Almond yields have increased substantially since the University of California guidelines for leaf potassium were first published in the early 1960s (Lilleland, 1961). Improved irrigation practices and increased frequency of pollenizer rows have driven the phenomenon, resulting in greater annual potassium removal by the crop. In crops such as pecan and prune (Sparks, 1977; Niederholzer, 1991), leaf K concentrations decline as crop load increases. We will determine whether the leaf K critical value varies with crop load in almond. Increasing numbers of growers and reputable analytical laboratories are concerned that the current UC guidelines for leaf potassium are inadequate. These guidelines state that for a mid-July leaf sampling, 1.4% K is adequate; 1.0% is marginal; and concentrations below 0.7% are deficient (Brown and Ryugo, 1995; Beutel, 1983).

The case for reassessing the potassium requirement of almond orchards can be made from several perspectives. From a scientific perspective, guidelines should be base don sound field experimentation. In economic terms, if the current standard is low, then potassium may limit yield; but, if the standard is sufficient but not tested, growers may waste their money by increasing K application rates. Additionally, a thorough study on almond potassium fertilization should include an assessment of potassium-dependent yield parameters (e.g. flower number, percentage fruit set and fruit set). We will determine which yield parameter(s) are affected adversely when tree K demand exceeds K availability.