In too many cases, soil samples are taken, samples are sent to the lab, results are returned, sent to the adviser and that’s the end of it.

Doing that only fulfils the regulatory objectives of soil sampling and no farming benefit is generated unless the results are acted upon.

The first and most important part of the results to look at is the soil pH. When looking at pH, ignore the SMP or buffer pH, as this is only used for calculating background acidity.


The target soil pH is 6.2 to 6.5, but many farmers who are good at farming clover will aim to be at the higher side of this range.

The soil sample results will outline how many tonnes of lime is required, usually in tonnes/ha.

Spreading any more than 5t/ha in any one year is not advised, so if a field is very deficient for lime, it may be better to spread the lime applications out over a number of years.

Then look at phosphorus and potassium levels. These are usually presented as both an actual concentration in terms of mg/l and also as a soil index.

Farmers should really be looking at both because there’s a big difference between a result for phosphorus of say 5.1mg/l and 7.9mg/l, even though both are in index three.


Fields that are low for potassium will have a high potash requirement, but, again, this is something that farmers need to be conscious of, because you want to avoid luxurious uptake of potash which could cause grass tetany and milk fever issues.

The best time to spread potash is in the autumn at rates of not more than 100 units/acre. Remember to make sure to fix lime first, before trying to correct P or K.