The main reason we apply lime to the soil is to adjust the soil pH but why do we want to bother doing that? Instead of this simple explanation I like to think backwards to get the real point of liming, at the end of the day most goals in cropping coincide with maximizing profitability while minimizing any negative effects on the soil and the surrounding environment (4R nutrient stewardship).

How liming fits in with this mindset is really simple, if your soil pH in your root zone is correct the maximum amount of nutrients in the soil profile are available for plant uptake without the need to be in excess to achieve maximum plant growth and production. The following chart shows the availability of different nutrients at different pH’s for most crops that we grow in southwestern Ontario.

As you can see an ideal soil pH would be 6.5 for optimum nutrient uptake and uptake really starts to drop off with most nutrients as the soil pH goes below 6.1.

The decision to lime a field or parts of a field are based on the soil pH from a recent soil test, the Buffer pH on the soil test gives us the indication of how easy the soil pH will change or how much reserve acidity there is which ultimately dictates how much lime we apply to the soil to achieve the desired pH.  The lime source will then dictate the amount needed to achieve this goal, in Ontario the recommendations are based on an agricultural index of the lime to be 75. The agricultural index is an indicator of limestone quality that combines the neutralizing value and the fineness rating so basically the ability of the lime to change the pH and how fine the lime is.

There are several sources of lime in the province and they can all vary in agricultural index so knowing this is key in determining the actual amount of lime you need to apply to the soil to achieve your desired pH. To further complicate the matter there are two types of lime, Dolomitic and Calcitic, the percent of Calcium and Magnesium will determine which lime is which. In general Dolomitic lime is applied to soils with low levels of Magnesium which are often sandier soils while Calcitic is applied to soils with high Magnesium levels which are often soils with more clay content.

With wheat harvest behind us, now is the perfect time to get soil sampling done apply lime if needed, get it incorporated into the soil to maximize your profitability and reduce any negatives effects on the surrounding environment not to just change the soil pH.