In this final Soil Therapy™ article, we will look at three trace minerals that are so often neglected by soil labs and consultants around the globe – molybdenum, cobalt and selenium. We remove a little of every mineral with each crop and it is common sense that replacement is an essential component of a regenerative recovery. We analyse soil tests from all over the world, and it is not surprising to find deficiencies of this trio in the majority of soils tested. Let's look at what this neglect might mean.
Molybdenum (Mo) - Unlocking a Sky Full of N
Nitrogen (N) is the most abundant mineral in the plant and there is no coincidence that an abundance of N surrounds us. 78% of the air we breathe is nitrogen, and this is effectively a "free gift" that can provide a great deal of our N requirements. However, the conversion of gaseous N into ammonium nitrogen in the soil requires support. A key is required to unlock this bounty, and that mineral catalyst is molybdenum.
Throughout this series we have seen the interplay of minerals, determining their effectiveness. Typically, that interplay is also impacted by microorganisms in their role as the bridge between the soil and the plant. Molybdenum and cobalt are both required to source nitrogen from the sky, but they do so in partnership with soil microorganisms. Once again, we recognise the inextricable interrelationship between minerals, microbes and humus, that we call "Nutrition Farming®".
Molybdenum (along with iron) is a core component of the enzyme nitrogenase. This is the all-important enzyme that facilitates the conversion of nitrogen gas into ammonium nitrogen in the soil. Our access to the 74,000 tonnes of nitrogen that hovers above every hectare is molybdenum-dependant.
Molybdenum is equally important when it comes to the conversion of nitrate nitrogen in the leaf through to more desirable proteins. The nitrate reductase enzyme triggers the first stage of this conversion and it is also made with molybdenum.
There are three other molybdenum-based enzymes, which are all involved in various forms of stress resistance. A crop lacking in molybdenum will also lack resilience. One of these three enzymes, aldehyde oxidase, is required for the formation of a plant hormone called abscisic acid (ABA). This hormone is involved in responses to both biotic and abiotic stress. Another of this trio, sulfite oxidase, triggers the conversion of toxic sulfites, from sulfur dioxide and amino acid decomposition, into sulfates, which serve as plant food.
Molybdenum increases in availability at a higher pH. Plant deficiencies are thus more likely in acidic soils.
Molybdenum is an anion that stores in humus. Just as the storage of boron and sulfur have suffered as a result of declining humus levels, molybdenum is similarly affected.
Excesses of major anions like phosphorus and sulfate sulfur can seriously impact molybdenum availability. If you are one of the many who have over applied DAP/MAP or gypsum, then consider countering that antagonistic effect with a molybdenum foliar.
Plants lacking molybdenum reveal symptoms of nitrogen deficiency, stunted growth and chlorosis in young leaves. When the deficiency is serious, the associated high nitrate component in the leaf can also lead to marginal chlorosis and necrosis on mature leaves.
Molybdenum deficiency is widespread on legumes, cauliflower and maize grown in acid soils, particularly those with high iron levels. Part of the big response seen when liming legumes comes from the increased alkalinity stimulating Mo uptake.
As I have mentioned previously, there is a powerful link between crop resilience and the balance of the two forms of nitrogen within the plant. The ratio between ammonium nitrogen and nitrate nitrogen in the leaf should be 3:1, and this ratio is an underrated player in plant resistance to pest and disease. High nitrates spell a weak, watery, flavorless plant that becomes a calling card for marauding insects. You will never achieve desirable levels of ammonium nitrogen in the plant if you have neglected the molybdenum key. The “free gift” from the atmosphere becomes the ammonium nitrogen that ensures this protective resilience ratio.
Just as protein primes the immune pump in animals and humans, plant immunity is also driven by protein. This is why it is critically important that we provide the tools to convert nitrate nitrogen to protein. When oversupplied in our food, the nitrate excess is damaging to our health. Nitrites reduce the capacity of our blood to carry oxygen and the subsequent oxygen starvation has been linked to cancer in over 200 studies. Molybdenum is effectively a dual-edged sword in relation to resilience. It helps achieve and sustain the protective 3:1 ammonium to nitrate nitrogen ratio while reducing destructive nitrate nitrogen accumulation in the leaf.
In our Soil Therapy™ reports, we like to see a minimum of 0.5 ppm of molybdenum. We find that over 80% of the soils we analyse around the globe are lacking this base requirement. Molybdenum is constantly removed from the soil with cropping, and requirements become higher as we pump our crops with nitrogen. Declining humus levels become a secondary stressor and as a result most soils would benefit from a little molybdenum. That small addition might be in the form of a seed treatment, liquid injection, a foliar, fertigation or as a dry fertiliser additive.
