Tillage is defined as the physical manipulation of the soil for the purposes of managing previous crop residues, preparing a seedbed for planting, controlling competing vegetation, and incorporating fertilizers and other crop production inputs. Tillage, when done at the correct soil moisture, allows the soil to fracture along the existing soil structural planes. The soil moisture should be such that soil aggregates will separate easily when worked, without the smearing or destroying the aggregates, which would occur if the soil is too wet. Tillage, and the subsequent residue management effects, will have a profound effect on soil processes and properties that directly impact crop production. Examples of these processes and properties are soil structure, water infiltration and movement in the soil, bulk density, aeration, soil warming, biological activity, and residue and organic matter relationships. Tillage also affects plant nutrient availability. This topic was discussed at the WFCA Conference in 2004 and will not be covered in detail in this paper.

The interest in soil conservation has resulted in increased production under conservation tillage. Researchers have found increased crop yield after several years of conservation tillage (notill), even though some measured soil physical properties appear unfavorable (Hill, 1990). Some of this effect has been related to increased continuity of pore space, more favorable soil water relationships, and the maintenance of soil organic matter (Karlen et al., 1990). Others have noted a Ayield drag@ associated with no-till that has been related to cooler soil conditions. This paper will outline some of the effects of tillage on soil physical and biological properties and how they may impact crop production.