Soil Mineral Nutrients Flashcards
What are the 6 MACRO nutrients? Which 3 are primary and which 3 are secondary?
PRIMARY:
- Nitrogen
- Phosphorous
- Potassium
SECONDARY:
- Magnesium
- Calcium
- Sulphur
Which of the 6 macro nutrients are LEAST likely to be deficient in soils?
Calcium
Magnesium
Sulphur
Explain how nutrient uptake works. How are they absorbed? How are they processed?
What does this process require?? And how do they get what they need for this?
Nutrients cross the cell membranes of roots and move into the vascular system to be delivered to the rest of the plant
They are passively absorbed with water
They are actively processed and can be moved against the gradient (ex. More is in the plant than in the soil)
REQUIRES ENERGY! Plants get energy from respiration
T or F: plants can be selective about what they uptake?
TRUE
What are the 3 primary soil minerals?
Nitrogen
Phosphorous
Potassium
Which of the 3 primary minerals is not found from minerals?
Nitrogen
How do the primary soil minerals form? (Except for which one?)
Except for nitrogen,
They form from
Weathering, dissolving or chemical reactions
What are 4 examples of primary minerals?
Olivine, biotite, quartz, feldspar
T or F: nutrients must be dissolved into an ion form to be available for uptake?
TRUE
Plant roots ____ ions and soil particles _____ ions?
Plant roots ABSORB ions
Soil particles ADSORB ions
What are 4 different sources of elements in soils?
- Soil solution
- Dissolved ions
- more readily available and easily taken up by plants
- leaches easier? - OM!
- large store (includes N)
- nutrients are released when OM is decayed
- can be large intermediate and long term store - Adsorbed nutrients
- clay and humus particles adsorb nutrients tightly bc of the colloids negative charge and the nutrients + charge
- CEC = H+ comes out of plant to swap with nutrient cations
What are the 3 main mechanisms of nutrient uptake? How do they work?
- Root interception/CEC:
- accounts for small amount (1% of soil occupied by roots)
- cations exchange from the plant and the soil - Mass flow
- occurs through solution - Diffusion
- actively moving across the cell membrane
How does root interception work?
The roots get ions directly from the soil solution - it’s own form of CEC or AEC
when the roots take a cation from the soil, they exchange an H+ ion into the solution
If an anion is taken up, the plant will release another anion
Plants can continually withdraw nutrients from the soil and replace them with H+ = alters pH of soil
H+ bond is so strong on CEC sites so cations can continually be released into soil solution and plants will continually withdraw cations from solution
How does mass flow work? And which nutrients is this most important for? What plant process drives mass flow of nutrients?
This is most important for NITRATE, SULPHATE, MAGNESIUM and CALCIUM
the movement of dissolved nutrients in the soil solution that move into the plant with water flow as the plant absorbs water
The ions will move with the water potential gradient (from areas of high concentration to areas of low concentration) = CAPILLARY ACTION
This process is driven by the transpiration of plants = the more water is taken in, the more nutrients get taken in
How does diffusion of minerals work? Which nutrient is dependent on this form of transportation to get into plants? What soil conditions does this process depend on?
The movement of ions to root surfaces in response to a concentration gradient (from high to low concentrations)
Phosphorous depends on diffusion to get into plants + K to a lesser extent = why P has a slow uptake
This depends on soil moisture, temperature and the ions distances from plant root surfaces
T or F: if a soil is dry, more diffusion of P will occur? Why?
FALSE
LESS diffusion of P will occur and it will be even slower
Diffusion depends on soil conditions to be effective and P cannot diffuse in the gradient if the soil is too dry
What 5 things affect plant nutrient uptake?
- Dry soils: lack of water impedes nutrient flow
- Temperature: rate of movement/reaction slows with low temp., respiration slows in cold temperatures, root growth slows, decomp of OM slows, diffusion slows
* colder temperatures = more issues up taking nutrients* - Saturated soils: plants cannot respire
- Compaction: slow respiration = plants lose energy to move nutrients
- Microbes: pathogens can slow uptake & mycorrhiza can assist uptake
What 10 things increase soil fertility? Name as many as you can
- High clay content
- High OM/humus content
- Good structure (good aggregation)
- Warm soil
- Moist soil
- Deep soil
- Good drainage
- Fertilization (depends)
- Healthy microbial population
- Neutral pH
What 10 things decrease soil fertility? Name as many as you can
- High sand content
- Loss of or lack of OM/humus
- Poor structure/compaction
- Too wet or dry soil
- Excessive irrigation or drainage
- Too hot or cold
- Root damaging pests
- Too acidic or alkaline
- Erosion
- Shallow soil
What is luxury consumption in plants? Which nutrient does this especially happen with? Can luxury consumption be harmful?
