NTS Soil Therapy™ is an in-depth soil analysis and nutrition programming service that has been the mainstay of NTS agronomy for the past 18 years. The easy-to-understand Soil Therapy™ reports ensure that growers are able to understand their mineral requirements in relation to balance and there are priority guidelines that can help in budget-related decision making. Until recently, we have offered a Prescription Blend™ service, but this usually involves base materials like lime and gypsum and these are often more cost-effective sourced locally. Now, you are simply advised what will be most productive and encouraged to address any requirements utilising the most cost-effective local materials. There are several key mineral requirements, relationships and soil structure considerations that may help you when deciding upon how best to allocate your nutrition budget. In this article we will consider five of these core understandings.
1) CEC – Understanding Soil Storage
CEC, or Cation Exchange Capacity, is a measurement on your soil test that indicates the amount of clay present in your soil. Clay is negatively charged and it attracts minerals that are positively charged, called cations. Over 70% of the minerals in the soil are cations, so clay is an important storage mechanism that retains these minerals in your soil to sustain plant growth and vitality. The higher the clay component of your soil, the greater the cation retention and the bigger the fuel tank (if we think of plant growth as a mineral fueled, energy system).
The CEC of your soil should also be a major determinant of how much and how often to fertilise. A light sandy soil, for example, has a small fuel tank and this low clay component means this soil can store only small amounts of cations. It is pointless applying any more fertiliser than what can be stored at any one time or you are simply wasting money. These soils really require spoon feeding to achieve their best and they are ideally suited to fertigation where you can easily apply a little, often.
In dryland farming, it is not quite so easy. Here, it is important not to apply too much starter fertiliser. Any ongoing nutrient requirements can be best addressed with side-dressing or foliar fertilising, in situations where the starter cannot be stored in light soils. Leaf testing is important to allow informed decisions but if you have not leaf tested, it is a simple rule of thumb to feed the crop immediately before flowering. This is the business end of the season. You can also look at your soil test to determine likely requirements and apply them as a foliar to ensure everything is in place for a maximum yield. Small amounts can be both cost-effective and very productive. A typical pre-flowering foliar in broadacre crops might involve the following:
Pre-Flowering Foliar Recipe
- 0.5 kg of solubor
- 500 grams of zinc sulfate
- 500 grams of copper sulfate
- 10 – 15 kg of urea
- 150 grams of NTS Fulvic Acid Powder™
- 200 grams Tri-Kelp™ Soluble Kelp Powder
- 150 mL Cloak™ Spray Oil
The best approach here would be to mix the above ingredients in a minimum of 100 litres of water per hectare, beginning with the solubor and then the urea. Fulvic acid and kelp are chelating agents and their presence also ensures the compatability of minerals that might otherwise be problematic. The urea will deliver nitrogen into the leaf in the amine form which is so easily converted to the protein required for seed development. The fulvic acid is a plant growth promoter in itself but it is primarily included to chelate the copper and zinc and increase the uptake of all minerals. Kelp is also a fertiliser in itself and it contains a powerful chelating agent called mannitol which will further increase nutrient uptake. Kelp also contains cytokinins, gibberellins, auxins and betaines which have been shown to promote plant growth and crop health at very low levels.
This combination will cost less than $20.00 (AUD) per hectare and, if these are the minerals required in your soil, you will get a great bang for your buck!
The term “cation exchange capacity” also refers to the fact that an exchange occurs in the root zone whenever a plant root accesses a cation from the clay colloid. The plant may take some calcium, for example, but when it does so, an electrical balancing act is performed. If the plant takes in a positively charged mineral, like calcium, it must release a positively charged mineral to maintain electrical balance. There is no gain in releasing another nutrient so the plant releases the mineral hydrogen, which has no nutritional value. Hydrogen is the acid element that determines the pH of your soil. As the cations (plant food) are removed from the clay colloid and exchanged for hydrogen, your fuel tank is emptied and the acidity of your soil increases. A soil pH of 5.2, for example, reveals clay colloids packed with hydrogen and a minerally deficient soil where the plants are lacking supportive nutrition.
If you have a medium clay soil with a CEC of 20 to 30, then you have much higher storage capacity and less need to spoon feed. As long as the fuel tank is not empty, these soils can deliver nutrition for extended periods. These are the soils that respond well to cation balancing strategies, where we try to achieve a cation balance involving 68% calcium, 12% magnesium, 3 – 5% potassium and less that 1.5% sodium on the clay colloid. The original soil balancing research conducted by Dr William Albrecht applied specifically to these types of soil.
However, we often find that playing the precise numbers game in very heavy soils is not always productive. These soils (with a CEC of 30 to 70) have such a large storage capacity that their need for extra inputs should always be confirmed with a leaf test. For example, if you have 7000 ppm of calcium on your soil test, that can often be enough. Always leaf test to see if the plant is accessing enough calcium before embarking on a liming program that may not be necessary. If the leaf levels of calcium are good there is simply no need to play the numbers game.
