Complex sentence: It is natural for soil to be turned over and mixed up periodically, usually seasonally; however, human involvement can expedite these processes, and can even change the landscape as well as the physical and chemical properties of the soil.
Split into simpler sentences: It is natural for soil to be turned over and mixed up periodically, usually seasonally. However, human involvement can expedite these processes, and can even change the landscape as well as the physical and chemical properties of the soil.