ISSUE 3   May 27, 2010

MINIMUM SOYBEAN STANDS

With the warm conditions during the second half of May, soybeans are germinating rapidly. However, early planted soybean seed may have been sitting in the soil for a long time. This is the time of the year for producers to evaluate soybean stands. Based on research and hail loss studies, the minimum stand for soybean is suggested to be around 75,000 plants per acre, which is approximately 50% of the recommended stand. If you use the "hula hoop" method of determining stand counts in solid seeded fields, you would need a minimum of 1.7 plants per square foot. With a 50% stand loss, yield reduction will be somewhere between 10-20% of the anticipated yield of timely planted soybean. However, soybean stands will not always be uniform throughout the field. In each field there will be places here and there with higher or lower plant counts. These uneven gaps between plants can potentially result in even lower yields, depending on how many gaps there are or the distance of spacings between the plants.

Soybeans have the ability to compensate for low populations by additional branching, setting more pods per plant and filling more seeds per pod. The plants in low population environments may have lower branches that might break before or during harvest thus increasing the potential for greater harvest losses. Also some of the pods will develop lower on the plant. Extra care and efforts during harvesting can reduce this harvest loss problem.

It is often a difficult decision whether to let a low population crop develop or to re-plant. Some producers have asked about seeding extra soybeans into the uneven or thin stand. In the case of poor stand establishment, replanting alongside the established seedlings, to patch up or thicken the existing stand, seldom improves yields. Repair planting often leads to timing difficulties with crop management like weed control and harvest date.

When dealing with unacceptably low stands, significant yield improvement will be best achieved when the original soybean stand is so poor that it needs to be destroyed and a new stand re-established. However, it is advised to replant with an earlier maturing variety to compensate for the shorter growing season left before the first fall frost. Producers also need to factor in the costs of additional seed, working the land, and planting. The yield potential of the later planted soybean will be lower when compared with timely planted soybeans.


Uneven solid seeded soybean stand will have reduced yield potential.

Hans Kandel
Extension Agronomist broadleaf crops
hans.kandel@ndsu.edu

 

LATE PLANTING AND REPLANTING CORN

About 20% of the state’s corn acres have not yet been planted and with the recent rains, planting will likely be further delayed in much of the state. The optimal planting period for corn for North Dakota is the first 20 days in May. Since we are now beyond this optimum period, should you decide to plant corn, chose a hybrid that is earlier than the "full-season" hybrids recommended for your area of the state (see Table 1). You may give up some yield potential, but an earlier hybrid will help minimize the risks associated with the crop being damaged by frost before maturity this fall and the hassles of dealing with corn that is too wet to harvest and profitably dry to safe levels before the snows begin to fall. Also, note that the final planting date for full insurance coverage for corn is May 25th except for Cass, Ransom, Richland and Sargent counties which have a final planting date of May 31st. Yield losses as planting is delayed from May 20 until June 8 can be in the order of 1 and 3% per day, with the largest losses likely when the growing season is cooler than normal (like the last two years).

Table 1. Recommended relative maturity of corn hybrids for various regions and planting dates in North Dakota.

Full season relative maturity zone

After May 20

After June 1

After June 10

75 or less

For silage only

Not recommended

Not recommended

75-85

<75-80

75-80 (silage)

Not recommended

85-90

80-85

75-80 (silage)

Not recommended

90-95

85-90

75-80

75-80 (silage)

92-102

87-92

80-85

75-80

With the recent warmer weather, most of the corn that was planted before the cool and wet weather that characterized the first two weeks of May has now emerged. This week there have been reports of poor corn stands that undoubtedly are associated with the prolonged cool soil temperatures characteristic of the first half of May. For fields planted in early May, now is the time to evaluate plant stands to determine if replanting is needed and would be profitable. Estimate you plant population by counting the number of emerged plants in a thousandth of an acre (17’ 5" and 23’ 10" row lengths for 30 inch and 22 inch row spacings, respectively) in about 20 places in your field and then multiple the average of those counts by 1,000. Use Table 2 to estimate the likely yield of your current crop and your likely yield if you replant. The worksheet in the extension publication "Estimating Yield and Dollar Returns From Corn Replanting" by R.L. Nielsen and published by the Purdue Extension Service (http://www.agry.purdue.edu/ext/pubs/AY-264-W.pdf) can be a useful tool in evaluating the profitably of replanting.

In most circumstances, the original stand of corn should be destroyed before you replant. Late planted plants that grow next to an early-planted plant will be at a competitive disadvantage and will very likely not produce an ear.

Table 2. Expected relative corn grain yield from various planting dates and harvest population using an earlier maturing hybrid than is normal for early plantings. This table was adapted from data contained in: A3353 Corn Replant/Late-Plant Decisions in Wisconsin by J. Lauer.

Plant Population

May 1a

May 20

June 1

June 10

June 20

 

--------------% of expected yield--------

32,000

100

80

64

45

18

28,000

95

78

62

44

18

24,000

91

75

59

42

17

20,000

86

70

56

40

16

16,000

80

65

52

37

15

12,000

72

59

47

33

13

The May 1st column assumes that a full season hybrid is used. All other columns assume that an earlier maturing hybrid is grown.

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


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