Wednesday, May 22, 2024

Managing your soil’s cation exchange capacity

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Cation exchange capacity affects the soil’s capacity to hold vital nutrients.
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Improving soil quality and health on farm depends on the cation exchange capacity of the soil being worked on.

The cation exchange capacity (CEC) measurement of the soil’s capacity to exchange nutrients needs to be properly managed to increase that health, Rainbow and Brown’s Grant Morris says.

CEC, whether large or small, affects the soil’s capacity to hold nutrients such as calcium, magnesium, potassium and ammonia nitrogen.

“A lighter soil like sandy soil will have a CEC of around 5 and will hold less of everything. It doesn’t take as much fertiliser to get the right nutrient balance for total saturation but the nutrient load can be easily stripped by cropping so it’s something you have to watch after each growing period. 

“Another soil may have a CEC of 10, which means it can hold twice as much nutrients for longer periods and doesn’t lose as much nutrients during cropping therefore reducing the need to keep adding more fertilisers. So understanding the type of soil you have is very important when trying to make improvements,” Morris says.

Soils with good CEC tend to have higher organic matter, better structure and increased microbial activity, which can reduce the need for costly soil amendments and interventions.

Overapplication of certain nutrients can lead to nutrient imbalances that negatively impact crop health and productivity. 

By tailoring nutrient applications and conditioners to the soil’s CEC, farmers can avoid these imbalances and at the same time contribute to sustainable and environmentally responsible agriculture, Morris says.

Potassium humate can act as a soil conditioner. It contains 50% humic acid, 15% fulvic acid and 10% potassium. 

Humic acid and fulvic acid are crucial in dissolving minerals and trace elements to make them more available to the plant for uptake. 

The addition of fulvic acid acts as a superhighway for nutrients to plant cells. As the soil quality improves the need for fertiliser decreases. Humate-rich soil acts as a carbon sink to help keep CO2 in the ground instead of escaping into the atmosphere.

Seaweed is another soil conditioner, containing more than 70 mineral, vitamins and enzymes that feed the microbes in the soil. 

Plant roots, including pasture roots, secrete exudates that the microbes feed off (into the rhizosphere). 

The microbes in turn release enzymes that help the roots take up water and nutrients. This process helps to boost crop yields, improves resistance of plants to frost and disease, increases the uptake of inorganic constituents from the soil and promotes vigorous growth of the plant or pasture. 

“Seaweed fertilisers are especially useful in organic farming. They contain almost every micro-nutrient in a fully chelated (immediately available) form. Seaweed contains alginates which act as very good soil conditioners.”

The alginates react with metals in the soil and form long, cross-linked polymers in the soil. These polymers improve the crumbling in the soil and swell up when they get wet. They also help soil to hold or contain moisture for a long time, he says.

This article first appeared in the October edition of our sister publication, Dairy Farmer.

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