Poor Fruit quality: is calcium the culprit?

In order to manage something, you must first measure it. Measuring helps you establish a starting reference point and then with succeeding sample analyses you are able to measure and track your progress. At the very least, a current soil analysis shows you where you are now. This can be helpful when you are looking at crop nutrient removal rates.

Here’s one example why you should be soil sampling:

Years back, I began consulting for a grower, to help improve the soil productivity in some of their orchard blocks. One apple orchard (on which we weren't consulting) had a significant internal fruit quality issue, specifically Bitter Pit, which is often referred to generally as a calcium deficiency. Before you stop reading because you don’t grow apples, please understand the principles applied here for better soil health management are applicable for all crops.

In this case, the grower was following the directives of the cooperative extension and pest control advisor; which were, “Your apples have bitter pit. Bitter pit is a calcium deficiency. You’ve got to add calcium to make the fruit stronger.” In this case gypsum applications were recommended and applied in the fall, every other year, whether the soil needed it or not...because it’s calcium.

Because we were just beginning to work together, I asked about the soil amending activities I witnessed happening, in this, and some of their other orchards.
[The following is an excerpt of our conversation.]:

I asked  “What are you amending with on that block?”

I was told that they were applying gypsum for calcium to make the apples stronger.

I asked if the block had Bitter pit problems and followed up by asking if they had a current soil analysis for the block and permission to take a look at it.

They responded, “There isn’t one. These apples need calcium, so we apply gypsum.”

I asked, “How do you know how much to apply OR if you need it all?”

 “It’s a standard practice in the industry and we apply gypsum for calcium and better fruit quality.” they said.

My response was, “Okay. So, we don’t know if your soil needs calcium or how much…but, is it working? How is your fruit quality?”

To which they replied, “Well…we still have bitter pit, if that’s what you mean.”

Now, you may have had similar experiences with underperforming blocks producing low-quality fruit, and there is a good possibility you might have had the thought, “I applied ‘Product X’ last year, but I’m not seeing improvement. How long does it take?'" Just because you apply an amendment or a fertilizer to the soil doesn’t mean it is readily absorbed for use. It takes time. Changing the soil takes time and resources. Having a treatment plan will help you stay on track and on schedule when building up soil health.

Okay, back to the grower example, there is a lot to unpack here. For starters, please understand there is rarely a “silver-bullet” or “set-it-and-forget-it” solution, when it comes to improving the soil health on your farm…and you can’t grow quality crops without healthy soil.

Here’s the problem, if you are applying amendments or fertilizers (and remember, these both directly affect the chemical properties of the soil chemistry and its health) without soil sampling, there are critical details you don’t know, like your soil pH, electrical conductivity (EC) or nutrient inventory levels. More importantly, if there are soil cation imbalances, which lead to inefficiencies, in uptake by the roots and potentially limiting efficient plant growth and development.

These are critical details that should be monitored and should be supplied with a Complete Soil Analysis (not all ag labs offer the same standard information). Armed with that information, you can then accurately plan a course of treatment action without guessing. 

Let’s now return again to the grower example. After talking with the grower a bit more about this block, they added it to our project list and we collected a soil sample to establish a baseline for the block that fall.

Here’s what we learned from that initial soil analysis:

The block had what we call a “medium-textured” soil with a cation exchange capacity (CEC) of 16. This told us what the ideal Base Saturation Cation Percentages should be for proper aeration and hydration of the rootzone. When in the proper proportions, calcium and magnesium combined should make up  80% of the total Base Saturation Percentage. The Ca:Mg ratio should have been 68%:12% respectively but was actually 68.1%:25.4%. This was a significant imbalance that was causing serious rootzone nutrient uptake inefficiencies.

Based on the new information from the soil analysis, the grower realized that there was adequate calcium already in the soil and applying more wasn’t the answer. In fact, calcium wasn’t the problem at all, rather cation imbalance was the problem causing the majority of the soil nutrient uptake inefficiencies. Resulting in the problems with the internal fruit quality. With this new information, we shifted our efforts from an emphasis on changing the soil chemistry, onto the soil biology, because we now knew there was plenty of nutrient inventory in the soil. The incorporation of a fermented soil microbial inoculant was added to the fall treatment schedule. This treatment was based on Dr. William Albrecht’s writings from 1953, “We have not yet understood, nor appreciated, agriculture as a collection of complex, but well-integrated, biological processes...We upset the biology, but cling to our technology.” The soil inoculation introduced a diverse blend of microbial species that were each specialized and efficient at etching and cleaving soil-fixed nutrients like calcium, in this case, for better plant availability and absorption.

Calcium does many things in the soil, but a main job for calcium, on a physical level is to loosen the soil. This improves rootzone aeration but also helps water, roots and microbes to more easily move throughout the root system. On a chemistry level, getting the calcium:magnesium ratio into proper proportion will also help to improve the balance of acid and alkaline properties where, in time, the soil pH will self-adjust to a slightly acidic condition which will improve nutrient availability. Magnesium is responsible for soil hydration and chlorophyll synthesis. In sandy soil types more is needed as it pulls soil particles closer together and slows the flow of water through the profile. But, these must be in the proper proportions, based on the soil CEC, in order to function properly, otherwise cation imbalance limits soil productivity.

In this grower’s case, the magnesium saturation percentage was double what it should have been and this reduced calcium availability to the plant. Because, in fact, when the magnesium level is too high, not only does it block efficient calcium absorption, it also becomes less available for plant use. As a result, special measures must be taken to free magnesium up for plant use and to aid in the process of getting the Ca:Mg ratio shifted into proper working proportions. In this case, much of this cation adjustment work was addressed effectively with the incorporation of soil microbial inoculations.

Here is the data archive from this apple block of the soil analyses showing its progress in improving soil health.

Over time, as we have continued to soil sample annually, we have seen gradual improvements in both the soil health and the fruit quality. The soil pH is adjusting naturally as soil cations move towards proper proportions. The magnesium is moving steadily downward, but will take time to reach a level of 10% based on the Cation Exchange Capacity value. The other significant detail we regularly see happen with the introduction our soil inoculation program is the CEC value increase. This we attribute to a number of positive changes happening in the soil, but regardless of the reason, the soil health and productivity improves. Throughout the growing seasons, the plant tissue analyses confirm that nutrient uptake efficiency is improving as well.

As you can see in this example where a block had a problem with internal fruit quality, the soil values improve over time. You need to have reasonable expectations when beginning a process like this one. We are encouraged to see how well cation ppm values are increasing without applying any additional amending materials since 2018. 

We are currently in the soil sample collection season with our growers. The window of opportunity will be closing shortly to collect soil samples, receive and analyze results and adjust your fall Nutrient Management Plan treatments. If you don't have a plan to make informed decisions about your fall treatments, contact us today. We can help you prepare your soil for next year's crop. 

Here’s to your crops’ success!