How Many Soil Samples Do I Need?

A perfect soil testing program would tell you exactly what nutrients you need to add to each part of your fields for optimum crop yields. This would account for all the variability in soil fertility that was naturally present in the soil as well as what we have imposed by our management. The reality is that we need to balance the cost of increasing precision against the value we can gain from this precision. 

What does Nutrient Management require?

The nutrient management regulations specify that a single soil sample can’t represent more than 10 hectares (25 acres). This is in line with the original field boundaries on many farms, and should capture much of the variability from past management. There is an option for including a larger area in a single sample, but this is only where the field has already been shown to be uniform. 

Where will it pay to sample more intensively?

The risk with sampling large fields is the loss of income from under-fertilizing responsive areas within the field, and over-fertilizing non-responsive areas. If there is going to be an advantage to intensive sampling, there has to a mix of responsive and non-responsive areas within the field, and they need to be arranged in such a way they can be measured, and managed. In low testing fields, the best investment is in fertilizer rather than in more precise testing. In high testing fields, the cost of intensive sampling to find the parts of the field that might be responsive to fertilizer will be larger than the value of any increased yield 

Smart sampling: dividing field sections to get the most information

When you divide your fields, the data you need the most will help to guide how to draw the boundaries between sections. The following table will help to guide your decisions.

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