If grain follows a row crop-as wheat after corn, soybeans, or field beans; oats or barley after corn, potatoes, beans, sugar beets-plowing is not necessary and the first tillage operation in preparation for the grain is a through disking of he seedbed. The spring-tooth or the field cultivator may also be used for this first operation. Usually the grain yield following such tillage is as good as that following plowing, or the difference is not great enough to warrant the extra cost of plowing.
In dry-land areas even stubble land is often disked rather than plowed in order to have enough straw and stubble at the surface to reduce blowing. If rye been seeded as a winter cover, it may be disked into the surface in the spring rather than plowed under, if tillage is done when the rye is not over 12 or 14 in. high and the job is thorough enough to kill essentially all the rye plants. Lighter soils are often disked rather than plowed, for it is comparatively easy to work considerable trash into these soils with a disk.
At least one exception to the disking of land previously growing a row crop must be made. If corn has been infested with the European corn borer, either the crop must be cut extremely short or the corn stubble and refuse should be plowed under. The borer overwinters as a larva in cornstalks, stubble, or large-stalked weeds. If plowed under, most of the larvae will be destroyed provided that a clean job of plowing is accomplished. If corn stubble and stalks are merely disked or if a considerable amount of such material is left on the surface, even though the land has been plowed, the larvae find shelter in this surface refuse and eventually emerge as moths to establish a new infestation.