This document discusses the best options for late-summer or fall forage production, highlighting that corn silage yields better than other crops like sorghum and soybeans when planted in June or July. It outlines nitrogen management concerns due to heavy spring rainfall and provides guidance on glyphosate application timing for corn and soybeans, emphasizing the importance of adhering to label recommendations. Additionally, the document covers the implications of late planting on soybean flowering and maturity, noting that adjustments can be made based on planting dates and environmental conditions.

1. Corn Silage. When looking at crop species options for
producing late–summer or fall forage, corn for silage still
yields more during June and July planting dates as com-
pared to crops like sorghum-sudangrass, soybeans, alfal-
fa, and small grains. Research at the University of Wis-
consin shows corn silage is the best choice for emergen-
cy planting at any date and location in Wisconsin. Despite
little or no grain yield on late-planted corn, it can achieve
relatively high quality as compared with other alternative
forage crops. Typically, planting an early-season hybrid
shows a quality advantage (Milk/T) over a full-season
hybrid when planting is delayed into June. However,
when planting is delayed to mid-June or July, early-
season and full-season hybrids produce similar silage
yields and quality as starch differences are small since
grain development is limited no matter the maturity uti-
lized.
Warm-season Grasses. Although lower yielding, warm
season grasses, such as sorghum-sudangrass, may be
options for growers who are interested in planting a crop
that can be harvested earlier than corn silage for emer-
gency forage. Warm soil and growing conditions are re-
quired for these crops to succeed. In addition, harvest
may only be a few weeks ahead of when corn silage is
harvested, with the first harvestable crop about six weeks
after planting.
Heavy spring rainfall causes concerns about nitrogen (N)
losses in corn fields and raises questions about the need
for supplemental N applications. There are two types of N
loss: 1) Leaching—movement with water below the root
zone, and 2) Denitrification—loss to the atmosphere. In
general, leaching losses are more likely on sandy soils
where water can move through the profile quickly. Denitri-
fication is more likely on medium and fine textured soils
that are not well drained. The exact extent of N losses
through leaching and/or denitrification following the heavy
rains is difficult to determine. Both of these loss process-
es occur through the nitrate form of N, so the potential for
significant loss is determined by the amount of the N sup-
ply that was in the nitrate form when the excess rainfall
occurred. Losses depend on many factors such as when
the N was applied, the forms of N applied or expected to
provide N for the crop, soil characteristics and soil mois-
ture.
Where fertilizer N was applied before planting, the timing
of the application and the form of N used are important in
determining the risk of loss. Keep in mind that losses oc-
cur through the nitrate form of N, and the timing of nitrate
formation is an important consideration in evaluating po-
tential losses. Fall-applied fertilizer N has a high risk for
loss following excess rainfall because most, or all, of the
N would be in the nitrate form by mid-May. For spring pre
-plant applications, ammonium forms of N such as anhy-
drous ammonia or urea are converted to nitrate-N in
about four to six weeks. Urea usually is converted to ni-
trate more rapidly than anhydrous ammonia. Nitrogen
solutions (28% UAN) contain half of the N as urea and
the remainder as ammonium nitrate. Essentially, when
this fertilizer is applied, it contains 75 percent of the N as
ammonium and 25 percent as nitrate.
Denitrification losses can occur within a few days if the
soil remains saturated or flooded and nitrate-N is present.
Warm temperatures and extended periods of saturated
conditions favor high losses.
Arnie Imholte
Field Agronomist
Matt Pauli
Product Agronomist
Aaron Prestemon
Field Agronomist June 10, 2013 - Issue 3
WALKING YOUR FIELDS® newsletter is brought to you by your local account manager for DuPont Pioneer. It is sent to customers throughout the growing season,
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Late Planted Forage Options
Nitrogen Management
(Source: Portions of this article were taken from ‘Evaluating
Nitrogen Losses Following Excessive Rainfall,’ Dr. Larry G.
Bundy, U of WI Extension Service.)
Table 1. Estimated denitrification N losses
influenced by soil temperature and days
saturated.
Soil Temp
(°F)
Days
Saturated
N Loss
(% of applied)
5 10
55-60
10 25
75-80
3 60
5 75
7 85
9 95
Source: Shapiro, University of Nebraska.

