Laboratory temperature-compensating calibration procedure for soil water content determination by reflectometry

Abstract

The water content reflectometer allows a temporal and spatial assessment in soil water dynamic. This work aimed to study the behavior of the sensor (CS616) for the period measurement in function to the temperature and soil water content. The tests were conducted at State University of Mato Grosso, Tangara da Serra municipality. We used PVC (polymerizing vinyl chloride) pipe to make six recipients (0.1 m diameter and 0.4 m height) and filled them with soil. For each one of them a sensor CS616 and temperature sensor (K type) were allocate in a central position. The soil water content for each recipient were fitted to 0.00; 0.06; 0.11; 0.16; 0.22; 0.27 m³ m^-3, and the samples were submitted to temperature gradient from 1.0 up to 40.0 °C. Data of temperature, and period response were recorded in a data logger. Notice that the temperature provides changes for period response val­ues (μs), and as greater the soil water content, as greater the temperature influence. From collected data, two models were fitted (linear and quadratic), and compared with manufacturer standard equations. For conditions in that study, the fitted quadratic model provide the best approach for the water soil content prediction.