Crop News and Notes Mike
Rankin Less white mold, greater soybean yields with a winter wheat cover crop During the past growing season, field experiments conducted by T. S. Maloney, Research Agronomist for Agri-Tech Consulting in Janesville, showed a significant yield increase for no-till soybeans planted into a winter cover crop. The winter wheat was seeded in October 1999 and then burned down with Roundup herbicide at planting (late April – early May). The strategy effectively forced early germination of white mold soil apothecia by maintaining a cool, humid environment early in the growing season and long before soybean flowering date. Compared to the no-cover crop control treatment, soybeans following the winter wheat yielded 10.3 bushels per acre more at Whitewater and 13.4 bushels per acre more at Janesville. There was no yield difference at Milton where brown stem rot depressed yields of all treatments. Maloney conducted experiments with spring-seeded cover crops (oats and barley) in the same year as soybean planting. This system was also effective in forcing apothecia germination but is more difficult to manage because the small grain isn't killed until after soybean emergence. Raising Non-Rotation Soybean
Depressed crop prices have some crop producers asking about the
possibility of growing 2001 soybeans back on soybean acres from 2000.
The theory is simply that a $5.12 county loan rate for soybean looks
better than the $1.78 loan rate for corn.
Additionally, soybeans don't require a large input of higher-cost
nitrogen.
Maximum yield potential will not be obtained without crop rotation.
This is true of every crop, not just soybean. For soybean, however,
it takes at least two years out of a crop rotation to be able to achieve
full rotation-yield benefits (somewhere around 10 percent increased yield).
However, UW crop rotation studies do not indicate a large yield loss
when second year soybean yields are compared to average yields obtained in a
corn-soybean rotation (0 –2 percent).
UW research also indicates differences in rotation effect between
tillage systems. For
conventional tillage, the yield loss between first-year soybean after five
years of corn and second-year soybean was 6.5 percent when averaged over the
past three cropping years. The
same yield loss in a no-till system was only 3.2 percent.
Crop rotation is always a good management practice.
However, if only corn and soybean are grown in rotation, the yield
penalty is less for growing soybean in two consecutive years than for
growing corn following corn. Flea
beetles pose threat to some sweet corn and seed production fields
During the summer of 1999, Stewart's Wilt was detected in Wisconsin
for the first time in 57 years. This
bacterial disease is spread by the flea beetle. Typically, symptoms appear
after tasseling and are characterized by long gray to green/yellow streaks
along leaf veins. Although most grain hybrids have good resistance to Stewart's
Wilt, sweet corn and inbreds planted for corn seed production are often
susceptible. The Wisconsin
Department of Agriculture, Trade, and Consumer Protection (WDATCP) conducted
an overwintering survey in April, 2000 to see if the flea beetle had
survived through winter. Normally,
this insect is subject to a winter kill-off in climates like we have in
Wisconsin. However, beetle
detections were found in ten Wisconsin counties (including Fond du Lac).
Once again in 2000, Stewart's Wilt was detected in some seed and
sweet corn fields. The WDATCP
conducted a fall survey to quantify the distribution of flea beetle in
Wisconsin. They surveyed 60
counties and 220 sites within the state.
Corn flea beetles were collected at 109 of the 220 sites encompassing
most of the southern two-thirds of the state.
Of the beetles collected, nearly half of them carried the bacteria
responsible for causing Stewarts Wilt.
Stewarts Wilt poses the greatest risk for seed corn producers.
More than 100 countries have quarantine restrictions that prevent the
export of seed to international markets.
If a field is infected (even one plant), it will cause a field to
fail inspection. Some sweet
corn hybrids do have high levels of resistance to Stewart's Wilt, however
most early hybrids remain susceptible. More nitrogen is needed with less tillage
Corn growers are reminded that higher nitrogen (N) rates are needed
with less tillage. This is primarily because mineralization of soil N is slowed
with high amounts of crop residue on the soil surface. Mineralization is simply the conversion of organic compounds
into inorganic elemental forms of N that a plant can use for growth.
The process is temperature driven.
When soils warm more slowly because of crop residue on the surface, N
availability is decreased. Officially, UW fertilizer recommendations state that if greater than 50 percent residue cover remains on the surface at planting, increase N requirement for corn by 30 pounds per acre for the first two years. Be sure to include any appropriate manure and legume N credits.
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