Agriculture Reference
In-Depth Information
tillage and with chemical inputs at rates recommended by university
and industry consultants. Crop varieties are chosen on the basis of yield
performance in state variety trials (e.g., Thelen et al. 2011). Beginning in
2009 (for soybean) and 2011 (for corn), we have used varieties genetically
modified for glyphosate resistance and (for corn) resistance to European corn
borer ( Ostrinia nubilalis ) and root worm ( Diabrotica spp.). Prior to this, we
had used the same seed genetics in all cropping systems. Wheat varieties are
in the soft red winter wheat class common in Michigan. Fertilizers (primarily
nitrogen, phosphorus, and potassium) and agricultural lime (carbonate
minerals that buffer soil acidity) are applied at rates recommended by
Michigan State University (MSU) Extension following soil tests. No crops
are irrigated. Herbicides and other pesticides are applied to all three crops
as prescribed by integrated pest management (IPM) guidelines for Michigan
(e.g., Difonzo and Warner 2010, Sprague and Everman 2011). Tillage for
corn and soybean includes spring chisel plowing followed by secondary
tillage to prepare the seed bed. Fall-planted winter wheat usually involves
only secondary tillage. Crop residues are either harvested for animal bedding
(wheat) or left on the field (corn, soybean).
 • The No-till system (T2) is managed identically to the Conventional system 
except for tillage and herbicides. A no-till planter is used to drill seed directly
into untilled soil through existing crop residue without primary or secondary
tillage. When prescribed by IPM scouting, additional herbicide is used to
control weeds that would otherwise be suppressed by tillage. The system has
been managed without tillage since its establishment in 1989.
 • The Reduced Input system (T3) differs from the Conventional system 
in the amounts of nitrogen fertilizer and pesticides applied, postplanting
soil cultivation (prior to 2008), and winter plant cover. Crop varieties are
identical to those in the Conventional system. During corn and soybean
phases of the rotation, a winter cover crop is planted the preceding fall and
plowed under prior to planting corn or soybean the following spring. A cover
crop is not planted during wheat years because winter wheat is planted in the
fall, immediately following soybean harvest. Nitrogen fertilizer is applied
at reduced rates relative to the Conventional system: at 22% of the rate
applied to Conventional corn and at 56% of the rate applied to Conventional
wheat, for a full-rotation reduction to 33% of the Conventional system rate.
Reduction in nitrogen inputs from Conventional management is expected
to be made up through atmospheric N 2 fixation by legumes in the rotation:
a winter cover crop of red clover ( Trifolium pratense L.) follows wheat to
precede corn, and soybean precedes wheat. A nonleguminous winter cover
crop of fall-planted annual rye grass ( Lolium multiflorum L.) follows corn to
precede soybean.
The Reduced Input system thus has five species in the rotation—corn/
ryegrass/soybean/winter wheat/red clover—so a crop is present at all times of
the year during the entire 3-year rotation cycle. Crop varieties are the same
as those used in the Conventional system, including genetically modified
varieties since 2009.
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