What is gypsum
Gypsum is the common name for calcium sulfate. It is a source of essential plant nutrients, calcium and sulfur. Gypsum can also improve the physical and chemical properties of soils. It is known to reduce erosion and surface water runoff.
There are two forms of natural gypsum, calcium sulfate anhydrite and calcium sulfate dihydrate. Anhydrite gypsum is insoluble and takes many years to breakdown in the soil. Calcium sulfate dihydrate gypsum is soluble and readily breaks down in the soil.
FDG Gypsum is synthetic gypsum that is formed from flue gas streams in industrial applications like coal power generation.
The purity of gypsum can vary greatly depending on the source. Low purity ag grade anhydrate gypsum may take applications of tons per acre to see a response. While high purity calcium sulfate dihydrate gypsum can improve yields and soil performance with applications of pounds per acre.
Diamond K only supplies the highest purity, naturally mined calcium sulfate dihydrate gypsum.
How to adjust soil pH
Soil pH is a measure of the acidity or alkalinity of a soil. Acidic soil are soils that are below pH 7 and alkaline soils have a pH above 7.
To raise soil pH, finely ground limestone (calcium carbonate) is the primary mineral used to raise soil pH. The amount of limestone needed to change pH is determined by how finely the limestone is ground (mesh size), the purity of the limestone, and the buffering capacity of the soil.
The buffering capacity of a soil depends on the clay content of the soil, the type of clay, and the amount of organic matter present. These factors determine the soil cation exchange capacity. Soils with higher buffering capacity require a greater amount of limestone to achieve an equivalent change in pH. A complete soil test is the best way to determine how much lime to apply.
To lower soil pH, acidifying agents or acidic organic materials must be added. Elemental sulfur (90–99% S), ammonium containing fertilizers (ammonium sulfate, urea, and ammonium nitrate) create an acid reaction in the soil. With prolonged use, over time, they can aid in lowering soil pH. The addition of acid (sulfuric acid, N-phuric or phosphoric acid, sulfurous acid derived from a sulfur burner) to a high pH irrigation water can help reduce the long-term effects of poor water quality and help reduce the pH of your soil.
How to fix alkaline soil
We recommend a complete soil test that includes base saturation and a complete water analysis report. This information will help in making fertilizer and soil amendment recommendations to adjust soils.
To improve alkaline soils, we need to know:
- The Cation Exchange Capacity and/or Total Exchange Capacity
- Electrical Conductivity
- Soil pH
- Base Saturation in percentage
- Base Saturation in PPM
- Bicarbonates (if present)
- Any nutrients that are too high
- Any nutrients that are too low
Once we have these measurements, we can determine a course of action to balance the Base Nutrients (Ca, Mg, K, Na, H). By adjusting and correcting imbalances in base nutrients we can bring the pH of a soil down and make all other nutrients more available to your plants.
Contact one of our agronomy specialists to help determine the correct course of action for your farm.
For more on how irrigation water quality impacts soil nutrients click here.
How to fertilize alkaline/sodic soils
People often refer to sodic and alkaline soils as the same thing, they are not. Each term has their unique properties and treatments.
Alkaline soils have pH values of more than 7 pH. Alkaline soils may also have free carbonate, bicarbonate, and /or high magnesium. When soils have a pH value of more than 8, they may have elevated concentrations of sodium,(>15%).
A sodic soil is a soil with high levels of exchangeable sodium (Na) and low levels of total salts.
It’s best to have a complete soil test conducted to identify which nutrients are contributing to your high pH.
Both alkaline and sodic soils cause poor soil structure, drainage and nutrient imbalances. High levels of exchangeable sodium and accompanying high soil pH affect the transformations and availability of several essential plant nutrients (pH chart of nutrient availability). For this reason, incorporating fertilizer management practices that address sodium and high pH should be the first step in your fertility program.
When the sodium in soil is high, you must replace it with calcium and leach the sodium out. For this process to happen, the calcium must solubilize in the soil solution. Only extremely fine ground calcium will do this. The most common form, and one of the best sources of calcium to leach sodium is calcium sulfate dihydrate.
