Organic Calcium and Iron Foliar Experiment
Many organic growers apply various nutritional products through foliar sprays.
I’ve observed foliar sprays grow in popularity over the last 10-15 years and I’ve developed a bit of a skepticism around their effectiveness (in organic production) for a few reasons:
We all have something called confirmation bias that can be summarized in the follow quote: “What a man wishes, he also believes. Similarly, what we believe is what we choose to see.” Once you invest time and money into something, there is a strong cognitive bias toward wanting it to work. There is an additional bias informally termed “boredom syndrome” in which most humans have the tendency to act, even when their actions are not needed. I wonder if both of these biases influence our gravitation toward foliar sprays. Plus, they just feel good.
When it comes to certain macronutrients (Ca, N, K) that can be up to 3-5% of the dry mass of plant leaves, the amount of nutrient applied via foliar is inconsequential in increasing the total nutrient needed across the entire crop. The vast majority of nutrients are always uptaken through roots. The lbs/acre of calcium applied in a calcium foliar is a drop in the ocean of what’s actually needed.
For certain micronutrients (specifically iron), the redox state of the ion is essential for plant utilization. Conventional synthetic chelates easily keep iron in a plant-available form (Fe+++), which is more difficult to do organically.
I consistently hear of positive crop responses from foliars—typically nitrogen (liquid fish or soluble amino acids) or magnesium (epsom salt). When a foliar has a strong and noticeable plant response, I believe that is due to the plant being in a deficient state. If plants are nitrogen deficient due to low uptake from the soil, and a grower sees a plant grow faster or turn more green after a nitrogen foliar, it’s because the plant was hungry. I don’t think a grower would necessarily see a response from a well-fed plant.
I don’t know of any organic growers who have performed proper split tests with foliars to determine if they’re actually doing anything. So I decided to give it a shot on my own farm.
My goal was to see some kind of evidence to justify the use of calcium and iron foliars. In other words, I wanted to throw the kitchen sink of foliars at my trees to see something. I wanted evidence to give me more confidence to use (or skip) future nutrient foliars. The goal was not a scientific study. So sticklers, please ignore the poor experimental design…
Various tests taken in 2022 and 2023 helped me identify that calcium and iron were low in my trees. I designed an informal experiment to see if organic calcium and iron foliars through the 2024 season would make a difference.
Block 1 experiment. Red is treatment receiving foliar sprays. Green is control receiving no sprays.
I broke my orchard into two control blocks and two treatment blocks involving three separate varieties of peaches. The treatment totaled 1 acre and the control totaled 1 acre.
I sprayed the treatment blocks with nine nutritional foliar sprays (calcium + iron) through the season. The first three sprays were with calcium product A, then next three with calcium product B, etc. Three products x three sprays each = 9 total sprays.
I didn’t do a single nutrient foliar spray on the control area all season.
After doing three sprays with a single product, I performed a sap test through Nova Crop Control on both the treatment and control blocks for one variety at a time so I could compare the results. I also performed tissue tests through Logan Labs throughout the season on the treatment and control. And of course, I watched closely to see if I could observe any difference in the trees or in the fruit yield/quality.
Additional Details
Most of these sprays were done in the morning when Delta T was at its 24-hour minimum. A few were done in the evening after the sun went down. I recorded the pH and EC of all foliar solutions. The first three sprays were performed at a tractor speed of 2.76 mph, but the other six were performed at 1.7 mph.
First Product & Results
The first three sprays contained Albion Metalosate Calcium-Boron at the max label rate performed between May 13-May 27th (once the foliage was fully out). One of those sprays had Albion Metalosate Iron at the lowest label rate.
The Nova sap tests on Red Haven performed June 4th showed no difference in any of the nutrients except iron and boron. Iron was 8.7ppm in the new growth and 18.5ppm in the old growth of the treatment, compared to 5ppm in the new growth and 5.7ppm in the old growth of the control. The difference in boron was much smaller. There were no other major differences in any of the other analytes including sap EC, pH, or brix.
Second Product & Results
The next three sprays contained AEA HoloCal at the max label rate performed between June 12-June 20th. Two of those sprays had Albion Metalosate Iron—one at the lowest label rate and one at the max label rate.
