11 June 28 - Colorado State University Extension

D. Bruce Bosley
Extension Agent/Cropping Systems
Colorado State University Extension
508 S 10th Ave., Ste 1, Sterling Co 80751
(970) 522-3200 Ext. 285
Crop Rotation
Rotating crops has been seen as a valuable cultural practice proven to reduce plant
diseases and pest problems as well as improving soil health and plant productivity. Agricultural
references to crop rotation have been found in literature from ancient Rome and civilizations in
Southeast Asia prior to 100 B.C. Northeast Colorado dryland producers have incorporated
rotations in their cropping system to make more efficient use of the rain and snowfall that we
receive each year. Most of our irrigated crops yield better and have fewer insect and disease
problems when grown in a rotation. It can be claimed that continuous irrigated corn is the one
exception in Colorado. We can attribute this in large part to our dry climate, advances in crop
genetics, and improvements in crop production and pest management practices. However, today
I’ll focus on those crops where rotation is beneficial especially in reducing crop diseases.
Irrigated and dryland wheat producers have often noted that while they can grow wheat
back to back in subsequent years the second crop never has the same yield potential as the first
crop even when rainfall and climate are favorable for winter wheat. Many farmers have also
discovered that their wheat crops yield better following corn and grain sorghum as well as other
crops in a multiple year rotation. Consequently, we see dryland producers raising three and four
year wheat based crop rotations that are both more profitable and better at protecting from soil
erosion than the traditional wheat fallow rotation. Many plant non-grass crops such as sunflowers
and experimenting with canola and peas to optimize the benefits of crop rotations.
Continuous cropping wheat and traditional wheat-fallow rotations often encourage soil
borne diseases. I have found damaging levels of Fusarium (dryland) foot rot on irrigated and
dryland fields in Northeast Colorado. It is best to rotate crops to reduce Fusarium foot rot
inoculum and avoid planting wheat following corn or wheat. Take-all is a significant risk in
irrigated wheat when growers plant it two or especially more years in a row. Crop rotation is the
most practical, economical and successful means of control of take-all. Rotations with soybeans,
other legumes, or corn is most satisfactory. A rotation with two years between wheat crops is
highly recommended.
Alfalfa suffers from many soil and crown diseases in later years of its production in
fields. Crown rot is chief cause for yield decline in alfalfa. Crown rot comes from a complex of
common soil organisms including Fusarium, Pythium, and Rhizoctonia. Crown rot arises
naturally with the age of the stand but is often increased by mechanical weed control efforts
when harrows or disks are used.
Stem nematode is another alfalfa disease that can occur in irrigated fields. Rotation with
non-host crops such as sorghum, small grains, beans, and corn on a 2- to 4-year basis should
reduce alfalfa stem nematode populations. Use longer rotations where stem nematode has
become a problem in a field.
Selection of nematode resistant alfalfa varieties can help in reducing this disease. Use
clean, nematode-free seed. Avoid moving contaminated farm machinery or livestock from an
infested field to a clean field. Avoid using contaminated wastewater or tail water. Keep manure
from feedlots where cattle have been fed infected hay out of clean fields. Also, cutting alfalfa
fields only when the top 2 to 3 inches of soil are dry should help reduce re-infestation. University
trials demonstrate that frugal applications of irrigation water to keep soil surfaces dry will
minimize spread into later cuttings.
Please contact Bruce Bosley for questions on these and other cropping systems topics at
(970)768-6449 or bruce.bosley@colostate.edu.
Extension programs are available to all without discrimination. If you have a disability for which you seek
an accommodation, please notify Bruce Bosley 7 days before the event. Colorado State University Extension, U.S.
Department of Agriculture and Colorado Counties Cooperating.