Date of this Version
Soil Management, National Corn Handbook, NCH-22, 1992, pp. 1-4.
If "tillage" is defined as the mechanical manipulation of soil, it follows, then, that a "tillage system" would be the sequence of soil-manipulation operations performed in producing a crop. Today, however, such a definition is recognized as inadequate. We know, for instance, that the management of non-harvested plant tissue (i.e., residue) affects both crop production and soil erosion, and that field operations in which the soil is not tilled have a marked influence on soil condition.
Therefore, in this publication, a tillage system is the sequence of all operations involved in producing the crop, including soil manipulation, harvesting, chopping or shredding of residue, application of pesticides and fertilizers, etc. But before describing and comparing the various tillage systems for corn, some terminologies and possible points of confusion need to be addressed. These have to do with primary vs. secondary tillage and the different ways in which similar tillage systems could be defined.
PRIMARY AND SECONDARY TILLAGE
For many tillage systems, the specific operations can be separated into "primary" and "secondary." Primary tillage loosens and fractures the soil to reduce soil strength and to bring or mix residues and fertilizers into the tilled layer. The implements ("tools") used for primary tillage include moldboard, chisel and disk plows; heavy tandem, offset and one -way disks; subsoilers; and heavy -duty, powered rotary tillers. These tools usually operate deeper and produce a rougher soil surface than do secondary tillage tools; however, they differ from each other as to amount of soil manipulation and amount of residue left on or near the surface.
Secondary tillage is used to kill weeds, cut and cover crop residue, incorporate herbicides and prepare a seedbed. The tools include light- and medium -weight disks, field cultivators, rotary hoes, drags, powered and unpowered harrows and rotary tillers, rollers, ridge- or bed -forming implements, and numerous variations or combinations of these. They operate at a shallower depth than primary tillage tools and provide additional soil pulverization.
Equipment that permits primary and/or secondary tillage plus planting in a single operation is also available.