Comprehensive non-phosphite foliar program on walnuts demonstrates substantial economic yield increases in three years in a row on fully replicated trial compared to grower standard fertility program.

While an extension on higher phosphite residue was granted by the EU in 2015 for four 4 years there are still continuing concerns about the use of phosphite based inputs in walnuts and other nut crops as a result of European Union regulations.  Because of this, in 2015 Agro-K began a multi-year trial with independent contractors, Brooks Bauer with Two Bees Agricultural Research & Consulting, Escalon CA to demonstrate that a comprehensive Agro-K soil and foliar nutrition program without phosphite based materials can improve nut meat yield.

This multi-year trial was initiated in 2015 and conducted with randomized complete blocks. The trial consisted of multiple tree plots of ‘Chandler’ trees replicated four to six times.  This same trial was conducted for three consecutive years on the same trees to demonstrate the cumulative effect of a science-driven nutrition program on yield and overall tree health.

All foliar materials were applied at 100 GPA.  BioMax Dual Action + was applied to the top of the soil and watered-in. Agro-K nutrient materials were applied at key points during the season based on plant physiology and peak nutrient demand timing.

The Agro-K program resulted in increases in the nut meats in each of the three growing seasons between 2015 and 2017 (see graph below).  The three-year average yield increase per acre was 1,287lbs. compared to the standard grower program.   The Agro-K program is meant to compliment a comprehensive agronomic soil program which is the foundation to overall tree health and consistent above average annual yields.

Maximizing profitability in your walnut orchard starts with maximizing nut set every year. Achieving consistency in set and minimizing alternate bearing cycles is the key to consistent above average yields, increased nut meat quality and higher profits. The secret is ensuring the tree has the right nutrients at the right time in the right forms and right mix.  Agro-K’s carbohydrate based foliar line including:  Vigor-SeaCal, Zinc Plus +4 DL and Micro-Mix DL are designed to help growers meet peak nutrient timings in the crop cycle.

BioMax Dual Action + is a unique soil applied product that has a dual purpose.  The first is to directly feed existing beneficial microbial populations (like Mychorrizae) in the rhizosphere to increase native beneficial populations that help to free up soil-bound nutrients and to naturally compete against soil borne pathogens.   The second purpose is to encourage root growth and increase root mass to improve nutrient foraging and uptake from the soil to support tree health while maximizing long-term tree growth and productivity.

Agro-K nutrient programs are based on a SCIENCE-DRIVEN approach with a clear understanding of the walnut tree physiology and meeting the tree’s peak nutrient demands throughout the season.  With bud break happening in the near future, the focus needs to be on early season nutrient demands and the environmental dynamics of the season. 

Ken Dart, Agro-K’s National Technical and Marketing Manager states – “cool and wet spring soils limit nutrient availability, root activity and nutrient uptake.  Growers that are interested in maximizing yield (consistently year over year) and quality should work to address spring nutrient needs by managing and meeting peak nutrient demand timings all season long so that the tree has reserves ready, but will also supplement with early spring foliar nutrient sprays.  You never want the tree to lack for nutrients at critical physiological timings.”

“In the spring, due to poor nutrient availability in the soil the tree will support its needs by utilizing nutrients stored in the roots and wood.  Foliar applied nutrients early season are needed to fully support the tree’s nutritional needs, to ensure more uniform bud break and to encourage faster early growth and larger leaves that will have more photosynthetic capability,” says Dart.

Dart cites these important nutritional facts:

  • The process of breaking dormancy is a very zinc-intensive process.
  • Walnut trees have a very large demand for zinc due to the very large and extensive root, leaf and vascular systems. All these tissues require zinc to function and grow.
  • The full potential of a good nut set won’t happen with small leaves and poor chlorophyll. Leaf size is dependent on adequate zinc levels while the leaves are forming – early peak nutrient demand. The key to making this work is having zinc in the buds, roots and vascular tissues applied at a time, and in a form that will be taken in, stored in these tissues and ready to go when dormancy breaks in the spring.
  • Chlorophyll production takes place as the leaves expand and requires Manganese, Magnesium, Iron, and Sulfur. If these are deficient as the chlorophyll forms, the leaves will not be as effective in capturing the light for photosynthesis (especially in the lower canopy) which leads to smaller nuts, weak lower limbs and terminals that are more vulnerable to the complex of diseases leading to lower limb die back.


For more information on Agro-K’s walnut trial research, fertility programs and Agro-K’s products contact your local dealer or Agro-K today. 1-800-328-2418, visit, or email