Mitigating heat stress

When leaf temperature becomes too warm, plants switch from photosynthesis dominant to photo-respiration dominant, and begin ‘consuming themselves’.

The threshold for C3 photosynthetic pathway plants is a leaf temperature of 78 degrees Fahrenheit (25.5 C). For C4 plants, the threshold is 86 degrees Fahrenheit (30C) leaf temperature.

Leaf temperature and air temperature are not the same. The healthier plants become, the better they are at cooling themselves. There are several mechanisms in play, topics for future blog posts. It is clear that plants with a waxy sheen on the leaf surface can have a leaf temperature as much as 8-10 degrees cooler than plants that lack nutritional integrity in the same climactic conditions.

When this threshold is crossed and photo-respiration becomes the dominant process, a few important shifts occur:

  • photosynthesis/sugar production drops or stops completely
  • plants consume the limited available sugar supply
  • plants consume any free/available lipids as an energy source (these are abundant in high energy plants, very low in plants getting nutrition from soluble ions instead of from living microbes.)
  • once the supply of available sugars and lipids has been used as, plants begin consuming their own proteins as an energy source.

80% of the nitrogen (proteins) contained in plants is in the form of enzymes. Breaking these down further weakens the plants ability to recover quickly. Protein catabolism also leads to the formation of ammonium, which is a requirement for  spider mite infections.

When plants experience periods of high heat stress, one of the best management strategies is to provide them with a surplus of energy in the form of sugars, oils, and sometimes proteins, to avoid the stress consequences of catabolism.

Foliar applications of sugars and sometimes vegetable oils can produce a tremendous crop response. In the past several weeks heat stress period, growers have reported some remarkable crop responses within 24 hours from foliar applications, both when applied proactively as a preventative, and during and after the heat stress. Rejuvenate inclusion in the foliar mix seems to consistently deliver clear visual results.


2021-07-16T07:01:46-05:00July 16th, 2021|Tags: , , |

Feeding plants to provide digestible nutrients for the following crop

The growers we work with who regenerate soil the most rapidly, and produce the most profitable crops, care for the cover crops as closely as their cash crops. Cover crops are planted with inoculants and nutritional support, and foliar fed. When you calculate the increased efficiency of a cover crop at 60% of it’s photosynthetic capacity as compared to 20%, and realize that it is sequestering three times more carbon in each 24 hour photoperiod, you quickly realize there is no other management practice which can build soil organic matter levels as inexpensively as harnessing the photosynthetic engine of a crop.

These crops can stimulate biology and build a large reserve of plant available nutrients that completely displaces the need for any soil applied fertilizers for following crops.

Here are some thoughts from my discussion with Gary Zimmer on this topic.

John: We’ve been talking about nitrogen management, and a few moments ago you were describing humic substances. One of the pieces that you and I spoke about in our prior conversation was the idea of delivering nutrients much more efficiently and much more effectively using carbon-based fertilizers. I think this ties in directly to our nitrogen management conversation, because what we’re really talking about is the need to have a balanced carbon-to-nitrogen ratio in the soil profile, and to hold that and to stabilize it and to keep it plant available. How does that concept of carbon-stabilizing nutrients transfer to other nutrients, in addition to nitrogen? And how do you utilize that?

Gary: I think this goes back to digestibility. In order to have the biology do its work and break it down, you need trace minerals. How do we make them available?  Some of them, like molybdenum, are pretty small additions. How do we take that addition in very small amounts and make sure it’s active and plant available? By burning up carbon, those nutrients get lost. That’s the whole thing with carbon. Let’s say I just put some of this stuff out there and grew a plant and then managed the digestibility of that plant. I’m now going to be more time released, and I’m going to be distributed better.  A farmer asked me the other day if he should put trace minerals on his cover crop. A cover crop is not a cover. It’s not covering anything―it’s actually a crop that you’re using to distribute minerals for the next crop, and you need to manage it accordingly. Managing the carbon ratio comes in line in terms of digestibility. If I’m too low on carbon or nitrogen, it’s going to take a long time to break down. I can set myself up for disease and insects, and I don’t get availability of my minerals.  I’m a dairy nutritionist. That’s how I got introduced to some of these things forty years ago―to create better feed for cows. When we started, I spent nine years at the university balancing rations based on a set of numbers. If you have more digestible feed and the mineral levels in your feed are higher, that highly digestible feed might have 95 percent of its minerals available to the cow. The stuff you buy in bags might only be 40 percent available.  When we started balancing rations for cows―and I think it’s the same thing with soils― once we started using highly mineralized, digestible feeds, we could actually cheat on numbers and cut down what we applied by at least 25 percent. We could back off those ration numbers with a lot of success once they started mixing minerals into highly digestible feeds.  In the soil it would work the same way. That’s why it takes several years to really get this going. For us as organic farmers, during that two years in transition from conventional to organic, we remineralized and grew cover crops to build up our soil. Once it was organic it was far from perfect, but we started getting a higher nutrient exchange. It’s all based on first getting out there and building carbon-biological cycles with plants and biology.

