Lime: The softer and finer, the greater the efficiency
In farming, some terminology creates more confusion than clarity. In arable farming, the pH value is one of them. It is easy to determine but not always accurate and it says little about nutrient conditions in the soil.
According to Prof. Silvia Haneklaus at the Plant Nutrition Institute of the Federal Agricultural Research Station in Brunswick: “The pH value is not an overall indicator of lime requirement.”
The two most important minerals, calcium and magnesium, are not only exposed to competition through acidifying nitrogen ions but can be displaced by potassium, ammonium or sodium. The FAL scientist recommends paying attention to calcium saturation. Furthermore, the two principal lime elements, Ca and Mg, should be present in a certain ratio, ideally 72 to 19 percent in the soil solution. What determines the efficacy of lime fertilisation is not the level of alkaline components but the reactivity of the lime, says Dr Werner Köster, former head of the Agricultural Testing and Research Station in Hamelin. But even concerning the determination of reactivity there are differing views. From his experience it would be best to distinguish between immediate and long-term effects. Replacement of the calcium that has migrated downwards in the topsoil or the magnesium that has been withdrawn is the priority; any suggestions of a long-term effect extending over more than ten years make no economic sense.
German fertiliser legislation has set the bar for fertiliser limes very low, believes Thomas Huntgeburth of Kalkwerk Herbsleben. The origins of limes and their composition should always be taken into account. The properties of the two main elements differ. “Calcium has a lower electrical charge than magnesium and possesses a smaller hydrate shell and thus higher reactivity,” says Thomas Huntgeburth.
Dolomite limes are generally very hard, with low solubility and therefore less reactivity; above pH 5.8 they are not effective, in Dr Köster’s experience, which suits them at best only for fertilisation in acid soils. Softer limes are more reactive generally; the same goes for fineness. Harder limes should be more finely ground than softer ones. Fractions above 0.315 mm are basically insignificant in effect.
In Australia it is usual to pay only for the finer material. Another measure is the surface area; the larger this is, the higher the efficacy. Dolomites consist of smooth particles; soft chalk limes are distinguished by their large surface area. Farmers should also pay attention to precise distribution when spreading. Lime acts on the place where it falls. Two calculation models exist that draw conclusions from the sieve fraction on the release of the lime within the following three years.
One formula is used by the US consultant Neal Kinsey; the other was developed at the former Fertiliser Research Institute in Leipzig by Dr P. Runge, who calls it the neutralisation value. According to Dr Runge’s formula, chalk limes display a neutralisation value of 45 to 50 percent; Devonian limes achieve 30 percent and dolomites 28 percent. Liming is one of the most important fertilisation methods for yield; on top of this, it also helps to stem erosion and save water.
Liming must not, however, be viewed independently of the supply of other nutrients. In areas with animal husbandry on light soils there is a danger of excessive phosphorus supply causing calcium deficiency, Dr Köster stresses.
Too much potassium reduces magnesium and calcium uptake.
An excess of magnesium should likewise be avoided, since this provokes calcium deficiency.