Published online by Cambridge University Press: 27 March 2009
The neutron method of estimating soil moisture content in the field has the advantage that once access tubes are installed no further disturbance to the site is necessary and readings can be taken repeatedly throughout the soil profile at a fraction of the time necessary for the gravitational method. However, measurement of moisture content in the surface layer of soil, the top 10 cm, has proved difficult since the source and detector must be at a depth less than the sphere of influence allowing some neutrons to escape to the atmosphere. This air-soil interface effect can lead to an underestimation of moisture content which is greatest in wet soil (Van Bavel, Hood & Underwood, 1954).