How gypsum can help improve soil structure

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Many are faced with reduced nitrogen bulges from previous years’ applications, deteriorating soil-available phosphorus and potassium levels and most of your sulphur is down the bottom of any crop roots’ profile.

With costs going through the roof, why is it I choose to discuss the use of gypsum? Occasionally you come across a soil test where the nutrition is spot-on but crop growth is less than desirable, so soil structure comes under the spotlight. Coupled to this are the eroded soils around our state, where some of this product will help in the recovery process.

Being made up of mostly calcium and sulphur tells me it is an excellent supply of these two handy elements for our depleted soils.

Sure, we add nitrogen and phosphorus to our soil program somewhat religiously but what about elements like S and Ca?

Gypsum can be mined from the soil naturally and was, in past years, created as a by-product from phosphatic fertilisers production.

With a cost price of more than $70 per tonne plus freight and application costs, using gypsum as a soil amendment can be costly to fix up soil structural problems.

Calcium has some important roles in the plant with respect to root and shoot development, along with major inputs into legume nodulation and nitrogen fixing by legumes, plus other strategic roles. So nutritionally, a single tonne per hectare will last several years of crop-growing.

However, when using this product as a soil ameliorant, I have observed rates as low as 0.5 tonnes per hectare. It really did work well enough to enable a good strike of wheat to emerge. If a soil test indicates heavy sodicity and basic paddock inspections are observing surface crusting after rain, poor water infiltration, crook aeration and just plain difficult to work mechanically, it is a fair bet gypsum will improve soil structure to the benefit of future plants.

The way gypsum works is as the calcium works its way down through the soil profile with rainfall, it replaces sodium (and possibly magnesium as well) ions on the clay with calcium ones. These displaced are free in the soil solution to get washed out the bottom of the soil profile.

A soil test should be performed to ascertain Soil EC, which is a measurement of the soil electrical conductivity. So with heavy rates, what can you expect and for how long?

It has been my experience crops respond both in shortened maturity times and large yield increases.

These results are due to more root extension through the soil, well aerated clay colloids, better rainfall or irrigation water retention – and I venture to say a much better strike and more vigorous seedling. These heavier rates cost but the soil responds quickly after a significant rain event. The time it last will depend on your farming practices. – Paul McIntosh is a former manager of Landmark Emerald, now based on the Darling Downs.

May 26th, 2013|