Irrigation and Gypsum EcoGEM Good Earth Minerals CoverUnderstanding Water Quality Problems and How Gypsum Can Help Solve Them

In a new report, Dr. Brent Rouppet, Ph.D., explores how your irrigation water can harm your soil, even when you think it is helping your plants. Learn more about your soil’s chemistry and discover the simple solutions that gypsum soil amendments can provide. Click here or on the thumbnail to the right to download Dr. Rouppet’s report.¬†(pdf)


Soil health is closely related to the quality of the irrigation water. The water may have too few or too many salts, depending on its source. This document explores the chemistry of water quality as it relates to soil.

In most irrigated agriculture, water comes from snowmelt runoff or underground aquifers. Either source could cause problems.

Snowmelt runoff is lacking the salts necessary to maintain soil and crop health in the western U.S. and many other parts of the world. Inversely, well water from underground aquifers often contains excessive salts, which can lead to saline and sodic soils and poor crop health.

Gypsum application can help improve soil and crop health in salt-deficient, saline, and sodic soils.

Problem: Not Enough Salt

Irrigation water from snowmelt is low in dissolved salts and has low electrical conductivity, or ECw. Over time, this pure, low-salt water leaches beneficial calcium below the root zone.

How Gypsum Can Help

The application of EcoGEM gypsum will quickly and effectively replenish calcium in the soil and help remedy low-salt irrigation water problems.

Rule of Thumb –¬†If ECw is less than approx. 0.60 dS/m, add calcium.

Problem: Too Much Salt

When water or soil has too much salt, crops suffer. Salts can accumulate in the root zone and destroy soil structure. Most crop plants cannot tolerate high salt levels, which place limits on the productivity of affected soils.

About 1/3 of all soils in arid and semiarid regions of the United States have salt accumulation, primarily the anions Cl-, SO42-, and HCO3- of the cations Ca2+, K+, Mg2+, and Na+. Salt buildup is an existing or potential danger on all irrigated land.

How it Happens

Salts in irrigation water from underground wells comes from the natural weathering of rocks and minerals. Salts also come from fertilizers.

Once deposited or released in the soil, salts are carried to the surface by upward-moving water, which then evaporates.

Continual application of water that contains salts (especially reclaimed water) continually increases soluble salt levels near the surface. Unless soils have good structure and periodic leaching, they become saline, sodic, or saline-sodic.

How Gypsum Can Help

Calcium can be used to replace sodium in saline and sodic soils. EcoGEM gypsum is the most convenient and inexpensive calcium compound for this purpose.

By cation exchange reactions, calcium solubilized from gypsum replaces sodium, leaving soluble sodium sulfate in the water, which is then leached out.

Problem: High Bicarbonate

Irrigation water high in bicarbonate (and other carbonates) will form free lime when the water evaporates.

Free lime can raise the soil pH and reduce available calcium. Further compounding the problem, available beneficial calcium is precipitated out when free lime forms.

The reduction of available calcium leads to loss of soil structure and reduced water infiltration. This disrupts the normal leaching process that usually prevents salt buildup in the root zone.

Did You Know? Bicarbonate is the most toxic anion that exists in relation to plant health. Any amount in excess of 5.0 meq/L is considered very high.

A Partial Solution

Add acid to irrigation water (e.g., N-pHERIC, pHAIRWAY, phosphoric acid, or sulfuric acid directly or via a sulfur burner).

Hydrogen from the acid neutralizes the bicarbonate into water and carbon dioxide.

 

After this reaction, the pH of the irrigation water is usually 6.0-6.2 (slightly acidic). The water applies a small amount of free hydrogen to the soil, which neutralizes only a small amount of free lime. Initially, the available calcium ions improve water infiltration.

However, as the bicarbonates continue to be neutralized, irrigation water deposits less free lime on the soil. Once the free lime is neutralized in the top three to six inches of soil, water infiltration will return to its original disorder.

How Gypsum Can Help

The addition of gypsum to acidified irrigation water will replace any calcium precipitated as free lime and will remove any bicarbonates from the soil solution. This will help amend and maintain soil structure.

Click here for the full report, including a saline vs sodic comparison chart and chemical equations demonstrating these concepts.