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In most overseas countries, this term is used specifically to refer to a fluid made by mixing high-quality fertiliser ingredients, previously finely ground to below 100 microns (0.1mm), with 40-60% water by weight. Because most ingredients used are quite soluble in water, a saturated solution is formed, with the rest remaining in suspension as fine particles. This is commonly aided by the addition of about 10% of a clay such as bentonite, capable of keeping the fertiliser particles in a suspended state for some hours without stirring.
In New Zealand, the term is, perhaps unfortunately, used more loosely, to the extent of being used to refer to virtually any flowable mix of fine particle fertiliser and or lime in water, most of which require constant stirring to avoid settling out. Such products are applied in a number of ways, including spray booms fitted with very wide nozzles or outlets, from buckets with spinners incorporated in the case of helicopters, or from trucks fitted with specialised on-board grinding, mixing and spreading equipment.
In most countries, this term can be used to refer to any mix of fertiliser and water, including those in which the fertiliser is fully dissolved in water (ie, a true solution) like urea ammonium nitrate (UAN). The term can cover a wide range of particle sizes and concentrations.
The term has not come into common usage in New Zealand. Because of this, and because of the deeply entrenched misuse (relative to overseas usage) of other terms, a prefered definition of fluidised fertilisers is ‘highly concentrated (less than 30% water by weight) liquid fertiliser products containing at least one of the major nutrients N, P, K and S, with or without lime, all with fine-form particle distributions’.
In most countries, this term is typically but not exclusively used to refer to any fertiliser in which all the ingredients are fully dissolved, ie, a true solution. In New Zealand, it has been most commonly used to describe both relatively dilute solutions of fertiliser in water, and such products containing partially-dissolved substances of organic origin, typically from seaweed or fish-processing waste. They are mostly applied, heavily diluted with water because of low ‘recommended’ application rates per hectare, through spray booms fitted with anti-clog nozzles.
Fine Particle Application (‘FPA’)
This term, not commonly used in many countries, has been used by some commercial entities, particularly helicopter-spreading operations, to describe mixes of finely-ground particles (typically below 100 microns) with water, and/or the application of these via spray booms. The name has been used to infer automatically increased effectiveness, regardless of whether it is present for a particular ingredient. There is typically a claim or at least inference that the total uptake of all nutrients occurs by foliar uptake, i.e. through the leaves, but the actual mechanism by which this occurs is never specified; neither is any hard scientific data provided to support performance claims. Partly because of very high costs of fine-grinding of all ingredients regardless of benefit, ‘FPA’ products tend to be recommended and sold at nutrient application rates that would be considered far to low to maintain production by agronomy and soil fertility experts.
A disadvantage of the ‘FPA’ term itself, besides the confusion over agronomic and cost-effectiveness relative to granular fertiliser for most ingredients, is its confusion with dry or deliberately dampened fine products such as RPR. These fine-particle are often sold deliberately dampened with a few percent moisture, with no other stated purposes other than to control dust and improve spreading accuracy. In fact, it has been scientifically proven that grinding RPR much below 100 microns, which FPA automatically does, confers no additional agronomic benefit because of the well-established common-ion effect between calcium from the RPR and that from the soil.
Most countries use this term almost exclusively to refer to relatively concentrated water-based organic manures, typically applied at high rates per hectare from tanker trucks fitted with special outlets. In New Zealand, the term is used by some to refer to what would be better described as a fluid inorganic fertiliser, especially ones containing a lot of large particles and/or only partially dissolved granules.
All such products are designed with the intention of most if not all of the nutrient content being taken up by the plant directly through the leaves (foliage). To assist in this, the nutrient ingredients are typically present in the form of highly-soluble chelated compounds, with wetting or ‘fixing’ agents added. They are supplied either in ready to use solution form or in powder form for completely dissolving in water. They are typically used on high-value crops only, because of their high cost per unit nutrient. The method by which foliar uptake is achieved or at least promoted is usually indicated to some degree.
Granular fertilisers are made by finely grinding all the components, some of which may then be subjected to reaction with one or more mineral acids, before passing the mix through a granulation drum or over a pan granulator, to produce approximately spherical granules, generally of 4-6mm diameter, before drying and hardening.
Another technique is ‘compaction’, where the finely-ground ingredients are squeezed together under high pressure, typically into a 4-6 mm thick continuous ‘biscuit’, which is then broken into granule-sized ‘chips’. Most potash is sold in this form.
