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ISSUE 1 MAY 4, 2000

CRUSTING
  
Dry regions of North Dakota have a high potential for crusting. Increased potential for crusting occurs
when planting into a dry seed bed followed by heavy rains. Crusting is usually most noticeable is in areas
with low organic matter and little surface residue, and especially in fields were excessive tillage was done.

    Crusting sufficient to prevent the coleoptile of a germinating small grain to penetrate the soil surface can
result in severe stand loss. When the crust is not broken the first leaf of the seedling will break through the
coleoptile and grow under the crust. Once this has happened seed nutrient stores are quickly depleted,
since the seedlings are not photosynthetically active, resulting in plant death. Consequently, managing a
crusting problem is a critical time issue especially during warm weather.

    Soil crusting can be alleviated in any number of ways as long as it does not disturb the sub soil. Light rain
is idea but when this is not in the forecast, a light harrow, double disc drill set very shallow, or rotary hoe are
examples of equipment that can effectively be used. The objective is to very gently break the soil crust.

 

CROP INJURY AND REPLANTING DECISIONS
    Every year less than desirable crop stands in some region, due to crusting or a host of other causes such
as frost, insect and disease injury, brings up the question of replanting. The decision to replant requires
careful assessment of crop injury, alternate crop choices and cultural practices related to crop growth and
development. Each case of injury should be considered individually.

    Any reduction in stand can reduce yield while leaf loss during early crop development has a smaller effect
on yield; however, as the crop matures it is unable to produce new leaves and then leaf loss is more damaging
to yield. Small grains have a large capacity to compensate for stand reduction through tillering and increased
head size. Leaf damage on young plants will be replaced but once the plant has reached the jointing stage its
ability to produce new leaves and tillers is lost.

    During early development the growing point of small grains is below the soil surface making it less
susceptible to injury, as the growing point moves above the soil surface it becomes more vulnerable. In this
early state, plants can suffer complete loss of above ground vegetation without plant death occurring.
Waiting several days following severe foliar damage occurs is essential to make an accurate determination
of stand reduction. The growing point is a good indicator of plant health, it should be white or cream
colored. Darkening or softening of the growing point usually precedes plant death.

    Optimum plant population for maximum yield in both barley and wheat is about 30 plants per square
foot. Reductions in the plant population will reduce yield albeit in a non not proportional manner. Under
favorable growing conditions good yields have been obtained with plant populations below 10 plants
per square foot. Replanting small grains should not be considered when populations are at 10 plants
per square foot or greater.

    The effect of planting date on yield is also important when considering replanting. Delays in planting
small grains past May 15 typically result in yield reductions on the order of 1.5 to 0.5 % per day. It is
difficult to compare yield of an early planted crop with a less than desirable stand and a much later
planted crop with an optimum stand, however, when the original crop is planted well before mid May its
yield potential may be better than that of a replant. Under dry conditions the availability of soil moisture
must be considered, as it may be depleted by the current crop and will be further reduced during replanting.

    The final decision on replanting should be an economic one, based on sound agronomic information.
If the cost of replanting is equal or greater than any yield gains, then exercise is the only thing gained. The
critical determination is the yield potential of the damaged crop compared to that of a replant, and the
cost of replanting.

Michael D. Peel
Extension Small Grains Agronomist
mpeel@ndsuext.nodak.edu

 

NDSU FIELD DAYS SCHEDULE
  
Below is a listing of NDSU Field Day Tours and other crop-related special events. Exact starting times
will be provided at a later date via this newsletter or other media releases.

 

MINIMUM STANDS FOR CROPS

   Dry soil conditions and poor seedbeds bring with it concern for erratic crop emergence and poor
plant stand establishment. Some crops such as small grains, canola, sunflower and soybeans can
compensate for low plant populations.

    Crops will compensate for stand reduction through tillering, branching or increased head or kernel
size. Listed below is the minimum stand of several crops to avoid major yield reductions when
making decisions on tearing up the field and replanting.

 

Crop

Minimum Stand

% of  Normal Stand

Small Grains

8-10 plants/sq.ft.

40-60

Flax

12-15 plants/sq.ft.

20-40

Safflower

2-2.5 plants/sq.ft.

40-50

Canola, Mustard

3-4 plants/sq.ft.

40

Sunflower

11-13,000 plants/a

50-60

Soybean

40-75,000 plants/A

25-50

Field peas

3-5/sq. ft.

