Balancing calcium, potassium, magnesium and sodium in the soil

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Cations such as calcium, potassium, magnesium and sodium are vital in the soil for maintaining soil structure, drainage, aeration, overall soil health and plant growth. .¹

Calcium is a necessary plant nutrient and plays a key role in maintaining soil structure. Calcium has the effect of increasing the space between clay layers in the clay colloid. It also flocculates clay where small particles are held together in fewer, larger aggregates. This allows more air space in soil and allows better water infiltration. Exchangeable calcium should be in the range of 65-80% of total cations present on clay colloids.³

Where the exchangeable cations are present in the correct ratio aim for a Calcium to Magnesium ( Ca:Mg) ratio greater than 2:1. The correct Ca:Mg balance favours microbial activity and plant nutrient uptake since calcium is an important carrier of nutrients both in soil and plant tissue. ²

Magnesium is also a necessary plant nutrient. It is usually present in sufficient quantities to satisfy plant requirements. Exchangeable magnesium should be in the range of 10 to 20% of total cations present³.

Where magnesium dominates the Ca:Mg ratio, the spaces between clay layers are reduced, resulting in limited air space and soil water infiltration potential. ² Reduce the magnesium percentage with the addition of calcium which can displace magnesium ions from the soil colloid.² If magnesium is more than 20% of sum of cations present it may result in potassium deficiency in plants.³

To balance a magnesium deficiency, apply dolomite which provides both calcium and magnesium, or apply magnesium sulfate³. 

Potassium is also an essential plant nutrient. Exchangeable potassium should be in the range of 3-8% of the total cations present³. If potassium levels are more than 10% of the sum of cations, it may cause magnesium deficiency in plants.³  To address a potassium deficiency, supplement with potassium chloride or potassium sulfate³. 

Sodic soils have high levels of soluble salts in the root zone which may affect water and nutrient uptake and adversely affect plant growth.³  For sodic soils with high sodium content, apply gypsum, calcium sulphate,  as the sulphate in gypsum will bind with sodium, removing sodium from the upper soil profile. The calcium in gypsum will replace the sodium on the soil colloid which improves soil structure and drainage.  

To balance a calcium deficiency, apply lime (calcium carbonate) which raises soil pH and increases calcium saturation. 

If soil pH is in the correct range, apply gypsum (calcium sulphate) as gypsum does not change soil pH and can be applied across the soil pH range. Gypsum works best when the base saturation for calcium is greater than 60%.

Talk to your fertiliser advisor about the benefits of applying gypsum to increase calcium reserves in the soil and to support soil structure improvements.

Gypsum is  a naturally occurring mineral. Winstone Gypsum is Bio Gro certified.

www.gypsum.co.nz

 

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