Regardless of whether granule or compaction technology is used, sizing is most commonly 4-6mm, for both ballistic (spreading evenness and width), and agronomic reasons. They are intended to pass through the foliage to the soil surface. On pasture, the rule of thumb is typically that the roots of each plant should have access to at least one granule as it dissolves in the soil. While this may be approximately true for applications of maintenance single superphosphate, it is most certainly not true for granular urea. In a typical dairy pasture, there are typically over 400 plants per m2. However, at a typical granular urea application of 30 kgN/ha (65 kg urea/ha), only 45 granules are applied to each square metre. In cropping situations, both granulated and fluid fertilisers are more commonly placed by specialised machinery close to the rows of plants or seeds, to improve proximity to roots.
Prilled (mini-granular) fertiliser
A new approach rapidly becoming popular in New Zealand is that of using ‘prilled’ or mini-granule fertilisers, typically in the 0.5-2.5mm diameter range. These provide literally 10 times more particles at the same weight applied as granules, meaning vastly more even coverage. Prilled urea supplied at 30kg N/ha typically supplies 500 prills/m2. Prills also have the further advantage if wetted that many will adhere to plant leaves, allowing some foliar uptake, but without the risk of ‘burning’ and ‘leaf scorch’ commonly induced by liquid and suspension/fluidised fertiliser N applied at more than 10 kgN/ha.
Some readers might remember this post from 3 years ago:
“The awarding of a $9.5 million Public Good Fund grant to Ballance late last year, for research into ‘Improving N and P efficiency and the development of biological pest control methods’ hopefully reflects a great leap forward in attitude by Ballance.
While there is concern that the grant will be spent on a variety of ‘dead-end’ research topics, rather than truly promising areas for advancement, recent comments from Ballance staff indicate a desire to make breakthroughs in nutrient efficiency…..Group One looks forward to seeing what research projects are initiated with the various research institutes and universities.”
So what has happened since 2011? Well, Ravensdown received similar ‘me too’ funding. But no new environmentally-orientated products have been released by either company. Ravensdown have even had to withdraw their only initiative, Eco-N, because of the possible repercussions from traces of DCD being found in milk. The levels are likely to be far too low to be harmful at all, but the problem is that no one had the foresight to establish a proven safe upper limit. So we just don’t know. Incredible.
Even sadder, Ballance resorted to ‘reinventing’ SustaiN(R), which is granular urea coated with the urease inhibitor NBPT, to minimise ammonia volatilisation. Ballance started promoting it very heavily in 2014, possibly after someone in Wellington got round to asking what had been accomplished with the $9.5 mil. The thing is, SustaiN(R) was developed and introduced to the market way back in 2002(!) by Summit-Quinphos (NZ) Ltd, long before Ballance bought the company out.
As it happens, when SustaiN(R) was released, it was damned with faint praise by Ballance, and by Dr Doug Edmeades of course, despite the wealth of trial data collected. Ballance conducted their own trials, which gave positive but less impressive results. It now appears that their trials were conducted on sites chosen on the basis that ammonia volatilisation was likely to be very low. Hmmm….
From all the data I have seen, it is clear that, unless there is rainfall or irrigation within a few hours after application, the efficiency of SustaiN(R) will be 20-40% better than regular granular urea. A very good start, but not in the same league as ONEsystem(R). I know, because I invented them both!
The cadmium (Cd) issue arose in New Zealand and Australia purely and simply because the manufacturing phosphate rocks both countries originally used to make superphosphate (Nauru and Christmas Islands) contained elevated levels (50-100 ppm) of Cd. All of this Cd ended up in the superphosphate, and therefore in the soil. Cd exists at low levels in all soils. But if too much is present in the fertiliser, the levels in the soil increase over decades to the point where elevated levels show up in pasture and then in animals, which concentrate it in their liver and kidneys, as happens to many poisons that cannot be excreted in the urine. The highest levels are found in soils which have had the highest application rates of superphosphate for the longest period of time; these are typically the dairy farms in the Waikato.
The highest levels of Cd are found in the liver and kidneys of young stock. To avoid the entry of excessive Cd into the human food chain, offal from young animals is not permitted to be sold for human consumption.
