Phosphate Facts – How to Stabilise P and Free Your Frozen Reserves (Part 1)

Imagine buying a new tractor and discovering six weeks later that it had lost 73% of its value. Contemplate your sense of loss, if weather extremes decimated 3/4 of your cash crop. There is a major investment made by many of us each year, where we actually receive just 27% of what we paid for. You would assume an outcry, farmers screaming, “scam!”, and demanding compensation.The industry that delivers this pitiful investment openly acknowledges these issues, but most of us remain unaware of our losses, or just adopt apathy and passively accept the inevitable.

DAP and MAP rank as Australia’s leading fertiliser investments. Most broadacre and horticultural enterprises will dutifully apply these granules each season, despite their amazing inefficiency. Within 6 weeks of application, over 75% of this soluble phosphate is lost. In fact, the CSIRO estimate that ten billion dollars of applied phosphate now lies locked up in farming soils. How does most of what you apply become part of this massive, frozen reserve. Here’s how it works:

All minerals can create bonds with other minerals due to their respective positive and negative charges, i.e., the positively charged cations are attracted to the negatively charged anions, like a nail to a magnet. The strength of the bond is related to the number of positive or negative charges involved. The mineral with the most negative charges is phosphorus. It has three charges, and this means it is strongly attracted to cations with two or more charges. Unfortunately, when it bonds to these cations, it becomes insoluble and no longer available to the plant.

There is a pH link to this phenomenon. In soils with a pH above 6.4, the most likely casualties of this pairing will be calcium and phosphorus. Hence, in the majority of our farming soils, both calcium and phosphorus are sidelined in this fashion. The resulting, insoluble tri-calcium phosphate effectively means that both partners in the pairing are removed from service. This is not a great outcome because calcium and phosphorus are two of the most important minerals for the most important process on the planet, photosynthesis.

In more acidic soils the triple negative P binds with minerals like iron, manganese and aluminium. Red soils derive their colour through a large load of iron oxide. Anyone farming these soils will know about the challenges of keeping P plant-available. Iron often has a triple positive charge so it is three on three, and the insoluble iron phosphate created is very difficult to break apart.

Is there a way we can minimise this 77% loss and a strategy where we can reclaim some of this frozen bank account? We shall discuss each of these issues separately.

Selecting Your P Source and Stabilising Your Investment

The first step in improving phosphorus management is choosing the most suitable phosphate fertiliser for your situation. If you are dealing with a 100-day crop, where you need an immediate phosphate hit, along with some nitrogen to kickstart root growth and vigour, then DAP/MAP has a role. You need to learn to buffer the acid burn and counter the lockup, but both are possible.

If your enterprise involves pastures, orchards or vine crops, there is little argument for the water soluble, super unstable P options. You are much better off using a slower release P source like Soft Rock, guano or reactive rock phosphate. These materials may take a few weeks to kick-in, but that time is your luxury. If you need available phosphate for a spring flush, then apply the slower release inputs six weeks beforehand. There is a fascinating USDA study, where a water soluble input was compared to a rock phosphate in order to compare P release over a 13 year period. The study involved Triple Super Phosphate compared to rock phosphate, with the same number of kg of actual P involved per hectare. In the first year, the Triple Super released more P, but in the subsequent 12 years, the rock phosphate released an average of 9.5 times more phosphate each and every year. Sometimes, it is much better to take a long term position.

Beating the Burn

The other major problem with water soluble phosphate is the extreme burning potential of phosphoric acid. Phosphorus is a scalding hot mineral. Think of a phosphorus torch. DAP and MAP consist of phosphoric acid, which has been buffered, by tagging the more alkaline ammonium ion. The problem is that the single charged ammonium ionises from its triple charged partner, quite soon after arrival in the root zone. Now we have raw phosphoric acid scorching all before it.

Many will be familiar with the evidence of acid burn on the roots of young crops. However, there is something, as sinister, but less visible happening beneath your crop. Mycorrhizal fungi are of immense value in your soil. They are effectively a massive root extension involving a network of fungal filaments, attached to your roots. These filaments increase root surface area tenfold, so everything the roots are offering is multiplied many times. This fine, tubular tag-on is not visible to the naked eye, so unlike other benefactors, like bees and earthworms, we are not as aware of its demise.

mycorrhizal fungi

Mycorrhizal fungi on roots

This hyphal root extension offers greater access to nutrients and moisture, while constantly releasing supportive biochemicals to nurture its host. Root knot nematodes are unable to coexist on a plant colonised by mycorrhizal fungi (AMF). The hyphae also release mild acid exudates, which break the bond between locked up calcium and phosphorus, and then transport the escapees to the plant. The least mobile of all minerals are phosphorus and zinc. They do not go into soil solution, but sit wherever they end up, and must be retrieved by the roots. This fungal extension allows much greater access to both of these energy essentials. In some soils, potassium can become trapped in clay platelets. It is the filling in a clay sandwich that only becomes available to your crop when potassium has been topped up to the point that it is virtually oozing from that clay confinement. This can be a costly affair, when it involves the most expensive major mineral. Your mycorrhizal workforce features filaments fine enough to drive between that sandwich and mine the contents. Many studies have chronicled an increase in plant-available potassium in these particular soil types.

