A PRELIMINARY EVALUATION OF THE AQUAFLEX SOIL MOISTURE SENSOR

Erik Feibert and Clint Shock

Malheur Experiment Station

Oregon State University

Ontario, OR, 2000

Introduction

The Aquaflex soil moisture sensor model SI.60C-03 (Streat Instruments, Christchurch, New Zealand) measures percent volumetric soil moisture content. The objective of this trial was to compare soil moisture data from the Aquaflex sensor and the neutron probe.

Materials and Methods

Two Aquaflex sensors 3 m long were installed in a microsprinkler irrigated hybrid poplar tree field on September 14, 2000 at the Malheur Experiment Station in Ontario, OR. The trees had been planted in April 1997 on silt loam soil on a 14 ft by 14 ft spacing. The tree rows are oriented northwest to southeast on the contour. The microsprinklers are located along the tree row and between trees. Each sensor was installed at 8-inch depth along the tree row and between two trees. The two Aquaflex sensors were connected to an Aquaflex datalogger model SI.74 and soil moisture was recorded every hour. The data from the two Aquaflex sensors was compared to data from two neutron probe access tubes taken from the same depth and from the same tree row and located adjacent to the Aquaflex sensors. Each neutron probe tube was installed between a microsprinkler and a tree and read twice a week. For the sensor comparison, only Aquaflex soil moisture data from the same time as the neutron probe readings were used.

Results and Discussion

Aquaflex readings closely followed wetting and drying of the soil (data not shown). The Aquaflex sensor estimates of soil water closely tracked the neutron probe estimates of soil water over time (Fig. 1). The Aquaflex moisture values were slightly higher than the neutron probe moisture readings. A regression of the Aquaflex data versus the neutron probe data showed a strong correlation with a slightly quadratic curve, reflecting the slightly higher Aquaflex moisture readings (Fig. 2). The Aquaflex datalogger was simple for installation, programming, and data retrieval. The Aquaflex software was easy to use, providing quick graphing of the moisture data. The data can also be moved to spreadsheet programs for further manipulation.

Figure 1. Volumetric soil moisture content over time from Aquaflex soil moisture sensors and neutron probe. Lines are the average of two sensors. Malheur Experiment Station, Oregon State University, Ontario, OR.

Figure 2. Regression of volumetric soil moisture content over time from Aquaflex soil moisture sensors and neutron probe. Data points are the average of two sensors. Malheur Experiment Station, Oregon State University, Ontario, OR.