Occurs when elements are high in the soil
Plants can take up more than they need and store them in cells to use later
This especially happens with K
This can be harmful if the plant is taking up something that becomes toxic in high concentrations like boron
How can luxury consumption create soil issues for farmers?
If a plant takes up an excessive amount of a nutrient from the soil (ie. K) and the plant is then harvested, the plant is taking the K with it and not releasing it back into the soil = the soil can become K deficient
Also, if there is a high concentration of K in plants, it can become harmful to grazing livestock
How does nutrient absorption through leaves work? Which nutrients is this relevant to? And is this a big or small portion of how nutrients are absorbed?
This accounts for a small amount of nutrient absorption
This occurs through the stomata of plants and is only relevant for micro-nutrients (B, Fe, Zn)
What are 7 main plant MICRO nutrients? Name at least 3
Boron Copper Chlorine Iron Manganese Molybdenum Zinc
What are the 3 MACRO nutrients from the air and water?
Carbon
Hydrogen
Oxygen
Nitrogen’s nickname? Why? Where is it found in plants?
THE BUILDER!
Nitrogen is necessary to BUILD every part of the plant (and other beings) because it is the BASIC ELEMENT OF PLANT (and animal) PROTEINS including DNA and RNA
Found in chlorophyll - used to capture energy from the sun
What is the main source of Nitrogen? Is nitrogen in this form available to plants?
Nitrogen gas (N2) makes up 78% of the earth’s atmosphere
But N2 is not an available form for plant uptake, so it must be converted/fixed into an available form
How does Nitrogen fixation work? Which 2 soil microorganisms fix nitrogen?
Nitrogen-fixing plants, LEGUMES (beans, alfalfa), grow specialized nodules on their roots and N-fixing BACTERIA (rhizobium) life in these modules and convert atmospheric N (N2) into a plant available form
What is Phosphorous’s nickname? Why? What forms are P usually found in the soil?
THE ENERGIZER!
P helps store and transfer energy during plant photosynthesis
It is also part of DNA and RNA of plant cells
Plants require P during periods of rapid growth
P is usually found in chemical forms in the soil that are not available to plants, so farmers must apply P fertilizer
What is Potassium’s nickname? Why?
THE REGULATOR!
K helps plants open and close the guard cells that surround the stomata
This is especially important in efficient water use
It is involved in more than 60 different enzyme systems
It helps plants resist diseases, aids in the production of starches and controls root growth
Which of the 3 soil macro nutrients is most limiting in agroecosystems? And which nutrient is also the one plants require most of? Why do they need so much of it?
Nitrogen!
They need N to be able to use carbohydrates and it’s a major part of their enzymes and proteins
Which forms of nitrogen do plants mostly uptake?
NO3 (nitrate) and NH4 (ammonium)
How N in enough concentrations benefit plants?
Speeds growth
Builds strong roots
Makes large amounts of chlorophyll - plants will be a darker green
Uses water efficiently
Utilize carbs to make proteins more efficiently
Grows productive crops
What happens to plants when there’s too much Nitrogen intake?
They can be easily injured and are more weak
More susceptible to insects
Early rapid growth can slow maturation
Slows ripening
Will put too much effort into leaf growth
Delays hardening off
Why is nitrogen the most mobile and readily lost nutrient?
Because it is negatively charged so it’s not adsorbed by colloids
What are the 4 different ways nitrogen can be fixed into soils?
- Lightning (smallest amount)
- Symbiotic fixation (largest amount)
- ie. legumes and Rhizobium bacteria - Non-symbiotic fixation
- ie. Cyanobacteria (free-living) - Industrial fixation
Nitrogen fixation converts ____ from the atmosphere into ____ or ____ in the soil?
Converts N2 (nitrogen gas) into NO3 (nitrate) or NH4 (ammonium)
What are 3 examples of field crops that fix N?
All legumes!
Alfalfa
Beans
Clover
What 5 factors influence N-fixation?
- Manure or fertilizer application:
If plants can receive N in an easier way that reduces their energy input, they will take up the easier one and stop fixing N - Low soil fertility:
Deficiencies in other elements will result in reduced N-fixation - pH: acidic soils will be less effective
- Temperature:
Cold temperatures will slow - Conditions that reduce microbial activity: the largest source of N-fixation is the symbiotic relationship between legumes and rhizobium bacteria
T or F: most terrestrial Nitrogen is found in OM?
