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UC Research Report: Nutrient balance important for almond tree health

Issue Date: March 18, 2009
Franz Niederholzer, University of California Cooperative Extension Farm Advisor, Sutter-Yuba counties

Nitrogen (N), potassium (K), boron (B) and zinc (Zn) are the fertilizer nutrients that most often deliver improved almond tree health and/or yield in California.

The following are key points to effective, efficient fertilizer practices for these nutrients in almonds:

  • Tree N demand drives N uptake. In mature orchards, crop load drives demand. Match your annual fertilizer N program to estimated orchard yield for that year.
  • A 2,000 pound nut crop uses roughly 100 pounds of N. To get 100 pounds of nitrogen into the tree, apply in the range of 200 pounds to 300 pounds of N to the active root zone under trees. Active feeder roots grow in moist soil. Fertigation is the most efficient way to deliver N fertilizer to the soil.
  • Time fertilizer N application to match periods of high tree N need. April-July is when nut growth is most rapid.
  • Sample leaves for nutrient analysis in every block, every year. July leaf sampling is the best monitoring tool that UC knows right now. Break blocks into smaller management zones if you see yield differences and can manage subzones in the block to maintain good overall yield for less fertilizer cost.
  • Individual tree July leaf N level of 2.2 percent means adequate tree N. Use 2.5 percent leaf N as the target in a block or orchard, so no trees in an orchard are deficient.
  • Individual tree July leaf K level above 1.4 percent means the tree has adequate K nutrition. A leaf sample target of 2 percent leaf K should avoid K deficiency anywhere in the block.
  • Potassium deficiency this year means reduced flower numbers and crop next year. Timing of highest tree K need is April-July. Spring fertigation is the most effective application practice. Use fall banding of fertilizer K in flood or solid set sprinkler irrigated blocks.
  • Foliar applications in the fall or spring are the best practice for getting zinc into trees.
  • June leaf Zn levels below 15 parts per million are deficient. Target block leaf levels between 15-20 parts per million Zn.
  • Boron is an essential plant nutrient, but can be toxic at high levels. Sample hulls for boron analysis at harvest. Adequate hull B is 80-120 ppm. Adequate July leaf B levels are 30-80 ppm for a single tree.
  • Bloom is the key time for good B levels in almonds. Fall or pink bud are the best times for boron sprays. Full bloom boron foliar spray may reduce yield. Gradually increase B fertilizer rates if you are not satisfied with your current program. Excessive B fertilization can dramatically reduce yield.

In 2008, researchers led by Patrick Brown at UC Davis began a very detailed study of how to best manage almond orchard nitrogen nutrition. This group will deliver new, important information in the next couple of years on more precise, cost effective practices for almond N nutrition.

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

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