Nutrient Management Research Database

There is nutrient-status variability both within an almond tree and within and between almond fields. Nutrient-status variability is related to changing soils, micro-climates, and characteristics of individual trees. The author argues that in-field variability in nutrient status has been overlooked by researchers when establishing critical values (CV) for nutrients to establish a fertilization program. In an individual tree, the CV is the minimum leaf- nutrient concentration needed to achieve 95% of full yield. However, to ensure that 95% of all the trees in an orchard are at this critical value and account for field variability, results of this experiment show that growers have to apply at least two standard deviations above the established CV for that nutrient. Growers have been criticizing CV as being inaccurate, and this is likely due to the field variability as shown in this work. Individual tissue sampling strategies only provide the "mean" field nutrient status and are of limited value, unless they can also estimate field variability. New sampling strategies should be developed to account for in-field variability, low-cost probes to monitor plant and/or soil nutrient status, and new models to determine nutrient demand and status should be developed. Further, yield prediction models to allow for early season adjustment of fertilization strategies and technologies to allow for variable rate application of fertilizers are also needed.

• An extensive sampling program was conducted in five almond (10-15 acre blocks) orchards across major growing regions of California.
• Variables recorded for each tree were:
  • May and July leaf nutrient status
  • light interception
  • trunk diameter
  • tree yields 

Results indicate that in order to ensure that 95% of the almond or pistachio trees in a given orchard were at or above the established Critical Value (CV), the field mean nutrient concentration was at least two standard deviations above the established CV.