Brett Petersen Kiwi Fertiliser and Golden Bay Dolomite

Sometimes farmers apply large dollops of lime, whether the soil needs it or not. They may repeat the exercise in about five years’ time.

Liming is no different to applying fertiliser. To maximise benefits, a soil test needs to be taken and the most important nutrients to be applied need to be determined. Calcium will most likely be one of those nutrients.

It is not good policy to plonk on large amounts of lime in order to raise pH. You can’t tell how much you need by looking at pH and you can end up tying up other nutrients, namely magnesium, potassium, boron, iron, manganese and zinc. Besides, a heavy application probably means pH is far too low, meaning productivity is already adversely affected.

Another problem with liming on its own is pushing magnesium levels down. If the magnesium was present in correct amounts at the outset, the depression will be on a one per cent-to-one per cent basis.

In 90 per cent of cases it will be deficient, so the decrease will be less than a one-to-one basis, but still significant. Among other things, it is a way of encouraging facial eczema, insects and stock health issues, including stock behaviour and worm problems.

Atom size

Magnesium holds water better than calcium owing to the small size of its atom, giving a larger surface area. It is the percent of base saturation that determines mineral adequacy, not the actual kilograms.

Drought tolerance will be dramatically improved when fertiliser practices are corrected. I have seen soil tests results showing 90 per cent calcium out of 68 per cent, and four per cent magnesium out of 12 per cent.

The hidden hunger in the crop was potassium, which was grossly affected. With so much calcium there is little room on the soil particles for potassium. This result requires sulphur to decrease calcium, as magnesium is in fact present in the soil but unavailable to the plant. If the calcium was thus decreased to 82 per cent, magnesium would increase to 12 per cent, and become available again.

Building magnesium

Dolomite will build magnesium, but we have yet to find evidence that serpentine, and mag oxide – products that have been applied for decades – actually build magnesium in the soil. The total percent of Ca and Mg should not exceed 80 on a PAL soil test.

Crops respond in different ways when the ideal percentage is not achieved. If magnesium, a determinant of nitrogen and phosphorus efficiency, is outside the 10-12 per cent sweet spot, maize yields will reflect that by tapering away from the optimum.

On the other hand legumes will not respond in yield until that 10-12 per cent range is achieved. Urea in particular reduces calcium in the soil.

Reduced biodiversity

Consequently, legume content, quality and biodiversity of pastures will reduce during time under a high nitrogen regime. For the addition of 200kg/ha of nitrogen, 400kg of lime is required to counter calcium losses.

Add to that the natural acidifying effect of growing 15,000 kg/ha of pasture; another 450kg/ha is required. This annual input needs to be properly managed. Magnesium requirements actually need to be calculated before calcium’s. Calcium and magnesium are vital for soils, plants and animals alike. Deficiencies of either or both result in serious economic consequences.

Calcium is much more effective with boron and silicon added. Calcium, boron and silicon are synergists and together they represent proactive cell strengthening that will reduce both disease and insect pressure.

String cell walls

The two minerals that can effectively create a strong cell wall are calcium and silica. Both of these minerals need boosting in most of the crops and pastures with which we work.

The key to harnessing their full benefits is boron, as this mineral activates both calcium and silicon. Boron opens the trapdoor between the chloroplasts and the rest of the plant.

During daylight hours plants manufacture sugar. At night a trapdoor opens to permit the sugar to drain from the chloroplasts, mostly to be used for growth.

If the sugars cannot drain, the plant becomes weakened; and a backlog of stored sugars is also easy prey for insects. High brix readings late in the day indicate an efficient plant.

A comparatively low reading in the early morning hours indicates efficient movement of sugars into growth or maintenance processes.

For further information on all important nutrients, see our website www.kiwifertiliser.co.nz