Chapter 9 SCSC

pH

the negative logarithm of the hydrogen ion concentration

active acidity

measureable with pH stick, IN SOLUTION

exchangeable acidity

EDGE of mineral, weakly held, found in highly acidic soils

residual acidity

inside/part of mineral itself, Al and H

pH buffer

something that resists change in pH

pH > 7 buffer

carbonates

pH 5.5 - 7 buffer

bound Al (hydroxyl) and humus

pH <5.5 buffer

exchangeable Al

pH < 3.5

free strong acid production

pH >7 nutrients

poor availability of macronutrients (Fe, Zn, Cu, Mn), soils have calcium

pH 5.5 to 7 nutrients

maximum P availability, max plant growth

pH 3.5 to 5.5 nutrients

• Exchangeable Al3+ can be toxic

• Plants have difficulty with nutrient uptake

pH < 3.5 nutrients

Free strong acids prevent plant growth, soils weather quickly

weak acids that increase soil acidity

rain, carbonic acids, organic matter

nutrients that add acidity

nitrification, plant uptake of NH4 and basic cations, leaching of basic cations

crop production elements that add acidity

fertilizer, crop removal, soil minerals

Aluminum is more

acidic than Hydrogen

liming

practice to increase soil pH

reaction of lime in soil

CaCO3 + H2O --> Ca2+ + CO3 2-

CCE

acid neutralizing strength of Cacium Carbonate

ECCE

reflects actual neutralizing ability

liming effect

• Rarely permanent

• Acidification is not halted

• Cannot remove reserve acidity completely

lime requirement

- depends on initial & target pH

- every 2-5 years

- 6 to 12 months before desired pH change

- what is the desired depth of pH change

dry regions

alkaline, aridisols, water limited, high pH, carbonate-rich, high salts & sodium, poor leaching of salts, high CEC

ET < Rainfall

no salt accumulation

ET > Rainfall

salt accumulation (dry regions/alkaline)

salinity

measure of total salts, electrical conductivity

sources of salt

weathering, fossil deposits, irrigation, poor drainage

sodium

exchangeable Na (ESP)

saline

high salts- Ca, Mg, plants struggle to grow

sodic

High Na, low salinity, pH > 8.5; poor infiltration, plants struggle with lack of water

saline-sodic

high Na, high salinity, can be transformed to sodic

reclamation of saline soils

-Leaching

- Drainage

- Monitor EC

reclamation of saline-sodic and saline soils

apply Ca (gypsum), leaching, drainage, monitor EC and ESP