Digging Dirt on Polymers

The View article on polymers, “An Idea That Just Might Hold Water� (March 20), was appropriately guarded in recommending their use. In the drought conditions we face, we should be seeking new ways to conserve water, but recent university research is not very supportive of polymers’ value.

Polymers do not change the amount of water a plant uses; they only increase the water-holding capacity of the soil. Many soils have adequate clay amounts, so capacity is not a problem.

There are indications that potted plants can benefit from polymer use, but the cost of field application is prohibitive. At $10 a pound for some polymers, and recommended rate of 15 pounds per 1,000 square feet, that money can go a long way toward improving the irrigation system. That’s what it boils down to, better irrigation management.

There are other problems with polymers that still need to be addressed. On established landscapes and lawns, it is impractical to apply polymers to roots that may be several feet under the soil surface. Polymers are not soluble or soil mobile to any great degree, so they must be placed where plant roots are located. Attempting to place polymers in established landscapes could cause root injury and further predispose plants to drought stress.

Polymers placed in soils are often exposed to high levels of salinity or water-soluble salts. Fertilizer and even irrigation water are the most common source of water-soluble salts. Work at UC Davis shows that calcium salts (commonly found in our area’s soils and water), as well as the various forms of iron found in the soil, disrupt the ability of polymers to absorb water, negating their potential value. Some polymers claim to resist soil salts, but these claims are not well documented in recent scientific literature.

BEN FABER,

JIM DOWNER,

UC Cooperative Extension,

Santa Barbara-Ventura counties