2. Glyphosate on Corn
Corn can be damaged by spraying glyphosate too late in
the growing season. Ears appear to have aborted kernels
or scattered pollination. It can be easy to diagnose when
only part of the field has been sprayed. There is a distinct
line and difference between
sprayed and unsprayed por-
tions of the field.
 Corn may be sprayed
broadcast or over the top
with glyphosate until it
reaches V8 stage or 30
inches in height (whichever
comes first).
 Corn can be sprayed be-
tween 30 and 48 inches
with a ground rig employing
drop nozzles that direct the
spray to the base of the
corn plants and avoids di-
rect application of spray
solution into the whorl of
the corn plant. It is ex-
tremely important to follow
the specified label for your
glyphosate product.
Glyphosate on Soybeans
Spraying soybeans with glyphosate can occur through R2
stage. Reproductive phases are as follows:
 R1--Plants have at least one flower on any node.
 R2--Plants have at least one flower open on one of the
two uppermost nodes (Four days after R1).
 R3--A 3/16 inch pod at one of the four uppermost
nodes (Ten days after R2).
After you see the first flower, you have approximately two
weeks to spray glyphosate to stay on label. This recom-
mendation is a clarification of previous definitions of
spraying glyphosate on soybeans throughout flowering.
Cover crops can serve growers in a number of important
ways. It’s important that crop selection decisions be made
after taking into account the needs and limitations of the
acres considered for cover crop establishment. Erosion
and weed management are two popular goals that cover
crop growers hope to achieve, but perhaps nitrogen man-
agement or forage availability are important to you as
well. In any case, there are a range of species and man-
agement levels that will fit some situations better than
others.
A useful tool to help you select a cover crop based on
your needs is provided by the Midwest Cover Crops
Council. Decision Tool: http://bit.ly/uEe85I.
Some important questions need to be address when
considering late-spring or summer planting of cover crops
to acres intended for row crops.
 Were pre-emergence herbicides used? If so, what are
the planting restrictions? The University of Wisconsin
has information about plant-back restrictions for some
common corn and soybean herbicides (http://
bit.ly/15jhiwc).
 Will the cover crop be used to scavenge applied nitro-
gen or is it meant to be a nitrogen source? Grasses
and other non-legumes tend to utilize applied nitrogen
and provide a harvestable crop, but this may limit crop
insurance options. Legumes, on the other hand will
produce good nitrogen credits for next year’s crop.
When a harvestable forage cover crop is used, delay-
ing harvest past November 1 may still allow the pro-
ducer to take advantage of crop insurance for prevent-
ed planting.
Grasses that will be potentially useful with a June planting
date include warm-season species such as sudan, mil-
lets, or sorghum. Oats are a good option as well; they
tend to establish quickly for good soil coverage. Clovers,
sweetclover and cowpea are legume options that will es-
tablish and also provide a nitrogen source for the follow-
ing year. Of course, mixes are available that provide
some benefits of both types of crops.
For June planting, consider an oat/clover mix over some-
thing with ryegrass or brassica (canola, rapeseed, tur-
nips) components as these prefer cooler spring weather
for establishment.
Using cover crops on ‘prevented planting’ acres may af-
fect crop insurance, so check with your RMA crop insur-
ance provider or advisor and make sure you understand
any implications of cover crop usage. A couple good
USDA resources include: http://1.usa.gov/17S1i6G and
http://1.usa.gov/10LMilP.
Restrictions on Spraying Glyphosate
Ear on left shows irregular
kernel set resulting from a late
glyphosate application. Ear on
right is from unsprayed plant
in same field. Photo: Clyde
Tiffany, DuPont Pioneer.
Cover Crops/Fallow Ground
Table 2. Green manure N credits for
commonly used legumes in Wisconsin
Crop < 6” growth >6” growth
---- lb N/ac to credit ----
Alalfa 40 60-1001
Clover, red 40 50-801
Clover, sweet 40 80-1201
Vetch 40 40-901,2
1
Use the upper end of the range for spring seeded
green manures that are plowed under the following
spring. Use the lower end of the rand for fall seedings.
2
If top growth is more than 12 inches before tillage,
credit 110-160 lb N/ac.
Source: University of Wisconsin

3. A late spring and wet conditions have delayed soybean
planting in some areas. This article addresses how later
planting affects soybean development and maturity.
Soybeans are ‘day length sensitive’ plants. This means
flowering and maturity are triggered by the length of the
night or dark period. When adapted maturity varieties are
planted before the middle of June, the flowering is trig-
gered by shorter days (actually longer nights) after June
21. For each three to five day delay in planting, flow-
ering and maturity are delayed only about one day.
That means that if you plant the same variety on May 10
and June 10 (30 days later), the flowering and maturity of
the later planting is delayed about six to ten days. This
happens regardless of the maturity of the variety.
Soybean Development
Flowering usually begins six to eight weeks after seedling
emergence, and continues for three to four weeks. How-
ever, flowering will occur earlier if soybeans are planted
late. Warm temperatures accelerate development, espe-
cially flowering. A full season soybean variety will normal-
ly flower in the first ten days of July. If there is a hot peri-
od in mid-June, it can flower up to two weeks earlier.
When this happens, and if there is good weather for the
rest of the season, higher yields result because of the
extended reproductive period. The soybean plant may
flower ten days earlier, but it won’t necessarily mature ten
days earlier because of day length controls. Generally,
yield increases as the length of the flowering to maturity
stage increases.
Warm weather in August or early September does not
hasten maturity much, unless it causes water deficit
stress. Sometimes, temperature is blamed for stress, be-
cause hot temperatures often accompany drought. A cool
fall does not delay maturity much either, although yields
may be reduced if the cool weather is accompanied by
heavy rain, causing disease. The flowering period is influ-
enced more by temperature, but maturity is more strongly
influenced by photoperiod. The rapid shortening of days
starting in mid-August drives the soybean to maturity;
temperature has only a small influence on maturity.
KEY SUMMARY POINTS
 Soybeans are able to adjust their final maturity to com-
pensate for late planting. Delayed planting will delay
the onset of flowering by only a matter of days, even
when planting is delayed for weeks. Harvest dates will
only be delayed by about one day for each three to
five day delay in planting.
 Normal maturity soybean varieties should be planted
at least until about June 10. Earlier varieties would be
induced to flower before sufficient vegetative growth is
achieved to produce top yields. Reduced vegetative
growth can lower yields by limiting the number of
available flowering sites.
 Even normal maturity varieties may be shorter when
planted in June. When the normal vegetative period of
six to eight weeks is shortened, the effect on the soy-
bean plant is usually reduction in height.
 Warm temperatures will induce earlier flowering and a
longer flowering period, cool temperatures will induce
later flowering and a shorter flowering period.
 Maturity is strongly influenced by photoperiod (day
length). Warmer or cooler than normal temperatures
do not greatly influence maturity. The rapid shortening
of days starting in mid-August drives the soybean to
maturity; temperature has a small influence.
Planting Date Impact on Soybeans
Photo: Pat Branick, DuPont Pioneer
Photo: Tom Doerge, DuPont Pioneer

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In this issue:
 Late Planted Forage
Options
 Nitrogen Management
 Glyphosate Restrictions
 Cover Crop Options
 Soybean Planting Date
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