The Nova sap tests on Glo Haven performed June 25th after this set of sprays showed no noticeable difference in calcium levels. Iron was 10ppm in the new growth and 20.8ppm in the old growth of the treatment, compared to 3.45ppm in the new growth and 5ppm in the old growth of the control. Boron remained slightly higher in the treatment despite no boron applied in this set of sprays. Interestingly, the treatment had lower sap brix, slightly higher pH, and slightly lower nitrogen.
At this point it’s worth mentioning that the difference in iron levels cannot be easily attributed to the first set of sprays or the second. There was likely an accumulating effect with each spray. This is an overall weakness of this experiment—it can be tough to attribute an increase to one product or another because the nutrients may be accumulating from one product to another as they’re applied one after the other. Again, the purpose was to observe any difference when doing foliars. At this point, there does seem to be a difference in sap iron levels.
Third Product & Results
The next three sprays were with Verdesian PolyAmine Calcium at the max label rate done between June 26th-July 7th. All three of those sprays had PolyAmine Iron at the max label rate.
The Nova sap tests on Suncrest performed July 8th after this set of sprays showed a difference in calcium levels! Calcium was 93 in the new growth and 86ppm in the old growth of the treatment, compared to 29ppm in the new growth and 19ppm in the old growth of the control. This seems like a major difference, and it does seem like the PolyAmine Calcium was solely responsible based on the major jump in concentration.
Iron was a whopping 58ppm in the new growth and 53ppm in the old growth of the treatment, compared to only 3.8ppm in the new growth and 3.7ppm in the old growth of the control. Assuming foliar residual is not impacting results, this is a clear difference.
There were no differences between any other analytes in the sap at this point in the season.
I also performed two Logan Labs tissue tests on July 8th to compare with the sap results. The tissue analysis showed the exact same pattern between the treatment and control: calcium at 1.32% in the control vs 1.61% in the treatment and iron at 64ppm in the control vs. 293ppm in the treatment. The only other nutritional difference observed was slightly higher nitrogen levels in the treatment, likely because most of the foliars contained nitrogen-based chelators. The nitrogen observation in the tissue was not consistent with the sap data, however.
Conclusions and Additional Thoughts
I originally planned to do another set of three sprays using a do-it-yourself JADAM “Quick Oyster Shell” solution. However, I decided to end the experiment because I observed the thing I was looking for: sap and tissue tests showing me that foliars of Ca and Fe can impact the concentration in the plant. Continuing to see elevated Ca and Fe levels with the fourth product wouldn’t necessarily tell me anything new.
Although this wasn’t intended to be a product comparison, it appears that the PolyAmine product was most effective at increasing both calcium and iron. Why? A major difference I measured was the solution pH of the products. The PolyAmine tank solution pH was 3.4, the Albion tank solution was 7.2, and the HoloCal tank solution was 8.3. EC, calcium ppm’s, spray speed, and other factors seem less important than this pH difference.
I believe the JADAM oyster shell product is a good candidate for future exploration as a calcium foliar because like PolyAmine, it has a low solution pH. Because it’s homemade, it’s very low-cost and the pH can be further adjusted based on the quantity of vinegar added. A simple trial involving three sprays of PolyAmine vs three sprays of JADAM would be enlightening.
I also believe a simple Iron sulfate + fulvic acid foliar is a good candidate for an iron foliar. It’s also very low-cost and the pH of the solution can be adjusted. (Be sure to start by spraying a single tree if using Iron sulfate as I’ve created phytotoxicity in the past spraying Iron sulfate at an excessive rate).
Nine nutritional foliars typically isn’t cost-effective for fruit orchards. In my experience, most growers simply mix nutrient foliars with their IPM sprays 2-3 times per season to avoid additional passes with the sprayer. While I was humbled and surprised to see a result after nine sprays, a handful of foliar sprays didn’t initially move the needle.
Therefore, I urge all growers to question their foliar sprays.
Are you applying what your plants actually need based on testing?
Do you have any evidence that the products you’re using actually work?
Please get in touch if you want to start testing to better identify nutrient bottlenecks in your crop. Or, contact me if you’d like help setting up a small farm trial to get at customized answers for your operation.