True
What is Mineralization of nitrogen?
The conversion of organic N (found in OM) into AMMONIUM
mineralization is an enzymatic process facilitated by microorganisms —> they break down the large organic molecules into smaller units until NH4 is released
What is the opposite of nitrogen mineralization?
IMMOBILIZATION
What is nitrogen immobilization?
The conversion of inorganic Nitrogen ions (either nitrate NO3 or ammonium NH4) into organic forms = OPPOSITE OF MINERALIZATION
Can occur through biological and non-biological processes
Can occur when OM requires more N than is available in plant debris - ex. A high C:N ratio in organic materials
Microbes will incorporate the mineral N from soil solution into organic compounds in their cells - IMMOBILIZING it- and will only be released when they die
How does the loss of nitrate compare to the loss of ammonium?
Nitrate is not bound to soil particles so it can easily be LEACHED
ammonium has a positive charge so it is fixed to soil particles and will be lost with the erosion of soil
The fate of Nitrate: 4 ways it can disappear?
- Immobilization by microorganisms
- Removal by plant uptake
- Leaching to groundwater
- Volatilization/denitrification
Also ammonification (NO3 —> ammonium) but not as important
What is nitrification?
The oxidation of NH4 converts it into nitrite (NO2) and then into NO3 (nitrate)
This is done by soil bacteria that get their energy from oxidizing NH4 instead of OM
T or F: Nitrite (NO2) is highly toxic to plants
TRUE it must be converted to nitrate or NH4 to be useable to plants
What is denitrification or volatilization?
An anaerobic process done by bacteria
If there are low rates of O2, bacteria use NO3 (nitrate)as an acceptor and reduce it into N2 (nitrogen gas) back into the atmosphere
6 ways nitrogen is lost
- Removed by crops
- Applied excessively in fertilizers = leached
- Cropped/bare soil prone to erosion
- Irrigation (increases percolation)
- Saturated soils = denitrification
- Liming will increase OH- and change NH4 into NH3 and water
5 fates of ammonium
- Immobilization by microorganisms
- Removal by plant uptake
- Volatilization (converted into ammonia gas)
- Nitrification
- Fixation to the inner layers of clays
T or F: ammonium can be fixed to clay surfaces? Why?
TRUE
because it is positively charged
T or F: ammonia volatilization is higher at higher temperatures and pHs?
True
What are the 6 processes that nitrogen is involved in? Describe them briefly.
- N-fixation: 4 different ways of converting N2 from the atmosphere into NO3 or NH4
- Mineralization: conversion of organic N found in organic material into plant available NH4
- Immobilization: conversion of NH4 into organic N through microorganisms
- Nitrification: the oxidation of NH4 converts into NO2 —> NO3
- Denitrification: when there is a lack of O2, bacteria will use NO3 instead and convert it into N2 to be released back into the atmosphere
- Ammonia volatilization: organic materials break down and release NH3 (ammonia gas)
3 types of N fertilizers
- Urea
- Ammonium nitrate
- Ammonium sulphate
Which nutrients in excessive amounts cause eutrophication in lakes?
Nitrates and phosphorous
What are the 3 primary sources of sulphur?
- atmospheric gases and dust
- sulphate mineralized from SOM
- sulphate adsorbed on soil minerals
what does sulphur deficiency look like in plants?
young leaves will look yellowy
What does nitrogen deficiency look like in plants?
older leaves will look yellowy
How does atmospheric sulphur form acid rain?
When sulphate is oxidized it converts to sulphuric acid and accumulates in the clouds until it rains
Sulphur can accumulate in the air through industrial emissions
How is sulphur connected to the mineralization of SOM?
Sulphides are converted into sulphate (SO4^2-) ion that is plant available
how can we test soils for sulphur needs?
plant tissue tests
Describe the Sulphur cycle
atmospheric sulphur (SO2) is deposited on the soil surface and is converted into sulphate (SO4) which is then taken up by plants or Organic sulphur is converted into SO4
What happens to sulphur in well aerated soils? which sulphides can contribute to extreme soil acidity?
Reduced forms of S (like elemental Sulphur) are subject to oxidation by chemical and biochemical reactions - when microbes consume O2 and release SO4 and H ions
iron sulphides contribute to extreme soil acidity
T or F: acid sulphate soils are naturally occurring? these soils are benign until they are oxidized?
