The Model can estimate water demandWater demand is an estimate of actual water use.Water demandWater demand is an estimate of actual water use. is an estimate of actual water use. based on poor, average and good irrigation management factors.
This is accomplished by developing an irrigation management factor for each crop, soil and irrigation system combination. The Maximum Soil Water Deficit (MSWD) is the maximum amount of water that can be stored in the soil within the crop rooting zone. An irrigation system applying more water than what can be stored will result in percolation beyond the crop’s rooting depth. Irrigation systems with high application rates will have a probability of higher percolation rates, a stationary gun for instance.
For each soil class, a range of four MSWD are provided, which reflect a range of crop rooting depths.
An irrigation management factor, which determines the amount of leaching, is established for each of the MSWD values for the soil types (Table 4). The management factor is based on irrigation expertise as to how the various irrigation systems are able to operate.
For example, Table 4 indicates that for a loam soil and a MSWD of 38 mm, a solid set overtree system has a management factor of 0.1 for good management while the drip system has a management factor of 0.05. This indicates that it is easier to prevent percolation with a drip system than it is with a solid set sprinkler system. For poor management, the factors are higher.
There are a total of 1,344 irrigation management factors established for the 16 different soil textures, MSWD and 21 different irrigation system combinations used in the Model.