soil nutrients

Soils exam 3 review

Nitrogen role

major part of amino acids, the building block of proteins and enzymes. Also important for chlorophyll.

Nitrogen deficiency signs

stunted, thin stems, chlorosis of entire leaf including veins with oldest leaves showing first. Mobile from old to new.

Nitrogen oversupply signs in plants

Enlarged but weak cells, lodging, delayed maturity, disease and pest susceptibility.

Nitrogen forms taken up

Dissolved Nitrate and ammonium

Nitrogen distribution (pools)

Most in atmosphere or crustal rock

Nitrogen distribution (fluxes)

Atmospheric nitrogen is held in triple bonds, must be fixed to be usable. Leaching transfers from land to water. Is returned back to the atmosphere via denitrification by microbes.

Nitrogen immobilization

the soil becomes devoid of nitrogen when microorganisms require more N than the soil can provide. They scavenge nitrate and ammonium.

Nitrogen mineralization

Most soil nitrogen is in large unobtainable organic molecules so it must be converted to inroganic forms like nitrate and ammonium.

Ammonia volatilization

Alkaline soils (pH > 7) promote the conversion of ammonium to ammonia gas, increasing volatilization.

nitrification

Nitrosomonas first oxidize ammonium to nitrite. Then nitrobacteria convert the nitrite to nitrate, increasing acidity.

ammonification

decomposers convert organic nitrogen from dead organisms or waste into ammonium

denitrification

nitrate converted to gaseous forms (N2). The final step of the N cycle.

N fixation

N2 to NH3 via the niotrogenase enzyme.

Phosphorous deficiency signs

stunted, thin stems, dark leaves, older leaves show fir4st

phosphorous role

essential to ATP, DNA, RNA, enhances flowering, fruiting, maturation, and photosynthesis

potassium role 

an activator for cellular enzymes, adjusts osmotic balance, opens stomatesp

potassium deficiency signs

leaf tip chlorosis or tearing edges first in older leaves.

The 4 available forms of potassium

1. in primary minerals

2. non exchangeable in secondary minerals

3. exchangeable on colloid surfaces

4. soluble in water

The 3 forms of phosphorous

1. organic (labile or protected)

2. calcium bound (inorganic)

3. Fe/Al bound (inorganic)

the types of organic phosphourous

Di and monoester, phospholipids derived from cell membranes

Under what type of C/N ratio is phosphorous immobilization likely

high C/N ratio

Calcium role

component of cell walls (stiffness), cell elongation and division, membrane permeability, enzyme

calcium deficiency signs

stuck leaves, stunted meristem, blossom end rot, poor roots

the 3 forms of calcium

1. minerals

2. organic complexes

3. exchange sites

magnesium role

central component of chlorophyll molecule, synthesis of oils and proteins, enzyme activation for metabolism

magnesium deficiency signs

chlorosis everywhere but veins, first appearing in older leaves

serpentine soils

little calcium, weathering from mafic soils

silicon is

the second most abundant element in crust

silicon role

rigidity, stimulates growth, alleviates other deficiencies/toxicity

phytolith

microscopic silica in cell walls that provides support and repels herbivores or fungal disease

hemicellulose vs cellulose

cellulose is a strong rigid chain like polymer while hemicellulose is weaker and branch like.

types of labile organic matter

living biomass, detritus, partially degraded tissue, free biomolecules

types of protected organic matter

protected tissue/cell walls , protected biomass, char

priming effect

increased decomposition of relatively stabile protected humus occurs due to enhanced biological activity.

how does C/N ratio impact rate of decomposition

low ratio speeds up decomposition while a high one causes immobilization.

immobilization

nutrients become locked up by microbial ise when they are converted from inorganic to organic

influence of climate on soil carbon

decomposition increases with warmer temps, precip erodes it away

most abundant, available form of P

carbon bound inorganic

ways plants access P

1. longer roots/hairs

2. exude compounds that release P from Fe/Al

3. acidify the rhizosphere to speed dissolution of Ca-P

4. exude enzymes that cleave P from organic compounds

5. exude growth stimulators to attract rhizobacteria

6. attract micorhizal fungi

Sulfur role

mimics that of N (protein synthesis)

sulfur deficiency signs

chlorosis of young leaves first, stunted growth