When your alkaline soil is due to free lime or bicarbonates, adding sulfur in the form of elemental sulfur, sulfuric acid, N-phuric, phosphoric acid, or sulfurous acid derived from a sulfur burner will help reduce the excess carbonates.
Alkaline/Sodic effects on nutrients
As previously stated, high levels of exchangeable sodium and accompanying high soil pH affect the transformations and availability of several essential plant nutrients.
Sodic soils are generally deficient in available nitrogen. Considerable losses of N in ammonia form due to volatilization are likely to occur in sodic soils due to their high pH. Crop yields in sodic soils are diminished unless additional nitrogen is applied to overcomer losses due to denitrification and volatilization. It is generally recommended that crops grown in sodic soils be fertilized at 25 percent excess over the rates recommended for normal soils.
Sodic soils generally contain high amounts of extractable phosphorus. If these soils contain sodium carbonate, the result is the formation of soluble sodium phosphates. However, when a soil contains significant amounts of sodium carbonate most of the soil calcium is in an insoluble calcium carbonate form and not available to the plants resulting in possible crop failures.
When gypsum, is applied to improve sodic soils, the soluble sodium-phosphates are converted to less soluble calcium-phosphates. Crops grown in freshly reclaimed sodic soils typically do not respond to additional applied P fertilizers for 4-5 years because of the highly available phosphate.
Several studies have shown that increasing soil sodicity resulted in reduced uptake of potassium by most crops. This is due to sodium and potassium antagonism.
Increasing soil sodicity nearly always results in an increased uptake of sodium and decreased uptake of calcium by plants. Plants will accumulate sodium in toxic quantities before the calcium becomes limiting for plant growth. When the soils contain appreciable quantities of free sodium and the soil pH is high, application of soil amendments is absolutely necessary.
High pH soil, low organic matter content, and presence of calcium carbonate strongly impact the availability of micronutrients to plants.
Several field studies have shown significant increase in crop yields due to application of zinc in high pH soil.
Iron is often limited in availability in sodic soils due to high pH and presence of calcium carbonate. Addition of iron fertilizers to correct the deficiency was generally not useful.
Boron and molybdenum are often present in toxic levels in sodic soils. Forages grown on sodic soils can accumulate toxic quantities of molybdenum. Applications of gypsum in sodic soils can reduce water soluble boron and molybdenum.
Why soil amendments need to solubilize in the soil to work
Irrigation water with high sodium, high bicarbonates and carbonates react with calcium and magnesium to precipitate into insoluble lime. Bulk applied amendments are less effective as they are changed into insoluble forms.
Soil applied ag grade gypsum works for about three irrigation cycles and then begins to leach out of the first inch of soil because of high sodium and/or bicarbonate levels in the irrigation water. Once the gypsum is leached out of the first inch, the sodium and/or bicarbonate again becomes dominant, and the soil structure is destroyed.
Applying soluble, solution-grade gypsum through the irrigation system continually provides soluble calcium to the soil structure keeping soils open for water infiltration. Soluble calcium sulfate dihydrate applied through the Diamond K applicator allows you to add calcium via irrigation systems when the crops most demand it for cell wall strength. Cell wall strength builds a longer lasting harvested product.
Why Soluble potash
Potassium (K, potash) in soil can exists in four states of availability. A small amount is in the soil water for uptake by plant roots. Most potash is less available because it is held on particles of clay and organic matter in the soil. It is also held within the layers of clay particles. It may be held loosely or strongly, depending on the soil type.
There is potassium that is very slow to release in native soil minerals such as feldspars and micas. Potassium in soil minerals is only released by weathering. The amounts available each year are not sufficient to supply the needs of crops with a large yield potential.
To ensure available K to plants, potassium must go into the soil solution. Most soils which have a clay content of 5%, applied potassium not used by the crop, will remain in the soil and will not move further down into the profile. Sandy soils with less than 5% clay, have a greater risk of potassium leaching. On these soils, soluble potash should be applied in small amounts, more often. The applications should be timed to suit crop uptake and total amounts matched to crop removal.
The Diamond K process for identifying problems
Recommendations without proper diagnosis is malpractice. Before we make any recommendations, we recommend a very specific soil and water test. Once we have the tests we can recommend a course of action for your farm. Contact one of our agronomy specialists to learn more about properly testing your soil and water.