We observed field variability of soilwater pressure along a 290-m transect through a field near Socorro, New Mexico. Pressures were measured by 94 individual tensiometers permanently installed at 3-m intervals along the transect at a 0.3-m depth. To monitor the tensiometers, we used a single, digital-readout, pressure transducer that could be rapidly connected by inserting a hypodermic needle through the rubber stopper seal at the top of the tensiometer unit. With this monitoring system a series of pressure measurements for the entire transect could be completed in 30 min. The transect was monitored several times during a 2-wk period following a 13-mm rainfall.
The observations show a gradual increase of soil water tension over time and a high degree of spatial variability; the tension ranged from 0.15 to 0.7 bars at a given time. Covariance analyses of the pressure data show that the variations are spatially correlated over distances of at least 6 m. The variance of pressure is observed to increase with mean tension; this trend agrees with predictions from stochastic theory.
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