They said it couldn't be done. Farmers in southern Colusa County, Calif., knew walnuts thrived on deep, fertile soils, in which their roots could sink 10 feet to anchor a towering tree. And they were convinced the land near Arbuckle, with its shallow soils and unpredictable clay layering, was suitable only for the more surface-rooted almonds that have been growing there since the 1890s.
But the determination of UC Cooperative Extension farm advisor John Edstrom and the low-risk opportunity to test prospective crops provided by the Nickels Soil Laboratory allowed the planting of walnut test plots in 1986 that opened the door to a new agricultural opportunity for local farmers.
The Nickels Soil Laboratory was created by Arbuckle farmer Leslie J. Nickels. When he passed away in 1959, Nickels had no heirs or close family. He made provisions to donate his estate for agricultural research, specifically naming the Regents of the University of California and the Colusa County Water District as administrators.
The primary crop on the 200-acre research facility in Arbuckle has always been almonds. Numerous research projects have been conducted on variety selection, nutrition and pest control, but the predominant breakthrough was in the application of drip irrigation.
“Yields went from about 700 pounds per acre to 2,000 pounds per acre when drip irrigation was introduced and perfected,” Edstrom said.
Even though almonds were doing well, Edstrom knew the cyclic nature of agriculture meant it was not a good idea for local farmers to keep all their eggs in one basket.
“Almonds are golden right now,” Edstrom said, “but there were periods when they were extremely unprofitable.”
He saw an opportunity for diversification in walnuts and asked the trustees of the Nickels Soil Laboratory to approve a high-density walnut planting. At first they were skeptical. A former trustee, retired Arbuckle almond farmer Greg Ramos, questioned the proposal.
“The Colusa County soil map showed that this area was not conducive to planting walnuts,” Ramos said. “If we were along a river, with deep soils it would've been a different story.”
Nevertheless, he said, Nickels made clear in his will the intention to support the planting of experimental crops, so the trustees agreed to set aside two acres for walnuts. Edstrom and his partner on the project, Glenn County farm advisor Bill Krueger, set up a walnut orchard with 202 trees per acre, compared to the 60 trees per acre found in a traditional orchard. He selected two varieties that produce a large proportion of walnuts on lateral buds, which allows for hedgerow planting and mechanical pruning. Each year, a giant hedger with eight 36-inch saws buzzed down one side of the tree rows, cropping back branches and encouraging fruit production. In alternate years, the opposite side of the rows would be pruned. Rather than being flood irrigated, as are most typical walnut orchards, this one was watered and fertilized using precise drip irrigation. The results were spectacular.
“Everyone was amazed. The UC walnut specialist had predicted failure,” Edstrom said. “Even Bill and I were amazed.”
In 2006, the 20th anniversary of that first walnut planting at the Nickels Soil Laboratory, the walnuts are still doing well. Acre-for-acre, the densely planted hedgerow walnuts produce yields comparable to traditional Colusa County walnut orchards being grown on deep, well-drained soils.