This textbook presents the concepts and processes involved in the soil-plant-atmosphere system as well as its applications in the water cycle in agriculture. Although reaching the frontier of our knowledge in several subjects, each chapter starts at the graduation level and proceeds to the post-doctoral level. Its more complicated subjects, as math and physics, are well explained, even to readers not well acquainted with these tools. Therefore, it helps students read, understand, and developing their thoughts on these subjects. Instructors also find it an easy book with the needed depth to be adopted in courses related to Soil Physics, Agricultural Management, Environmental Protection, Irrigation and Agrometeorology. It serves also as lexicon to engineers and lawyers involved in agricultural, environmental cases.