Farming today faces new pressures. On the one hand, good production levels are necessary for farm profitability. On the other hand, the levels of fertiliser input this requires can lead to nutrient enrichment of streams, rivers and lakes. What to do?

We have to focus more on just what happens to fertiliser nutrients after application, and find out what loss mechanisms can be reduced. Ironically, with phosphate (P) we have problems at both ends of the spectrum. On many soils, and particularly the allophanic ash soils, P is ‘fixed’ onto aluminium (Al) on the surface of soil clay particles. These soils used to be called highly ‘P-retentive’. It is fashionable in some quarters today to say they have a ‘high P storage capacity’, but this is a misnomer. As your dictionary says, a store is somewhere you put something until you need it, and can then take it out of.

However the P fixed on clay particles, especially allophone, just gets stuck, retained, or fixed (any of these words are accurate), more and more tightly, more and more deeply under Al, over time. Even when you stop putting maintenance P on, the rate at which P is ‘desorbed’ into plant-available form is far, far to slow to maintain good production. “Stored’ indeed!

The great Joe Karlovsky from MAF’s Ruakura Research Station calculated over 40 years ago that to maintain a high level of production on a dairy farm on allophanic ash soil required 15 kg P per year more than it took to maintain exactly the same level of production on a low P-retention soil. Today, Overseer gives about the same difference in requirements. There is anecdotal evidence that the rate of P fixation is slowly declining, but if it is, it is very, very slow!

Unfortunately, while applying higher rates of fertiliser P to these soils helps offsets fixation losses, it also means a lot more fertiliser granules sitting on the surface after application. As these slowly dissolve into the soil over a few weeks, they are susceptible to some of the P – either dissolved or as particles – being washed into waterways by rainfall-induced run-off. The more P that has been applied in one hit, the bigger the risk.

Small, frequent applications of P would greatly reduce the risk of run-off, but at prohibitive cost. A far better solution is to find ways to reduce the amount of P that gets fixed in the soil, so we don’t have to put as much on in the first place. Very exciting research in this area is being done in several countries, with very promising results. In Vietnam for example, where I have been involved in research into improving fertiliser efficiency for 8 years, the treatment of DAP with ‘anti-fixing’ additives has literally halved P requirements for rice grown on acid soils. Another option is to use part of the P in slow-release form such as RPR. The P from RPR is not soluble in water, so is far less prone to loss in run-off. This fact is recognized in Overseer. Another part of the solution is to apply fertiliser in fluidised form, so it quickly gets below the surface.

As in most field of endeavour, necessity is the mother of invention. I think our environment, our water, is telling us that it is high time we took some of these ‘inventions’ a lot more seriously.

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We all know that lime is necessary to maintain the fertility and health of the soil, and to provide vital calcium. In New Zealand’s acid soils, most of the lime needed to maintain production is used to overcome soil acidity, that is, to increase the pH. In most soils, the biggest acidity problem is not the hydrogen ion (H+), but multivalent metallic cations of aluminium, manganese and iron. These are far more toxic to plants, and plant root growth in particular, than hydrogen.

However using lime is an inefficient and very expensive way to control these toxicities. Once a soil has became sufficiently acid to be suffering some toxicity, typically indicated by a pH of 5.5 or below, or a KCl-soluble aluminium level of 3 or more, treating the problem with lime requires a heavy capital application of at least 2-3 tonnes per hectare.

‘AlpHa’ provides a targeted solution to the problem. AlpHa is a patented combination of polymers and silicates that very efficiently binds the soluble, toxic forms of aluminium, manganese and iron, mimicking the action of chelates excreted by roots of some aluinium-tolerant plant species, and enabling high production to be maintained at a lower soil pH.

It is also important to understand that the soil pH, and with it soluble aluminium levels, vary considerably over very small distances, spatially and vertically. Much of this variability is believed to be caused by urine deposition. Initially, the pH rises – by 2 pH units or more – in the affected area, due to the heavy content of nitrogen in the form of urea, which also greatly increases pasture growth. However, as the urine-N is converted to nitrate it is easily leached, taking cations with it, and acid is produced. The end result, over 1-3 months, is a soil pH 0.5 – 1 units below the starting point, and frequently low enough to increase soluble aluminium to toxic levels.

Normal soil testing, in which 15-20 soil cores per paddock are taken and mixed together to get a ‘representative’ sample, can easily mask the presence of aluminium toxicity. It can also be present below the standard 0-7.5cm soil test core, inhibiting root growth below this depth, and consequently restricting nutrient uptake and greatly increasing susceptibility to drought and pulling.

Essentially, AlpHa allows the optimum average soil pH to be lowered from 5.5 to 5.0. This greatly reduces, in fact can altogether eliminate, the requirement for a capital lime application, and allows production to be optimised with far less maintenance lime in the future. Combined with 100 kg/ha of FertME zero-coarse lime, as little as 2 litres per hectare annually of AlpHa will maintain a healthy, non-toxic soil and ensure maximum response to fertiliser nutrients, especially if these are applied in fluidised form, to allow both foliar and root uptake.

AlpHa is produced by Adavanced Agricultural Additives Ltd, and is available for aerial application in fertME fertilisers.

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Fluid fertilisers are defined in New Zealand as high-solids products containing only 10-20% water (just enough to allow them to be kept agitated and spread through specialised equipment). Unlike what are commercially defined as ‘fpa’ (fine particle application) in which all ingredients are finely ground regardless of benefit and cost, each individual ingredient in fluid fertilisers is present in a range of particle sizes to suit that nutrient.

The main factors deciding the particle size range chosen for each nutrient are (a) whether it is possible and intended for some or all of that nutrient to be taken up through the leaves, as in a foliar fertiliser, and (b) what sizing will allow passage of the particular ingredient through the plant canopy to the soil, with as many individual particles as possible, with a totally even spread, to optimise nutrient uptake.

‘Liquid’ fertilisers got a deservedly bad name in New Zealand beginning in the 1980s, because of blatantly dishonest and misleading claims that the tiny amounts of nutrient being applied per hectare at the rates recommended by the seller would maintain production. Typically, these products were applying less than one kg/ha of the key nutrients, and trivial amounts of trace elements. They made huge profits for their suppliers, but cost farmers dearly. Several such companies added growth promotants and ‘greening’ agents to their products, to create an impressive but fleeting visual benefit.

This type of con has arisen again recently, but wrapped in a more sophisticated, single-invoice ‘package’ of on-farm ‘advice’ and application. Nutrient application rates remain massively below maintenance requirements.

Unfortunately, this has distracted attention from the enormous benefits of true fluid fertilisers, as described above. Fluid fertilisers have all the advantages of sold fertilisers – relatively low cost products designed to maintain and improve soil fertility and plant growth – but avoid their disadvantages of dust, segregation of components during handling, transport and spreading, and entry of nutrients into waterways.

In addition, fluid fertilisers offer a combination of important advantages – extremely accurate placement (thereby allowing deposition of nutients into waterways to be avoided), extremely even coverage of much smaller-sized particles than granules, optimising both leaf and root uptake, and the easy addition of both solid and liquid additives, additional nutrients, seed and insecticide. In particular, the additives can include cutting-edge products that greatly increase both P and N efficiency and reduce losses.

For all these reasons, I believe that ‘fluids’ are the way to go. The water content is simply the carrier, the means to ensure that the nutrients and additives required to optimise productivity on each given farm can be applied in the most cost-effective manner, in any terrain, in any weather.

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