Agriculture Reference
In-Depth Information
Prior to 2008, weed control in corn and soybean phases of this rotation
was provided by tillage and by applying herbicides at label rates only within
rows (banding), so overall application rates were one-third of the amount
applied in the Conventional system. Additional weed control was provided by
mechanical means—rotary hoeing and between-row cultivation several times
after planting. Since the use of glyphosate-resistant varieties was initiated in
2009, weed control for soybean currently relies on herbicide (glyphosate) as
in the Conventional system. Weed control in wheat is provided mainly by nar-
row row spacing (19 cm [7.5 in.]) with no additional tillage; herbicide is only
rarely applied to treat outbreak weed populations.
• The Biologically Based system (T4) is similar to the Reduced Input system
except that neither nitrogen fertilizer nor pesticides are applied in this
system and no genetically modified crop varieties are used. The system is
entirely dependent on leguminous N
2
fixation for external nitrogen inputs,
which supplements the 6-8 kg N ha
-1
yr
-1
received by all systems in rainfall
(Hamilton 2015, Chapter 11 in this volume). Cover crops are as described for
the Reduced Input system. Weed control is provided by tillage and by rotary
hoeing and cultivation after planting. This system is certified organic by the
USDA, but differs from conventional organic systems because it receives
no manure or compost. This creates a system that is as reliant as possible on
internal, biologically based nitrogen inputs.
In addition to four annual cropping systems, we have three perennial cropping
systems, one herbaceous and two woody:
• Alfalfa (T6) represents a perennial herbaceous biomass system. Alfalfa
is grown in a 6- to 8-year rotation with the duration defined by plant
density: when the stand count declines below a recommended threshold, the
stand is killed with herbicide and replanted. Because alfalfa reestablishment
can be inhibited by autotoxicity, a break year is needed in the rotation and
a small grain such as no-till oats or winter wheat is grown for one season
in between alfalfa cycles. Alfalfa is commonly harvested three times per
growing season for forage. Fertilizer (mainly phosphorus, potassium, and
micronutrients such as boron and molybdenum) and lime applications follow
MSU Extension recommendations following soil tests. Varieties are chosen
on the basis of MSU yield trials.
• Poplar (T5) represents a short-rotation woody biomass production system.
In 1989 hybrid poplar clones (
Populus
×
canadensis
Moench “Eugenei”
([
Populus deltoides
×
P. nigra
], also known as
Populus
×
euramericana
“Eugenei”), were planted as 15-cm stem cuttings on a 1 × 2 m row spacing,
with nitrogen fertilizer applied only in the establishment year (123 kg N
ha
−1
). A cover crop of red fescue (
Festuca rubra
L.) was planted in 1990 for
erosion control. Trees were allowed to grow for 10 years then harvested in
February 1999 when they were dormant and frozen soil prevented undue
soil disturbance. For the second rotation, trees were allowed to coppice
(regrow from cut stems) and were harvested in the winter of 2008. After a
