Plants require water, obviously. Soil fertility is also needed for adequate plant growth. Need proper amount of nutrients:
Macronutrients: C, H, O (air and water), Ca, Mg, N, P, K, S(soils)
Needed in large quantities
Micronutrients: Cu, Fe, Mn, Ni, Zn, B, CL, Mo
Needed in small quantities - mostly derived from geologic material and occur during weathering
Note: N, P, K are the usually the most needed nutrients
Nutrient Additions
Nutrient rich parent material
Organic matter content can hold nutrients
i.e. leaves falling from trees
Inorganic fertilizers
Nutrient Losses
Leaching
Soil Humus Importance
Soil warming, good soil structure (gummy materials such as lipids, proteins, etc. to help bind soils), Good porosity to aeration and water holding, supplies nutrients, energy source (carbon) for soil fauna, pH buffering and CEC, sequestration of contaminants
the more humus that you have, the healthier your soil is