In addition to the quantity of residues remaining following harvest, a variety of types of residues is also important. The goal should be a minimum of three different species in a rotation, more if possible.
The percent of the time that living roots are present during a rotation is also important. The period that active roots are present varies considerably, ranging from 32% of the time for a corn-soybeans rotation to 57% for a beans-wheat rotation to 76% for a three-year beans-wheat-corn rotation (table 11.1).
As mentioned above, when soils are covered with living vegetation for a longer period of time, there tends to be decreased erosion as well as a decreased loss of nitrate and less groundwater contamination.
|Table 11.1: Comparison of Rotations: Percent of Time Active Roots Are Present and Number of Species|
|Rotation||Years||Active Rooting Period (%)||Number of Species|
|Dry beans-winter wheat||2||57||2|
|Dry beans-winter wheat/cover||2||92||3|
|Dry beans-winter wheat-corn||3||72||3|
|Corn-dry beans-winter wheat/cover||3||76||4|