ISSUE 8    June 23, 2005

SOYBEAN: STAND COMPENSATION AND YIELDS

Soybean have the remarkable ability to compensate for reduced stands through aggressive branching. University of Minnesota research suggests that even substantial reductions in plant stands has negligible impact on yield. The data below from the National Hail Insurance Services handbook supports this research.

Soybean Stand Reduction Loss

- ROW WIDTH -

Plants/A

 

Yield % Optimum

30"

15"

7.5"

Plant Count

103

52

26

180,000

100

92

46

23

160,000

100

80

40

20

140,000

100

69

34

17

120,000

99

63

32

16

110,000

97

57

29

14

100,000

94

52

26

13

90,000

90

46

23

11

80,000

86

40

20

10

70,000

82

NOTE: All plant counts are made on the basis of "number of plant in 10 feet of row."

As the above table indicates, reduced soybean stands can produce acceptable yields. However, weed control management may need to be closely watched. Incomplete canopy closure can create additional weed pressures.

 

CANOLA AND HAIL DAMAGE

Canola in North Dakota is now near the bolting stage or is just starting into the bloom stage of development. Hail has been reported in some of the canola production areas of the state. Plantings in seedling stages can have stands reduced by 50% and still produce acceptable yields. An average stand of 11_12 plants/ft2 can be reduced to 4/ft2 before yield losses exceed 10 percent. Prior to bolting and flower development, canola can withstand hail without much economic loss. Canola with leaves that are torn and shredded suffer only partial loss, while leaves bruised on the main vein or torn and broken will be lost. Leaf area destroyed will result in seed yield loss. Seed yield losses in canola is approximately 25 percent of leaf area lost. If leaf defoliation is 50 percent, then yield loss would be approximately 12.5 percent.

Canola plants injured in late bolting or early flowering stages seldom die. The well developed root systems and ability to rebranch and develop secondary flower clusters help the plants recover. When buds or flowers are destroyed, the canola recovers rapidly by development of flowers which normally would have aborted. New branches also develop from growth buds lower down on the plant. Seed yield loss will depend on both percent leaves and branches lost. For example, if canola has 60 percent lost branches 7 days into flowering, seed yield loss is estimated at 18 percent, whereas 21 days into flowering, yield loss would be an estimated 60 percent. If hail strikes late, such as during pod filling or ripening, plant recovery is not possible. The time needed to develop new growth, flowers and mature is limited before a killing frost. Canola seed yield loss if injury occurs at the ripening stage depends directly on the loss of branches, individual pods and seed knocked out of pods. Severe hail losses have occurred in canola swaths in past years.

Duane R. Berglund
Extension Agronomist
Duane.Berglund@ndsu.edu

 

CORN GROWTH STAGING

Corn growth is now starting to accelerate with the arrival of more summer_like weather. Early planted corn in the southeastern region of the state is approaching the 6th leaf stage. At the five leaf stage, the corn plant switches from vegetative growth to reproductive growth as the growing point stops initiating leaves and begins initiating the tassel. At the 6 leaf stage, ear shoots begin to form. The number of kernel rows on the developing ear is determined relatively soon after it begins development and is largely determined by genetics, and less so by the environment. The length of the kernel row and therefore the total number of potential kernels, however, is determined during a longer period of time (6 leaf stage through one to two weeks before tasseling). Severe stress during this stage can shorten the length of the cob and reduce yield potential. Nevertheless, stress during ear development is far less damaging to yield potential than stress during and shortly after pollination, as the potential number of kernels developed typically exceeds the number that can be pollinated filled.

Certain management practices are growth stage dependent; therefore, properly identifying the growth stage of your corn crop will be important to ensuring that management practices are applied at the appropriate time. This is particularly true of the application of herbicides. When growth staging a crop you should begin by obtaining a representative sample of plants from the field or part of the field of interest. Remove any soil attached to the plants so that you are able to observe the roots and crown. Vegetative growth stages of corn are defined by the number of leaves. Counting leaves in corn is fairly straight forward as the process is not encumbered with tillers and leaves on tillers as is the case in small grains. However, care must be taken to ensure that the earliest leaves are included when counting leaf numbers. The first leaf is small and often dies and is torn from the plant early in the growth of the plant. The first leaf has a blunt tip. Look for sheath remnants at the crown of the plant if you suspect that the first leaf (or second for that matter) is missing. Include only those leaves that have a collar. Include all leaves, even those that have been damaged by hail or frost. The total number of leaves that a plant will developed is more or less fixed for a given hybrid; leaves that are stripped from the plant will not be replaced by additional new leaves.

In order to determine the growth stage of older plants that have lost their lower leaves, uproot the plant and split the stem with a knife through the root ball. At the very base of the stem, identify the first visible internode. Internodes are the white area between the more yellow bands of the nodes. The first obviously visible internode should about to 3/4 inch in length. The node directly above this internode will be the fifth node, and the leaf arising from this node will be the 5th leaf. Find that leaf and continuing counting leaves from that point.

In corn, management recommendations can also refer to the height of the plant, rather than leaf stage. For example, certain herbicides can only be applied to corn less than 12 inches tall. The plant height in this case is measure from the base of the plant to where the upper most leaf reaches without stretching it out.

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


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