Soil Science 10
What is the pH of rain?
(pH of non-polluted rainwater is 5.6 due to equilibrium with atmospheric CO2); between 5 and 6
Unsaturated flow
when large pores are filled with air. This type of flow is dependent on soil water potential (matric potential) and on hydraulic conductivity. More water, more conductivity. If there isn't much water, clay soils have more conductivity than sandy soils because of capillaries.
Micronutrients
zinc, copper, Iro
Addition of lime to acid soil increase or decrease Al toxicity?
Decrease
What processes are responsible for the renewal (exchange) of soil air? Diffusion
Mass Flow--due to pressure differences between soil air and outside atmosphere (i.e. evapotranspiration air sucked into soil...rain forcing air out of pores) Diffusion--flow of gas molecules according to gas concentration gradient
What is a potential?
Matric potential (dependent on texture and structure and water content), osmotic potential (dependent on salt concentration), gravity potential (due to differences in elevation). All combine to make up the difference in energy level between soil water and pure water.
Plants get these nutrients from water and air
Nitrogen, phosphorus, potassium
Why are some soils naturally acidic while others are basic?
Organic material breakdown, weathering and climate...and time (leaching), bases can get chemically weathered out and leave a soil acidic and in dry climates basis can accumulate and make it too basic
What factors affect the bulk density of a soil?
Particle Density Texture (sand > clay) Soil structure Concentration of SOM Cultivation
Why does soil air contain more carbon dioxide than the atmosphere?
Plants respire and produce CO2, as do soil microorganisms. Also, when decomposition occurs, more CO2 is released. All of these processes account for more CO2 in soil than in the atmosphere.
Increasing salt content of soil will increase osmotic potential?
Salt decreases osmotic potential (how it moves due to salt, moves from high to low)
Which soil have greater heat conductivity, Saturated soil or Air dry soil?
Saturated soil...heat travels through water much faster
water holding capacity of soil increases
increasing organic matter of soil
Chlorosis
lack of chlorophyll
Macronutrients
nitrogen, phosphorus, potassium
What soil factors affect cation and anion exchange capacity?
pH affects, high pH, higher CEC, lower AEC
Buffering capacity in soil
the amount of acid or base a buffered solution can soak up before its pH will start to change significantly
Define albedo.
the fraction of radiation reflected by a surface.
How does albedo influence soil temperature?
the more that is reflected, the less hot the soil.
What is capillary porosity?
water held in soil pores against the force of gravity (micropores),climbs against gravity
Compare a sandy loam to clay loam. Which has more capillary water? Which has more non-capillary water?
A sandy loam has more macropores, so it has more non-capillary water. A clay loam has more micropores, so it has more capillary water.
Which way does water flow?
Always flows from high energy to low
Conversion of organic nitrogen to NH4+ is called
Ammonification
How are soil oxygen and carbon dioxide concentrations related in a soil profile?
As you move deeper, soil is more impacted so there is less air space. There is also more CO2 because deep roots are producing it.
What is the difference between bulk density and particle density?
Bulk density includes solids and pore space (weight of oven dry soil/volume) while particle density includes the weight of solids only (weight of solids/volume).
How do you measure bulk density? What assumption must be made to calculate porosity knowing bulk density?
Calculated by total weight of oven dry soil/volume of soil. Must be oven dried.
Which soil have greater heat conductivity, Sandy soil or Clayey soil?
Clay soil has higher heat conductivity
How does compaction affect heat flow? aeration? porosity?
Compaction presses the particles closer together, which means the heat transfer via conduction is greater. However, air space is decreased because porosity is decreased
Define gravitational water, permanent wilting percentage, field capacity, and plant-available water.
Gravitational water = water that is not held against the force of gravity ...micropore water Permanent wilting percentage = the water percentage of the soil at which plants can't extract water to maintain metabolic processes...tighter than 15 bars Field capacity = max amount of water that can be held by soil after free drainage has stopped and all non capillary water is gone. -1/10 to -⅓ bar Plant-available water = AWHC, water held in soil that plants can use.... FC - PWP
What are the negative consequences of acid soil conditions?
Harmful to fish and other wildlife and can negatively affect the growth of plants
How does pH affect cation exchange capacity (CEC)?
Higher pH, higher CEC
What is cation exchange?
How many cations can be held to soil particle surfaces. An exchange due to pH dependent charge. Higher pH, higher CEC
How is the energy required by plants to extract water related to pore size (larger vs smaller)?
In saturated flows, hydraulic conductivity is dependent on the size of pores. For unsaturated flows, capillary activity like in clays becomes the primary pathway for movement.
What soil factors affect the gas diffusion coefficient (rate of gas movement)
Lower bulk density=high porosity which means an overall greater gas diffusion rate
Conversion of NH4+ to NO3- is called
Nitrification
What is non capillary porosity?
water held in soil pores but not against the force of gravity (gravitational waters--macropores)
Base saturation increases as
Soil PH increases
Why is soil pH such an important soil property?
Soil pH is a master variable that affects a wide range of soil properties - chemical, biological and physical.
How does the magnitude of daily and annual changes in soil temperature change as a function of depth?
Soil temp rises and falls with weather patterns. But as you go deeper, these fluctuations are less and less large.
How is texture related to porosity (total, macro & micro)? To bulk density? To soil structure?
Texture is related to porosity because the amount of micro/macro pores determines how water and air can flow through the soil. So if a soil has a lot of clay, which has lots of micropores, there is more porosity than in sandy soils which has lots of macropores. Texture is also related to bulk density because bulk density includes poor space, so texture affects it. The same is true for soil structure because texture affects total porosity, which is a part of soil structure!
How are soil moisture content and matric potential related?
The drier the soil, the tighter the remaining water is held..so the matric potential becomes lower.
Why do sands typically have less plant-available water than fine-textured soils
The macropores in sand don't attract water as well as micropores in smaller texture materials. Also, clay soils have more capillary action.
What is base saturation and how does it change as a function of pH?
The percent of soil exchange sites (CEC) occupied by basic cations (Ca, K, Mg, Na). Base saturation increases as pH increases.
Why do plants wilt in soils that may have as much as 20% moisture
The permanent wilting point
How does the heat capacity of wet soil compare to that of a dry soil?
The wetter the soil the higher thermal conductivity because heat transfers better from soil to water than from soil to air.
Addition of lime to acid soil increase the soil pH?
Yes, Lime increases base saturation, increases calcium nutrient availability, and decreases aluminum toxicity.
How is excess soil acidity corrected?
addition of lime
How can excess basicity be corrected?
addition of sulfur and ammonium
Saturated flow
all pores are filled with water. This type of flow is dependent on hydraulic force (gravity potential) and hydraulic conductivity. Macropores move most saturated water flow and texture and structure affect the flow because of porosity influencing conductivity.
