Soil water content measurements are made at 5 depths at each of 89 (2" O.D. diameter) aluminum access tubes on the Control transect and at every 5th station (19 access tubes) on the nitrogen fertilized Treatment transect using a neutron probe (Campbell Model 503DR Hydroprobe). Transects are 2.7 km in length and run parallel to each other with the center line of each transect approximately 75 meters apart. Stations are 30 meters apart.
Measurements are taken at 30cm, 60cm, 90cm, 110cm, and 130cm. Measurements taken at 2 week intervals from April 1982 to 1987, monthly since. Count rates are recorded for each depth and access tube. Five standard count rates are taken before and after, and after reading each 20 access tubes. Count rates are also taken in 6 lysimeters along the transect at the above listed depths. If any readings were not measured, the missing depths have a zero in the raw data set of count values. These are changed to "." in converted water content data set. Calculated water content values equal to less than zero are changed to zero in converted water content data set. Converted soil water content values are a volume/volume relationship and represent cm3 water/cm3 soil. Different probes have been used at various times. See PROBE.HIS file for probe use descriptions and regression equations used.