The reasons why some phosphate rocks are higher in Cd than others is not completely understood. Different hard ‘manufacturing’ phosphate rock deposits and different RPR deposits can contain very different levels of Cd. There can even be wide variation in levels within a particular deposit (more about this later). The concentration of Cd is thought to be largely due to the level of Cd in whatever organic matter is present in the phosphate rock as mined; that is, little is present in the phosphate rock crystal lattice itself. For this reason, the Cd can be removed by roasting the phosphate rock at high temperature. The organic matter in the phosphate rock is burnt off, along with the Cd in it. Ideally this is captured from the emissions. This roasting is expensive, and it also reduces the solubility of the phosphate rock, so it is not so suited for deposits that are used for direct application.
Internationally, most high Cd phosphate rocks (even those that otherwise are suitable for direct application) are used to make phosphoric acid. The reason for this is that most of the Cd precipitates out of the phosphoric acid and ends up in the gypsum. The phosphate fertiliser made from this phosphoric acid generally contains less than 20% of the amount of Cd originally present, but the enriched level in the gypsum by-product reduces its suitability for land application purposes, such as improving soil drainage and reducing salinity.
The science – and pseudo-science – of how Cd is managed by the industry in NZ
I first brought the issue of Cd accumulation to NZ farmers in the 1990s. Quinphos Fertilisers initiated a self-imposed limit of 2 ppm Cd for each % P in a product. This meant that an RPR containing 13% P could not exceed 2×13 = 26 ppm Cd. I based this limit on some excellent published independent scientific research conducted by Massey University, which showed that, at this level of Cd, there was no accumulation of Cd in the soil, and therefore in the food chain. At the time, we were importing Egyptian ‘Kossier’ RPR which contained only 12 ppm Cd, and Tunisian RPR, which ranges from 20-25ppm at the western end of the deposit to about 80ppm at the eastern end. We insisted that we receive RPR only from the low-Cd end; none of our shipments exceeded 25ppm. Averaged over the two RPRs, we had 19 ppm.
After years of ‘deny, deny’ that there was even an issue, the industry very slowly moved to adopting a self-imposed Cd limit of 280 micrograms of Cd per kg of P in any phosphate fertiliser. This equates to a 25 ppm Cd limit for a 9% P super, or 36 ppm for an RPR containing 13% P, nearly 40% higher than Quinphos’ maximum limit. This just isn’t good enough.
A decade ago the industry in effect admitted the seriousness of the Cd situation it had got NZ farmers into by introducing a ‘4-class’ categorisation of Cd in NZ soils. Farmers whose soils were in the highest Cd category could now only use fertiliser containing almost zero Cd.
What are the implications for RPR users? There are no RPRs with absolutely zero Cd (a cynic would say that the only motivation for having this pointless category at all was to prevent RPR being used). The main RPR now being imported by the industry (Sechura) is right at, or above, the industry’s own limit of 36 ppm. I have visited the Sechura deposit in Peru (as well as virtually all the other RPR deposits), as part of consultancy work for an international mining company. Unlike say the Algerian RPR deposit, which is essentially one thick homogeneous layer all containing 16-20 ppm Cd, Sechura has 8 different layers separated by clay; these layers range from 20-60 ppm Cd, with the lowest Cd layers being at the bottom. It is simply not possible to selectively mine the lowest Cd layers without enormous cost increase. The minimum weighted average achievable with current mining methods is about 38 ppm in my assessment. An importer may fluke one shipment at say 32 ppm, but the next is just as likely to be 45 ppm.
The very good news is that there are plentiful supplies of low Cd RPR. The Arad deposit in Israel is one. The Red Sea coast RPR deposits in Egypt are another. NZ’s underwater Chatham Rise phosphorite nodules – not mined as yet – are another. By far the biggest known to date, and already being mined, is the huge Algerian RPR deposit. All these RPRs are sufficiently low in Cd to lead to a slow but sure decline in the Cd levels in NZ and Australian soils if used as the source of phosphate.
A very sharp solution to a big problem has its first demo
Spikey® is a very innovative solution to the serious problem of leaching of nitrate-nitrogen from cow urine patches on grazed pastures by Pastoral Robotics Ltd, a member of Group ONE.
Excess nitrogen (N) in pasture and feed is excreted by the cow mainly as urea-N in the urine. This urea-N gets converted, firstly by an enzyme and then by soil bacteria into ammonium-N then nitrate-N. This is the form of N preferentially taken up by plant roots, but the problem is that the amount of N returned to the soil in the small areas affected by urine is far greater than the pasture can usually recover. Much of the nitrate-N, which is highly water-soluble, gets leached through the soil by rainfall and irrigation. It finds its way into groundwater, streams, rivers and lakes, where it contributes to weed growth and algal blooms. Nitrate-N in drinking water is a precursor to carcinogens and has been linked with deaths in young children.
