Soil conditioning

Soil conditioning improves the chemical, physical and biological properties of the soil that affect fertility. Three important factors are the neutralization of soil pH, the improvement in soil structure and optimized nutrient availability at neutral pH.  It is well known that optimal soil pH can enhance crop growth. Scientific studies by Kirchmann et al. showed that the optimal pH for many crops is even higher than commonly recommended with highest yields being achieved at pH 7.3-7.5. 

Soil conditioning products are usually made from calcium carbonate or other mineral sources. They work by correcting acidity caused by an excess of hydrogen ions which are taking up exchange sites in the clay humic complex of the soil. When calcium carbonate dissolves in the soil, the carbonate ions react with the excess hydrogen, leaving the calcium ions to fill the empty exchange sites. The newly formed carbonic acid breaks into water and carbon dioxide.  For more information on soil conditioning read our technical article here.

Several of Omya’s range of soil conditioning products certified for Organic use. 

We recommend annual application of soil conditioners. Omya products are highly reactive and will correct acid soils in just one season. This means they can be applied in lower quantities, more regularly than agricultural lime, which is traditionally applied every 3 – 5 years. Annual application is important to maintain soil pH in the optimal range, improving nutrient availability, soil health and crop yields.

Omya offers a range of soil conditioners, from granules or liquid to wettable and fine powder products. The choice of product depends on the crop and the equipment available to the farmer. In general, granulated products are most suitable for field crops, while for orchards granules or liquids may be used. For irrigated areas, granules application is possible only during soil preparation. Once the crop is established, we recommend using either liquid or wettable powder products that can be applied with irrigation equipment.

The neutralization of soil acidity is a chemical reaction between limestone and hydrogen particles. The finer and purer the product, the greater the surface area exposed to the soil, resulting in higher reactivity and quicker neutralization. A coarse material such as ag lime, with fewer particles, has less surface area than the same volume of material in finer particles. Omya’s products are ground to an ultra-fine particle size and then granulated to allow you to spread them efficiently. Our highly reactive granulated products will optimize pH much more quickly than ag lime.

The traditional recommendation of ‘a ton to the acre’ of ag lime has no scientific basis and is often recommended regardless of pH or soil type. When you use ag lime, it is only the fine fraction that is effective, as the coarse particles (greater than 0.25mm diameter) have little agronomic effect and generally remain on or near the surface. Much of the ag lime applied is therefore wasted. Omya products have been micronized to less than 0.1 mm diameter, which means the surface area is maximized to be 100% reactive with acid and, as a result, a lower volume is required.

It depends on your soil type, the CEC (cation exchange capacity) and rainfall. In our experience, the pH will start to improve after four to six weeks, and good results are achieved within three months.

Once your soil is balanced you can maintain it with more regular applications at much lower rates. You can generally apply Omya’s granulated or liquid products at lower rates several times for the cost of one application of ag lime without suffering a decline in pH between applications.

On light, sandy soils (a CEC less than 12) the products will react more quickly at lower volumes, so a more frequent application at lower rates is needed, most likely on an annual basis.

On heavy soils (a CEC over 20) a higher application rate is needed to change the pH but, because the soil holds and releases over a longer period, less frequent applications are required (every 2 to 3 years).