1. Soil preparation
Prior to planting, the soil needs to be prepared, usually by some form of tillage or
chemical "burn-down" to kill the weeds in the seedbed that would crowd out the crop or
compete with it for water and nutrients. Tillage methods can be divided into three major
categories, depending on the amount of crop residue they leave on the surface. Residue
slows the flow of runoff that can displace and carry away soil particles.
Conventional tillage - Until the last decade or so the standard tillage practice
for corn was use of the moldboard plow for primary tillage followed by several
secondary tillages and mechanical cultivation after the crop was up. Now about
two-thirds of row crops are planted without use of the moldboard plow
(Allmaras et al., 1997), and mechanical cultivation is often limited to one, or no
operations.
Reduced tillage is usually done with a chisel plow and leaves 15% to 30%
residue coverage on the soil.
Conservation tillage leaves at least 30% residue coverage on the soil.
Conservation tillage methods include no-till, where no tillage is done at all and
seeds are placed directly into the previous season's crop residue; strip-till, in
which only the narrow strip of land needed for the crop row is tilled; ridge till;
and mulch till.
Herbicides are used in all these methods to kill weeds. In no-till systems, the herbicide
is applied directly on last season's crop residue. In the other methods, some soil
preparation takes place before the herbicide is applied. A common myth is that more
herbicide is used with conservation tillage methods, but in fact farmers rely on
herbicides for weed control under all tillage systems, and the amount used is more or
less independent of tillage method.

2. Soil Preparation Operations and Timing
Source: USDA - Natural Resources Conservation Service
Tillage can occur anytime between harvest of the previous year's crop and spring
planting. In the eastern Corn Belt, most tillage is usually done between March and May
for corn, and can be as late as early June for soybeans. In some cases, tillage is done in
the fall, after harvest. In southern states, planting can be considerably earlier or later
because of their longer growing season. The optimum time for tillage (to prevent soil
erosion) is just before planting. However, wet spring weather can often make it difficult
to get equipment into the field as early as needed to optimize yield. Late planting can
seriously reduce yields. For example, in the eastern Corn Belt, corn yields are reduced
by 1 bu/acre for each day after May 1 that planting is delayed.