2) The Zinc Link – Sizing the Solar Panels
A zinc deficiency can be the most costly of all mineral shortages because zinc is needed for the plant to produce auxins, the hormones that govern leaf size. The leaf is the solar panel that drives photosynthesis. The larger the leaf, the greater the surface area for sunlight, water and CO2 to work their magic and produce the glucose-building blocks that fire the plant. Conversely, a zinc deficiency compromises the most important process on the planet. Little Leaf Disorder in citrus, for example, is a zinc deficiency and it has a major, negative impact upon production.
Broadacre soils in Australia are notoriously zinc deficient and, if a limited budget prevents the correction of the deficit, then a zinc seed treatment can help to ensure delivery of this key mineral for the crop cycle. Zinc seed treatment is simple and inexpensive. It typically involves applying 3 litres of a zinc-based concentrate, diluted with enough water to just coat a tonne of seed. I am obviously biased but I believe that the best option is Zinc-Life™ from NTS. This seed treatment product is based upon a zinc oxide concentrate micronised down to an incredibly small, 0.1 microns. This concentrate contains a whopping 65% zinc along with a range of germination enhancers and seedling kick-starters.
Zinc is also important as an activating synergist for phosphorus. There is a big benefit in trying to achieve the ratio between these two minerals that has proven most productive. The ideal phosphorus to zinc ratio is 10:1 in favour of phosphorus. If you can achieve this ratio then both minerals will deliver their best. The ratio is actually more important than the numbers game. If, for example, your soil test reveals 30 ppm of phosphorus and 3 ppm of zinc then you have the perfect 10:1 ratio. In this case it would be counter productive to increase the levels of either mineral without also increasing the partner mineral to maintain the all-important ratio. In this example a grower might choose to apply a starter fertiliser involving DAP at 250 kg per hectare. Zinc should then be applied at a rate to maintain the desired ratio. This might involve around 10 kg of zinc sulfate per hectare. NTS Agronomists offer free advice to maintain the required precision.
3) Potassium and Magnesium – The Relevance of Ratios
Another key mineral relationship in the soil is the potassium to magnesium ratio. Potassium (K) is a big player in sugar movement and hence it has a big impact upon both the size and flavour of all produce. A potassium shortage in the latter half of the season can be particularly costly, as it will have such a negative impact upon yield. A deficit of potash at this time can sneak up on the unprepared because there is such a draw-down of this mineral during the business-end of the season. If you are monitoring with an Horiba Potassium Meter, you will see K levels plunge from the onset of flowering. This relates to heavy sugar requirements for the sizing of fruit and grain.
Potassium is the most mobile of all minerals and it will often depart the lower leaves to satisfy demand higher up in the plant. Traditional leaf analysis does not necessarily pick up this depletion of K in the lower leaves because we are collecting leaf samples from where the potassium has moved (at the top of the plant). This is where your potassium meter is worth its weight in gold. You simply monitor the lower leaves and the upper leaves and there should never be more than a 10% variation in potassium. If the potassium in the top leaves is substantially higher than that in the lower leaves, then immediate action is required to preserve yield potential. In this instance, the best strategy is to combine the fertigation of potassium sulfate with a foliar involving a pH neutralised, high analysis liquid potassium like K-Rich™ from NTS.
However, sometimes the potassium deficiency is not just related to a K shortage. Magnesium (Mg) is a potassium antagonist when it is oversupplied and this excess can negatively affect potassium uptake. The key is to try to achieve the ideal ratio between these two minerals to sponsor maximum performance of both. In the process of analysing thousands of soil and leaf tests over the past couple of decades we have discovered that if we aim for equal parts per million in the soil of both magnesium and potassium, then we achieve optimum plant uptake of both minerals.
This is obvious in leaf test data, but we discovered another fascinating relationship when comparing soil tests to leaf tests in this context. We found that achieving equal ppm of K and Mg in the soil also increased the plant uptake of phosphate. In fact, in some cases it had more impact upon phosphorus uptake than the actual application of phosphorus. You may be wondering about the mechanics of this relationship. Here’s how it works. Magnesium is a phosphate synergist that supports the uptake of P while potassium is a phosphate antagonist when oversupplied. When we achieve the perfect 1:1 K to Mg ratio, we see perfect uptake of both, and phosphorus uptake is also maximised. It’s a neat trick and it can be very productive.
The one other issue we should address here relates to the best way to address a shortage of magnesium when trying to improve your K:Mg ratio. Many people mistakenly apply magnesium sulfate to the soil to correct a magnesium deficiency and wonder at their lack of long term response from this practice. The reality is that magnesium sulfate is the most leachable form of magnesium. It is what you are trying to create when applying gypsum to improve soil structure. The sulfate component of the gypsum bonds with magnesium and forms magnesium sulfate. The soil tightening effect of excess magnesium subsides as this mineral leaches from the root zone. Why would you apply a mineral to your soil in a form that is certain to leach? Magnesium carbonate is a much better option. Minerals in the carbonate form are stable and do not leach. NTS supplies magnesium carbonate as Nutri-Mag™ Magnesite and this is the most productive way to build magnesium in your soil.
