SOIL AND WATER CHEMISTRY PROBLEMS, SOLUTIONS AND FACTS (PART 3)

WATER

Water quality is highly dependent on the source of the water, which in most irrigated agriculture is either from snowmelt runoff or from underground aquifers accessed by wells.  Snowmelt runoff is lacking the salts necessary to maintain soil and crop health in California, the West, and many other parts of the world.  Inversely, well water sources often contain excessive amounts of salts, which are detrimental to crop and soil health. Both situations require calcium sulfate applications to sustain crop and soil health.

Snowmelt Runoff: Not Enough Salts:

A critical property of irrigation water is ECw, electrical conductivity of the irrigation water, (the amount of total dissolved salts in the irrigation water).  The problem with using water from snowmelt runoff is the low amount of total dissolved salts it contains (ECw).  Since pure water does not conduct electricity and salty water does, the more salts in the water the greater the conductance of electricity.  The rule of thumb for ECw is: if less than approximately 0.60 decisiemens per meter (dS/m), then calcium must be added.  The reason is because the pure water is contributing to leaching beneficial calcium below the root zone over time, and is not being replenished.

The application of EcoGEM’s calcium sulfate will quickly and effectively remedy low-salt irrigation water problems.

High Salts (Both Soil and Irrigation Water):

The opposite of when irrigation water is too pure is when the water contains too much salt. When soil and/or water have too much salt, the sodium, chloride and other harmful salts have detrimental effects on plants not only from the aspect of high levels of sodium in the soil in relation to levels of calcium, but also from high salts themselves.  Besides destroying soil structure, high salts in waters and soils can be harmful or fatal to the crops/plants when it accumulates in the root zone.  Sodium and chloride are particularly toxic to ornamentals and woody plants.

About 1/3 of all soils in the arid and semiarid regions of the United States have some degree of salt accumulation, primarily the anions Cl, SO42-, and HCO3 of the cations Ca, K, Mg, and Na.  The primary sources of these salts are weathering of rocks and minerals, ground and irrigation water, and fertilizers.

Once deposited or released in the soil, the salts move to or remain near the surface of the soil by upward-moving water, which then evaporates, leaving the salts behind.  Most crop plants cannot tolerate high levels of salts; therefore, placing limitations on some salt affected soils.  Salt buildup in an existing or potential danger on all irrigated land in the United States.  Continual application of water, all of which contains salts (especially reclaimed water), will continually increase the soluble salts in soils unless the soils have good soil structure and periodic leaching.

By cationic exchange reactions, calcium is used to replace sodium in saline and sodic (high sodium) soils (reaction 7 above).  The calcium will replace any sodium on the cation exchange complex (CEC).  What happens chemically is: calcium solubilized from gypsum replaces sodium leaving soluble sodium sulfate (Na2SO4) in the water, which is then leached out.

This is another reason for the application of EcoGEM’s calcium sulfate. Of all calcium compounds gypsum is considered the most convenient and inexpensive for this purpose.

High Bicarbonate in Irrigation Water:  Add an acid source to neutralize the bicarbonate in irrigation water so additional free lime (CaCO3) in the soil or irrigation system cannot form (reaction 4 above).  Also, the addition of gypsum to irrigation water will replace any calcium precipitated as free lime and will remove any bicarbonates from the soil solution (reaction 6 above).

Bicarbonates and carbonates will form free lime when the water evaporates (reaction 1 above), and this results in several negative consequences:

  1. When the water evaporates, the free lime has the ability to raise the pH of the soil and reduce available calcium. Also when free lime forms, available beneficial calcium will be precipitated out, further compounding the problem of not having enough calcium in the soil.
  2. The reduction of available calcium leads to loss of soil structure and reduced water infiltration that also reduces the normal leaching process by which salt buildup in the root zone is prevented.

Note:  Bicarbonate is also the most toxic anion that exists in relation to plant health.  Any amount in excess of 5.0 milliequivalents per liter (meq/L) is considered very high.

Benefits of Acid Injected Into Irrigation Water:

There are many forms of injectable acids that include (but are not limited to) N-pHERIC, pHAIRWAY, phos acid, sulfuric acid and sulfur burners.  Farms/parks/grounds are able to utilize acid for neutralizing bicarbonate and in some cases to increase water infiltration.

With the injection of acid into the irrigation water, hydrogen (H+) neutralizes the bicarbonate into water and carbon dioxide (reaction 2 above).  Acid can be introduced to the irrigation water either by a liquid acid (one of the above sources) or by a sulfur burner, which ultimately injects sulfuric acid into the irrigation water.

The pH of the irrigation water is usually lowered to a level of 6.0-6.2.  When the pH of the water is at this level, the amount of bicarbonate that remains in the water is approximately 1.0 me/L. While the addition of acid to the irrigation water will neutralize bicarbonate, there is a limited increase in water infiltration.  Since the pH of the water is not very acidic, the water is applying only a small amount of acidity or free hydrogen to the soil.  The acid will, therefore, neutralize only a small amount of free lime in the soil.  The neutralized lime will ionize to calcium ions (reaction 5 above)] therefore improving water infiltration.  As the free lime is neutralized in the top three-six inches of the soil, the acid will have less free lime to react with thus reducing the water infiltration.  Since the acid is primarily neutralizing the bicarbonate in the water, there will be less free lime being deposited on the soil for the acid to react with.

The first year of water injected acid applications, the water infiltration does tend to improve.  However, in the second and subsequent years the infiltration will return to its original disorder.  That is why the addition of EcoGEM’s calcium sulfate (gypsum) along with the acid is recommended to help amend and maintain soil structure.

SALINE/SODIC CLASSIFICATION OF SOILS

Class                           E.C. (ds/m)        pH           SAR (or ESP)       Soil Physical Condition

Normal                      <4                   <8.5                            <15                 Normal

Saline                         >4                   <8.5                            <15                 Normal

Sodic                          <4                   >8.5                            >15                 Poor

Saline/ Sodic            >4                   > or <8.5                    >15                 Poor