By Joe Traynor

You may be overlooking hidden treasure on your farm. Hint: your irrigation well. If your well water contains significant amounts of dissolved calcium, you are the owner of a valuable liquid farm asset. On a pound per acre basis, it is likely that more gypsum (calcium sulfate) is applied to California farmland than any other fertilizer or soil amendment.

Low-calcium soils are prevalent in many areas of the stare. VVhen calcium is depleted, soil structure deteriorates to the point where water infiltration is impaired; irrigation efficiency is reduced and crop yields decline due to lack of water and poor root aeration. The use of low-calcium irrigation water over a period of years builds up a calcium debt in the soil that must be repaid. All irrigation project water is low in calcium and perhaps half of all groundwater is also low in calcium.

Many California farms apply calcium sulfate (gypsum) to maintain soil permeability by maintaining a good calcium balance in the soil. For many crops, this boost in calcium also provides stronger cell structure which in turn gives firmer produce - quality fruits and vegetables that have a longer shelf life and that are more resistant to decay organisms.

Application of gypsum has become a standard practice where low-calcium water is used in irrigation. Gypsum machines, fed by gypsum silos, can be seen dotting the landscape where low-calcium water is used. High-analysis gypsum is dissolved, via agitation, in the machines and metered into the irrigation water. This calcium-laden water maintains soil permeability and also provides a calcium boost for crops.

"When our well water shows a gypsum deficit, we apply gypsum; if there's ample calcium in the water, we save on gypsum costs," says Steve Paul, a San Joaquin Valley almond grower who farms with his brother, Brent.


NOT CHEAP
Enriching irrigation water with calcium is not cheap. Often 1 ton of 95% gypsum, at $68 per ton, is needed per acre each growing season.

Many growers use cheaper low-analysis (55%) pit-gypsum and apply the material directly to the soil. Although pit gypsum is much cheaper than high-analysis gypsum, by the time application costs (and the concurrent drawback of soil compaction) are considered, the low cost of soil applied gypsum is largely offset.

Jerry Rivers, chemist and UC Davis graduate, designed the first gypsum machine in 1987 (known at the time as the Domtar Machine). Jerry is considered the ag gypsum guru. "There are now about 5,000 gypsum machines in the United States and Mexico, the vast majority in California," he says.

Rivers also runs an agricultural lab (Growers Testing Service, Visalia)
and his lab has analyzed many well water samples.

"Many wells are high in calcium; some wells in the San Joaquin Valley deposit more lime [calcium carbonate] than gypsum," he says.

When making gypsum recommendations, the first thing Rivers looks at is the calcium content of the irrigation water. But he also cautions growers about the use of calcium sulfite anhydrite. Even though it has a higher analysis (because it contains less hydrate), it can clog screens and lines because it is less soluble. It's a worthwhile caution, but virtually all gypsum currently used in machines is calcium sulfate dehydrate.

A significant amount of groundwater in California contains dissolved calcium sulfate. A simple water analysis will determine if your well is also a gypsum "gold" mine.

If the calcium level in your well exceeds 50 ppm (2.5 milliequivalents per liter) it is likely that your well contains dissolved gypsum. A significant amount of sodium and or bicarbonate will negate some of the calcium in the water. Calcium levels in the water should be higher than sodium levels and also higher than bicarbonate levels. The lab that analyzes your water (or your farm advisor) can tell you its net gypsum content after accounting for sodium and bi-carbonate.

Growers' fortunate enough to own wells with significant dissolved calcium sulfate also own a gypsum mine. They never have to spend money on gypsum. Owning such a well is an important asset for a piece of agricultural property, one that can enhance its value up to $1,000 per acre. There will come a time when the calcium content of groundwater will be a major consideration in farmland transactions. (It already is for some savvy buyers.)

It's no longer economical to mine gold in California, but a number of California farmers are mining gypsum. If you own a gypsum mine, consider yourself lucky.

- Joe Traynor is a consultant-writer and author of "Honey - The Gourmet Medicine," published last year.