John: Essentially, Gary, what you’re describing is that farmers should grow their cover crops as a ration for soil biology―similar to growing a ration for rumen biology. In saying that, do you believe that farmers should manage their cover crops as carefully and as well as they do their actual crops?

Gary: Yes, I think those cover crops are my reserve to hold and release the kind of minerals that I want to release.  The other day a guy asked if he could just spray homogenized trace minerals onto his cover crop. I don’t know whether they get absorbed or where they go; I think that’s certainly not a bad idea. Then asked if he could use a cheaper source of those minerals, and I said that they still have to be able to get into the plant. I’m not sure how that would really work. But it starts with the process. The last thing I want them to do is spend money on something and have it just be another stone added to the big pile of stuff that we already have in our soil.

John: We have observed that our most successful growers―those who have regenerated soil health the most rapidly and who have achieved the greatest crop responses―manage their cover crops as carefully as they do their crops. They use foliar sprays and will put on fertilizers; they will manage those crops as well as they do the crops that they’re actually harvesting.

Gary: I’m 100 percent in agreement with that. I was just at some farms that had some really poor stands of alfalfa, and their cover crops were half a stand. They said that they weren’t getting much success. But they didn’t really have a very good cover crop or a very good alfalfa stand to work back into the ground to feed the soil―obviously they’re not going to get all the benefits.  I think you’re absolutely right. I think that’s a huge ticket to using cover crops. As a dairy farm, we only leave our alfalfa in one or two years. We like to take that beautiful, lush stand of alfalfa grasses and let it get up to that highly digestible stage and work it back into the soil. And people say, “Oh my gosh―I could be feeding that to my cows!” But I say that I am feeding it―to my soil livestock. They need to be just as well fed as our cows.

2020-06-25T08:53:52-05:00July 7th, 2020|Tags: , , , |

Considerations for spraying microbial applications

To produce the most effective response from applications that contain living microbes, we need to consider the path through the sprayer nozzle and the environment on the leaf surface or within the soil once the product is applied. 

It is best to have spray pressures below 55 psi to reduce or avoid sheer at the nozzle. Higher pressures can produce a sheer force with a markedly negative effect on living organisms in the solution. 

When applying products that are suspended in solution and with larger particle size, such as mycorrhizal fungi which can have a spore size up to 50 microns, use larger nozzle and screen sizes. We generally recommend a 50 mesh screen or even no screen in some cases. 

When applying products to the soil surface that will not be incorporated, add humic substances or dark-colored material such as molasses to the solution to protect organisms from UV. I suspect (but don’t know for certain) that this may be less necessary when applying to the leaf surface, since organisms which can survive on the leaf surface can likely handle UV exposure. 

Combine the inoculant with a biostimulant to develop a ‘synergistic stack’ of products that produces a much greater performance than either product by itself. These could be materials such as humic substances, seaweeds, food sources, prebiotics, enzymes, etc.

And by all means, avoid adding antimicrobials into the spray solution, at any concentration. This means you don’t use water that contains chlorine, chloramines, or anything with a similar antimicrobial purpose. Don’t add ionic or salt forms of boron, zinc, manganese, or copper. After all, in the right concentrations, each of these minerals are very effective antimicrobials. We need to consider not only the solution in the spray tank but also the concentration of the droplet when it begins drying on the leaf surface or soil surface. 

Field experience indicates it seems to be ok to add chelated or complexed forms of these minerals that aren’t immediately absorbed by the microbes in the solution, yet are quickly absorbed by the plant while the droplet is still liquid on the leaf surface.

2020-04-06T18:14:27-05:00April 7th, 2020|Tags: , , , |

The essential nutrients needed to increase photosynthesis

Most commercial crops are photosynthesizing at only a fraction of their inherent capacity. The limiting factors that keep them from reaching their potential are most commonly inadequate water, carbon dioxide, not enough manganese, not enough chlorophyll, and too high leaf temperature. 

Water is obvious. The solutions to infiltrating and retaining large volumes of water in our soil profiles to produce drought proofed soils are known and will be described more in the future.

Carbon dioxide as a limiting factor is often not considered as it should be. The most important reason to have high organic matter content soil is so we can lose the organic matter as CO2 while we have a green plant to capture it. In crops that are efficient photosynthesizers such as a perennial polyculture of well managed grazed forages, corn, sugarcane, and many others, carbon dioxide levels can be depleted in the local air to less than 100 ppm by mid-morning on a warm day. For the rest of that day, photosynthesis is limited by CO2 supply. 

