Irrigation scheduling needs to begin with a discussion on soil and soil water. This is the basis of irrigation scheduling.
Coarse soils, such as sands and gravels, have relatively large pores. However the number of pores is small when compared to a finer textured soil. Fine soils, like clays or clay loams, have relatively small pores. Having many small pores means that a fine textured soil can hold more water than a coarse textured soil.
Coarse sandy soils can have roughly 0.5 inches of available water per foot of soil depth. On the other hand, silt loam soils have roughly 2 inches of available water per foot of depth. Crops can use about half of the available water without any yield reduction. With the large range of available water for different soil types, it becomes clear that a better understanding of soil water and soil physical properties is needed before fine tuning an irrigation schedule.