Boron’s Role in Sap Uptake

I realize Marschner doesn’t make the role of boron very clear. I refer to Marschner’s second edition on silicon, pages 417 – 426. Marschner classifies silicon as ‘beneficial’ rather than essential. Boron he considers essential, pages 379 – 396. Although he acknowledges their close similarity, he doesn’t make the connection I do. And Marschner is, I reckon, the best of the lot as far as academia is concerned. For instance he does make a connection between manganese and silicon, which I reckon is a very important connection, (p. 423).

Unfortunately an over-reliance on such tools as gas chromatographic/mass spectroscopy tends to miss some of the broader connections in nature. We get a snapshot at a point in time and it fails to reveal the processes that are going on.

For example, I work directly with farmers who farm on a commercial scale. I was lecturing in Atherton, QLD Australia and remarked the appropriate way to apply boron was with humic acid because humic acid was food for the microbial species that took up boron and silicon. I mentioned applying a rate of 25 kg/ha boron stabilised humate granules. These are 3% B. A mango farmer in the audience made a note, 25 kg/ha boron. I got an emergency call while in the states from a colleague in Queensland saying the farmer–who we both knew–had applied 25 kg/ha solubor (disodium octaborate tetrahydrate which is nearly 21% B) and the bark is splitting on his trees and his fruit is starting to split open. What can he do? I knew the farmer had a tipper truck and bobcat, so I recommended he go to a diatomaceous earth deposit in the not too distant vicinity (90 km) and load up his truck with DE and crush and spread it like he was frosting a cake (about 1 cm thick) and water it in. He did this and the fissures in his bark and fruit closed up. He saved his trees and his crop.

My reasoning was that boron embeds itself in the capillary linings of the cellular transport system in the xylem, and if the ratio of boron to silicon was too high and the sap flow too great, the remedy would be more silicon to correct the ratio. The next year this farmer came in to our depot in the industrial park near Atherton and gave us all a case of mangos because he was picking the best crop he’d ever grown.

This sort of macro rather than micro evidence is often dismissed as anecdotal–as if what we see in the big picture can only be accepted if we can demonstrate at the micro-level what is going on and it gets published in the peer reviewed literature. I don’t accept those limitations. I can do a paper disc chromatogram and see the charged particles (dominated by the cations Ca, Mg, K and Na) adhere to the central region of the disc and the silicon particles flow to the periphery since they are the most non-polar, or have the least charge. Urea, if present, actually will out-strip the silicon as being the most non-polar and mobile–but it is a minor component in relation to silicon complexes.

That’s proof enough for me at the chemical level that silicon is the non-polar contrast to the polar lime, but you could take it further and analyse cell walls and connective tissues and compare them with cell nuclei and see the contrast there too. I don’t want to go too far toward isolating details because I think it is an unnecessary detour unless we first look at the evidence of our senses and see what the bigger picture tells us about the on-going processes in nature. Isolated details are fine, but they don’t do much for understanding the processes in the wider realm of nature. Once we understand the processes the details make more sense. We need to understand the silicon process is one of containment and transport and the boron process stirs up the silicon process, makes it ‘thirsty’ and this drives nutrient uptake and sap flow. Then I think we are getting somewhere. To understand that too much sap pressure will cause the bark to split and fruit to fissure, then it becomes clear that when you have too much sap pressure (boron) for your transport system (silicon) you need to strengthen your transport system (more silicon). That got the farmer out of some very serious trouble because he could have lost his whole orchard. As it was, his mistake ended up improving his production. I take that as evidence I had correctly observed the boron process and its interaction with the silicon process. I don’t think that’s going to get me past peer review into publication in a scientific journal, but it is all the evidence I need.