4) The Marvel of Molybdenum – Understanding the Mighty Midget
How could a mineral required in such minuscule amounts deliver such a major outcome? Your soil should contain just 0.5 ppm of molybdenum but, in its absence, there is quite a price to pay.
For a start, you will require more costly nitrogen from a bag because you have limited your access to free nitrogen from the atmosphere. Molybdenum is an essential ingredient in the enzyme, nitrogenase, which is manufactured by nitrogen-fixing organisms to convert gaseous nitrogen in the atmosphere into ammonium nitrogen in the soil. If you maximise your access to free nitrogen you not only reduce production costs and enhance profitability, but you also improve plant health and reduce the need for chemical intervention.
However, there is a second way that molybdenum can reduce chemical use, which is even more exciting. In intensive horticulture, nitrogen is very often over-supplied and usually in the nitrate form. Nitrates always enter the plant with water and this can have a nutrient diluting effect. In fact, it is a rule of thumb that high nitrate levels mean low brix levels (brix is a direct measure of nutrient density) which, in turn, increases the likelihood of insect attack. Insects are the garbage collectors on the planet and if you grow nitrate-packed garbage the rubbish removalists arrive on cue!
Nitrate nitrogen is stored in the leaf until it is converted to protein. This conversion requires another enzyme called the nitrate reductase enzyme. If the plant lacks the building blocks to manufacture this enzyme, then nitrates do not convert to proteins and the pest pressure builds in line with the nitrate accumulation. The chief building block for the nitrate reductase enzyme is molybdenum. Some crops like cucurbits, carrots and beans have a particularly strong requirement for molybdenum, but all crops are dependent on the mighty midget to access the ‘free gift” (atmospheric N) and to convert nitrates to proteins.
Many soil tests do not even measure molybdenum but, when it is tested, it is very often deficient. A famous New Zealand study looked at the benefit of adding small amounts of molybdenum into the fertiliser program when growing canola and lucerne on both light and heavy soils. The researchers recorded yield increases ranging from 38% to over 600% when this missing link was present.
5) The Bounty Of Boron – Much More Than a Calcium Co-Factor
Many growers are now aware of the declaration by American consultant, Gary Zimmer. Gary states that “calcium is the trucker of all minerals but boron is the steering wheel”, in reference to boron as a calcium synergist. There is no doubt about the validity of the claim. I have seen large areas limed to no avail, but for the want of a few kilos of boron. In fact, you have often wasted your hard-earned money if you apply calcium to boron-deficient soils without addressing the boron shortage.
However, boron is a major mineral player in its own right and a shortage can also have a serious impact upon soil life. Boron is critical when a plant is entering the reproductive stage and, as this is the business end of the crop cycle, it can prove costly to ignore the boron connection. Most avocado growers, for example, have learnt their lessons about applying boron before flowering. The avocado tree has a notoriously low fruit to flower ratio. The tree is covered in flowers but only a small percentage become fruit. Boron determines the length of the male pollen tube and thereby offers a substantial increase in fruit set.
There are very few crops that do not benefit from an inexpensive foliar spray of boron before flowering. This typically involves a kilo of Solubor with a kilo of NTS Soluble Humate Granules (pre-dissolved) per hectare. The humic acid increases the uptake of boron by over 30% and it is also something of a fertiliser in itself. Boron-deficient grain will struggle to fill the head or cob and is often mistaken for poor pollination. Boron is a mineral that we like to see in luxury levels on a leaf test, but this is a rarity. There are several reasons for such widespread boron deficiency ranging from neglect and mineral mismanagement to low levels of humus in the soil.
Boron is a negatively charged mineral, called an anion, and the only storage system for this mineral in the soil is the positively charged humus colloid. Humus levels globally are only one third of what they were a few decades ago and consequently the capacity to store and retain humus has been seriously compromised. One way around this problem is to apply your boron in a pre-stabilised, non-leachable form. NTS Stabilised Boron Granules™ will hold your boron in the root zone without leaching. Humic acid features multiple positively-charged sites to which boron can attach. In this case you get the best of both worlds – non-leachable boron, along with the root boosting, soil-life promoting, flower enhancing, soil cleansing benefits of humic acid.
Boron can also impact soil life. Sugars accumulate in the chloroplasts (the sugar factories) before half of them are translocated down to the roots each day. 60% of this half is exuded from the roots to feed and promote beneficial microorganisms (30% of total glucose production). Both the plant and the microbes understand this “give and you will receive” deal and there are multiple benefits on both sides. The translocation of the sugars from the leaves to the roots is controlled by a trapdoor that opens in the late afternoon to facilitate the transfer. The optimum functioning of this trapdoor is determined by boron. An advanced boron deficiency can lock the gates and, as a result, the soil life goes hungry. In this instance, a couple of dollars worth of foliar-sprayed boron can be the difference between a fully functioning soil foodweb and a hungry, unproductive microbe workforce. Micronutrients can be a costly oversight when neglected!