If a solution to this problem is not found, dairy farms will either have to reduce stocking rates and farmer incomes, or put considerable capital resources anf ongoing maintenance and management in housing cows in sheds, from where the effluent can be collected and spread evenly over the entire farm. This would represent the end of year-round grazed dairy farming as we know it in New Zealand, and are known for it the world over. So there is a real problem.
PRL directors Geoff Bates and Bert Quin believe that the solution to this problem is provided by Spikey®, the result of two years intensive research and development by the agritech engineer and soil fertility scientist, both of whom have strong business skills as well.
Spikey® is basically a combination of a considerable number of spiked metal wheels on an axle which detect individual fresh cow urine patches (up to several days old) by measuring the surface soil conductivity at very small intervals. It is currently towed across the pasture by quad bike or ute, but ultimately it is intended for this to be done by the small robotised vehicle Mini-ME® currently under development by Pastoral Robotics Ltd. Spikey® detects then sprays any fresh urine patches with a proprietary combination of totally safe products which are already widely in use applied to pastures for other purposes; all have proven to be totally safe environmentally.
Both technologies had their first on-farm technical demonstrations to an audience of leading nitrogen and the environment researchers on January 23. Both technologies performed right up to the expetations of PRL, and promoted lively discussion. It was agreed than testing of the Spikey® technology in a grazed dairy farm situation where nitrate leaching could be monitored was the ideal next step.
Then, on February 12, Geoff Bates will be presenting their results to an audience of over 200 scientists, advisors, regional council staff and farmers at Massey University’s FLRC Conference.
Dr Quin believes that the net cost of detection and treatment would be very easily negated by combining the technology with switching from granular urea as the main source of fertiliser N to ONEsystem® . This utilises spray technology to wet prilled urea, treated with the urease inhibitor nbpt. Independently-run trials under grazing as shown a massive reduction of 50% in the amount of N required to grow a given amount of extra grass.
RPR is a natural, slow-release mineral formed on the sea floor over hundreds of thousands of years. Deposits that have been raised above sea level by changes in sea level or earthquakes are cheaper to mine.
When RPR is applied to acid soils, the soil acid attacks the phosphate mineral, releasing plant-available P in a sustained fashion. True RPRs release P fast enough to easily maintain the growth of high-producing pastures, with only a few limitations.
The science of using RPR in limiting situations
The first is that the soil has to have some level of acidity; otherwise the RPR will remain undissolved (as it has for eons in the North African desert). Because all pastoral soils in NZ and virtually all in Australia are acidic anyway, this isn’t an issue. It was originally advised that RPR should not be used at soil pH levels above 6.0, which is still slightly acidic (neutral pH is 7.0). The only reason for this recommendation was that RPR did not perform too well on a site that had a soil pH of 6.4. But this site also happened to have a very low rainfall (550mm). On farms with higher rainfall or irrigation, especially where existing soil P levels are already at or close to recommended maintenance levels, RPR has been shown to work perfectly well at soil pH levels up to 6.4. Few if any pastoral soils have been limed to a pH higher than this; it is simply not necessary for optimum production and induces trace element deficiencies.
The slow-release nature of RPR makes it less suitable where a rapid increase in soil P levels is required, eg in dairy conversions. This is particularly the case on high P retention soils.
Here are my recommendations for using RPR in less than perfect situations –
- Capital applications in very low soil P levels (less than two-thirds of the bottom of the recommended range):
Use a mix of RPR and a low-gypsum (non-superphosphate) soluble P, eg TSP, DAP or TSP. The water-soluble component should make up at least one half of the total P applied, until soil P levels reach the recommended range.
- Very low rainfall (<700 mm, no irrigation):
Following the end of a drought, apply the first P application as TSP, DAP or MAP.
- Soil pH in the range 6.4-6.7:
Use a mix of RPR and TSP, DAP or MAP. The water-soluble component should make up at least one-half of the total P applied.
- Very high P retention soils (PR>96%).
Use a mix of RPR with TSP, DAP or MAP for the first 5 years. The water-soluble component should make up at least 33% of the total applied P.
What exactly are you getting for your money?