Manganese is needed for water hydrolysis. When water is absorbed from the soil and moves up into the leaf, the first step before water can participate in photosynthesis is that the H2O molecule is split to H and OH ions, hydrogen and hydroxyl. This water splitting process is called water hydrolysis and is completely dependent on manganese. Even when you have perfect environmental growing conditions, perfect water, temperature, sunlight, and carbon dioxide, if the plant does not have abundant manganese, photosynthesis will be slowed.

Chlorophyll levels can often be increased by making sure that plants have adequate levels of magnesium, iron, and nitrogen. Nitrogen is seldom low because it is one of the nutrients much used to cover up other imbalances, and is frequently over-applied. Magnesium is easy to correct with a foliar application, and also frequently low. Iron is almost universally low in plants, contrary to most soil and plant tissue analysis reports, because the (oxidized) form of iron reported on these assays is not physiologically active in plants. Any of these three nutrients can be used to quickly give plants a dark green color by increasing chlorophyll. Since nitrogen is generally abundant, magnesium and iron usually produce the biggest economic crop response. Leaf sap analysis can identify precisely what is needed.

When leaf temperatures are too high, photorespiration becomes dominant instead of photosynthesis, and plant energy levels begin dropping, ammonium is produced in leaf tissue as a result of protein catabolism, and plant immunity is quickly reduced. There is not a direct correlation between leaf temperature and air temperature. Healthier plants remain cooler for much longer at higher leaf temperatures, through a variety of mechanisms.

Look for more detail on each of these in future posts. 


2020-03-16T13:54:54-05:00January 15th, 2020|Tags: , , |

Foliar Feeding with pesticides in the tank

Why would you add toxins to your food? ~ Michael McNeill

(When asked whether it is appropriate to add foliar fertilizers to a spray mix which contained fungicides or insecticides.) 

It is fairly common to combine nutrients and biostimulants with toxic compounds in the same tank mix, but is this really what is best for plants?

Sometimes a combination is the only application logistically possible, but field experience suggests that separating foliar fed nutrients and pesticide applications will produce a bigger crop response to the foliar fed nutrients.

Foliar feeding in a combination with pesticides is better than not applying the needed nutrients at all. Applying nutrients and biostimulants without the toxins is best. 


2020-03-16T13:52:31-05:00January 11th, 2020|Tags: , |

Managing the Point of Deliquescence

Managing the point of deliquescence (POD) of a foliar spray solution can tremendously increase the performance of the products applied, particularly in drier climates with low humidity, and when the products applied are ionic salts.1 

It is also possible for plants to absorb insoluble non-ionic nutrients through the leaf surface through endocytosis. For non-ionic products, the point of deliquescence is less critical but still important and useful to manage. 

The point of deliquescence is described as the humidity threshold at which an ionic salt material dries into a crystal on the leaf surface. When humidity is above the point of deliquescence, the salt residue on leaf cuticle dissolves and can be absorbed. When the humidity is below this point, a solid residue remains on the leaf surface and penetration into the leaf stops.

Because of this effect, foliar sprays should be applied in the evening to take advantage of the higher humidity at night.

In addition to the ingredients mentioned in the article, a useful tool to increase the point of deliquescence when applying non-ionic materials are ocean mineral solutions with a low sodium content, which are generally quite hydroscopic and keep the foliar solution liquid on the leaf surface for a longer period.  Urea is also a useful material in this regard.

The reference below describes the POD and speed of foliar nutrient absorption across the cuticle for various ionic nutrient compounds.

  1. Schönherr, J. Foliar nutriton using inorganic salts: laws of cuticular penetration. in International Symposium on Foliar Nutrition of Perennial Fruit Plants 594 77–84 (actahort.org, 2001).


2020-03-16T13:50:52-05:00January 7th, 2020|Tags: |

Foliars as a tool of soil regeneration

Without the contribution of plants, ‘soil’ is only decomposed rock particles.  

Plants contribute sugars, organic matter, carbon, the energy that sustains microbial populations. 

Plants, through photosynthesis, are the only way we have of bringing new energy into the system.

The photosynthetic engine of most crops is only running at 15%-20% efficiency. (Charles Tsai, et al.) It makes sense to increase the efficiency of this engine as much as we are able.

The first priority of a successful foliar application is to increase photosynthetic efficiency. A foliar application that only addresses nutrient deficiencies and does not increase photosynthesis will not be nearly as effective as a foliar which does both. In fact, a foliar which does not increase photosynthesis can facilitate more efficient extraction of soil nutrients and increase soil degradation. Foliar design matters.

