The Phosphate Equation
 

By Graeme Sait

 

The unparalleled, 100% price increase in DAP/MAP in just a few short months has generated shock waves throughout agriculture, as reality bites and growers begin to understand that peak oil means peak prices. Prices for urea, pesticides and diesel have also risen considerably but it is a special set of circumstances that is responsible for the massive blow-out in prices for the world’s largest selling fertilisers, DAP and MAP. Key contributors include a 400% increase in raw material costs combined with reduced manufacturing plants (linked to rationalisation) and huge demand due to the US ethanol boom. Energy price hikes have also contributed to the blow-out. The upside of this dramatic increase in production costs is that many growers are now forced to re-evaluate the efficiency and cost effectiveness of their phosphate fertilising. In doing so, many have realised that unstable, acid-treated phosphate, where up to 70% may be lost to lock-ups, was dubious value at $650 (AU) per tonne but it is an extremely poor investment at double that price. Let’s look more closely at the phosphate investment in crop production - let’s look at how this mineral works in the soil and in the plant, how we can increase the efficiency of phosphate fertilisers and how we can reduce costs without loss of production.

 

When P Runs Out of Puff

The inherent problem with soluble phosphate fertilisers is that they are incapable of delivering what they promise. They are soluble phosphate concentrates which theoretically reduce transport costs in comparison to rock phosphate but their high octane potential is not matched by their performance. Phosphate is a triple negatively charged anion which means that it is strongly attracted to positively charged cations like calcium, iron and aluminium. The fact is that when P forms a bond with these other minerals it becomes insoluble and is no longer available to the plant. This “lock-up” can begin to occur within hours of application but it is generally agreed that most of your DAP/MAP is tied up within six weeks. This costly phenomenon has been largely accepted by a farming fraternity conditioned to think that phosphate is chiefly required for early root establishment. Why complain when you achieved the promised kick-start? What is not understood is that there is actually a much higher demand for phosphate during the critical reproductive stage than during the initial vegetative phase. In fact there is twice the need for phosphate during the flowering and fruit/seed filling period and this is usually when your P has run out of puff. How can we prevent this lock-up and its obvious effect upon our production potential? The answer lies in three strategies. We must stabilise soluble phosphate, combine soluble with slow release forms and stimulate the release of our massive frozen phosphate reserves in the soil (estimated to be worth over 10 billion dollars (AU) by the CSIRO).

 

Protecting Your P Investment

In soils with a pH over 6.4, soluble phosphate combines with calcium and reverts to its parent material, i.e. it becomes insoluble tri-calcium phosphate or rock phosphate. Unfortunately it is now more insoluble than standard rock phosphate, so the trade off for a kick-start becomes questionable. There was some fascinating research conducted by the US Agriculture Department several years ago, investigating the release patterns of rock phosphate v’s triple super phosphate. The study revealed a staggering difference in the P release capacity of the two materials. Although the triple super completely outperformed the rock phosphate in the first year, the reactive rock stormed back and achieved over 400% more P release over the following 11 years of the study (see chart on page 2).



 

The secret to protecting your P investment is to stabilise your DAP/MAP to prevent it from combining with other minerals and becoming insoluble. This involves the use of humates - the multifunction marvel that has become the keystone of the biological revolution over the past decade. When a small percentage of soluble humate granules are combined with acid phosphate granules the two granules dissolve at similar rates and a phosphate humate is formed. If this occurs prior to the inevitable lock-up with calcium or iron then you have stabilised your P and helped to ensure full season phosphate availability.

This strategy is proving increasingly popular around the globe and it is particularly appealing in light of several research papers demonstrating the cell sensitising capacity of humates. Cell sensitisation involves an increase in the permeability of the cell membrane of treated plants to increase nutrient uptake by up to 30%. In theory, this means that fertiliser efficiency can be increased by 30% with the combination of soluble humates. Certainly it is a safe bet to cover the cost of the humate inclusion by dropping the equivalent value in DAP or MAP and you will always do better, i.e. if you were using 150 kg of DAP, for example, then you would include 7 kg of NTS Soluble Humate Granules™ at a cost of around $23 (AU) and reduce your DAP by 12 kg to cover the cost of the humate inclusion. 7 kg of Humate Granules™ is equivalent to 40 litres of 12% humic acid and this input applied directly into the root zone offers much more than just phosphate stabilisation. Humic acid is both a plant growth promoter and a powerful soil-life promotant and it is this biological promotion which is the key to releasing your frozen reserves of phosphate.

