Exam 4 Flashcards
Acid in terms of chemistry
A substance which gives off h+ ions, and is a solid
Under what climatic condition are you likely to have more soil acidification?
High rainfall areas
What does ph indicate?
The degree of acidity or alkalinity of the soil.
What does ph measure in terms of chemistry?
The quantity of H+ ions
What is the precise difference in H ion concentration between a soil with a ph of 4 and one with a ph of 6
4=10 to the 4th
6=10 to the 6th
Equals 100x difference
How is an acid soil neutralized?
A base must be added
Acid+ Base = water + salt
Name the 3 major causes for the development of soil acidity
Al compounds
Loss of basic cations (by leaching)
Plant removal
Natural sources of acids
Non-natural sources of acids
Natural Acid rain OM Clays Oxidation of n & sulfur compounds Release of AL from exchange sites and oxides Non-natural Fertilizers Acid rain
Discuss the connection between the release of al compounds and ph in the soil?
There is more H+ to be released
Fertilizers that increase soil acidity?
Nitrogen and sulfur containing fertilizers
What is the target range for most plants?
6.2-6.8
Wh might a low ph be bad for plants?
Changes the form of nutrients which makes them unavailable to plants
Effects of acid soils.
Microorganisms
Macronutrients
Micronutrient
Microorganisms-are inhibited
Macronutrience- are all reduced in availability
Micronutrients-malibdumum & boron have low availability. Copper cobalt manganese iron zinc become extra available= toxic
What are other effects of increased al solubility in acid soils?
Interferes with plant development harms microbes
What is lime?
Compound that neutralizes soil acidity
2 ways lime reduces acidity?
Release oh negative which binds with h+
Calcium pushes h+ off cec
Effects of over liming
Soil structure collapse
5 liming materials
Calcium carbonate Calcium oxide Best Calcium hydroxide Dolomite Slag Marl Ash
Effects neutralization of lime
Purity
Fineness
Indicators of liming needs
Ph
Base saturation
Selection of liming material
Cost Effectiveness Nutritional value Other nitriances Ease of using Water content low
Reduce effectiveness of low ph
Not altering the ph
Gypsum
-reduce al
Add nutrient
Soil characteristics effecting om
Cec Whc Soil aggregation Nutrient supply Microbes habitat
What is dry matter composed of?
90-95% c h and o
5-10 comes from soil
Organic compounds in soil
Carbohydrates*
Decomp of om
1 enzyme oxidation
2 nutrients are releases
3 biomass is resistant to future degradation
Effects of low air and cold o2
Will slow decomp
4 aspects of organic residue quality
Composition
Location
Particle size
C/N rationp
C and N connected in residue
Microbes consume carbon but need n to do so
C/N ratio groups
10/1 humus
20-30/1sufficient n in s for decomp
30/1+ n from soil is required for decomp
Decomp process
Om added to soil Micobes eat Nitrate in soil drops Co2 rises C/N r drops Om is consumed microbes die co2 drops nitrate released 4-8 weeks
Comprises om
Everything living + formerly living
Humus
Compounds created from organic compounds created by microbes
Benifits of om in soil
Release of nutrients Cec increase Better soil structure Buffer ph change (if on soil reduce erosion)
Why om bad?
Allelopathy
Global carbon cycle needs
330 kg ha yr
Effect c in soil
Vegetation type
Climate
Texture
Cultivation
What form of n so plants prefer
What is second best?
Nitrate
No3- no2-
Ultimate source of n
Atmosphere
4 sources of n
Biological fixation
Climatic
Natural fertilizers
Synthetic fertilizers
N conversion of biological fixation?
N2-NO3
How much does nit fix provide?
50-80%
rest from soil
Free living n fixing organisms
Blue-green algae
Azospirullium
Azotobactor
Symbiotic n fixing organization
Bacteria living in plant roots (legumes only)
% of n from inorganic form?
2-5% of total n
Mineralization?
Immobilization?
Mineralization - nitrate or no4+
immobilization - organic *** bad
Process of nitrification
NH3-NO2- -NO3-
Microbe cause reaction through activity
Process of denitrification
NO3- -NO2-NO-N2O-N2 bad
Microorganisms cause reaction
6 forms of n are connected
NH3 NO2 NO3 NO N2O N2
What causes change in forms of n to occur?
Microbes activity
Use of sulfur in plants
Enzyme and vitamin production
Part of photosynthesis
How sulfur enter plant? What chemical form?
SO2 leaves
SO4- roots
6 pools of sulfur
Organic compounds Primary minerals Elemental sulfur Clay compounds Soil solution as so4- Atmospheric
