Methods and apparatuses to activate, modify, and sanitize the surfaces of granular, powdered, or seed material placed in a continuous flow of a low-temperature, reduced-pressure gas plasma. Said plasma may be created with radio-frequency power, using capacitive-inductive, or a combination of both types of discharge. The plasma is generated at pressures in the 0.01 to 10 Torr range. RF frequency ranges from 0.2 to 220 MHz, and correspond to a plasma density between about ne×108-ne×1012 or 0.001 to 0.4 W/cm3. Inserts and electrodes may be temperature controlled to control process conditions. RF discharge may be pulsed or modulated by different frequency in order to stimulate energy exchange between gas plasma and process material. The apparatuses may be grounded, biased and mechanically activated (e.g., vibration, rotation, etc.).