The gas exchange cannot occur and plant growth decreases. Alfalfa, for instance, increases in need from the 10-20th day after cutting until it levels off until the next cutting. Barley, however, will peak and then declines in water need. Infiltration or seepage moves into the soil surface for subsurface storage or deep percolation into the aquifer. Soil saturation and runoff occurs when all the air pores in the soil have been filled.
Clay soil holds the most water and sandy soil the least.
Another measure of agricultural water use efficiency is the agricultural production per unit of water. In this case, the land will be placed on the market, either voluntarily or involuntarily, and its price reduced, reflecting the water price increase. Under these conditions, the final effect is likely to be a change in the financial status of the person who owns the land and perhaps also the person who farms the land rather than the type of crop grown. To make any decision regarding an irrigation practice, detailed information is needed about soil properties, the system's capital costs, operation and maintenance costs, new management skills, the availability of water, the effect on water and energy use, and the effect on yields and quality. Most irrigation system improvements will only be made if such a change will increase the net returns of the farming operation.