P, Ca, B and Si — plus carbon
Gary Zimmer has his BIG4 nutrients: phosphorus, calcium, boron and magnesium. In the Sacramento Valley of Northern California, about 95 percent of our soil is high in magnesium. Magnesium is at 35 percent or more in most areas, creating very compacted soils that have difficulty breathing. Magnesium also creates antagonism with nitrogen applications, along with other cations such as potassium and calcium.
In my own BIG4 I do have phosphorus, calcium and boron, but I’ve added the undervalued silicon. I feel we also need to add carbon to the equation since it makes the BIG4 operate much more efficiently. I have noticed that when I get these four nutrients in line, the plant functions at a high level and is very resilient to abiotic stresses.
Top of the Order
Phosphorus is the leadoff hitter. It is fundamental component of the BIG4 due to its versatility. Phosphorus plays a vital role in virtually every plant process that involves energy transfer. High-energy phosphate, held as a part of the chemical structures of adenosine diphosphate (ADP) and adenosine triphosphate (ATP), is the source of energy that drives a multitude of chemical reactions within the plant. The most important chemical reaction in nature is photosynthesis, and the energy to help complete this process is captured in ATP. The ATP is then available as an energy source for many other reactions that occur within the plant.
Moreover, phosphorus is vital for genetic code transfer and the development of new cells. Large quantities of P are found in seeds and fruit; it is essential for seed formation and development. An inadequate supply of P can reduce seed size, seed number and viability.
Phosphorus availability in the soil can sometimes be difficult due to its propensity to lock up other nutrients, especially iron, calcium and aluminum. This is where having good organic matter or adding humates with your phosphorus applications helps chelate and minimizes tie up with other elements in your soil. Other problems that can occur with poor phosphorus uptake can be due to the antagonistic effects of excess sulfur or zinc in the soil. You would hope to have a one-to-one ratio between phosphorus and sulfur, and you would also like to have a 10:1 ratio of phosphorus to zinc in the soil.
Conventional P inputs are in the form of DAP (diammonium phosphate) and MAP (monoammonium phosphate). These forms are very soluble with irrigation. If your soil is compacted or has low organic matter, the availability will be short; it starts to tie up within two hours in some cases. Some studies show that about 20 percent of what’s applied gets used, and the rest gets locked up. Many crop consultants love that instant “wow factor” when applying these types of fertilizers, but after two weeks or so, the effect is gone.
There needs to be an adequate supply of phosphorus throughout the season. I’ve seen many times when crops have run out of P at the end of the season, making it difficult to finish the crop or, in the case of perennials, compromising bud development for next year’s crop. Using manure compost or soft rock phosphate will provide a much steadier release of P. I like using both; there seems to be a synergism when applied together. I also like adding leonardite and sulfur to the soft rock phosphate to give it quicker availability for the current crop year. The continued use of soft rock will become more available throughout the years at a rate much more efficiently than annual synthetic P inputs can achieve.
On Deck
Next up is calcium. A beloved nutrient from my early consulting days, it plays a pivotal role in both plant and soil health. In our high-magnesium soils, calcium is critical to get the soil opened so we can get air exchange and water infiltration. Calcium improves the plant by strengthening cell walls, improving stem flexibility and helping it cope with stress from diseases and pests. Calcium also aids in uptake of other minerals, which is why Gary has called it “the trucker of all minerals.”
Calcium is difficult for the plant to uptake, plus once it’s taken up it is immobile. So, a constant supply throughout the growing season is important. In the course of doing so, one must be careful not to oversupply nitrogen. Overapplication of nitrogen shuts down potassium first, and then it shuts down calcium.
Calcium also helps foster a healthier biological environment. Mycorrhizal fungi and calcium love one another; if you’re trying to increase your fungi-to-bacteria ratio, implementation of calcium is critical. If you use soft rock phosphate as an amendment, then that mycorrhizal fungi will help break the phosphorus-calcium bond in the soft rock.
Other natural sources of calcium include gypsum (calcium sulfate), limestone, dolomite, aragonite, and wollastonite. Sources used in conventional agricultural include calcium nitrate, calcium chloride and calcium thiosulfate. I see overuse of these products creating self-induced problems with disease and pest pressure. Excess nitrate nitrogen will antagonize phosphorus and sulfur uptake, plus more energy (10-12 percent) is required for the plant to convert the nitrate form to amino acids. The energy it takes to convert nitrate N to amino acids lowers Brix levels in the plant, thus creating an invitation for sucking insects to enjoy a lovely meal. Unconverted nitrate nitrogen in the plant creates more susceptibility to fungal diseases.
Overuse of calcium chloride can create excessive chloride levels, which in turn antagonize phosphorus and sulfur uptake. As I’ve mentioned in a previous article, high Cl invites web-spinning spider mites to your crop.
