The AM400 was only tested at one location with a clay loam textured soil. Accuracy of the probes was initially determined by using regression to compare available soil moisture percentage calculated from the readings of the various sensors to the value calculated from the readings of a CPN 503 soil moisture probe. There are a few limitations for this method of comparisons. A single reading soil moisture reading at a specific depth does not necessarily accurately represent variations in soil moisture for a 20 to 30 cm depth interval. Additionally, the soil moisture monitoring probes were not placed in exactly the same location as the neutron probe at a sample site.
Soil moisture can vary over fairly short distances, especially within an irrigated field.
At a few sites, available moisture calculated from the neutron probe readings were consistently higher or lower than that calculated from the readings of the various soil moisture sensors. Comparison of slope of regression line between neutron and theta soilmoisture probe at one location. The only difficulty with the probe came during installation. The soil auger provided by the supplier for installation of the polycarbonate tubes was inappropriate for clay textured soils. It would be more effective if the auger came equipped with a t-handle so more force could be exerted when auguring in dry clay or clay loam textured soils.