ISSUE 11   July 13, 2006

FIELD PEA HARVEST GUIDELINES

Pea growers need to carefully monitor the crop as it nears maturity in order to harvest on a timely basis. Harvest timing is especially important if the crop is to be marketed as seed, or to meet contract specifications for human food or specialty feed markets.

Field pea generally reaches physiological maturity in 85 to 105 days depending on the variety. Field pea may be swathed before combining or straight (direct) combined. Peas are normally swathed if a variety with prostrate type of growth is grown, there is uneven crop maturity, or heavy weed pressure is present. When swathing peas, vines and pods should be a yellow to tan color. The crop matures from the bottom pods upward. Yellow-cotyledon peas should have seed that has turned yellow in color.

Field peas should be combined when the seed contains 14 to 20% moisture, to reduce splitting and cracking of the seed coat. At this moisture level, the seeds are firm and no longer be penetrated with a thumbnail. Also, pea vines must have turned yellow (no green color present) otherwise harvest will be extremely difficult.

Straight combining is possible depending on variety grown and harvest equipment available. Short-vine and semi-leafless pea grain varieties have characteristics that are adaptable to straight harvesting compared to varieties with indeterminate and prostrate-vine growth. For example, semi-leafless peas have a more open canopy, remain erect longer, and dry down more rapidly after a rain or heavy dew compared to conventional vining varieties.

Direct harvesting can be accomplished using a combine header with a floating cutter bar or a flex header. Also, attachments such as lifter guards and pickup reels reduce losses and improve harvest efficiency. Direct harvesting of weak and prostrate vine cultivars is most efficient with an aggressive pickup attachment and a lead coulter on a standard combine.

Correct combine settings and operation are important to maintain seed quality. Low cylinder speeds of 350 to 600 rpm, should be used to minimize seed cracking or splitting. Initial concave settings of 0.6 inch front clearance and 0.2 inches at the rear are suggested. Also, adjust combine settings as weather and harvest conditions change. Combine and all portable augers should be operated at full capacity and at low speeds to minimize seed coat damage and reduce splits.

 

HAILED SOYBEANS MAY COMPENSATE

Yield loss in soybeans is determined by the stage of growth of the soybeans at the time of damage and the degree of plant damage. Damage can be due to leaf defoliation, stand reduction, stem damage and pod damage. The calendar date and pest control later also affect ultimate yield.

Check stands 7-10 days after a storm to determine the stand reduction. Determine the current stand versus the original stand. Count these losses as total losses if the plants are totally damaged below the cotyledons. Shredded or cut stems may lead to bruised plant stems. Mild bruising may only break in the outer stem tissue but severe bruising may expose the central stem tissue and lead to more losses. Unfortunately, bruised stems that recover may break any time before harvest as they are weakened. They may lodge and make harvest very difficult. It is very difficult to determine yield loss from bruised plants until harvest.

Defoliation is a measure of the leaf area destroyed by the storm. Leaf loss on soybeans during vegetative stages has little effect on yield (if only the leaves are shredded); however, defoliation during reproductive stages does affect yield. Added damage to stems and branches may also decrease yields more, depending on the weather events the remainder of the season and if additional disease or insect damage results on damaged soybeans. The further along in maturity, the more detrimental effect on yield.

Growth Stage

% Defoliation

 

10

40

60

80

100

% Yield Loss (estimated- with no flower/pod loss)

R1 - R2

0

5

7

12

23

R3

2

6

11

18

33

Loss of excess flowers beyond the normal losses on soybeans or losses of pods will increase yield losses.

Duane Berglund
Extension Agronomist
duane.berglund@ndsu.edu

 

ESTIMATING SMALL GRAIN YIELD BEFORE HARVEST

Winter wheat will soon be ready for harvest and early planted spring small grains are not be far behind. With the exception of kernel weight, the components that comprise yield are now more or less fixed and yield can be estimated with some degree of confidence. For those that have not been very successful in "eyeballing" the yield of a crop, the following procedure can help you obtain a fair yield estimate of a field. This is an adaptation of a procedure previous described by Dr. Duane Berglund, NDSU Extension Agronomist.

