Introduction to Soils Flashcards
Why is knowledge of soils important for forage production?
- Provides foundation for plant growth
(Source of water and nutrients) - Matching the correct forage species to the
soil type(s) is vital for maximizing yield,
quality, and stand health - Understanding a particular soil and its
limitations and strengths will help in
making decisions involving costly inputs
What is soil?
Soil is the mixture of minerals, organic matter, gases, liquids, and organisms that together support plant life
What makes up the “ideal soil?”
50% solid matter (~45% mineral, ~5% organic matter)
50% pores (~25% air, ~25% water)
What is organic matter?
Fresh and decompsed vegetation, microbes
What does the chemistry of the soil consist of?
- Mainly pH: neutral, acidic, alkaline
- Clay composition: water and nutrient holding capacity (cation exchange)
What are some factors that determine soil properties?
- Topography: area of water accumulation
- Biotic factors: Vegetation, microbial activity, animal activity, macroinvertebrate activity (worms)
- Time: formation (i.e. geologic) and degredation (i.e. lifetime –> very short)
What are the classes of soil texture?
- Sand: 2.0 to 0.05 mm
- Silt: 0.05 to 0.002 mm
- Clay: < 0.002 mm
What does knowing the soil texture tell you?
- Water flow potential
- Water holding capacity
- Fertility potential
- Suitability for many urban uses like bearing capacity
What are the properties of sand?
- Has the least amount of surface area: low water holding capacity/drought prone; high infiltration rates/good drainage
- Little chemical reactivity
*
What are the properties of silt?
- Greater surface area and water holding capacity than sand
- Little chemical reactivity
- Highly erodible
What are the properties of clay?
- Chemically charged (negative charge): affects pH (acidity)
- Greatest nutrient holding capacity
- Greatest water holding capacity: not available to all plants
What soil pH is optimum for plant growth?
pH: 6 to 7.5
What is the importance of pH?
- Proper plant root function and microbial activity
- Availability of soil nutrients
What is an acid soil and where is it predominantly located?
- Located: usually highly weathered soils, high
precipitation, humid environments –> Eastern U.S. - Acid soil: Less than 6.0 usually compromises crop performance
Acid Soil: pH < 7.0
What is alkaline soil and where is it perdominantly located?
- Located in arid and semi-arid environments –> Western U.S.
- Crop growth performance limited above 8
Alkaline Soil: pH > 7.0
What are the types of alkaline soils?
- Calcareous: Derived from CaCO3 (limestone), low in sodium –> very productive soils
- Saline: High in salts (chlorides and sulfates), low in sodium (Na)
- Saline/sodic: High in total salts with high Na, high Na disperses clay –> making it impermeable to water
- Sodic: Low in total salts but high in Na, pH 8.5 to 10.0
- Saline/sodic and sodic an be reclaimed with gypsum
Bolded are the two most common in the U.S.
Where does most organic matter come from?
Vegetation in varying stages of decomposition
What is humus?
hue-mus
Fairly stable end product of organic matter decomposition
* Long-term, stays in the soil for a long time
What is the importace of soil organic matter?
Major source of nutrients: increases soil’s nutrient and water holding capacity
What are some long-term ways to increase OM?
OM: organic matter
- Cover crops
- Residue management
- Reduced tillage
- Permanent perennial pasture and hay
What is Liebig’s Law of the Minimum?
The most limiting nutrient
* Growth will be limited by the least available nutrient
What ratio do plants use nitrogen and phosphorus?
3:1
Nitrogen: Phosphorus
What is an aggregate?
A single mass or cluster of soil (clod, crumb, block, prism)
What is the importance of soil aggregates?
- Drainage
- Healthy root environment
