Feb. 9, 2012Vol. 42, Issue 4

Research Aids Growing Northern California Olive Oil Industry

An expanding market for olive oil and new growing methods (pioneered by growers from Spain who have invested locally) have made growing olives for oil economically feasible and, potentially, highly profitable. Rosecrance, with a PhD in pomology and agricultural ecology from UC Davis, has been working closely with Bill Kruger, UC Davis farm advisor in Glenn County, researching high-density planting and deficit watering, two of the main methods distinguishing olive oil and table olive growing. The farmers moving into the olive oil industry need to know how to manage plantings, how to prune, how to fertilize and irrigate.

rich rosecrance kneeling in olive garden“Around 2000, Spanish investors came to set up a high-density olive growing industry in Northern California,” said Rosecrance. “Typically, this kind of endeavor tends to be large—a grower would not be planting fewer than 100 acres. This group, California Olive Ranch, bought a lot of land south of Oroville and Artois and near Corning, and then they set up a nursery and a mill and planted olives. They also contracted with local growers, guaranteeing a good price for their crops.” There are now approximately 10,000 acres of three varieties of olives—Arbequina, Arbosana, and Koroneiki—in Northern California, said Rosecrance.

One of the things that makes these varieties conducive to high-density systems of planting is that they fruit on much smaller branches. Yields can come in the second and third year, earlier than table varieties, and the dense and shorter trees can be harvested mechanically.

The experimental olive orchard at the University Farm is divided into four deficit irrigation sections. Each section has one row of the three kinds of olives mentioned above, and a row of an experimental variety from Spain, Chiquitita, that will be planted this spring. Each of the sections can be watered on its own irrigation schedule. Student researchers, who will determine the experimental models, will monitor the sections to determine optimum irrigation patterns. The goal is to reduce the amount of water wasted and encourage optimal growth and fruiting.

Rosecrance said that a research trial several years ago found that although increasing irrigation increased yield, it decreased quality. The current trials will explore regulated deficit irrigation further—for example, one experiment will be to shut off the water near the end of fruit ripening, during pit hardening, to determine effects on quality.

Another question that Rosecrance and the student researchers are exploring is whether the trees can be trimmed with a hedger, which is necessary to keep them at the right height for harvesting. The high-density planting is relatively new, and Rosecrance discovers new information all of the time. He recently attended a growers’ convention and learned about the possibility of training the young trees along the trellises that are already in place, much like the practice of espalier. Such training would fill in the rows horizontally, as opposed to the “Christmas tree” model with taller, bushier trees that was first envisioned. It could be an innovation that would facilitate more efficient trimming and harvesting.

The olive-planting research project at the farm was made possible by a number of partnerships between the University and private businesses and individuals. The Agricultural Research Initiative, with a matching, in-kind contribution of Kruger’s time, funds the project. Matt Lohse, olive ranch manager at Carriere Family Farms near Willows, organized the orchard planting. The young trees, irrigation and trellis systems, land development, and labor were donated by local businesses, including saplings from NursTech, irrigation system design and installation by Durham Pump, soil preparation by Matt Anchordoguy Co., and trellising by A and J Vineyards. California Olive Ranch has donated money and expertise. Kelp Products LTD donated $5,000 for testing of their product on tree growth.

“The long-range purpose of the research project at the farm is, of course, to support the new industry,” says Rosecrance. “But as important is that it will expose our students to a new industry, and they will be involved in learning how to manage it. There is a real benefit to our students in being involved on the ground of a new industry.”

Kathleen McPartland, Public Affairs and Publications