Crucial calcium

The Albrecht system of liming ensures optimum soil pH and the correct level of all-important calcium.

Crucial calcium
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When Prof William Albrecht penned his views on liming in the first half of the past century, he immediately crossed swords with the soil scientists of his day. This was because he had discovered that liming adds calcium to the soil, a critically important element in plant nutrition. Conventional soil scientists maintained that optimum plant growth can be achieved only when soil acidity has been corrected. In other words, lime should be used to correct soil acidity.

For Albrecht, lime is applied to supply calcium. Hence the clash. But he proved his point by applying calcium – without acid-neutralising carbonates – to acidic soil and measured a significant improvement in plant growth. Albrecht also showed that when soil minerals were correctly balanced, soil pH reaches the desired level.

First, though, it’s necessary to know the calcium and magnesium content of the lime. Without this information, it’s impossible to work out accurately how much lime should be applied. Equally important is the fineness of grind. This largely determines how much calcium and magnesium will become attached to the soil colloids within three years after application. Albrecht also developed the formula to calculate how much lime (whether calcitic or dolomitic) and gypsum to apply.

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The other half
Recently, I visited – for the second time – a farmer in the Standerton area who has a large mixed farming operation. He has his heart set on accelerated lambing and part of his forage requirements is produced under a 32ha centre pivot. On my first visit to the farm, I had advised him to plant a mixture of fescue, cocksfoot, white and red clovers, birdsfoot trefoil and chicory, as this would give him excellent spring, summer and autumn forage. This he did.

But now only half the land is producing an acceptable amount of forage. The other half is lagging far behind, despite a generous application of nitrogen. What went wrong? Soil reports show a satisfactory level of phosphorus and excellent levels of sulphur, iron, manganese, zinc and copper. Potassium is somewhat short on the poor half, but it’s unlikely this is the primary cause of the problem. Soil acidity can also be ruled out: the water pH varies from 5,8 to 6,2.

What did strike me, however, is the marked difference in calcium and magnesium base saturation levels. Even on the better section of the land, the calcium level is unsatisfactory. Calcium base saturation is only 51% – the optimum is 68%. Moreover, at 25%, magnesium is excessive – the optimum for this soil is 12%. In the poorer section of the land, calcium measures 42% and magnesium 25%.

Like magic
On paper, the difference between 51% and 42% may not seem much. In practice it is massive – 6t/ ha of lime is required on the better half of the land, whereas the poorer half needs 11t/ha! In addition, adding calcium will reduce the base saturation of magnesium, benefiting plant production; soil high in magnesium has a poor air- and water-holding capacity.

All of this is due to the fact that the recommended lime was not applied – a very costly error. There can be little doubt that when this is remedied there will be a major transformation in productivity of the pasture over the entire land. Applying calcium works like magic on soil that is seriously deficient in this all-important plant nutrient.

John Fair is a leading expert on pastures. He heads up Fair’s Biofarm Assist, and can be contacted on 058 622 3585 or [email protected].