Capacitance probe calibration for an Ultisol Udult cultivated with sugarcane by soil tillages

The use of moisture readings by the indirect method has been increasing in recent years, such as the use of a frequency domain reflectometry capacitance (FDR) technology, but the use of this equipment requires a calibration for the soil. Usually these equipments are calibrated by soil layers, but the calibration of an FDR sensor by different soil tillage has never been performed. Therefore, this study aimed to: i) calibrate a frequency domain reflectometry capacitance probe (FDR) for a Ultisol Udult; ii) evaluate the calibration by Bland-Altman’s methodology; iii) calibrate the equipment for the same soil by applying four different soil tillage systems (conventional tillage, minimum tillage, minimum tillage with deep subsoiling, and no-tillage); iv) evaluate whether calibration separated by soil tillage is more effective than without separation. The experiment was carried out using split-pilot design on the premises of the Santa Fe plant, municipality of Ibitinga-SP-Brazil. Probe calibration reached up to one meter deep and generated four regression curves, one for each soil tillage system with the soil bulk density and macroporosity affecting the Diviner 2000 equipment calibration. Manufacturer’s soil calibration proved inadequate based on Bland-Altman’s methodology. It was used soil tillage systems as separation factor to calibrate the equipment, which increased the determination coefficient in 16 % in relation to soil calibration. Soil tillage, by modifying the structure of soil physical attributes, also affected the calibration of the Diviner 2000 equipment, proving that in an area where different soil tillages occurs, one calibration must take place for each soil tillage.