 

Unlocking the Frozen Bank Account

If you assume that some 70% of everything you have ever spent on phosphate is lying in a frozen bank account in your soil then there is considerable motivation to find the key to that reserve. This quest becomes even more urgent when you realise that your original investment has now more than doubled in value. You don’t need to assume the existence of this phosphate mother lode because now you can test for it. A test monitoring total P reserves will show you how much you have to work with. If you have a light sandy soil you may not have retained sufficient phosphate to have accumulated much of a reserve to release, but it is not unusual to see a standard phosphate reading of 30 ppm and a total phosphate reading of 1500 ppm in a heavier soil. Red soils are notorious for their P-fixing capacity as it is iron oxide that creates the red colour and acid phosphate fertilisers begin converting to insoluble iron phosphate days after leaving the bag. So how do we reclaim this insoluble reserve? It’s all about soil biology and the promotion of certain species that specialise in phosphate solubilisation. These creatures include all of the beneficial fungi and several species of bacteria.

 

Fungi and Phosphate

Soil-life analysis throughout Australia and beyond has revealed that modern farming methods have decimated populations of beneficial fungi in our soils. This includes mycorrhizal fungi who burrow into the plant roots and then grow masses of fragile, pipelike extensions which effectively serve to increase root surface area by over 1000%. It also includes saprophytic fungi whose chief role is to digest cellulose and convert crop residues into precious organic carbon. The latter may well become the most important species on the planet as climate change bites and scientists finally recognise that the only way we can reverse the accumulation of CO2 in the atmosphere is to return it to the soil as organic carbon (humus). Cellulose-digesting fungi produce a very stable form of humus which is exactly what is desperately required if we are to avert a climate change calamity. Fungi continuously release organic acids which solubilise locked-up soil phosphate in much the same way that the more harsh sulphuric and phosphoric acids are used to solubilise rock phosphate in the manufacture of super phosphate, DAP and MAP. The chief difference is that the organic acids continue to generate a trickle feed of plant-available phosphate, on a daily basis, while single applications of the soluble phosphate concentrates continue their reversion to the insoluble form with each passing day. Ironically, the man-made phosphate fertilisers are major culprits in the decline of beneficial fungi in our soils. They were intended to improve phosphate nutrition but have often served to compromise natural biological recycling. This phenomenon can actually be observed by the grower by inspecting the plant roots and checking for the presence of a visible fuzzy coating on each root. Unbuffered DAP and MAP can often burn off this fuzz, producing a clean white root that can no longer recycle phosphate. This is a huge sacrifice because you are now dependent upon P from a bag and like the junkie craving his chemical fix, your plants have effectively become addicted to expensive, applied fertiliser.

 

Learn to Love the Fuzz

The rhizosphere is the zone immediately surrounding the plant roots where all the biological action happens. The plant is constantly dumping 30% of its total sugar production into this zone to feed the workforce which delivers its minerals, fixes nitrogen, protects from disease and solubilises (recycles) locked-up phosphorus. It’s not hard to understand that this is a zone that should be protected at all costs if we are to minimise toxic rescue chemicals and reduce fertiliser requirements. Any military strategist knows that to target a country’s industrial precinct is to cripple that country’s economy. The root zone can be thought of as the equivalent to the plant’s industrial centre but it is not a warring opponent who is doing the damage but the very farmer charged with nutrition management. DAP and MAP are essentially phosphoric acid with an ammonium ion attached to reduce the acidity. However, the ammonium phosphate ionises apart in the soil and the root zone is subjected to the burning power of raw phosphoric acid. New US research suggests that this burning effect is a major reason for the decimation of mycorrhizal fungi in our soils but other soil life players can be similarly affected. Many growers have noticed the difference in nodulation in legumes grown with DAP v’s legumes started with a natural phosphate like guano. They are literally witnessing the difference between support and assault. Nitrogen-fixing bacteria can be compromised by phosphate burn as can protective species and phosphate solubilising organisms. The fuzz which forms on the roots of most cereal, vegetable and pasture crops is a direct indicator of the heath and productivity of the root zone and can be negatively affected by all harsh acidic inputs including nitric acid, chlorine, sulphuric acid and of course phosphoric acid.

