Monday, April 7, 2014

Soil tests show high sodium.

Our soil test this year are showing high levels of Sodium in the soil. This is due to a lack of rainfall 'flushing' the soil.

Sodium destroys 'soil structure' by causing the individual soil particles to repel each other. The particles migrate into the soil pores and hinder water and air transport. Symptoms of high sodium include puddling of water at the soil surface, run off after rain and the leaf symptoms below:

Heat stressed vines with some symptoms of salt uptake.
Salt (sodium chloride) burn in the Clare Valley 2014.

Excess soil sodium in the McLaren Vale and Langhorne Creek regions arises from the use of high sodium irrigation water.

Calcium is the antidote to sodium, promoting soil aggregation. Calcium displaces sodium from the soil particles, allowing it to be leached from the rootzone with rainfall and irrigation.

If sodium occupies more than about 10 to 15% of the soil cation exchange capacity there is degradation soil structure. Calcium will typically occupy 50 to 70% of the cation exchange capacity.

Calcium sulfate (CaSO4), better known as gypsum, is the most frequently used Ca source for the restoration of high sodium soils. Gypsum can be applied to the soil directly, and is dissolved by rainfall.

In recent years high calcium products that can be applied through the irrigation system have been developed. These work best if the soil is wet and then follow up rainfall occurs.

Calsap has calcium and sulphur supported active organic acids. These acids keep the calcium in suspention and prevent it blocking up your irrigation system. This was the main issue with the first 'liquid gypsum' products on the market.

Cost per hectare -


Gypsum @ 2.5 tonnes/ha = $100/ha
Calsap @ 20 litre/ha = $160/ha (2x applications = $360/ha)

A liquid gypsum maybe a good option on small vineyards where the labour and organisation of spreading is a problem. In a comparison between products suggested, gypsum provides a far greater amount of Ca and S, yet does not move much passed 100-200mm in depth depending on rainfall and irrigation. In contrast, Calsap is soluble and can move to a depth the same as rainfall and irrigation water depth.

If the aim is to remove Na from the profile and root zone, then Calsap will have a greater success in delivering the response required. If Ca is required, then gypsum is the preferred option.

Alternatively, a more responsible and economic approach maybe to incorporate both products.

The aim of this is that Calsap will remove Na from the profile, while gypsum will be used as a barrier and prevention strategy if the soil profile dries to a degree that may allow Na ions to re-draw up the soil profile. Therefore, the gypsum will stop the replacement of Na as it increases in concentration up the soil profile.

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