Adapted from a talk given by John Kempf, founder of Advancing Eco Agriculture
Based on our work with crops for disease management and fruit quality, we know that nutritional integrity of plants is the foundation for producing extraordinarily healthy crops.
A tremendous body of research correlates specific diseases with specific nutritional imbalances. For instance, research studies have documented that powdery mildew in cucurbit crops is associated with manganese deficiency, and that apple scab is associated with deficiency of cobalt. The research correlating many more different diseases with specific trace mineral deficiencies and other nutrient imbalances is available as well.
In our work with farmers, we had been using soil analysis and dry matter-based tissue analysis to evaluate the nutritional integrity of crops, and then make adjustments both during and between growing seasons to balance the nutritional profile. After doing that for a six year period, we were becoming increasingly frustrated with dry matter based tissue analysis because we were unable to draw any correlations between the nutritional profiles on the tissue analysis and crop performance and yield. All research said there was a correlation, but we were not able to see correlation in the laboratory data.
Five years ago we started experimenting with plant sap analysis. We have now used this technology very intensely in our agricultural management systems for the last four years. It has proven to be very sensitive, correlating perfectly to what we see happening in the field. In fact, it is so powerful that we can use sap analysis to view a plant’s nutritional profile to predict disease or insect susceptibility.We have never been able to do that before. And not only do we have the capacity to predict problems based on nutrition, we also have the knowledge and information to prevent disease and insect problems from happening.
To manage plant health and a plant’s nutritional integrity, we need to be able to monitor it. You can only manage what you can measure. In a lot of production agriculture there is a giant blind spot by not knowing what the nutritional integrity of our crops really is. Historically, the assumption has been to use soil analysis, and balance the minerals according to the soil test and that would grow a very healthy crop. If the soil test is low in calcium, we add more calcium. If it’s low in phosphorous, we add more phosphorous. And that is not incorrect, but it is incomplete.
Growers don’t care about balancing soil so that they get a perfectly balanced lab report. They care about growing a really healthy crop. That is what’s important. The crop and the plant itself is the final report card. It’s possible to have a perfectly balanced soil test and still have a crop that is extremely unhealthy. Mineral balance in the soil does not necessarily correlate with mineral balance in the plant. This is a blow to the belief that healthy soil produces healthy plants.
In the soil profile, biology always trumps chemistry. You can have a perfectly balanced soil test from a chemistry perspective, but if you have poor biology your crop is not going to be healthy. The converse is also true: you can overcome some mineral imbalances with aggressive biology by growing a healthy crop.
Plants move nutrients around using two types of transport tissue. Phloem moves energy from the sugar source (leaves) to the three plant sugar sinks — the new growth at the top of the plant, the root systems, and the fruit. The phloem does not transport calcium or magnesium. The other type of transport tissue — xylem — moves water and nutrients from the root system to the upper part of the plant. The phloem tissue that moves sugar from the leaf to the fruit has a 75% sugar content and is a thick, syrupy solution.
Since calcium and manganese are not translocated in the phloem, we need a constant supply of calcium and manganese every day. On the day that calcium and manganese is not being supplied, the new growth at the top of the plant, or whichever point the water flow is going, has the potential to become deficient.
Plants have a 24 hour photo cycle where sugars are being produced in the leaves and then being moved to the three sugar sinks. Plants will do everything in their capacity to keep the new growth shoots perfectly balanced with nutrition. They will sabotage other parts of the plant to keep new growth healthy with optimum nutrients. During the framing and vegetative stages the sugar sinks are the new growth, and during the fruit fill stages the sugar sink is the fruit. At these points, if there is a nutrient deficiency, the plant will sabotage older leaves to fill newer leaves, and newer leaves to fill fruit.
The plant sap analysis team in the Netherlands developed a chart featuring a circle divided into four quadrants. All the positively charged elements — cations — are on the left side. The negatively charged elements — anions — are on the right. The upper half contains all of the macronutrients and the lower half contains all the micronutrients and trace minerals.
We understand that soil has a finite mineral holding capacity or cation exchange capacity (CEC). Each soil can only hold so many cations and so many anions. What the team in the Netherlands described with this chart is that each plant cell also has a finite mineral holding capacity. They identified that calcium, potassium, magnesium, sodium, and ammonium antagonize each other. In other words, when the bucket is full, nothing else can be introduced. An excess of one of these elements — for example, potassium — will create a deficiency of calcium or magnesium. But that deficiency can’t be fixed by adding calcium, since the problem isn’t a calcium deficiency problem, but an excess of potassium problem. We need to apply the antidote to the excesses and allow the deficiencies to correct themselves on their own.
The same holds true for anions. An excess of nitrate, sulphur, chloride, or phosphorus can create deficiencies of the others. Then we have some interesting synergistic relationships diagonally across the chart between phosphorous and zinc, for example, and between calcium and boron. Four nutrients — nitrogen, phosphorus, potassium, and magnesium — are considered highly mobile. They are moved around inside the plant structure very quickly to wherever the plant needs them. Sodium, sulphur, and chloride are moderately mobile. They don’t move around as fast but they do move around inside the plant system. Calcium, however, has no ticket to ride. It is not mobile because it cannot be moved by phloem transport.
Micronutrients are another conversation entirely.
All of the nutrients across the top half of the chart, with the exception of calcium, are very mobile. They can move around and we can measure the difference of the nutrient levels in the new leaves and the old leaves. Each sap report shows the nutrient levels of the new leaves and old
Mineral Holding Capacity
Plant cells have a ﬁnite mineral holding capacity.
When one cation or anion is excessive another will be displaced to make room for it.
There is a synergistic relationship between the minerals in opposing quarters.
Cation macronutrients, have a synergistic relationship with anion micronutrients (Ca/Si-B).
Anion macronutrients have a synergistic relationship with cation micronutrients (P/Zn-Mn).
All macronutrients except calcium are mobile in plants.
Plants attempt to maintain ideal levels in new growth.
Comparing old and new leaves can show nutrient movement and early imbalances.
Cation / Anion Balance
There is a strong correlation between anion / cation balance and plant immunity.
Anion and cation balance is regulated by calcium and phosphorus, the heaviest macronutrient cation and anion respectively.
leaves side by side, and we look at the differential to understand exactly what is happening. If, for example, we have a sap report of tomatoes showing potassium levels in the new leaves to be 3,000 parts per million, and potassium levels in the old leaves to be 7,000 ppm, we conclude that this plant has an adequate supply of potassium.
The way we draw that conclusion from those numbers is because there is a surplus of potassium in the old leaves. The plant wants to keep the perfect balance in the new growth, so it puts any surplus in the old leaves at the bottom. So we have 4,000 ppm more potassium in the bottom leaves than we do in the top. If there’s a deficiency, those numbers will be reversed.
We are learning that different varieties of the same type of plant will have different nutritional requirements. Some strawberry varieties require 60 percent more nitrogen and 50 percent less phosphorous than another variety on the same soil type. Sap analysis and comparison allows the grower to customize nutrients in large commercial operations on a variety-by-variety basis to get optimal results.
The bottom line is that we are no longer dependent on historical laboratory data for a desired value, because plants themselves have the opportunity through sap analysis to tell us in real time what nutrients they need.