Dicalcic (aka lime-reverted superphosphate) has been around a long time. When properly made, the water-soluble P component in super, called monocalcium phosphate or MCP, is fully converted after crushing by chemical reaction with lime, to a different form of P called dicalcium phosphate or DCP (hence the name ‘dicalcic’).
A well made straight superphosphate should contain at least 90-95% of its total P in the form of water-soluble MCP. The difference between this – say 8.0% P and the total P content of say 9.0%, is comprised of agronomically very ineffective, unreacted manufacturing phosphate rock and various complex iron-aluminium-calcium phosphates of very dubious value to plants. Interestingly, since the demise of the Fertilisers Act, superphosphate manufacturers now clearly imply, in the way they and their field staff use the total P rather than the water-soluble P content of super to calculate how much super to apply per hectare, that this non water-soluble P component is all plant-available.
Chemically, it should only be necessary to thoroughly mix in 30-35% of lime by weight to achieve full conversion of the MCP to DCP over a couple of days. For a variety of reasons, the main one I think being reducing the amount of mixing effort required, much higher proportions of lime – typically 50% – are used. This means that the total P of the product has been diluted from 9.0% P to only 4.5%, and what was water-soluble MCP component of say 8.0% P, to a mere 4.0% P of DCP.
It is extremely important to ask and try to answer the question “is it worthwhile for the farmer to use dicalcic and why?”
Manufacturers and suppliers claim that (1) the DCP form of P is a far more efficient per unit P than is water-soluble MCP, and (2) the lime content helps the plant to utilise all soil nutrients. DCP is not water soluble, but unlike the very unavailable forms of non water-soluble P in straight super, is very easily converted to plant-available water-soluble P in the soil. Probably the main specific advantage of applying P as DCP instead of MCP is that, by being initially non water-soluble, it avoids much of the severe run-off risk that the water-soluble P in straight super faces, when a rainfall or irrigation-induced surface water run-off event in the weeks after application can easily result in a kg or more per hectare of P ending up in the nearest waterway.
This is the direct cause of much of the increasing eutrophication of our lakes and rivers – nitrate leaching from urea and cow urine patches being the other major contributors.
As deeply serious as this is environmentally, it typically represents less than 10% of the P that is applied. So how does this fit with the claims that dicalcic super only needs to be applied at the same rate per hectare as straight super – in other words, at only half the rate of P, clearly implying that it is somehow twice as effective per unit P as straight super.
Rather than totally rubbish this claim, as some of my ex fellow scientists have done and continue to do, we need to dig a bit deeper, if you will excuse the pun. In my experience, farmer observation, despite the fact that it may not be based on the results of scientifically-conducted, fully replicated and statistically analysed trials, are not to be ignored. Time is a great leveler. I believe it is no coincidence that the deepest farmer support for dicalcic super is in areas of yellow grey and yellow brown soils, particularly where there is ready access to cheap lime, and family continuity in farm ownership, meaning long-term observation of cause and effect, and the passing on of these observations.
It so happens that the yellow grey earth soils in particular are known to be (a) capable of accumulating huge amounts of P in very inert organic form, and (b) capable of having this organic P mobilised if lime is applied. I observed this for myself on the ultra-long term superphosphate trial at the MAF’s Winchmore Irrigation Research Station where I was stationed from 1974-82. When the whole trial was limed for the first time for 20 years in 1975, there was a massive mobilisation of soil organic P into plant available form, as measured by Olsen P soil tests and plant uptake.
The question within the question then, is whether applying dicalcic super annually is any more effective than applying straight super annually, and is there a need for a heavy rate of lime separately every 5 years or so, even on these soils? Most agricultural scientists would say no. I would say probably yes, with some provisos, and certainly not to the extent of being able to halve the rate of application of P long term. My estimate is that a 25-30% reduction is possible.
The remainder of the benefit in improved efficiency that cannot be explained by the 10% improvement resulting from reduced P run-off comes, I believe, from the intimate contact between P – now, remember, in the alkaline DCP form – and lime in dicalcic super provides a stimulation of soil microbiological activity, resulting in improved turnover of all nutrients held largely in organic form, meaning not just P, but N and S and trace elements as well. Faster turnover of nutrients provides more opportunity for root growth and nutrient uptake.
