SCSC 301 Exam 4

Saline/ Non-sodic

-White alkali

-Soil flocculated and permeable

-Leaching occurs with large quantities of water (25 inches)

Non-saline/ Sodic

-Black alkali (the worst of all)

- not permeable (no leaching)

- add Ca salt (gypsum) to replace all the exchangeable Na (2x normal rate)

-salt concentration in soil will increase (EC will increase)

- Gypsum will not contribute to pH change

-Ca replaces exchangeable Na and flocculation of colloids and improves permeability

- with leaching pH decreases

Saline/ sodic soil

-initially permeable

-Add gypsum (2x normal rate)

-leach for 25 inches

Sources of Nitrogen

-Electrical Discharge

-Commercial fertilizer

-Symbiotic N-Fixation (Rhizobium)

-Plant residue

-Animal residue

-Non-symbiotic N-Fixation

-Acid Rain

Non-Symbiotic N-Fixation (autotrophs)

-Free living

-Blue - green algae

- Aerobic (Azotobacter)

-Anaerobic (clostridium)

-Acid precip (transportation)

Levels of Non-symbiotic N-fixation

- blue-green algae- 6-20 lb/ac/yr

-Aerobic (Azotobacter) 13-83 lb/ac/yr

- Anaerobic (Clostridium) 4-28 lb/ac/yr

-Acid rain - 4-8 lb/ac/yr

Symbiotic N2 Fixation

-Rhizobia bacteria live in plant roots and convert N gas to NH3

-Leguminosae family (legumes)

-Fixation rates:

-Soy bean 65-115 lb/ac

- Alfalfa 125-335 lb/ac

Nitrogen Losses

-Crop/ plant removal

-dentrification

-immobilization

-leaching

-fixed by clays

-volatilization

-erosion

Nitrogen cycle

-Mineralization

Organic N -> Inorganic N

Nitrogen cycle

Aminification (heterotrophs)

Organic N -> NH2

Nitrogen cycle

Ammonification (heterotrophs)

-NH2 compounds -> NH4

Nitrogen cycle

Nitrification

NH4 -> NO2

NO2 -> NO3 Chemautotrophs

Nitrification must have O2 to occur

Soil Conditions affecting N Cycle

-aeration

-best pH is 6.5-7.5 (n cycle is acidic)

-moisture is best at field capacity

-temperature is best at 20-30*C

-Anarobic Conditions (dentrification)

-Volatilization

-Immobilization

Management of N avaliability

-choose source of inorganic N to match the crop

-NH4 is most reduced form

-NO3 is most oxidized

-Maintain optimum conditions for mineralizaton

-Add N to plants at the time they need N

-Maintain or increase OM

-C:N ratio of 8-12:1

Sources of Nitrogen

-Urea

-Ammonium nitrate

-Angydrous ammonia

-ammonum sulfate

-in aerobic conditions all will convert to nitrate (leachable)

Mineralization of N from Humus

-2% of soil OM mineralizes/ year

-5% of soil organic matter is N

Environmental Problems

-leaching to ground water

-EPA drinking water standard

- blue baby syndrome

-High nitrate concentrations in surface water

-contributes to eutrophycation

Sources of Sulfur

-Plant (~0.2%)/ animal (~0.5%) residue

-Minerals in soil

-gypsum

-pyrite

-Fertilizer

-atmospheric pollution

Losses of Sulfur

-Plant uptake

-Erosion

-Leaching

-Volatilization (marsh)

-S in sulfate is 6+

-S in sulfide is 2-

Processes in sulfur cycle

mineralization

-organic S -> inorganic S

Oxidation-reduction/ Absorption desorp

Elemental Reduction Sequence

-NO3-

-Mn4+

-Fe3+

-SO42-

CO2

Sulfur Availability

Location

-industry

-marsh

Texture

-finer texture soil = more S, sandy soils maybe deficient

Soil pH

-as solubility increases, pH decreases

-leaches easier in acid soils

Phosphorus General Info

-essential for plant/ animal life

-P in soil is slowly or not available to plants

Phosphorus Sources

-Mineral (apatite)

- Plant residue

-Animal residue

- desorption from hydrous Fe and Al oxides (sesquioxides) & silicate clays

-fertilizers

P location and Reserves

-Morocco & China make up 64%

P losses

-Crop removal/ uptake

-Erosion/ surface runoff

- leaching in sandy soils only or where P add is organic rather than inorganic

-Fixation with Al & Fe

-Reversion back to apatite in Ca rich soils

-Immobilization

-Absorptions to Fe & Al oxides and silicate clays

-Occluded P

P soil characteristics

-Most P in soil is not plant avaliable

-P form is pH dependent

-P does not undergo oxidation-reduction

-best pH is 6-7

P in acidic soils

H2PO4- & HPO42-react mainly with Al & Fe and possibly Mn and become insoluble

P in alkaline soils

H2PO4- & HPO42-react mainly with Ca and possibly become insoluble

Factors Affecting P Solubility & Avaliability

- Soil pH

- OM & mineralization rate

-Organic vs inorganic P

-particle size and solubility

-Amount of Ca, Fe, Al, etc. avaliable to react with P.

-Soil temp & moisture

Soil Management for P

-pH 6-7

-High OM level

-Good Microbial conditions

-only use 1/3 of applied P in a yearly application

-application of P at agronomic rates

- utilize banding or injecting fertilizer

-Soil stratification & sampling

P deficiency symptoms

-occur in early spring usually

-purpling leaf

-stunted growth

-spindly growth

Potassium Info

-Of the abundant elements in soil

-Part of Micaceous minerals

-basic cation

K sources

-Minerals (Micas & feldspars)

-Plant residues ~1-2%

-Animal residues/ manures ~0.5-3%

-Fertilizers

-KCl (sylvite) is lised as K2O on fert bags (often called potash)

K Reserves & location

-100 deposits of K of commercial quality

-100k brine deposits

-Canada & Russia have 76% of them

-250 billion tons with a reserve of 18 billion tons and 8.3 commercially exploitable

##-##-##

what elements

N-P2O5-K2O

Potassium losses

-Crop uptake/ removal

-Leaching

-highest in sand (acid soils)

-Erosion

-Runoff

-Fixation

-clay micas

-vermiculite will increase K+ upon oven drying

-smectite will decrease K+ upon oven drying

K Supplying Power is a function of

-most plant available K is on exchange sites

-The kinds and amount of K-bearing is present in soil

-particle size of minerals

-Solubility of the minerals

K Supplying Capacity

Function of the K held in the structure of soil minerals (native amounts of K)

Management for K

-Apply K in small quantities 1-3 times a year

-if more than 150 lb/ac are need then split up the application

-K has high salt index

-Multiple applications reduce

-leaching and luxury consumption

Nutrients that occurs in Strongly Acidic Soils

-Iron

-Magnese

-Boron

-Copper & Zinc

Nutrients that occurs in Strongly Basic Soils

-Phosphorus

-Potassium

-Sulfur

-Calcium

-Magnesium

-Boron

-Molybdenum

pH of water & CO2 equalibrium

5.7

Agents of