Soil mineralogy
The central concepts for a Oxisol
They are dominated by Fe/Al oxides that are acidic, which are variable charged clays. They are pH dependent with a high IEP. At pH 5 (most common here in HI) you expect a net positive charge because it is getting protonated. This is why it has low CEC and fertility.
Define saturated water conductivity and what difference does it make in a Oxisol vs a Vertisol
Definition: The ability of soil to transmit water
Difference: An Oxisol has higher saturated water conductivity due to Fe/Al oxides causing oxide cementing which clumps the soil particles together causing stronger aggregates and allows water to flow more quickly through the soil. Compared to a Vertisol, the high shrink/swell potential close up large pores and restrict water flow. Vertisols are prone to flooding.
Why does smectite have high CEC?
Hint: Isomorphous substitution
Smectite has high CEC because it is a permeant charge clay with a negative surface charge. Isomorphous substitution allows for a atom of a similar size to replace an atom on the crystal structure to result in a change of surface charge. (Al for Mg)
What percent of N will be mineralized in green waste compost (1% total N), chicken manure (3% total N), Fish meal (9% total N). and no the total N is not the answer. We are looking for the percent mineralized.
Green waste compost: 10%
Chicken Manure: 50%
Fish meal: 75%
Improves Soil Physical Properties, Improves Soil Chemical Properties (Increases CEC), Improves Soil Biological Properties
Does the crystalline structure of the primary minerals in the two rocks affect weathering rates?
Yes. Granite has a more complex crystalline structure that resists weathering. Conversely, basalt has a simpler crystalline structure with weak ionic bonds and is more susceptible to weathering compared with granite.
Definition: The chemical binding of phosphate by Fe/Al clay surfaces and amorphous clays.
P fixation in soil orders: P gets fixed in Andisols due to the amorphous clay surfaces (ferrihydrite)
Can you acidify a Vertisol?
Yes, but it is challenging. They need a high buffering capacity so they can become alkaline and resistant to pH change. It also needs acidifying agents like aluminum sulfate or acidic fertilizers like ammonium sulfate.
A corn crop requires 150 kg/ha N. Calculate how much quantity is required in Urea 46-0-0?
150/0.46= 326 kg 46-0-0
How does CEC develop on ferrihydrite?
ferrihydrite is pH dependent and hydrogen is making the clay surface positive (Protonation), ferrihydrite has lots of organic matter which stabilize and increase the nutrient retention. Due to OM, ferrihydrite is able to hold nutrients and influence soil fertility. (Without OM ferrihydraite has naturally low CEC)
Answer the questions about this soils using the elements of the taxonomic name: Very-fine, sesquic, isohyperthermic Anionic Acrudox
Soil Order
Rainfall distribution
Mineralogy
Is this a fertile soil?
Can you find this soil in temperate regions?
1. Oxisol
2. Udic
3. High in Fe/Al oxides (Kaolinite)
4. No. Due to it being highly weathered, nutrients and minerals are leached out and highly acidic iron oxides remain.
5. No because isohyperthermic indicates a tropical climate that's very warm year round
What is the isoelectric point and how does it relate to the fertility of oxisols?
Definition: In pH, the number of positive surface charge equal the number of negative surface charge on variable charge colloid surfaces
Relation to fertility of oxisols: In oxisols the isoelectric point is high causing low fertility because the surface charge is positive (AEC). This shows why we need to lime to raise pH and allow for the soil to have a more negative surface charge to raise CEC.
In a synthetic fertilizer is N always avalible?
Yes, because the N is soluble in synthetic fertilizers
A corn crop requires 150 kg/ha N. A horse manure compost has 1.3% total N.
150/(0.013x0.1)= 115384 kg/ha
Compare and contrast a vertisols, oxisols, and andisols.
Both vertisol and andisols have high fertility compared to a oxisol, which has low fertility. Vertisols have high shrink/ swell potential with unstable aggregates compared to a oxisol which has low shrink/ swell potential, stable aggregates, and good drainage. A andisol has low bulk density, high porosity, and good water retention. You guys can add more im just lazy.
