HIGH NA, LOW HCO3/CO3

Amendments: Gypsum, soluble Ca materials, S-based acid to combine with soil-applied lime to form gypsum.

Purpose: Supply sufficient Ca+2 to replace Na+ on CEC sites so that the Na+ can be leached.

Management: Core aeration, good leaching program.

HIGH TO MODERATE NA, HIGH HCO3/CO3 If RSC >1.25 and adj SARw > 10 meq L-1, then acidify. If HCO3- + CO3-2 <120 ppm and RSC < 0 and adj SARw <10meq L-1, acidification should not be needed.

Problem: High HCO3/CO3 content in the water reacts with Ca and Mg to precipitate insoluble lime. The excess soluble Na increases the ESP on the soil CEC sites and will eventually cause sodic soil formation with structural deterioration.

Amendments: Acidify water and apply lime to the soil to form gypsum (50kg (100 lbs.) lime needed to react with every 48kg (98 lbs.) H2SO4. For example, 50kg (100 lbs.) H2SO4 applied per acre-foot irrigation water would need to react with 52kg (104 lbs.) CaCO3 per acre to form 66kg (136 lbs.) gypsum per acre).

Management: Core aeration, good leaching program.

ULTRA PURE WATER (EC < 0.50 dSm-1)

Sources: Snow melt, continuous heavy rains from monsoons/hurricanes and low ECw ground water.

Problem: Strips cations and salts from surface (1-cm zone), causing crusting and reduced infiltration. Accentuated when ECw <0.20 dSm-1.

Symptoms: Reduced infiltration on level sites. Greater runoff on sloped areas. Slower drainage in low areas.

Management options:

Increase salt concentrations at the soil surface by application of gypsum, phosphogypsum, or sulfur + lime.

Increase salt concentration in the irrigation water to ECw > 0.50 dSm-1 by using calcium sulfate or calcium chloride.

Increase dissolved Ca in low-salinity water by 1.0 - 4.0 meq L-1, which raises ECw by 0.075 - 0.30 dSm-1 and improves soil infiltration by 100 - 300%.

Core aeration

HIGH Ca/Mg, HIGH HCO3/CO3, LOW/ABSENT Na LEVELS

Problem: Insoluble lime precipitates, often at soil surface. On sands with limited particle size surface area, calcite coatings form on particles, bridge between particles, and fill the pores, thereby sealing the surface and reducing water infiltration.

Conditions favoring calcite deposition:

Sandy soils are more susceptible than fine-textured soils.

High water use in arid climate resulting in high annual additions of calcite.

Light, frequent irrigation favors surface deposition of calcite under high ET conditions.

Deeper, less frequent irrigation favors calcite deposition at depth of water penetration.

Long growing season with high annual total water applications containing calcite.

Amendments:

Acidification of the water

Acid-forming fertilisers [(NH4) SO4]

Sulfur application to (calcite) soil surface to form gypsum.