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Trial-and-error research benefits organic almond growers

Issue Date: September 9, 2009
Bob Johnson

A large-scale trial of the challenges of organic almond production on eight acres of the Nickels Soil Laboratory orchard in Arbuckle is already producing some useful information for growers considering going organic.

A team of University of California researchers is closely monitoring the results of different strategies for solving the major issues of weed control, fertility and disease control within the constraints of organic certification. Although the trial was only planted in the spring of 2006, the researchers have already learned from some of their original false steps.

Bill Krueger, University of California Cooperative Extension farm advisor, discusses different strategies that organic almond growers can use to control weeds.

"Our biggest challenge so far has been weed control," said Bill Krueger, UC Cooperative Extension farm advisor in Glenn and Tehama counties.

Their original method of choice was propane flaming. This worked relatively well, although the combined cost for the propane and its application was around $265 an acre compared to less than $100 an acre for weed control in the nearby conventional almond plots.

However, despite careful application, the flame damaged the drip line far too often, and meant added work and cost of repairing or replacement.

"We met out here in 2007 and decided to convert to buried drip," Krueger said. Today, buried double drip lines are used to irrigate the organic trial. This system allows them to flame for weeds without damaging the drip line. And there may be a disease control bonus because buried drip does not raise the humidity of the orchard floor.

Another organic weed control system that looks promising is covering the ground in the rows with woven cloth. The thick, dark cloth runs three feet on each side of the row of trees. It prevents weeds from emerging to compete with the trees, and could turn out to be a cost competitive system.

Krueger stood by the trees with the dark woven cloth as he discussed organic weed control options with growers at the 32nd annual Nickels Field Day.

"The cost for just the material is around $800 an acre, so it depends on how long it lasts," Krueger said. "If it lasts five years it will be economically competitive with the flaming. If it lasts longer than that it may become competitive with the conventional weed control."

Because the cloth is doing a good enough job in controlling weed competition, those organic trees are slightly, but measurably, larger than trees still treated with the propane flame weedcontrol method.

There has been a trial-and-error process in learning how to use the woven cloth. The researchers hoped the edges would be held down in the wind by the grass cover crop growing between the rows. That happened eventually. The two rows of three-foot-wide cloth are also held in place by staples, both on the edges and in the middle.

Krueger said if he were to do it again, he would seriously consider using a single six-foot-wide piece of cloth and planting through it.

"We expect to get to the point that leaf and bloom diseases are our main problems, not weeds," Krueger said.

Copper is being applied in the dormant season and sulfur in the spring to keep disease pressure down in the organic plots.

Almond varieties thought to be less susceptible to leaf and bloom diseases were chosen for the trial.

"We notice we have less bloom and leaf disease with Nonpareil, particularly brown rot," Krueger said.

The organic trial is 75 percent Nonpareil, and 25 percent Fritz as a pollinator variety. The spacing was laid out so every Nonpareil tree has a Fritz next to it.

Fertility poses the next great challenge in the organic trial. The first significant harvest figures should come from this year's crop. But early measurements indicate the organic trees are not getting enough nutrients.

"Even with all the treatments we're putting on the organic trees, we're still not getting enough nitrogen. The transitional trees are larger and they have more nitrogen than the organic trees," Krueger said.

Four tons of a plant-based organic compost, 30 pounds of nitrogen as sodium nitrate and an additional 30 pounds of nitrogen in Agrolizer are already being applied to the organic trees.

Despite this nearly $300 annual investment in organic fertility, compared to less than $200 for the conventional trees, the organic trees are still slightly smaller and have slightly lower leaf content of key nutrients.

The organic trees were just 2.25 percent nitrogen by leaf analysis in 2008, compared to 2.34 percent for the conventional trees and 2.44 percent for the transitional trees. The organic trees also had lower leaf zinc than the other trees. And the organic trees are slightly smaller in circumference than the conventional or transitional trees.

One set of trees in the trial was started conventionally, and then converted to organic methods. The purpose of this alternative is to learn if it is easier to convert trees that were started with the aid of conventional fertilizers and herbicides than to start trees with organic methods.

(Bob Johnson is a reporter in Magalia. He may be contacted at

Permission for use is granted, however, credit must be made to the California Farm Bureau Federation when reprinting this item.

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