On the island of Oahu, where might you find the three different soils and why?
Ustert:
Ustox:
Udox:
Ustert: Cracking clay soils are found in drier leeward areas, like Kaena, because it forms in seasonal wet/dry climates from basalt
Ustox: Found on gently sloping areas, like Waianae, as they are reddish soils that form in intense weathering, high rainfall, and leaching over long periods
Udox: Found in high rainfall areas, like koolau (windward side), because they are highly weathered, deep, and clayey soils.
Name two important soil symbiotic relationships, for each describe the (a) partners, (b) the mechanism, and (c) the benefits.
Rhizobium (BNF) & Mychorrizae
1. Rhizobium:
A BNF symbiosis between plants and microbes. Partners: Legumes and Rhizobia. Mechanism the plant provides energy (sugars) and shelter (root nodules) for the microbes, and in return, the microbes convert atmospheric nitrogen (N₂) into usable ammonia (NH₃) via the nitrogenase enzyme. This only occurs in the absence of oxygen, so the plant produces leg (?) hemoglobin that binds the oxygen, rendering the nodule anoxic.
2. Mychorrizae:
Partners: Fungus and Plant roots. Mechanism: This fungus colonizes plant roots and creates hyphae (an extension of the root system). The hyphae system reaches beyond nutrient depletion zones in the soil to absorb water and essential minerals (like phosphorus, nitrogen, zinc, and copper). These are transported to the plant, while the plant provides the fungus with sugars/carbohydrates produced during photosynthesis, which the fungus needs for energy and growth.
3. Benefits:
Rhizobium - Keep O2 out, exchanges needed nutrients, makes N2 plant available
Mychorrizae - For the plants, better water uptake, better nutrient uptake, and soil aggregation. The fungi receive sugars/carbohydrates produced during photosynthesis, which the fungus needs for energy and growth.
Describe a Hydradand (In terms of ferrihydrate) and how the clay mineralogy is related to fertility.
Hydradand: Highly weathered, low CEC, high p fixation.
Relation to fertility: High surface area but lacks stable crystalline structure which makes this soil easy to weather. High p fixation, which makes orthophosphate unavailable as it is fixed in the interlayer spacing. High in Fe/Al oxides.
The same cabbage crop needs 40 kg of P based upon soil test report with a P buffer coefficient of 0.2. (A cabbage crop requires 180 lbs N per acre)
If the farmer use 10-30-10, how much must be added?
40/(0.2) = 200 kg P
to get P2O5: 200/0.44=455 kg P2O5
to get 10-30-10: 455/0.3= 1,515 kg 10-30-10 per ha
In relationship to saturated hydraulic conductivity, assign vertisol and oxisol to the soils below:
(rate of water movement. distance/time)
Soil A: 88mm
Soil B: 2.6 mm
Explain why
Oxisol is soil A
Vertisol is soil B
Oxisols have stable aggregates and due to oxide cementation the particles in this soil act like sand, making the movement of water in soil higher. Vertisols have high shrink/swell which closes the pores causing less water to move through and soil and flooding
Name everything about 2:1 clays. CEC, mineralogy, etc.
High internal and external surface area, high CEC, fertile, permanent charge clays (Negative surface charge) Smectite and vermiculite, high shrink/swell,
Ustic moisture regime
Ustic means it has a wet season and a dry season
Nitrogenase is considered one of the most important biomolecules because it enables
BNF
For a cabbage crop (180 N), the farmer wants to use cow manure with NPK of 2-1-0.5. Assume only 25% of the N in the manure will become plant available in the crop cycle.
Calculate the amount of manure to add.
Calculate the amount of K added.
amount of manure to add: 180/(0.02*.25) = 36,000 kg manure/ha
amount of K added: 36,000*0.005*0.83 = 149 kg K/ha
Explain how water moves through the soil and into plants from matric potential, gravity, and osmotic potential.
Water moves down into the soil due gravity and eventually stops due to the matric potential. The matric potential carries water from high areas of water potential to more low (negative) areas in unsaturated soils. The osmotic potential then dissolves ions to attract water molecules and lower energy state so the plant to uptake the water.