What is the difference between Bulk conductivity and Pore conductivity?

The bulk conductivity of a soil is the conductivity of everything in the volume being measured, including the water, nutrient ions, the soil particles and any organics (including the roots) in the soil. It is affected by the moisture content of the soil.

The pore conductivity is the conductivity of the water in and around the soil pores. This is effectively the conductivity of the water that is available to the plant to consume. This is affected by temperature and requires a minimum water content to measure.