The almond orchards with higher yields this year could be most in need of available potassium early next spring, according to the Potash and Phosphate Institute.

A recent issue of Better Crops with Plant Food, published by the institute, summarized a University of California study evaluating results of potassium applied through drip irrigation to Nonpareil almond trees at Modesto, Calif., during 1998-2000.

Almond fruit, including the kernel, shell, and husk, is the chief sink for potassium and contains the equivalent of about 55 pounds of potassium oxide for each 1,000 pounds of harvested kernels, said Edwin J. Reidel, a former UC graduate research assistant now pursuing a doctorate at Cornell University.

He said that very low leaf potassium (0.7 to 0.8 percent for non-fruiting spurs) in a heavy crop year is associated with a limitation to productivity.

Although potassium deficiency does not affect yields in the year it is indicated by leaf testing, it does reduce yields in subsequent years as a result of greater spur mortality and fewer overall flowers.

The effects of potassium applications are site- and cultivar-specific and may vary by soil type, application technique and irrigation method, Reidel said.

“However,” he added, “since most of the fruit potassium is contained in the hull and because Nonpareil almond has a relatively large hull compared to other cultivars, it should be possible to match potassium fertilizer application to the predicted crop size.”

He suggested growers and consultants become aware of whether the soils in their area are likely to fix significant amounts of applied potassium and then make adjustments accordingly.

In the study the highest yields were from treated plots having leaf potassium concentrations ranging from 1.4 to 1.7 percent. Yet, some plots at the 1.7 percent level yielded no better than the controls, suggesting other factors also limited yield.

Reidel concluded that since the early spring is the time of rapid vegetative growth and fruit development, it is likely the most critical time for potassium availability.

Other researchers were Patrick H. Brown and Steven A. Weinbaum, both of the Department of Pomology at UC, Davis, and Roger A. Duncan, Stanislaus County farm advisor.

The Almond Board of California and the Potash and Phosphate Institute supported the project. Cooperators were Modesto grower Pete Mihelis and Art Bowman of Salida Ag Chemical.

California Department of Food and Agriculture statisticians forecast the 2001 crop at 850 million meat pounds, up 21 percent from last year. Average nut set per tree is up 26 percent from last year.

e-mail: dbryant@primediabusiness.com