This paper describes spatial variation maps of soil electrical conductivity (EC) obtained by both spectroscopic and capacitance methods using on the go soil sensor ( a real-time soil sensor -RTSS)　SAS 1000, commercialized by Shibuya Kogyo Co. The experiments were conducted over a 2 year period on an experimental Hokkaido farm with an alluvial soil type. The comparison in soil EC records between the spectroscopy and the capacitance were also discussed. The spectroscopic approach used the soil reflectance of 350-1700 nm wavelengths at depths of around 0.2m, followed by application of chemo-metrics to predict soil parameters including soil EC. The records were influenced by mechanical vibration of tractor and other factors. The capacitance approach used the soil capacitance by the probe of the electrode on the tip of the penetrator to monitor the cutting soil while the quality of data was strongly influenced by the state of the interface between the soil and blade. Results show that there are significant differences in variation patterns of soil EC maps by spectroscopy and capacitance sensor methods. In addition, an area of high error in soil EC prediction and soil EC measured by capacitance sensor was observed. This may be attributed to “build-up-edge phenomena” causing error readings by the capacitance sensor.

Latest research was done in August 2009 and will be conducted again in November 2009. Research continues with a focus on examining and comparing both sensors to confirm the relationship between those sensors and to determine the nature and causes of EC variability. In order to do this, the relationship between several soil properties are being analyzed, such as soil moisture, soil organic matter, nitrogen, etc. Besides attempting to describe the spatial pattern of EC, this paper will also attempt to describe the temporal stability of the spatial pattern of these fields.