Other major soils, especially the allophonic ash soils whose depth and drainage, combined with reliable rainfall, have made them the mainstay of dairy farming in this country, store proportionately far more of their P in inorganic form fixed to clay particles. They have a naturally higher rate of biological activity and this, combined with a natural high pH buffering capacity, means that there is not the same extent of P-release benefit from lime. The real challenge on the ash soils is finding out how to prevent the P being fixed by allophone clay before the plant can use it. But that’s another story.
RPR, S and (reasonably) fine lime
So, I’ve said that dicalcic is possibly 25-30% more efficient per unit P than straight super and lime applied separately on the yellow grey earth and possibly yellow brown earth soils, but not much elsewhere. It is also better for the environment because of reduced run-off. But it is about 40-50% more expensive on an applied basis. So is there a better way? I believe there is – blends of RPR, S and reasonably fine lime. Let me explain why.
If we go back to dicalcic for a minute, it is made by reacting straight super with lime. Manufacturers of single superphosphate (SSP) have gone to the trouble of acidulating a non-recative phosphate rock with concentrated sulphuric acid, to convert the phosphate into a plant-available form, and then semi-granulating it so it can be handled more easily. This costs money, and the product has no liming value. So where is the logic in taking that, crushing it up again, mixing it with lime to change the type of phosphate into a non water-soluble form again, all to give the final product a liming equivalent of 50% of the same weight of lime? No wonder it costs 40% more per unit P than SSP!
So all in all, an expensive process, which also results in high transport and spreading costs per unit P because of the low P content. Lets say you want to put on 15 kg of available P per hectare, typically enough to maintain 10 SU/ha. At 4.0% P available P in dicalcic, that means 375 kg/ha is required. This will also provide the liming equivalent of about 135 kg/ha of lime – the typical annual requirement on a reasonably high-producing non-ash soil. However, the reality is that few users of dicalcic put on this amount, because of the high transport and spreading costs, and therefore soil P levels continue to slowly decline, while soil pH tends to be more or less maintained.
Lets look now at RPR and lime. RPR, or reactive phosphate rock, typically contains 12.5-13% P. (Warning 2015: recently, some suppliers, including at least one of the large companies, have been importing completely unbeneficiated RPR ore from Peru containing about 40% inert clay, reducing the P content to 7-8%. Often, it is claimed to be much higher, such as 11.5%P. To do this is theft. Sometimes, it is blended with a non-RPR to increase the overall citric solubility. This is also theft. If you are in any doubt whatsoever about the P content of what you are buying, tell the supplier you well be taking a representative sample from the truck when it arrives at the farm, and getting it analysed at an independent laboratory such as Hills).
The definition of an RPR as used in New Zealand is a natural phosphate rock which, because of the way it was formed, will dissolve fast enough per year to supply sufficient P to maintain the growth of a high-producing pasture at soil pH levels of up to 6.0, which is all you need.
RPR automatically contains some of its high calcium content in carbonate form, which is what lime is, and it gives each tonne of RPR the liming ability of 0.5 tonne of high-quality lime. This is actually what makes RPR more ‘reactive’ – meaning more quickly released into plant-available form in the soil – than ordinary phosphate rock, which has to be acidulated with sulphuric or other acids. It also consumes soil acidity during this process.
So, lets say you wanted to put on 15 kg P/ha as RPR (120 kg RPR/ha). Add in 10 kg/ha of fine elemental S, which is all you need because it doesn’t leach unlike the sulphate-S in super and dicalcic, and you still have a net liming effect of about 30 kg/ha. To maintain soil pH in the 5.6-5.7 range typically requires an application of 150 kg lime/ha annually. This 150 minus the 30 from the RPR/S leaves 120 kg/ha to be added in as lime, giving a total application of 240 kg/ha of this 50/50 mixture.
Note that the lime does not need to be expensive $200/tonne superfine minus 20 micron lime. Minus 100 microns is fine enough, and doesn’t cost the earth (typically $70-80/t). To that the components of the mix (RPR, lime and elemental S) are all very evenly distributed as they land on the ground, we need to apply the mix in a slightly damp form. A dry mix will be subject to segregation and drift.
A damp mix may not discharge evenly from the truck or aircraft, and in fact can be very dangerous in the latter case. A high water-content suspension will be very expensive to apply because of the cost of transporting and spreading the weight of water. In addition, the likelihood of settling out of high water-content, so-called ‘suspensions’ in aircraft tanks means application rates can be variable.
A high-solids fluid – typically only 15-25% water – actually stays far more uniform, because the water content is far more tightly held. Further, each droplet as it lands contains the same proportion of the components. But the cost of making the fluids, keeping them mixed in the aircraft tank during application is just too high (see 2011 costings).
