Reusing Ag Drainage Water An Option For West Side Farm Sustainability

December 14, 1998

FRESNO, Calif. -- If they're treated right, eucalyptus trees can grow beautifully in the sticky black soils of the Tulare Lake basin, a fact that fits another piece in the complex jigsaw puzzle that will eventually reveal the sustainable, economically viable long-term farming potential of the San Joaquin Valley's west side, according to UC scientists.

Growing eucalyptus trees could be part of a water reuse scheme for farmers who, to maintain agricultural production well into the future, must consider adopting measures beyond the currently standard evaporation ponds to dispose of drainage water, said Jim Oster, UC Riverside soil scientist.

Sequential water reuse is a system where farmers use ag drainage water from one crop, such as lettuce, to irrigate a more salt-tolerant crop, such as cotton, some forages or eucalyptus trees. The water may be used once again on extremely salt-tolerant crops before the much-reduced volume of water is pumped into a comparatively small evaporation pond.

"We demonstrated that eucalyptus trees can be grown in the Tulare Lake basin with saline drainage water. We believe the same techniques will work with this kind of water at other sites. We know the trees can be part of a sequential reuse system," Oster said. "However, while you wouldn't need as large an evaporation pond, the combination of pond and trees would take more land. That's somewhat discouraging."

Using just the eucalyptus trees for water reduction, the evaporation pond area is reduced by 70%, but the total of tree plus pond area is 1.9 times greater than if all the drainage water is disposed in an evaporation pond.

Nevertheless, Oster said he is encouraged by the results of his study on eucalyptus trees, funded with a $300,000 grant from the United States Bureau of Reclamation and conducted in cooperation with the Tulare Lake Drainage District.

In a remote Kings County site, trees were grown with and without the soil amendment gypsum. The untreated trees grew slower, had yellow leaves and many died. The gypsum-treated trees were lush and green.

Gypsum applied in the fall dissolves in the soil during the rainy winter months. Where sodium is high, gypsum's introduction counteracts soil particles' tendency to adhere together and form a layer that resists water infiltration and causes rainwater to pond in the field. Untreated soil dries to rock-like hardness.

In a complex chemical process, gypsum maintains the pores in the soil through which water and air can penetrate.

"Simply trying to push a shovel in the soil shows the profound difference between the two treatments," Oster said. "I had to chip away at the untreated sites, but needed only a solid step on the shovel in the rows treated with gypsum."

Planted in 1994, the trees were ready for their first firewood harvest in November 1998. The highest-yielding variety, where gypsum was used, yielded nearly 1.3 cords per acre, while in untreated plots it yielded about half as much. The best yield, however, does not appear to offset the land, plant, labor, gypsum, irrigation and other costs.

But that doesn't mean eucalyptus can't be tapped to help solve the ag drainage problem. Agricultural economist Keith Knapp of UC Riverside studied the economic efficiency of sequential reuse. He said it may make sense to use agri-forestry to dispose of drainage water.

"We found that there's a lot of uncertainty, like the price farmers receive for the wood they produce. Depending on what you assume, it may or may not make economic sense," Knapp said.

He suggests that, in tackling the west side drainage water disposal problems, farmers should consider using a combination of strategies -- including efficient irrigation practices that reduce drainage, sequential reuse and evaporation ponds.

"Farm incomes may not be as high as they would be if farmers could dispose of the drainage externally," Knapp said. "But the land need not go out of production."
-end-


University of California - Division of Agriculture & Natural Resources

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