ISSUE 2    May 11, 2006

MINIMUM STANDS AND REPLANTING

A number of environmental and management choices can result in poor seedbeds, which brings with it concern for erratic crop emergence and poor plant stand establishment. If its too dry or perhaps in some areas of the state crops have been seeded into wet or muddy conditions, with poor stand establishment occurring. Some crops such as small grains, canola, sunflower and soybean can compensate for low plant populations.

These crops will compensate for stand reduction through tillering, branching or increased head or kernel size. Listed below are the minimum stands 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

60-75,000 plants/A

35-50

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.

How about a replant to improve the stands? Remember that a replant decision costs dollars and extra time. In many cases the later planted crops will yield less that the early planted and lower stand established crop. The later replant also may put the development of the crop into a more stressful period, such as a high temperature, drought or risks of fall frost. Also, the harvest period would be extended into the fall when weather conditions can be difficult.

Expected yield reductions when planting after May 15 in North Dakota.

Crop

% Yield Loss/Day

Wheat
Barley
Oat
Soybean
Irrigated Corn
Dryland Corn
Flax
Dry Bean
Crambe
Canola

1.5
1.7
1.2
0.8
1.2
1.0
2.3
0.3
0.9
1.9

Refer to NDSU Extension Circular A-934, "Replanting after Early Season Crop Injury" for further information. Also available on the web at: http://www.ext.nodak.edu/extpubs/plantsci/crops/a934w.htm

 

SEED CANOLA NOW

As we get later into the planting season, itís suggested that canola (a heat sensitive crop) be seeded first and then complete small grains, corn, sunflower and soybeans. Research has shown that canola yields drop quickly if planted late.

For canola planted acreage south of U.S. Highway 2, its suggested canola always be planted before small grains and, if possible, before May 15. For the NE and growing areas north of Highway 2, canola should be planted no later than May 25.

The optimum planting date for canola is late April to mid-May. Canola yields have decreased sharply across most of the state (except the northeast) when canola is planted beyond mid-May.

Canola is more sensitive to heat stress than all small grains, flax, and other cool season broadleaf crops, thus the utmost importance to seed canola early. Canola is also quite tolerant to spring frosts.

It is suggested to seed canola at a rate of 5 lbs/A under most field conditions. An optimum seedling plant population is 16 plants per square foot or 600,000 plants per acre. A good stand is 10 to 12 plants per square foot whereas, a minimum stand of canola is 4 plants per square foot. The recent rains in the state should allow for shallow seeding of Ĺ to 1 inch for rapid emergence. It is not recommended to broadcast seed canola and cover by harrowing or other forms of tillage. Stands and emergence of seedlings have been erratic when broadcast seeding occurs. For additional information on canola, see Canola Production Field Guide, NDSU Extension Cir. A-1280. Also available on the web:

http://www.ext.nodak.edu/extpubs/plantsci/crops/a1280.pdf

Duane Berglund
NDSU Extension Agronomist
duane.berglund@ndsu.edu

 

EMERGENCE OF SMALL GRAINS AND CORN

Early planted small grains have emerged in much of the state and there have been reports of corn emergence in a few locations this past week. Establishing a good stand is an essential first step in producing a high yielding crop. Emergence begins when seeds imbibe sufficient water to hydrate and activate enzymes used in breaking down stored products in the seed and in assembling compounds and other enzymes needed for growth. As germination continues, the radicle, which gives rise to the primary root system, emerges from the embryo, followed by the coleoptile. The coleoptile elongates until it reaches the surface of the soil. The first true leaf will extends through the coleoptile as growth continues. The maximum length of the coleoptile is determined by the genetics of the variety or hybrid. Elongation of the sub-crown internode (also referred to as the mesocotyl) can push the coleoptile to the surface of the soil when planting depth exceeds the potential length of the coleoptile. The deeper the depth of seeding the longer the sub-crown internode. The crown of the plant establishes at the top of the sub-crown internode. During the earliest stages of growth, the growing point is located at the level of the crown, typically about an inch below the surface of the soil unless the seed was sown shallower than this depth. The secondary root system arises from the crown. As you evaluate how successful you were in reaching your target plant population this spring, you might consider the following factors that impact emergence.

Planting depth - The optimum planting depth for small grains and corn is between 1.5 and 2 inches. Planting deeper than this optimum is a common practice when the surface of the soil is dry. Small grains are able to emerge from depths greater than 2 inches, but the percent of the seeds establishing and seedling vigor usually decline as the depth increases as the reserves in the seed needed for growth are limited by the size of the kernel. Planting corn 1.5 to 2 inches is recommended primarily to ensure uniformity in emergence. Corn germination and growth require temperatures above ~50 F. Since soil temperatures tend to be colder and more variable early in the spring at depths greater than 1.5 to 2 inches, planting deeper can induce variability in the timing of emergence. On the other hand, seeds placed too shallow may not immediately germinate if the soil dries out before the seed imbibes enough water to initiate germination. Another risk of planting too shallow is poor secondary root development when the crown establishes near the soil surface if conditions become hot and dry soon after emergence. Any factors that introduces variability in emergence can cause plants to exert uneven competition with each other, thus reducing overall yield.

Soil temperature - Small grain emergences requires about 180 accumulated growing degree days (GDDs). Small grain GDDs are calculate using a base temperature of 32 F. Corn on the other hand requires about 125 accumulated corn GDDs for emergence. Corn GDDs are calculated using a 50 F base temperature. As an example of how corn and small grain GDDs differ, in the first week of May there were 149 GDDs for wheat and only 53 GDDs for corn in Fargo. Growing degree accumulations this year for wheat planted in mid-April are probably slightly ahead of average and fairly typical of the first week of May for corn.

Variety - The length of the coleoptile in small grains can vary significantly from variety to variety. There is

a very good correlation between coleoptile length and the height of a variety at maturity - shorter semi-dwarf varieties tend to have shorter coleoptiles than taller traditional height varieties. Varieties with longer coleoptiles are able to establish better from greater seeding depths than those with shorter coleoptiles.

Seed Quality - The best predictor of emergence potential of a seed lot is still the germination test. Always use seed lots with high germination. Results from research conducted last year found that the accelerated aging test in small grains was a poor predictor of seed lot performance, meaning that seeds lots with poor germination after accelerated aging established about as well as those with good germination after accelerated aging. Additional research is underway this year. Small grain seed lots with high levels of scab, low falling numbers or that were subject to freezing temperatures during grain filling should be avoided. Past research has also shown that in some environments (i.e. deep seeding) seed size can occasionally be important for success in establishing an optimum stand in both corn and small grains.

Diseases - Seed and seedling diseases can reduce plant stands, particularly if emergence is delayed due to cool wet conditions. A number of fungicides are currently registered for use as seed treatments to protect seeds and seedlings from a number of pathogens.

Other factors - Other factors that can impact emergence include crusting, poor soil-seed contact, insect damage (corn maggot and wireworm can be problematic in corn), and salt injury from placing too much fertilizer with the seed.

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


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