Caring for your soil needs rethink

14 March, 2022

Avoca managing director Bryce Manderson believes it is time for farmers and lifestyle block owners to re-think how they manage soil health and fertility.

The company is a leading provider of lime and fertiliser mixes in Northland, South Auckland and Waikato, and Manderson says many landowners underestimate the benefits of lime.

Lime itself – calcium carbonate – provides calcium to soil and plants. Calcium ensures efficient plant uptake of water and nutrients, carbohydrate storage in plant leaves, nodulation and nitrogen fixation in legumes, and encourages earthworm activity.

With fertiliser prices at an all-time high, Manderson says it makes sense for farmers to ‘sweeten’ their soil by boosting pH levels through applying lime.

“Lime maximises returns from money spent on fertiliser, reduces soil acidity and significantly increases availability of important plant nutrients – a key benefit of liming.

Lime increases availability of important plant nutrients – phosphorus, nitrogen, potassium, calcium, magnesium and trace elements like boron and molybdenum,” says Manderson.

“I liken lime to being like a multi-powered super-hero because it fosters optimum availability of all other nutrients, so it provides great bang for your buck. You only have to talk to farmers who have a regular liming programme to understand the benefits.”

Manderson says if soils are too acid or too alkaline, nutrients sitting in soil that already existed there or have been added via fertilisers and other soil amendments over the years will not be available to plants.

“So, it’s important to maintain a pH of 6.3-6.5 to optimise the availability of all these nutrients.”

The major nutrients (Ca, Mg, N, P, S, K, and Na) as well as the trace elements Mo and B are most available in near neutral soils, whilst other trace elements (Fe, Mn, Cu, Zn) are more available in acidic soils.

“Of course, rainfall and plant-soil chemical interactions naturally increase soil acidity. On top of that, landowners are responsible for acidification through abundant use of fertilisers on our agricultural land.

“All of these factors steer our soil pH levels below the optimum required for maximum nutrient availability. Applying lime will increase the pH of your soils, creating conditions for greater nutrient availability, and therefore increased productivity,” says Manderson.

He also says it is worth remembering that sulphur is required by plants in similar amounts to phosphorous. Liming not only increases soil pH to that which is optimal for sulphur availability, but in doing so, increases microbial activity allowing for the

mineralisation of OM-S (the major proportion of sulphur in most soils), making it plant available.

“Liming to increase your soil pH to at least 6.0 will optimise magnesium availability. Magnesium is important for plants however, deficiencies are most visibly observed through livestock health issues, for example hypomagnesaemia. Lactating cows are most at risk of this condition resulting in reduced milk yields, and death of the animal in extreme cases,” says Manderson.