In the process of gathering soil samples for use in laboratory investigation, errors can occur at several stages:

sampling errors

selection errors

measurement errors

**Sampling errors.** Sampling errors
cannot be eliminated entirely. Since sampling means to take a part, errors
can be reduced by careful selection.

**Selection errors.** Selection
errors can occur when a sampler, eager to do a good job, over-samples
the borders of a field. Sampling in rocky areas can also cause error.
The errors often cancel each other. Otherwise the sampler may employ the
two-step procedure of the simple random sampling which is designed to
eliminate selection errors.

**Measurement errors.** These types
of errors arise in various circumstances:

When the measurement taken is not the true value of the unit. One example is the random error. A random error takes place when cores of soil are mistakenly assigned constant weights, even though they are variable.

As a result of variations in analytical techniques. Fortunately, random errors of measurement tend to cancel each other as the sample size becomes larger.

Bias errors arise either because tare weights are ignored or because of an offset calibration of the appropriate curve.