Soil sampling – why every farmer should do it and how to take accurate samples

Soil samples analysed by Teagasc show that 90% of Irish soils tested have sub optimal soil fertility levels (pH, Phosphorous (P) or Potassium (K)).

Soil sampling has been highlighted as one of the key steps to addressing this issue, and identifying which nutrient is lacking and where they are required.

However, going out and taking samples without a plan may not be the best approach as these soil samples must be representative to produce good results.

The process of soil sampling is critical. According to Teagasc’s Mark Plunkett and there should be at least 20 soil cores taken from an area no greater than 4ha.

These samples should be mixed together to make one sample which represents the area tested.

The soil cores should be taken in a W shape across the sampling area or field. This means that the majority of the area is adequately represented and the variability within the area is also accounted for, he said.

The depth of the soil sample is also critical, and samples should be taken at a depth of 10cm to give a true reflection of the soil fertility levels, he said.

When the core is taken at an inadequate depth the soil test result may be inflated as nutrients such as P become more concentrated towards the soil surface over time especially in permanent grassland fields, he said.

At least three to six months should lapse between the final application of P and K before soil sampling, ignoring this will result in inaccurate soil test results.

Farmers should also avoid areas which could result in an artificial spike in fertility. These areas include field gates, areas around feeders or other areas where animals tend to collect, he said.

According to Plunkett, soil analysis is a relatively small cost and costs in the region of €0.50/ac/year, but the result will be the basis of a three to five year nutrient plan.

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