The nutrients which need to be present in adequate supply to increase photosynthesis are nitrogen, manganese, iron, magnesium and phosphorus. Obviously, many others are also important, but these are key.

We can use foliars as a tool for soil regeneration when we use them to increase photosynthetic efficiency and transfer a larger portion of plant photosynthates to the roots to feed soil biology. 

When a well designed foliar is applied, the spike in photosynthesis can be observed in sap sugar content and dissolved solids, or brix. (Measured actual sugars on a plant sap analysis is best by far. Brix can be highly variable because of environmental conditions.)

After a successful foliar application, the photosynthetic rate will gradually drop back down, but not quite down to the previous baseline. With each successive application spike, and return to baseline, the baseline level increases. When photosynthetic efficiency baseline improves to a high enough plateau plants contribute more carbon energy to the soil than they withdraw mineral energy and the entire ecosystem becomes self-sustaining.

The drop back to the new baseline can occur quickly or slowly, depending on the level of ecosystem health. In a compromised and degraded ecosystem, the spike may last for as little as 3-5 days before it drops back down. In a healthy soil, with good biology, the elevated spike may last for as long as 5-6 weeks or even longer. 

The healthier soils and plants become the fewer foliars are needed until the point is reached where they are completely unnecessary to sustain a level of health where plants are completely resistant to diseases and insects.

While on the pathway to this point, we can still use the photosynthetic efficiency spikes to produce interesting and valuable effects. If we have the presence of larval or sucking insects,  a spike in photosynthesis is often successful in giving them a dose of sugar they can’t tolerate.

A slide from an academy presentation. Academy.regen.ag

2020-03-16T13:49:53-05:00January 4th, 2020|Tags: , , , |

Foliar feeding of plant nutrients

I have long been an advocate of foliar feeding nutrients as one of the most financially rewarding applications that can be made to a crop, and the practice has become mainstream in many regions. 

Thus, it comes as a surprise that in some areas growers still consider foliars to be an ineffective tool. I would suggest they are ineffective only when they are not properly designed and applied. 

Some of the first published papers on foliar feeding I have read were based on research conducted for the Atomic Energy Commission by Sylvan H Wittwer and Harold B Tukey in the late ‘40s and ‘50s. Their congressional testimony is as relevant and exciting today as when it was first published. (Approximately 1952?)

I cleaned up the document and made some slight edits to make it more readable, but kept all the underlining in the original report. You can read the 24 page report (and bibliography) here. You will find valuable and intriguing information. Here are some excerpts:

  • not only can plants absorb nutrients through the roots, but also through the foliage, the fruit, the twigs, the trunk, and even the flowers.
  • the most exciting news is the foliage feeding of plant—that plants can take up nutrients through the foliage. Here is a case where the farmer has really gotten ahead of the scientist as so often happens. He has learned that foliage feeding is helpful and he has adopted the practice. 
  • The first point I should like to make is that the materials do enter the leaves rather easily.
  • In the final analysis, we find that a leaf is a very efficient organ of absorption. We find that the materials move into the upper surface of the leaf as well as the lower surface. We find that it enters at night and during the daytime. Further, we find the leaf surface of a 12-year-old apple tree in Washington State to be equivalent to one-tenth of an acre, even though that tree only occupies about one-hundredth of an acre. So there is a large feeding area.
  • Not only do these materials enter rather easily—and this is interesting, too, because all the textbooks used to tell how the plant was covered by an impervious cuticle—now we find textbooks are re-written and the leaf is reported as a beautiful mechanism for absorption. 
  • If we apply it to the leaf we find it moves downward through the plant—at the rate of a foot an hour. It is very interesting that it moves so freely. If we apply it to a middle leaf it moves both ways very effectively.
  • We have seen that materials are absorbed by the plant and move rather freely in the plant. The amounts may at first seem relatively small, but to off set this handicap, the efficiency is high. In fact, this is the most efficient method of applying fertilizer to plants that we have yet discovered. If we apply these materials to the leaves in soluble forms, as much as 95 percent of what is applied may be used by the plant. If we apply a similar amount to the soil, we find about 10 percent of it to be used. 
  • For example, the soil may be cool and low in phosphorus at just the time it is needed by a transparent vegetable or strawberry plant. Or there are cases where the soil locks up certain materials that are applied, like potash and magnesium. Under such conditions we find leaf application very significant and very effective.
  • But now we are highly suspicious that here may be a case where materials are actually being leached out of the leaves maybe by overhead irrigation, maybe by rain, and having a profound effect upon the crop.  


2020-03-16T13:44:48-05:00December 20th, 2019|Tags: , , |
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