The simple solution is to spray the dry mix with about 5% water as it leaves the aircraft. Instead of more than doubling the spreading cost as with suspensions and fluids, it adds a mere 5-10%.
Dicalcic Super vs Wetted RPR/S/Fine Lime – Cost Comparison Example
Objective – to apply hill country maintenance P (15 kg/ha) and S (12 kg/ha as sulphate or 10 kg/ha as fine elemental S, plus sufficient lime, in fine enough form, to stimulate soil microbial activity and maintain soil pH.
|dicalcic super (dry) |
|RPR/S/fine lime (wetted)
|Required fertiliser application||360 kg/ha||244 kg/ha|
|Cartage to farm||$20/t||$40/t|
|Cartage (per ha basis)||$7.20 /ha||$9.75/ha|
|Spreading cost/ha (air)||$28/ha||$29/hac|
|Saving/ha/yr with RPR/S/lime||$28.50 (23%)|
|Annual saving (300 ha farm)||$8550.00d|
Notes: prices ex Ballance price list
(a) ex Wairoa
(b) ex Hastings, assuming $383 for RPR/S and $100/t for finer lime and blending – 50/50 blend gives $241.50/t
(c) $4/ha lower rate for lower fert weight/ha, plus 10% for water spray
(d) the $8550 will pay for a trip to Disneyland for the family, or a new quad
This demonstrates the large savings in maintaining hill-country P, S and liming.
Lime (and the calcium it brings with it) should be treated no differently than the fertiliser nutrients. That is, we should be striving to keep pH levels as near to the optimum hill country of 5.6-5.7 continuously, rather than suffering a widely varying soil pH during a 5 year cycle.
Final Comments: Other options such as fixed-wing application of annual superphosphate plus capital lime (say 1 tonne/ha every 5 years), or RPR/S plus reduced capital lime are typically slightly cheaper averaged over 5 years. However, what often happens is that, if cash-flow is not good when the capital lime is due, the pH can fall to a level where aluminium toxicity becomes a real problem, reducing pasture growth and N fixation by clover, which in turn will have a negative effect on soil biological activity.
Farmers must be alert to the existence of unscrupulous ‘muck and mystery’ merchants who use the mask of attractively sign-written helicopters and very slick marketing to promote the use of very costly low-nutrient dilute sprays which are claimed to contain components that will free up nutrients locked up in the soil. It would be good if these components could be shown to achieve something, and unfortunately this has not been the case. By the time you realise this, in 2 or 3 years, your production will have fallen 10%. Sad but true.
Current New Zealand dairy production could be very considerably increased, with only half the current amount of fertiliser urea being used, if granular urea was replaced with ONEsystem(R) the use of wetted, prilled urea incorporating the urease inhibitor nbpt. Total cost to the farmer would fall dramatically, with the halving of urea costs, and the same or marginally higher spreading costs. Losses to the environment would be greatly reduced, as any input into Overseer® will quickly confirm.
The urine-N leaching problem can be solved with the Spikey(R) technology, avoiding capital-intensive cow homes. The ONEsystem(R) and Spikey(R) technologies can be easily combined, at a total treatment cost less than just using granular urea to reach a certain level of production. A real win-win outcome.
Liquid fertilisers started to proliferate in New Zealand in the 1970s. Most of these were dilute extracts of seaweed or fish by-products, often augmented with small amounts of inorganic fertiliser NPK. Almost invariably they relied on unproven claims of massively greater nutrient efficiency than solid fertilisers, and the presence of various ‘growth stimulants’, to distract attention from the almost invariably miniscule amounts of nutrient being applied at the ‘recommended’ rates. Profit margins were of course considerable.
The claim by Maxicrop in a national TV advertising campaign in 1985 that “3 pints will feed an acre” lead to public criticism of the company’s claims, and a scientifically simplistic statement by MAF scientist Dr Doug Edmeades on a ‘Fair Go’ TV program that the product ‘did not work’ by a scientist from the MAF’s Agricultural Research Division, resulted in an $11 million defamation law suit by Maxicrop. Dr Bert Quin, at the time Chief Scientist for Soil Fertility at the Division’s Ruakura Research Centre, was appointed as Scientific Advisor to Don Matheson QC, who successfully defended the year-long case for the MAF. Dr Edmeades later joined the defense team to prepare MAF witnesses.
