Charles Sturt University
Graham Centre for Agricultural Innovation

Organic matter, lime and subsoil acidity

Soil acidity is a significant challenge for farmers - reducing crop production and restricting the choice of crops and pastures to acid tolerant species.

A new strategy to target subsoil acidity is the focus of PhD research Mr Hoang Han Nguyen from Charles Sturt University’s (CSU) School of Agricultural and Wine Sciences.

He’s investigating how adding organic matter in combination with lime to the soil surface layer can address acidity in the subsoil.

The research

Hoang Han NguyenThe most common strategy to improve crop yield in acidic soils is to raise the soil pH. This is relatively easy to achieve at the surface layer (0-10 cm) by applying soil amendments such as lime (CaCO3) or dolomite (CaMg(CO3)2). However, acidity in the subsoil, the soil layer bellow 10 cm of the soil profile, is difficult to correct because of the relatively low solubility of liming materials and the slow movement of the amendments down the soil profile.

Addition of organic amendments can ameliorate acidic soils. The organic matter also increases the pH where it is placed but also the soil layers below it.

The aim of Mr Nguyen’s PhD research is to better understand this complex interaction between the lime and the organic matter amendment and how this impacts the soil layers below the place of incorporation.

Putting it to the test

Mr Nguyen’s first experiment, conducted in glasshouse conditions, indicated that an organic amendment such as lucerne pellets not only increased soil pH at the incorporated layer but also raised the pH of the soil layers below it. In contrast, the addition of lime only increased pH at the incorporated layer.

The research also found that when lucerne pellets in combination with lime, were incorporated into the surface soil layer it increased pH of the layers below the placement greater than lucerne pellets alone.

Now to the paddock

Hoang Han Nguyen in the fieldThese glasshouse house results will be evaluated under field conditions during the next two years. In these field trials, Mr Nguyen will evaluate the effects of that amelioration strategy on soil pH at subsoil layers.

He’ll also examine the impact of the strategy on crop growth in field conditions, using different varieties including some sensitive to soil acidity.

It’s hoped the results from the field trials will contribute to the development of an innovative amelioration strategy to manage subsoil acidity in agricultural systems of the region. The research also aims to identify which organic components in lucerne pellets are responsible for increasing soil pH at the soil layer below the amended layer.

Mr Nguyen was awarded a Vietnam Government Scholarship, and is supervised by Dr Sergio Moroni, Dr Jason Condon and Mr Alek Zander from CSU and Dr Guangdi Li from the NSW Department of Primary Industries (DPI).

Contact: Mr  T: 0468462014 E:


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