The Influence of Roots on the Accuracy of Soil-Moisture Measurements Taken with a Neutron Moisture Meter

The effects of roots on soil-moisture measurements taken with a neutron probe were studied. These effects were observed under three different soil-moisture conditions, with different sized roots, and with varying distances between the access tube and root. The moisture conditions used were air dry, field capacity, and saturated. Large roots can greatly affect neutron soil-moisture measurements when the access hole is drilled through the root. Positive errors as large as 52 percent were found when the soil moisture was at field capacity. With dry and saturated conditions positive errors of 43 percent and 38 percent respectively, were found. In most practical field situations, where the access hole is not drilled through large roots, root material appears to have very little effect, if any, on neutron soil-moisture measurements. The largest positive error found, when the access holes were not drilled through the roots, was only 8 percent. This occurred at a point where the access tube was in contact with the outside of a root.