Your irrigation requirement partly depends on how much water your soil can store for future use. Therefore, the first step in calculating your irrigation needs is to determine how much water 1 cubic foot of your soil will hold. Most pores in clay loam or fine-textured soils are medium to small in size and can retain considerable water in the numerous pores due to strong surface tension. Most pores in coarse-textured sandy soils are large in size, but there are fewer of them and they retain little water. Once the root area is completely wet, it will not hold more water.
Additional water percolates below the root zone and is wasted.
Fertilizer may leach below the roots and contaminate groundwater. Calcium also is leached, resulting in soil acidification and poor nutrient uptake. In addition, too much water can cause root rot. Careful water management or preplant deep soil ripping is needed to control these conditions. The total amount of water your soil can hold in 4 feet is 6 inches.