For wheat:

  1. Sample at least at least 8 randomly selected areas that are representative of the field as a whole. Avoid head rows, hill tops and bottom areas, unless they comprise a significant proportion of the field. For fields that vary considerably in their yield potential you will need to make more measurements and include samples from the various areas of the field that differ in yield potential.
  2. Count the number of spikes in a three-foot row. If the seeder placed seeds in paired rows or in a band, count all of the spikes in both paired rows or in the entire width of the band. Do not include spikes that are small and have few kernels or that emerged late and will not mature before harvest.
  3. From the row of spikes that was just counted, select 6 spikes randomly. Count the number of spikelets on each of these spikes, omitting the bottom-most and top-most spikelets and average the numbers to get the average number of spikelets per spike.
  4. Determine the distance between the rows. If the row spacing of the seeder is not known, measure the distance between several rows or if bands of seeds were sown, measure the distance between the left side of one band to the left side of an adjacent band.
  5. Use the above numbers in the following formula:  Bushels/acre = (#spikes/three ft row x average number of spikelets per spike x 2.3 x 0.142)/row spacing (inches).

The value 2.3 is the number of kernels that develop on average in a spikelet. If the crop is severely stressed use 2.1 instead of 2.3. The other number, 0.142, is the product of several other numbers that takes into account the average weight of a kernel and converts the output of the equation into bushels per acre.

As an example, if you counted 70 spikes in a three foot length of row with a 7 inch row spacing and the average number of spikelets per spike was 10, then the estimated yield for this area of the field would be: (70 spikes/three ft row x 10 spikelets/spike x 2.3 kernels per spikelet x 0.142)/ 7 inch rows = 32.7 bu/acre.

For Barley:

Use the same procedure as described above. Instead of counting spikelets, count the number of seeds per spike. Then use the following formula:

Bushels/acre = (Spikes/three ft row x average number kernels per spike x 0.2723)/row spacing (inches).

As an example, if you counted on average 70 spikes in three feet of row with a 7 inch row spacing, and 33 kernels per spike on average, then the estimated yield for this area of the field would be: (70 spikes/three ft row x 33 kernels per spike x 0.272)/ 7 inch row = 89.8 bushels per acre.

 

POLLINATION AND DROUGHT STRESS IN CORN

Most of the corn crop in North Dakota will soon be tasseling. The appearance of the tassel signals the onset of the pollination process. Corn is now using between 1/4 and 1/3 of an inch of water per day. Unless we get some additional rain, much of the corn crop will be moisture-stressed during pollination this year.

Pollen shed usually begins two to three days prior to silk emergence and continues for five to eight days with peak shed on the third day. Most pollen is shed in the morning after the dew dries off. Pollen generally is shed from the center of the tassel first and by the lower branches last. Corn pollen can be carried by the wind for considerable distance, though most settles within 20-25 feet of the plant from which it was shed. Pollen grains can remain viable for up to 24 hours, but are sensitive to very hot and dry conditions. The predicted high temperatures and low humidity this next week could significantly reduce pollen viability and impact seed set.

Corn is most sensitive to drought stress just before silking to 22 days after silking. The sensitivity at this stage partially due to the fact that the male and female flowers are separated by a considerable distance and because pollen and silks are sensitive to hot and dry conditions. When corn is severely stressed prior to flowering, silk growth is delayed and pollen shed will occur before the silks have emerged resulting in barrenness. Unless we get some rainfall to alleviate the drought stress that is developing in much of the corn crop this year, the potential for reduced seed set will increase as the corn plant continues to transpire and deplete the moisture that is currently available in the soil.

Tasseling and silking in corn
Good synchrony between pollen shed and silking,
as shown in this photo, is needed to ensure good seed set in corn.

Joel Ransom
Extension Agronomist - Cereal Crops
joel.ransom@ndsu.edu


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