TRUE these are sediments or organic substrates (peat) that have formed under waterlogged conditions
TRUE once they are drained or excavated or otherwise oxidized, the sulphides react with oxygen and produce sulphuric acid (VERY ACIDIC)
what are the 7 benefits of phosphorous for plants?
- energy storage and transfer in photosynthesis
- essential for rapid periods of growth
- helps stimulate early root growth
- aids in fruiting and seed production
- young plants and actively growing roots require lots of P
- important for water usage and uptake
- hastens maturity
T or F: soils usually contain large amounts of P, but it is mostly unavailable to plants
TRUE
most P is fixed and unavailable for plant uptake
T or F: Phosphorous is extremely pH dependent
TRUE
the reactions that fix P are very pH dependent
T or F: tropical and old soils have the most P
FALSE
they have the least and this can contribute to food shortages
T or F: P uptake can be a challenge for plants due to its slow mobility and low solubility?
TRUE
T or F: plants with a mycorrhizal relationship can obtain P easier?
TRUE
Which form of P can plants absorb?
PHOSPHATE
How does the fixation of Phosphates prevent leaching? what negative effect does P fixation have for plants?
Phosphates readily react with the soil and become part of the soil particles in the process of fixation. Fixation can prevent leaching, but also puts P into a form that plants cannot use
What are the 3 pools of Phosphorous?
What is the 4th?
- Solution P pool
- Active P pool
- Fixed P pool
- residual P: accumulated residue of P from fertilizers
What is the Solution P pool?
it is a very small pool that only contains a fraction of P
soluble P
What is the active P pool?
P on the surface of solids that is easily released into the soil solution
this occurs on CEC sites
What is the fixed P pool?
inorganic phosphate compounds that are very insoluble and organic compounds that are resistant to mineralization
P that is very hard to release
this P is in the clay structures
What are the 5 components of P? which ones belong to which pools of P?
- primary minerals
fixed? - mineral surfaces (clays, Fe, Al oxides, carbonates)
ACTIVE - secondary compounds
ACTIVE - Soluble/soil solution (phosphorous, HPO3, H2PO4)
SOLUTION - organic P (microbial, plant residue, humus)
mix of FIXED AND ACTIVE
4 ways Phosphorous is added to the soil
- atmospheric deposition
- mineral fertilizers
- plant residues
- animal manures and OM
3 ways Phosphorous is lost from the soil
- leaching (minor)
- run off and erosion (major loss)
- plant uptake and crop harvest
T or F: soil has both organic and inorganic forms of P?
TRUE
T or F: plants must break down the organic P into inorganic forms in order to use it and this is called MINERALIZATION
TRUE
T or F: soil particles can have a significant amount of active P that can cause environmental problems (ie. eutrophication) if they are lost and the main method of this loss is EROSION?
TRUE
How does Phosphorous move through the soil?
mostly DIFFUSION
but also mycorrhizal association (small distances and slow)
Why is phosphorous so unavailable to plants? which pool of P does this account for?
It is a REACTIVE compound, so it will bond to other elements very quickly.
this makes up the FIXED pool of
In alkaline soils which elements will P join with? in acidic soils?
Alkaline: bond with Ca
Acidic: Al or Fe
T or F: soil OM reduces Phosphorous fixation and therefore makes it more available to plants? why?
TRUE!
the more OM, the more available P!
because, OM will bind with Fe and Al (or Ca) and use up all the CEC sites so P can remain available
T or F: in clay soils, phosphates can replace the OH and become part of the clays?
TRUE
If you had a clay soil, what 6 ways would you maintain available P in your soil?
- the pH needs to be between 6-7
- soil must be uniformly moist so the P can move by diffusion
- soil needs proper aeration and Oxygen to break down the organic phosphates and plants need O to take up nutrients
- symbiotic relationships with mycorrhiza to increase uptake absorption
- decreasing conditions that can slow root growth (slow root growth = slow P uptake) - ex. warm temperatures will increase uptake – use plastic covers?
T or F: synthetic P fertilizers are very soluble and are very inefficient
TRUE
a large amount of the P will quickly fix and the rest will move into the solution pool and be lost to run off
Why is P an issue in water systems?
P is usually limiting in water systems so if it is added, it increases growth rapidly = mass algal blooms = eutrophication
why are erosion and run-off such a major reason P is lost?
erosion carries away the P that is fixed to the soil particles
P that is in the dissolved pool will move with runoff water - a concern because there is an immediate effect
What 5 management techniques can prevent P from being lost through erosion and runoff and entering water systems?