In a famous NZ study conducted in the South Island with two crops on two different soil types, the addition of a cup of sodium molybdate (250 grams) per hectare to the standard superphosphate fertiliser resulted in yield increases ranging from 38% to over 600%. The supply of atmospheric nitrogen to N-deficient plants is the only possible explanation of these phenomenal results.
There are several things that impact molybdenum availability and uptake, including the following:
Light, sandy, low humus soils will often be molybdenum deficient, as will acidic, high iron soils.
It is always advisable to apply molybdenum with humic acid to create a stable complex that resists leaching.
The foliar route is most efficient, so NTS products like Nutri-Key Shuttle Seven™ become effective correctives. Nutri-Key Moly Shuttle™ can also be used as a foliar.
Seed treatment with molybdenum can be particularly effective and inexpensive.
Sodium molybdate featuring 39% molybdenum, is the most readily available form of molybdenum. It can be foliar applied at 70 – 150 grams per hectare, fertigated at 300 grams per hectare or broadcast (in a blend) at 0.5-1 kg per hectare. Note: Always combine sodium molybdate with humic or fulvic acid.
Some crops are particularly molybdenum hungry, for example, cucurbits, legumes and carrots. Most producers of these crops have recognised this requirement and hence, foods like squash and green beans are considered to be good molybdenum supplements for humans.
Molybdenum, if oversupplied on animal forage, can antagonise copper uptake and create copper deficiency in livestock. If you have overstepped the mark in this fashion, the best strategy is to apply gypsum to antagonise molybdenum uptake, and thus reduce the Mo concentration in your crop to non toxic levels.
Cobalt (Co) - Mother’s Milk for N-Fixers
We have discussed the fascinating interplay between minerals, but a second essential component of the Nutrition Farming® philosophy involves the nurturing of important microbial relationships in the soil. Underpinning and supporting this mineral/microbe dance is humus, the single most important determinant of profitability and farming fun.
When we consider the role of cobalt, we need to think in terms of microbial support and relationship building.
One of the most important microbial relationships in the soil is that between Azotobacter and mycorrhizal fungi. Here's how these organisms support each other: Azotobacter need a constant supply of plant-available phosphate to create ATP (adenosine tri-phosphate), the battery that powers the enzyme needed to fix nitrogen. These nitrogen fixers congregate in the midst of mycorrhizal hyphae to access the phosphate that is constantly mobilised by the acidic exudates of the fungi. In turn, mycorrhizal fungi need a constant supply of supplemental N to build the protein involved in their massive networks of hyphae. It is often suggested that if we can foster this relationship, then the soil is humming and we will be smiling at the end of the season. If we are introducing Azotobacter via NTS products – like Nutri-Life Bio-N™ or Nutri-Life Bio-Plex™, in conjunction with a mycorrhizal inoculum like Nutri-Life Platform® – then we had better ensure that cobalt is present to ensure a successful union.
Trace minerals can never be ignored if you are seeking to reduce problems, because they are invariably part of key enzymes involved in resilience. Cobalt is no exception, as you will see when we consider the roles of this micronutrient.
Cobalt is required by all nitrogen fixing organisms and it is often missing in our soils.
Three necessary enzymes are cobalt-dependent. These include methionine synthase, which is integral to healthy protein production. Ribonucleotide reductase is needed for DNA synthesis. Finally, methylmalonyl coenzyme A mutase is required to produce the iron-based substance in rhizobium called "heme". This blood-like substance is essential for nitrogen fixation. When you pinch a healthy legume nodule, the red colour indicates nitrogen fixing potential based on sufficient cobalt.
Cobalt is the building block for the coenzyme, cobalamin (vitamin B12), an essential nutrient for microbes, plants, animals and humans.
B12 deficiency is common in livestock and humans but livestock are much more widely supplemented than us. Lethargy is a common symptom of B12 deficiency in people.
Cobalt is a cation that is difficult to source as a fertiliser. Cobalt sulfate is the most common soluble form of this mineral, but it is dangerous to handle in concentrated form and hence rarely available for purchase.
Products like Nutri-Key Shuttle Seven™ can be used to provide cobalt on a crop-by-crop basis.
In our Soil Therapy™ reports, we aim for a minimum of 2 ppm of cobalt in the soil. Around half of the soils we test do not contain that minimum requirement.
We can add cobalt sulfate to our Prescription Blends to build soil levels, but more commonly, we suggest that the mineral be provided in fertigation or foliar applications, preferably early in the season.
Seed treatment for legumes is both productive and cost-effective. However, a study of peanuts, conducted by Petra Marschner, demonstrated that the best response was achieved with a combination of a seed treatment and two foliar sprays of cobalt. In fact, in this research, this combination increased the number of nodules by almost 90% and it increased the legume yield by over 50%.