40-70

Dry Beans
     Navy
     Pinto

45-60,000 plants/A
28-40,000 plants/A


50-60
40-50

Even stands below 12 plants per square foot of barley and oats have yielded near normal because they
typically tiller more than spring wheat which typically tillers more than durum. Refer to NDSU Extension
Circular A-934, "Replanting after Early Season Crop Injury" for further information. Also
available on the web at:
www.ext.nodak.edu/extpubs/plantsci/crops/a934w.htm

Duane Berglund
Extension Agronomist
dberglun@ndsuext.nodak.edu

 

REVERE SOYBEAN AND THEY WILL RESPOND
    Soybean varieties differ in their ability to emerge at different soil temperatures and from different
depths of planting. Recognize varietial differences and you will be rewarded by producing a better crop
of beans. All varieties germinate and emerge at 85F but many have very limited germination below 59F.
Target soil temperatures of 60F or above for optimum soybean planting conditions before proceeding into
the field. Plant soybeans a maximum of 2 inches deep, trying to optimize planting depth to only 1-1.5 inches.
Soybeans should never be planted in dry soil. The minimum seed moisture uptake required to germinate
soybeans is 50% of the seed weight. Soil moisture should be sufficient to allow soybean seed to imbibe
water, but not too flooded. Soil moisture levels too high combined with low temperatures allow soybean
seeds to be attacked by soil fungi and decay. Soils too low in moisture can also be detrimental to soybean
seed. Water stress can reduce both the rate and percentage of germination in very sensitive crops such as
soybean.

    Effect of Water Stress on Germinability* and Subsequent Radicle Growth

    (* Germinated for 96 hours at 29C (84F))

 

Species

Radicle length (mm)

0 bar

-3 bar

-6 bar

-10 bar

 

(soil moisture conditions)*

Dandelion

13

15

6

0

Bitter sneezeweed

4

1

1

0

Hemp sesbania

10

7

0

0**

Jimson weed

33

22

13

0

Soybean

68

12

0

0**

Prickly sida

32

38

33

16

Pearl millet

124

125

94

102***

*Where field capacity is 0 bar and progressively drier soil conditions are at –3 bar to –10 bar.
**very sensitive *** not very sensitive

    Be careful when moving or loading seed to the planter. Soybean seed is very fragile, more than most
seed as can be seen at harvest when very low crop moisture can result in cracked soybeans. A 10% reduction
in germination can occur simply from throwing soybean seed out of a truck and onto a concrete floor or
onto hard ground. Try not to let seed fall more than a foot when handling bags for planting. Test any saved
and stored seed for intactness of the soybean seed coat, germination under stress, germination percentage
and seed viability prior to planting.

 

IN CORN WEED CONTROL, CORRAL THE CULPRITS EARLY
   Early season weed control can present detrimental competition to corn. Field studies conducted in 1998-99
to evaluate weed competition on soil moisture, plant nitrogen level and yield in glyphosate-resistant
(Roundup-Ready) corn have shown that your early weeds help write the epitaph on the crop. Single
applications of Roundup were made postemergence on major weed species including giant foxtail, common
waterhemp, and velvetleaf. In 1998, significant corn grain yields were seen when giant foxtail was allowed
to only reach 4-6 inches before the first spraying of the Roundup. Significant reductions in nitrogen content
in the corn tissue collected was also found when the giant foxtail was allowed to reach 9-12 inches before
any herbicide treatment was applied. Moisture reductions from the weed competition was not consistent,
instead it varied depending on location and rainfall pattern. Adequate precipitation in the early part of the
season, however, showed that competition for soil moisture was not a major factor contributing to the
yield losses seen. Competition for nitrogen appears to be yet another contributing factor to yield losses
from early-season weed competition.

 

READY YOUR ROUNDUP TO COINCIDE WITH THE CLOCK

   Timing of your herbicide application may make a difference in weed control and crop competition effects
from the weeds not only during the season but also from the time of day the application is made. The label
on Liberty, used with Liberty-Linked corn, specifies that applications be made between dawn and two
hours before sunset to avoid reduced weed control. A study to examine the influence of time of day on
herbicide effectiveness was run at the University of Minnesota in 1998-99 with the use of Roundup and
Liberty on annual weeds. Roundup rates of one pint (0.37 lb ai/A) and one-fourth of a pint (0.09 lb ai/A)
as well as Liberty at one pint (0.26 lb ai/A) and one-half of a pint (0.13 lb ai/A) were applied with and
without the use of an adjuvant. When adjuvant was used, a combination of 20% non-ionic surfactant and
80% ammonium sulfate was used. All treatments were applied with 10 gallons per acre of water.
Applications were made at 6AM; 9AM; 12 noon; 3PM; 6PM; 9PM; and, 12 midnight. Visual ratings
and biomass samples were taken. Both Roundup and Liberty were affected by the timing of the herbicide
applications. Annual weed control was greatest at 3PM and at 6PM with the least weed control occurring
with applications set at 9PM and 12 midnight. Adjuvant use with both Liberty and Roundup generally
increased herbicide efficacy but did not promote better weed control when the application was made at the
poor timings of 9PM or 12 midnight. Increasing herbicide rates helped in annual weed control but could not
overcome the influence the time of day had over herbicide efficacy. Other studies across the country, have
shown that specific weed species and herbicide mode of activity may also influence optimal timing for
herbicide application.

Denise A. McWilliams
Extension Crop Production Specialist
dmcwilli@ndsuext.nodak.edu


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