In the Hole
Hitting in the third spot is boron. This is the only non-metal trace mineral. It is mined from dry salt lakes, mostly in California and Turkey. It comes in two forms: sodium borate (borax) or boric acid. There is no synthetic boron at all.
Boron is notoriously lacking in a majority of farming soils; you should have one ppm minimum in your soil. In our area we have either too much boron or not enough. Boron and calcium are reliant on each other — without one or the other, their functionality is minimized greatly.
Just like calcium, boron is primarily involved in the structural and functional integrity of the cell wall. Boron, along with calcium, is vital for cell division, and without them root elongation will be compromised. These two nutrients also partner up with pollen-tube growth. This year we found in our almond crop that this was extremely important due to the poor weather we had during pollination. Without optimum calcium and boron levels in the blossom, the pollen tube had a hard time finding its way to the ovary.
There are many calcium deficiencies, such as club root in brassicas, bitter pit in apples, and cracking on carrots. Boron drives the formation of calcium pectate, which is hugely important in the strength of cell walls; in the absence of this super-resistant material, invading fungi are much more able to use their enzymes to break down these barriers and intrude inside the cell wall. Boron is also necessary for allowing potassium to be available at the stomata; without proper stomata function, photosynthesis can be compromised due to lack of carbon dioxide taken up by the leaf.
Boron is also critical for the movement of sugars throughout the plant, so boron deficiency will limit root exudates, thus preventing biology from getting its food source. Boron is needed in legumes for nitrogen fixation. Boron, along with molybdenum, as part of the nitrate reductase enzyme, are needed to convert nitrate to the all-important protein.
Boron deficiencies have been linked to verticillium wilt, powdery mildew and rust (manganese, copper and zinc deficiencies can also contribute to these diseases). Boron is important for single-cell bacteria and algae, but it can be fungicidal. So, adding boron to a fungicide treatment can be beneficial, though you should use the boric acid form to keep the pH at a desired level on foliar applications. Boron is also critical for the plant to produce good levels of vitamin C and glutathione (the most important nutrient for your liver), which are both important for the plant’s immunology —- as well as the consumer who eats the produce. In many conventional agriculture systems, high nitrogen and potassium applications reduce the uptake of boron, thus lowering the vitamin C content in the fruit.
Cleanup
Now it’s time for our cleanup hitter: silicon. Silicon is the third piece of the trio that includes calcium and boron. In a regenerative landscape you can liken this to the NPK trio that the conventional model loves.
Fall boron applications can be used to stimulate the release of silica. The silica opens the pathways (xylem and phloem) in the plant to allow better uptake of calcium, giving us the critical calcium needed in perennial plants that bloom prior to leafing out. We talk about calcium and boron for cell strength, but silicon is equally important. In research by Dr. Wendy Zellner, silicon-fed plants are not just physically stronger — their internal immune response, or physiology, is enhanced. This allows them to respond and to adjust to adverse growing conditions more quickly.
Silicon also helps with environmental stress, such as salinity, drought, temperature extremes and heavy-metal stress. Silicon is especially prevalent with monocots — in fact, rice has higher levels of silicon then nitrogen; the silicon increases stem strength, which reduces lodging in cereal crops.
I’ve been using a silicon product to help alleviate high-aluminum levels. It also has the ability to remove other unwanted metals such as cadmium and lead. Let’s say you overapplied zinc; you can use silicon to disable the zinc, thus preventing phosphorus antagonism. Adding a little humic with some soluble silicon will help reduce salt stress — the humic acid buffers the sodium while the silicon immobilizes the unwanted excess sodium.
Silica is the most abundant element in the soil, but most of it is unavailable. A healthy, disease-resistant soil should probably have 100 ppm of mono-salicylic acid, although most soils are lucky enough to have a third of this — though soils farmed regeneratively using biological inputs should have much better levels. Applied silica can also increase the availability of phosphorus and vice versa.
There are manufacturers starting to come out with available liquid forms of silicon, combining them with calcium or potassium, or as a standalone. There are also injectable solution-grade powders available, derived from wollastonite or diatomaceous earth.
I could list many more diseases that silica has been known to reduce, but a good book to reference is Mineral Nutrition and Plant Disease; it details what calcium, boron and silica are capable of when it comes to disease suppression. With the three of them working together, I’ve seen incredible things happen. By the way — you can’t sleep on manganese for disease suppression. It didn’t make my BIG4, but it’s worth a mention — just ask Don Huber.
In conclusion, keeping the BIG4 at abundant levels, with the right infusion of carbon, will undoubtedly lead to enhanced plant performance, greater resilience, and profitability to the grower.
Jim Pingrey is an agronomic consultant in California’s Sacramento Valley.
