Question:
With the typical soil in southwest Amarillo, does gypsum or sulfur
help much?
Answer:
This question is among the more common ones asked. Many of the
lawn/garden
retailers in Amarillo recommend gypsum. They claim that gypsum should
open
up the soil. There are some applications where the addition of gypsum
improves
soil structure and water infiltration into the soil.
The following article is by Dr. J.R. Feucht, Colorado State University Cooperative Extension Specialist
| Gypsum is a salt - calcium sulfate - and when added to
calcareous clay
soils (the typical high calcium soil in Colorado), does no more than
increase
the already high calcium content. Thus, gypsum + calcareous clay =
gypsum
+ calcareous clay. In other words, adding gypsum to a soil that does
not
need calcium is a waste of money. Also avoid adding gypsum to a saline
soil (soil high in salts). Gypsum increases salt levels.
The use of sulfur in a clay soil high in calcium also has been acclaimed by some as a method of breaking up a tight soil. While sulfur added in small amounts over a long time eventually can improve the condition and reduce soil alkalinity, this practice generally is not advised because the sulfur reacting with the calcium simply forms gypsum. The only soil that can be benefitted by adding gypsum is a soil high in sodium, called "sodic soil" or "black alkali." These soils normally are found where there is a high water table and poor drainage. Such soils are hard and cloddy when dry and take water very slowly. Few plants can survive in them. |
Dr. Feucht accurately identifies the use of gypsum on a sodic soil. Saline-sodic soils (soils high in both salts and sodium) will also benefit from the addition of gypsum, or sulfur if the soil already contains calcium (sulfur and calcium form gypsum). In a sodic soil, the gypsum dissolves slowly, and some of the sodium ions on the soil are replaced by calcium ions. Sodium causes things to disperse, which is the reason it is a primary ingredient in lye and many other detergents. The result of high sodium is poorer soil structure and water infiltration into the soil. Calcium promotes aggregation, and so over time, will gradually improve structure.
Generally, addition of gypsum or sulfur are not economical practices for our soils. Many of our soils are high in calcium and have caliche (a form of calcium carbonate) at shallow depths (6 inches to 5 feet). Any soils with caliche will not benefit from the addition of gypsum, though in rare instances, sulfur might help.
I encourage soil testing. Information and materials required to collect a soil sample and send it to a laboratory are available from your local County Extension office. Soil testing provide information on pH, several nutrients, sodium and salinity. The soil test report will also include a recommendation if you request it. If the soil sodium levels are high and sulfur is low, the addition of sulfur will, over time, improve soil conditions as gypsum is formed, and calcium replaces sodium in the soil. If the sodium levels are low, do not add gypsum or sulfur.
The soils in most arid and semiarid regions contain some sodium. Additional sodium may be added in water used to irrigate, as is the case with water from Lake Meredith. The Canadian River Municipal Water Authority (CRMWA) has taken preventive measures to lower the salt content of the lake. Additionally, they are mixing it with water from the Ogallala aquifer to improve the water quality. Some producers in the region are using water from the Santa Rosa aquifer which generally has a much higher sodium content than the water from the Ogallala aquifer. This is not in their long-term best interests since sodium will ruin the water intake.
The soils in this area are tight because they have a high clay content. It is not feasible, on the scale of a lawn, to add enough sand to improve the texture. It is more practical in a small garden to add some sand and some compost or manure to loosen the soil. Many lawns are compacted because of the total disregard contractors have for what happens after construction. Most of the time, the lawns are established without ever attempting to alleviate the compaction caused by the construction.
Caliche at shallow depths (less than 12 inches) poses many problems. Caliche forms a barrier to water movement, so water will pond on top of the caliche. Even in the hottest days of summer, this can result in plants drowning from lack of oxygen (too much water) in the root zone. Irrigation management is crucial in these soils. If possible, it is beneficial to break up the caliche and mix in compost, especially under perennials. Caliche also buffers the pH around 8, and often limits availability of iron. Many evergreen trees in this area suffer from a caliche-induced iron deficiency. Iron sulfate is the most economical, commercially available source of iron fertilizer.
This brief page attempts to address some of the more common questions about gypsum and caliche. If you have other questions, please feel free to contact Dr. Clay Robinson (alias Dr. Dirt).