- conservation tillage to keep P in the soil
- cover crops to continue the P cycle
- buffers in the waterways
- retention wetlands
- riparian buffers
What does P deficiency look like in plants?
If there is a P deficiency, plants will translocate the P to the newer leaves and leave the older leaves stunted, in fewer amounts, and smaller
they can also turn purple
What are the 5 sources of Phosphate?
- weathering (apatite)
- strip mines that create trailing ponds
- excreta (from animals and humans)/sewage sludge
- bone meal
- mycorrhiza
T or F: phosphate is a finite resource?
TRUE
Globally, where are the largest reserves of phosphates? Where is the least?
largest: China, Northern Africa, and Middle East
Least: Canada, Australia
What is the natural form of P? and how is it released?
P comes from APATITE
the availability of P is restricted by the rate of release of the element during weathering
Apatite dissolution through carbonation is a key control on ecosystem productivity
How does manure/excreta provide P?
there is Phosphorous in foods, so excreta contains P
very efficient form of manure
How does bone meal work as an input of P?
it is a mixture of finely and coarsely ground animal bones and slaughter-house waste products that is a slow release fertilizer primarily used as an organic source of P and proteins.
How do mycorrhiza make P available to plants?
mycorrhiza break down compounds that contain P and penetrate roots
In the symbiotic relationship between mycorrhiza and plants, what do they fungi receive in return?
plants give the mycorrhiza amino acids and sugars
T or F: it is very difficult to test for P in soils? why?
TRUE because of the 3 pools, it’s unavailability and pH
How can P be tested?
Using a chemical extractant
What are the 3 components of Potassium in the soil?
- Primary minerals being weathered (mica, feldspars)
UNAVAILABLE K - K solution
- secondary components and mineral surfaces
What are the 3 additions of Potassium to the soil?
- animal manure and OM
- fertilizers
- plant residues
What are 3 ways Potassium can be lost from the soil?
- crop harvest
- run off and erosion
- leaching (minor)
T or F: leached K is an environmental problem
FALSE
T or F: Potassium is a component of SOM and plants contain organic compounds with K in them?
FALSE
T or F: sandy and organic soils lose K easily and do not hold onto it well
TRUE because it is on the CEC sites
T or F: soils contain large amounts of K and it is soluble and readily available to plants?
FALSE!
soils do contain large amounts of K, but it is fixed and unavailable
Where are the 4 places K can be in the soil?
- in Primary Minerals (mica, feldspars) that will release it due to weathering
- non-exchangeable positions in Secondary Minerals (vermiculite) is slowly available or strongly held between clay layers - FIXED
- on CEC sites: readily available, lots are found on the surface of particles
- In soil solution: readily available and an immediate source of ions to be taken up by plants = Exchangeable Potassium - this can be leached severely in sandy and organic soils
5 ways K benefits plants?
- promotes growth because it is mostly in the cell solution rather than in organic molecules
- increases osmotic function and enzyme activation functions
- opens and closes stomata
- uptake of water through roots
- helps move sugars around plants - important for ripening fruits
what does K deficiency look like in plants?
uncommon except in sandy/organic soils
older leaves will yellow in necrotic margins (outside)
plants will have a low disease and drought tolerance
late maturity
What is a major caution for adding K fertilizers to clay soils?
It quickly ages clay soils and reduces the CEC because it refills the space between clay layers with locked-in K and damages edges of clays
What are some management techniques to maintain K in your soil?
- Crop removal slowly removes readily available forms of K and may need fertilizers to replace
- applying fertilizers only when plants need it (ex. in high fixing soils or coarse soils with high leaching potential)
- return manures and leave plant residues on soil to allow soil to replenish the K naturally
- excessive K in forage can cause issues for livestock
What are the two kinds of tests for micronutrients? when would you use which one?
- Soil test:
- boron, manganese, zinc - Plant analysis:
- copper, iron, Mb, chlorine, nickel
What are 3 things to consider in terms of micronutrient needs of crops?
- know which crops need extra which micronutrients
ex. corn needs more zinc - understand that extreme soils will have issues:
ex. high/low pH
sandy soils
heavy clays
low/high OM
erosion/compaction - weather issues: extreme temperatures/rainfall/droughts
T or F: sandy soils likely have micronutrient deficiencies?
TRUE
Which soils are susceptible to micronutrient issues?
coarse soils
low OM soils
sandy soils
