species attack plant roots
Rhizosphere
Populated by a greater abundance and diversity of microorganisms than is the bulk soil
