It is important to remember that tile drainage does not remove plant available water from the soil. Clearly, the greatest benefits of tile drainage are realized in wet years--but because drainage promotes deep root development, crops will have better access to soil moisture in dry years. During extremely dry years it is conceivable that a tile-drained field might have less available water at some point during the growing season than an undrained field. Whether or not this would offset the early-season positive effects of drainage is unknown. In general, where poorly drained soils exist, crop yields will be more uniform from year to year with tile drainage.