Finally, AMF produce a sticky, carbon-based substance called glomalin. It is now understood that glomalin is the triggering mechanism for humus building in your soil. In fact, 30% of all organic matter is created by the stimulatory power of this remarkable substance. The problem is that we have lost 90% of our AMF, in the farmed soils across the globe. They have been collateral damage, in an industrial extractive approach where we have sliced and diced with excessive cultivation and poisoned them with fungicides, herbicides and nematicides. However, it has been recently determined that a major contributor to the demise of AMF, is the use of unbuffered DAP and MAP. When these fertilisers ionize, the raw phosphoric acid sizzles these micro-fine hyphae, like putting a blowtorch to human hair.

The good news is that you can repopulate with mycorrhizal inoculums quite inexpensively (Nutri-Life Platform® from NTS is my obvious favorite), but what is the point if you plan to sizzle up your new workforce at the first opportunity? Is there a way to buffer the burn, and protect your new workforce? The answer is a most definite “yes!”

Harness Humates to Soften the Sizzle

Humic acid has moved from an “alternative” curiosity to become a mainstream marvel in the past decade. Most growers are now aware that this carbon-dense extract from ancient organic matter can provide multi-leveled support for the soil, the crop and your soil life. Humic acid improves soil structure through multiple biological and physical processes. With a CEC of 450, it has obvious mineral retaining benefits, particularly in a sandy soil with a CEC of 5. Humic acid chelates cations to increase plant availability. It complexes anions, like phosphorus, boron and sulfur to reduce lockups and leaching. It is also a great tool to buffer salt and acid extremes, and it is a powerhouse biostimulant. Humic acid increases the sustainability of DAP/MAP and Super Phosphate in several ways including:

1) Buffer the burn - Humic acid is a carbon-dense protector that can neutralise the destructive impact of phosphoric acid on both the roots and the attached AMF. NTS Soluble Humate Granules™ can be combined with granular acid phosphate at the rate of 5 kg per 100 kg to buffer the burning.

2) Activate the AMF - humic acid is the most powerful, known fungal stimulant, so you will be both protecting and stimulating your beneficial fungi, including AMF and Trichoderma (both found in Nutri-Life Platform®). All fungal inoculums should be combined with humic acid as a “lunchbox” for the new workforce. This practice has been shown to maximise colonisation and performance.

nts soluble humate granules and nutri-life platform

3) Alleviate the lockups - the big benefit from combining 5% humic acid with acid soluble phosphate fertilisers relates to the stabilisation of unstable P. When the NTS Soluble Humate Granules™ dissolve at the same rate as the granular phosphate, there is an immediate formation of a phosphate humate. This stable compound will make P available for the full crop cycle (vs locking up within 6 weeks). Now, your expensive investment will not become insoluble calcium phosphate, iron phosphate or aluminium phosphate. While phosphate is critical for early root growth, there is actually 120% more requirement for P when you reach the business end of the season (after flowering). Observe the difference that full season, P availability can make to your bottom line.

4) Magnify the P response - Humic acid is well researched in relation to a phenomenon called cell sensitisation. Here the permeability of the cell membrane is increased to allow uptake of 30 – 34% more nutrition. Both humic acid and fulvic acid can trigger this increased uptake.

4) Stimulate the soil-life - most agricultural soils are lacking beneficial fungi. The loss of their protective potential is a big price to pay, but there is something else they offer of equal importance. One of the prime requirements for a healthy productive soil is good management of gas exchange. This relates to how well your soil breathes. How easily does oxygen, the most important of all elements, enter your soil. How freely does the byproduct of oxygen metabolism, CO2, exit the soil, to be sucked up by the plant for photosynthesis. The better you manage this soil breath capacity, the better you do. Beneficial fungi create the soil aggregates (crumb structure) around the roots that improve gas exchange. When you combine humic acid granules with your granulated phosphate, you have introduced the most powerful known fungal stimulant right into your root zone. The subsequent aggregation and associated oxygen can be of much benefit.

5) Do all of this free-of-charge - we have found that the inclusion of NTS Soluble Humate Granules™, with your phosphate fertilisers, with all of the potential benefits described above, can essentially be achieved at no extra cost. Due to the increased uptake and stability, you can safely reduce your DAP/MAP inputs to the value of the humate inclusion. For example, if you are using 100 kg of DAP per hectare in broadacre scenarios, you can include 5 kg of NTS Soluble Humate Granules™ and reduce you DAP by 10 or 15 kg to pay for this inclusion. Trial a paddock and you will understand. It is rare to see a grower, whom has combined DAP and humates, ever return to using unbuffered, unstable, acid phosphate.

In Part 2 of this article we will look at a range of productive strategies to unlock your frozen reserves.

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