One of the key benefits of adding humates to any of these acid fertilisers is to buffer the damage potential and to protect both the roots and the microbe workforce. “Learn to love the fuzz” is not a police PR slogan lifted from the flower power 60’s but rather a call to action for growers to begin to work with nature rather than against her in 21st century agriculture.

 

Legumes, Fulvic Acid and Phosphate

Green manure legume crops are a proven tool to release locked up P or to speed the release of applied rock phosphate. Legumes produce acid exudates which help solubilise insoluble phosphate. When worked into the soil they also promote phosphate solubilising organisms to further boost phosphate release. Lupins are a favourite of mine. Recent NZ research revealed increases of up to 20% in phosphate uptake and yield when a lupin crop preceded a maize crop on a field fertilised with varying rates of rock phosphate.

The ratio of clover to grasses plays a big role in pasture productivity. When clovers decline so does production. Fulvic acid has a big role to play in helping to improve the clover component while also directly assisting phosphate release in its own right. Fulvic acid can promote phosphate release at low application rates. There are several papers quantifying this capacity in Professor William Jackson’s famous book on humates called “Organic Soil Conditioning”.

NTS Soluble Fulvic Acid Powder™ can be productive at just 500 g per hectare. This rate of application can also have a direct and profound promotion of clover growth and germination. We often receive feedback about pastures that sprout swards of clover following fulvic acid applications. The most recent report came from NSW pecan grower, Geoff Bugden, who sent photos of the amazing clover explosion in his inter-rows following a fulvic spray (see photo on page 4).

Introducing a P Recovery Team

There are various organisms capable of phosphate solubilisation. Mycorrhizal fungi, for example, can be introduced at planting using Nutri-Life VAM-Tech™ as a seed or seedling treatment or these spores can be combined with compost tea or specialist inoculums like Nutri-Life 4/20™. These fungi burrow into the root and then begin a powerful symbiotic relationship where they deliver a constant flow of phosphate to the plant in return for glucose and other plant exudates.

Soil bacteria including several Bacillus species can also be introduced to unfreeze the frozen P reserves. Nutri-Life Bio P™ is a liquid concentrate which includes these phosphate solubilising specialists. This product is simply applied via fertigation or boom spray at just one litre per hectare. It has proven particularly valuable in red soils where locked up P abounds.

Nutri-Life 4/20™ is one of Australia’s largest selling inoculates and part of the reason for this product’s popularity is the five species of phosphate solubilising organisms that are present in this blend. This product must be brewed for 24 hours but it can achieve significant P supply for as little as $10 (AU) per hectare. This becomes a very appealing proposition in the face of the recent price hikes for acid phosphate fertilisers. However, an equally attractive strategy to secure an inexpensive supply of P is to introduce cellulose-digesting fungi to your soils to speed the digestion of crop residues.

 

Turning Residues Into Riches

The analysis of soil-life is a monitoring strategy which has been widely adopted by the biological farming movement. The shortage of beneficial fungi in conventionally farmed soils is a common test finding. These creatures seem far more susceptible to modern rescue chemistry than their brothers in arms, the beneficial bacteria. The loss of this soil life has far reaching implications. In fact, it could be argued that cellulose-digesting fungi, the species charged with converting crop residues into soil carbon, are the single most important life form on the planet at this particular time. Certainly they may prove of profound importance to farmers, who will eventually be paid carbon credits for sequestering carbon in the soil utilising these creatures.