An unfortunate by-product of this case is that the merit and potential of any form of liquid fertiliser was downgraded massively in the minds of most fertiliser researchers and applicators in New Zealand, with the result that very positive developments being made in other countries, with high-solids suspension fertilisers especially, created little or no immediate interest in New Zealand.
However, the last few years have seen a marked resurgence in interest, lead initially by the use of helicopters in the North Island and fixed-wing aircraft in the South Island, to provide reasonably-competitive, near-sustaining rates of nutrients and fine lime, in high-solids suspension or ‘fluid’ form, to hill country. This resurgence in recent years has been assisted by evidence – now proven in scientific studies – that fluidised urea, to which urease inhibitor has been added, is vastly (typically two and a half times) more efficient in producing extra dry matter (DM) per unit N than is granular urea.
Two groundspreading technology companies, one of which (Quinspread Technologies Limited), Bert Quin had a commercial interest in, have introduced new technology that allows urea and other fertilisers to be converted on–truck into concentrated fluids, during the spreading operation, resulting in far greater pasture growth responses per kg N applied.. However, very high capital and maintenance costs of the equipment combined with narrow (10m) swath widths, have greatly restricted the uptake of this technology. Dr Quin left Quinspread Technologies in 2013 to pursue his dream of greatly reducing the cost of improving the efficiency of urea. The assets of this company are now owned by entities associated with N.T. Wealleans Ltd of Hinuera, Waikato. Dr Quin’s endeavours have since resulted in the development of ONEsystem®.
Questionable Practices Continue
Recent market entry by new companies heavily promoting products that provide little in the way of vital nutrients to replace losses – at the ‘recommended’ rates of application – has caused considerable concern. For the farmer with little fertiliser and soil fertility knowledge, it can be very difficult to see through a sophisticated syrup of ‘healthy soil biology’ jargon and product performance claims that are unsupported by any credible evidence. Just as concerning however, is the scaremongering tactics of some so-called ‘independent experts’ who prefer to blindly promote obselete products and practises rather than do any new research themselves.
Continuing use of fertiliser N dramatically alters the ryegrass-clover equilibrium, giving 10-40% increases in annual pasture production with no obvious (in the short-term) adverse affects on soil biological activity, provided inputs are not much more than 100-150 kgN/ha annually. Exceeding this – as is now very commonly done on dairy farms – increases the risk of a variety of adverse and interconnected effects occurring.
A frequent consequence is the virtual complete disappearance of clover – a very nutritious and N-fixing plant – from the sward. Adverse effects of increased stocking rate include soil compaction, reduced soil aeration and drainage, pugging, restricted root growth and pasture pulling, reduced soil biological activity, declining soil organic matter content (including carbon of course), increased animal nutrition problems and increased losses of nutrients – particularly N and P – to the environment.
The introduction of serious clover pests such as the stem weevil in recent years have forced many dairy farmers to use greatly increased quantities of fertiliser N to replace N no longer being fixed from the atmosphere by clover, and/or to use increased quantities of brought-in feeds such as palm kernel to maintain milk production. This has tended to exacerbate other problems, including those mentioned above.
More and more farmers are becoming increasingly concerned with what they feel is the ‘health’ of their soil. In a virtual absence of systematic surveying and research by the Crown Research Institutes (CRIs), and a ‘not our problem’ attitude from the big fertiliser companies, more farmers are turning to alternative, largely unproven nutrient mixes and soil amendments.
At the very least, it should be a requirement for suppliers and consultants to supply specific information regarding the quantities of nutrients per hectare that are being applied in any nutrient mix, and why these recommended applications differ from ‘Overseer’ recommendations if this is the case, particularly for the major nutrients. “Overseer’ is a long, long way from being perfect, but it is a long way better than doing nothing to assess actual nutrient requirements and losses. I give it a 6 out of 10. Likewise, companies selling soil ‘amendments’, whether they be aglime, fine lime, humates, seaweed or fish extracts etc, should state what these amendments are specifically intended to achieve at the recommended rate of application.
Sadly, in fact incredibly for a country whose entire economic health is dependent on sustainable agricultural production, New Zealand’s universities and Crown Research Institutes employ a grand total, according to our information, of one, yes that’s one, trained and full-time employed soil microbiologist! It is shocking how little we actually know about the microbes and fungi so vital for so many things, probably the most important of which is maintaining the biological activity and health of our soils.