1) The soil is important for the plants because that is where they get their nutrients and food to help them grow and healthier plants or crops. Water conservation is important to manage the water as a sustainable resources and to protect the water environment for human needs for everyday living.
2) The reason why people and farmers plants cover crops is because it helps reduce heavy water flows when it rains and lead to dirty water and ruin the soil nutrients. The roots on the plants impact together the soil leading to a somewhat clean water. Prevent to loss the nutrients and to keep the soil in one place to hold the nutrients.
They help the Hawaii Ahupua'a by reducing the soil erosion going to other place like river or beach.
3) Three career in agriculture that I know are plant pathology, soil scientist and conservation specialist