There are two types of humus, active humus and stable humus, and it is the stable form which offers the long term carbon sequestration in the soil that is so desperately needed. The creation of stable humus involves a process where fungi wrap together particles of organic matter and clay to form a clay/humus colloid which remains in the soil for many years. There is a tremendous opportunity, in any situation where crop residues are available for decomposition, to introduce “the missing link”(cellulose digesting fungi) and build soil carbon while improving poor fungi to bacteria ratios in the process. This might involve stubble in broadacre crops but it could equally involve the fallen leaves from deciduous orchard crops or the root matter from harvested vegetables. Inoculums of cellulose digestors, like the NTS product Nutri-Life Accelerate™, can offer benefits beyond carbon building. These inoculums often involve species like Trichoderma, which improve the ratio of beneficial to non-beneficial organisms and release plant growth promoting compounds while they convert residues into carbon riches. They are very inexpensive and they can also serve to help release locked up phosphorus in the soil. These creatures really expand in numbers when they have abundant food available and now your soil contains trillions of creatures who are constantly releasing organic acids which solubilise phosphate.
Selecting the Most Suitable P Source

Regardless of whether you choose to stabilise your soluble P inputs with humates or reclaim some of your frozen reserves with introduced biology, there is still the management decision about which is the best type of phosphate to use in different crops and soil types. For example, there is absolutely no logic in selecting acid phosphate fertilisers in pasture situations or in orchard crops. In both cases you don’t need instant phosphate so why pay through the nose for the unnecessary? Soft rock phosphate kicks in within a few weeks and continues to deliver P for a much longer period and yet it is half the cost per unit of P in comparison to DAP/MAP. There is an important strategy for maximising the P release of soft rock phosphate in pasture situations. If a soil test reveals that your soils are acidic because they lack calcium (a common scenario in most pastures) and they also lack phosphorus (an equally common scenario), then you have the perfect chance to maximise the performance of soft rock phosphate. Never apply lime in this situation! Instead you can use your acidity to speed the release of soft rock which also contains 24% calcium to help with your calcium deficiency. Six to twelve months later you can apply lime as at that point you should have already ensured a good supply of plant-available phosphate to the pasture crop.

Soluble acid phosphate may be necessary in broadacre crops and in vegetable crops, to achieve a kick start through a boost to early root growth, but in many row crop situations you would be better off using a combination of DAP/MAP and guano. 30% to 40% of the phosphate component of guano is citrate-soluble so you get a combination of release patterns. The combination of citrate-soluble and slow release is a great way to gain full season phosphate availability and to reduce your P losses through the lock-up of soluble phosphate. It varies between crops and soil types but often, if you are prepared to experiment, you will find that guano alone will out perform DAP/MAP and this is a worthwhile discovery because guano is now significantly cheaper, per unit of P, than the soluble phosphates. Some of the large forestry companies in QLD have trialled various combinations of guano and DAP and have eventually decided that guano delivers a more desirable tree structure. It really is worth experimenting in your soil and your conditions to find out which P source is most efficient and most cost-effective.

 

Using Foliars to Free Phosphate

The performance of root zone biology is a direct reflection of how well the above ground plant is photosynthesising and delivering sugary feeds to the roots and beyond. The great benefit of foliar fertilising is not just linked to the relatively tiny amount of nutrition you have supplied the plant. Foliar feeding is all about chlorophyll management and maximising that green pigment in the leaf a lot more cost effectively than feeding the soil (foliar fertilising is regarded as 12 to 15 times more effective than soil fertilising). The flow-on effects of chlorophyll density are largely biological because the rootzone organisms are now receiving more plant exudates and well-fed workers are always more productive. This includes the organisms responsible for phosphate solubilising, so a foliar program can prove a great way to reduce your phosphate inputs. Leaf tests ensure precision in chlorophyll management.

Triacontanol is a fatty acid that has proven to be an exceptional plant growth promoter. The key to this growth was identified in research which demonstrated that tiny amounts of this natural material boosted chlorophyll density by up to 30%.

Triacontanol has been a component of many NTS foliar fertilisers for over a decade but now it is available as a stand-alone plant growth promoter and chlorophyll booster called Nutri-Stim™ Tricontanal.

 

In Conclusion

In a world of soaring input costs the potential for better phosphate management beckons every cost-conscious producer. In the process of discovering how to do it better there is every chance that an awakening may occur - a realisation that the future of agriculture lies in working with a natural system rather than against it.

If this paradigm shift occurs then a negative has become a positive and the whole planet will benefit from the increased adoption of biological principles in agriculture.


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