If you are a livestock producer, you are probably already supplementing with cobalt, B12, or both, because you understand the multiple benefits (including rumen health). However, it is always a good strategy to get these nutrients into the pasture, where they are far more bioavailable. Nutrients in the pasture are 98% bioavailable. The pasture contains all of the cofactors that support and magnify the utilisation of each particular nutrient. That is why it is far better to get your own nutrition from your food rather than the supplement shelf.
In ruminants, cobalt affects fertility, cellular longevity and the absorption of fats and carbohydrates. There are recent suggestions that this micronutrient may be a key player in preventing ketosis and Johne’s disease.
Selenium (Se) - Managing the Missing Mineral
Australian and NZ soils are second to the African continent in terms of selenium deficiency. We are one of the few companies that regularly test for the mineral and it is almost always missing in action. Livestock producers have supplemented with selenium for decades in recognition of links to problems like White Muscle disease. However, we have neglected the rest of the food chain and, consequently, most of us are selenium deficient. Hopefully the advance of Nutrition Farming® will help to address that serious oversight.
Selenium is required to produce glutathione peroxidase, the most powerful enzyme protection system in animals and humans. It is also considered the single most important mineral for our most important organ, the liver.
Recent research has revealed a selenium link to plant resilience and yield. In one Finnish study, a potato crop supplied with three foliar sprays of selenium at 250 ppm concentration, delivered a 31% increase in net tuber weight. When asked to explain the phenomenon, the scientists attributed the exceptional response to reduced photo oxidative stress. This might sound like science jargon, but it is actually quite simple to understand. Ask yourself how a plant can withstand UV radiation for 12 hours a day, when every other life form suffers free radical damage from persistent sun exposure. How does the plant protect itself? Well, the Finnish researchers discovered that, just like animals and humans, the plant uses glutathione peroxidase to protect itself. When that enzyme system is supported with selenium, the plant suffers less photo (sunlight), oxidative (UV damage) stress. As a result, energy that might have been required to drive alternate protective mechanisms is now available for production (hence the yield increase). This exciting finding is part of a group of new studies suggesting that selenium should not be overlooked in any nutrition program.
In multiple studies, selenium has been shown to help counter abiotic stress events like cold, drought, floods and salinity.
A new body of research suggests that selenium is also an invaluable tool to help counter heavy metal stress. This mineral reduces both the uptake and translocation of heavy metals.
Selenium regulates antioxidant activity in plants to boost plant resilience.
The improved recovery from environmental stress associated with selenium is really quite profound. Recovery from stress is fast-tracked through the rebuilding of the cell membrane and chloroplast structures, as well as recovery of the damaged photosynthetic system.
Very small amounts of this mineral are required for animals and humans. The ideal rate for humans is just 200 micrograms per day, but most of us should be supplementing at this rate on a daily basis. Selenium deficiency is almost universal in our part of the world, unless you are supplementing.
Brazil nuts are the highest natural source of selenium and they are a better option than supplements. Once again, the food source features the supporting cofactors that improve uptake of this mineral. The most important of these supporters is Vitamin E, which is found in luxury levels in Brazil nuts.
Kelp is the highest natural source of selenium for plants, particularly when applied as a foliar. However, kelp does not contain anything like the 250 ppm that enhanced yield in the Finnish study.
We are seeking 0.6 – 2 ppm on our Soil Therapy™ reports, but we almost never encounter anything close. Again, it is no surprise. We have had decades of crop extraction, with no replacement, in Australian soils that began life with low selenium.
Kelp and fish fertilisers deliver a little selenium because the ocean still contains this anion, but the research world is delivering a plethora of studies suggesting bigger gains through serious selenium supplementation with purpose-built foliar fertilisers.
Our largest selling fertiliser, Triple Ten™, is one of the very first fertilisers in the world with a formula featuring 198 mg/L of selenium. It is one of several reasons that Triple Ten™ is such a special, total cover, liquid fertiliser.
Some crops are selenium accumulators. All brassicas fall into this category and this is one of the reasons that broccoli and kale are so beneficial to our health. Garlic is also a selenium accumulator. There is a considerable marketing opportunity to boost the selenium component of garlic with foliar sprays of Triple Ten™ and to then market your high-selenium, medicinal garlic accordingly.
Selenium and sulfur compete within the plant, so high gypsum applications can affect the uptake of selenium. This is one of the reasons we limit single applications of gypsum to just one tonne per acre (2.5 tonnes per hectare).
This concludes this eight-part series. It might prove productive to print out all eight parts from blog.nutri-tech.com.au, so that you can regularly refresh your memory as to how you can use nutrition to boost your production, reduce your problems and increase the pleasure factor in your farming.
To go back to Part 1 of this feature, please click here.