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."
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Contact: Jeannette Warnert
jwarnert@uckac.edu
559-225-5611
University of California - Division of Agriculture & Natural Resources
14-Dec-1998