Monthly soil water content measurements are made at 10 depths (where
possible) at each of 10 access tubes at each of the 15 LTER-II NPP
sites using a neutron probe (CPN Model 503DR Hydroprobe). The counts
of thermalized neutrons are adjusted for the decay rate of Americium
241, then converted to soil water content using individual site
regressions. Soil water content is a volume/volume relationship and
represent cm3 water/cm3 soil. Data are provided at 30cm intervals from
30cm to a maximum of 270cm soil depth, shallower when an impenetrable
caliche layer is reached. Field readings may include one at 300cm;
however, the value for the deepest depth of each access tube is removed
from the calculated soil water content data because of the effect of
measuring greater soil volume directly below the probe than that of the
more shallow depths.
