Ag Alert: Sun cleans soil ahead of crops

Farmers in the San Joaquin Valley are beginning to experiment with soil solarization. (Courtesy of Achim Raschka/WikiMedia Commons)

Fans of global warming can take comfort in the potential benefits that increased heat might have for agriculture, particularly in California’s Central Valley.

Already at work in the warmer Imperial Valley at the state’s southern border, the extreme heat of soil solarization is killing soil borne diseases, weeds and some insects for organic growers, saving them the cost of sprays and some cultivation. It is generally effective for three seasons, a distinct advantage over some other soil preparations that must be done every crop year.

Holtville farm advisor Pratap Devkota estimates that the use of solarization by organic growers in Imperial County is 100 percent. He makes no prediction about the extent to which it might be used in the San Joaquin Valley, but he is aware that the method continues to be evaluated at the Kearney Agricultural Research and Extension Center in Parlier.

Some Central Valley organic growers have been taking advantage of the solarization method for 25 years or more, but they have to schedule its application carefully to take advantage of prolonged periods of bright sunshine without neglecting other crops in different stages of growth.

The Imperial County growers employ the area’s extreme summer heat by spreading plastic over the beds they have prepared for planting just before summer temperatures begin their climb into the hundreds. They precede the application of the plastic mulch by an irrigation. Dirt clods on top of the plastic sheets help keep them from flying away.

A month of incessant sunshine heats the covered soil enough to discourage weed and disease growth, and insect proliferation, preparing the beds for planting after the plastic is stripped away.

Various thicknesses of the clear plastic are used. The ideal is a covering that allows the necessary temperature build-up and heavy enough to resist the breezes that can cause it to balloon and blow away.

While solarization cleanses the soil beneath the plastic covering and debilitates soil-borne insects, it can’t prevent other insect pests or disease from attacking crops planted after the soil is uncovered. More conventional methods and materials are selected for those chores.

Most utilization of solarization in the Central Valley has been in Kern County at the valley’s southern extreme. Organic growers of high-value vegetable crops have been its most consistent users.

Predictions by those studying climate change are not precise, but the data they use indicates that the Central Valley’s vast acreages will receive higher temperatures in the years ahead. Whether temperatures will be high enough to encourage more soil solarization is open to question.

The application of the treatment now in Imperial County is limited to annual crops produced on soil beds, especially the very marketable vegetable crops. In most cases, Imperial Valley is the primary supplier for the national market at specified times in the marketing year. Utilization for tree, vine or field crops which dominate the agricultural picture in the Central Valley may not be forthcoming.

Increasingly warmer climates predicted by the climate change community need not inspire consternation or panic. As flexible as the state’s farmers are, positive adjustments can be expected. The sun has been their friend, and their determination backed by imaginative research can maintain the relationship.

In the meantime, farmers’ customers and the rest of the non-farm population can take comfort in the predictions that increased temperatures can be expected over time, not overnight. Hand wringing to the contrary, positive investigations of ways to make a warmer sun more useful and more widely acceptable can lead to a truly brighter future for California’s Central Valley.

Don Curlee :