Infiltration deals the mechanism of entry of water into soil from surface water, rainfall or irrigation. Beside, hydraulic conductivity deals flow rate of water per unit area. We may say... ability of fluid to flow through material.
The infiltration rate describe the ability of fluid to penetrate through the surface of the upper layer of soil. Percolation describes the movement of water through the soil after the entery. Hydraulic conductivity; however is a lump parameter measure the ability of soil to transmit fluid. Hydraulic conductivity reflect both the soil properties as well as the property of fluid.
Percolation term usually refers to loss of water from a particular soil layer. Can have positive and negative impacts depending on purposes in various fields.
Simply, infiltration: entry of water into the soil (ground surface of soil). (Here, word “entry” is important to understand this concept). For a particular point or location, Initial infiltration rate (rate of entry of water) is high, but afterward it decreases. Finally it become constant.
Hydraulic conductivity: flow rate of water through the soil (layer or colunm or profile). it could be vertical hydraulic conductivity or horizontal hydraulic conductivity base on direction of flow of water. Thank you.