ssc exam 3

cation exchange capacity (CEC)

sum of total cations that a given soil can absorb

higher CEC soils

clayey soils and soils with humus (organic matter)

cation exchange influences

strength of adsorption, relative concentration of cations in the soil solution

ismorphic substitution

process in which one element substitutes another of comparable size in the crystalline structure. permeant charge

pH dependent charge

broken ends of clays carry a charge. Charge can change based on the pH. Lower pH = more H+ will attach to the broken ends.

acid soil pH

below 7.0

metals toxic to plants at low pH

Fe, Mn, Cu, Zn

P binds at low pH to

Fe/Al

P binds at high pH to

Ca

buffering capacity

soils ability to resist change in pH

active acidity

H+ or Al3+ in the water of soil and a measure of how acidic the soil is.

Exchangeable acidity

H+ and Al3+ that are on exchange sites of clay or OM negative sites

Residual acidity

H+ or Al3+ that are bound to clay or OM and NOT exchangeable

benefits of liming

crop yield improvement, nutrient availability, improved microbial activity, improved legume fixation of N

Calcium Carbonate Equivalent (CCE)

Neutralizing value of any liming material compared to pure calcium carbonate

factors to increase lime

higher: CCE, buffering capacity, CEC, pure lime, smaller lime particle, clay

soil colloid

fine, chemically active particles in soil

phyllosilicate

clay minerals constructed from tetrahedral and octahedral sheets

2:1 phyllosilicate clays

two tetrahedral sheet to one octahedral sheet. (illite, younger soils (mollisols, alfisols), shrink swell soils (vertisols))

1:1 phyllosilicate clays

one tetrahderal sheet to one octahedral sheet. (kaolinite, older/more weathered soils (spodosols, utisols))

iron and aluminum oxides

just octahedral sheets. common in highly weathered soils (oxisols)

humus

organic matter fraction that has decomposed sufficiently so that the source material is no longer recognizableprop

properties of humus

darker color soil, very chemically reactive, buffers soil pH, high CEC

nitrate lost easily by

leaching

ammonium lost easily by

volatilization

symbiotic biological N fixation

bacteria fix N2 to plant-available forms for plants to use

mineralization

biological conversation of unavailable organic N into plant available inorganic N (organic N to ammonium to nitrate)

immobilization

biological conversation of plant available N into unavailable organic N

ammonification

conversion of organic N to ammonium by microorganismswh

ammonification properties

needs warm temps, good soil moisture, oxygen supply. makes soil more basic (higher pH)

nitrification

conversion of ammonium to nitrite and then nitrate

nitrification properties

needs warm temps and well-drained soil. makes soil more acidic (lower pH)

nitrosomonas

mediates ammonium to nitrite

nitrobacter

mediates nitrite to nitrate

volatilization

removal of N from the soil by turning it into a gas that leaves the soil

denitrification

conversion of nitrate to a gas from of N (N2)

denitrification properties

needs warm temps, low oxygen, high organic matter

crop uptake and removal

removal of N by plants and then removing plant residues from the field

law of the minimum

if one growth factor/nutrient is deficient, plant growth is limited, even if all other factors/nutrients are adequate. plant growth is improved by increasing the supply of the deficient factor/nutrient

structural components

carbon, hydrogen, oxygen

primary macronutrient

nitrogen, phosphorus, potassium

secondary macronutrient

calcium, magnesium, sulfur

mass flow

dissolved nutrients move to the root in soil water that is flowing towards

diffusion

nutrients move from higher concentration in the bulk soil solution to lower concentration at the root

root interception

roots obtain nutrients by physically contacting nutrients in soil solution or on soil surfaces

a bag of 10-10-10 fertilizer

10% plant available N, 10% P2O5, 10% K2O

a bag of 16-0-8 fertilizer

16% plant available N, 0% P2O5, 8% K2O

phosphorus binds to

Fe and Al oxides (so it stays where it is placed in the soil)

how is P most likely to be lost

erosion (moves little within the profile)

what soil texture has lowest buffering capacity

sand

what soil texture needs most amount of lime to change from pH 4 to 5

clay

what plant element is needed in the largest quantity

carbon