till, dig
耠 centers on working the soil: tilling or digging the ground to prepare it for planting.
耠 combines 耒 (a plow-like farming tool) with 合, which likely contributes the sound. The character is associated with tilling or digging soil.
The left side 耒 is a plow, and the right side 合 suggests joining or fitting together. Picture a plow fitting into the earth, turning the soil as you till the field.
For コウ, imagine a farmer tilling the soil while a cow watches nearby: cow -> コウ, and the plow digs into the ground.