‘AlpHa’ – the perfect partner for lime

Posted on April 2, 2012 by Murray Kimpton
Dr Bert Quin, fertiliser and soil fertility consultant.

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.