Millimeter scale sensor array system for measuring the electrical conductivity distribution in soil

• We fabricate the EC sensor array system which is comprised millimeter sensor chips.
• We make model soil that is constant sandy soil particle size and moisture content.
• We measured the soil solution EC distribution of model soil in real time.
• The model soil EC of different fertilizer concentration to be equilibration.
• The EC increase due to dissolution of the solid ammonium sulfate has been confirmed.

In precision agriculture, the efficient use of fertilizer in order to minimize consumption is important. The amount of fertilizer supplied needs to match the amount consumed by the plant. However, it is difficult to estimate the amount absorbed by the roots. The absorption of the fertilizer has to be determined by continually measuring its distribution on a millimeter scale, which is the scale of the around root. In this study, we developed an electrical conductivity sensor array system that can be used to continuously measure the distribution of fertilizer with clarity using several millimeter sized electrical conductivity sensors inserted in the soil. The electrical conductivity sensor array system measuring unit is comprised an array of five electrical conductivity sensor chips which size is 5 mm × 5 mm. The distribution in two different model soil mixtures was measured continuously using the ECSAS to confirm its capability for measuring the diffusion of the fertilizer. The progress of fertilizer diffusion was confirmed with the change in ECw decreasing over time. The ECSAS was used to measure the distribution of ECw in model soil with the dissolution of solid fertilizer for six days to examine the validity and characteristics of the ECw measurements and the benefits of the ECSAS. As a result, it was confirmed that ECSAS can be used to measure the change in the distribution of ECw due to the dissolution and subsequent diffusion of solid fertilizer in real time on a scale of less than a centimeter. Thus, we consider that the ECSAS will become a very valuable system for continuously measuring the dissolution and diffusion of fertilizer in small areas of soil such as on the scale of rhizospheres.