ISSUE 13   August 13, 2009

ROW SPACING AND LIGHT INTERCEPTION

During one of the plot tours this summer, producers were asking about the optimum row spacing for soybeans and dry bean. Growers have traditionally used 30 inch row spacing for soybean and dry bean. In general the soybean research at NDSU has indicated that reducing 30 inch row spacing to narrower intermediate row spacing increased yield potential. There is a lower chance of yield response reducing intermediate row spacing up to solid seeded soybean. However, this depends on the growing season and other environmental conditions. Advantages for narrow row soybean include: moisture conservation, early crop canopy closure to help control weeds, increased yield potential, reduced erosion, increased harvesting efficiency, and the opportunity of using small grain equipment for planting and harvesting. Increased light interception is considered the main factor explaining the higher yield potential in narrow- compared to wide-row spacing in soybean. Greater light interception during the vegetative and early reproductive periods provides the energy for increased yield potential in narrower row seeded soybean. We are experiencing a cooler than normal season in 2009. We estimated the percent canopy cover in some of our soybean and dry bean experiments the first week of August. Looking down on the canopy we visually evaluated the percentage of land area covered by green plant tissue. A cover of 65% indicates that there was still 35% of the soil area visible observed directly above the plot. The lower cover numbers indicate that more sunlight directly reached the soil surface and therefore was not used in photosynthesis. As the angle of the sunlight changes during the day, the interception of light by the plant may vary. Although wider rows have more visual bare ground from the top, this does not mean that the plants intercept proportionally less light as compared to the percentage of bare ground. Looking carefully on the soil surface one can see the shaded and bright sunlit soil and even 30 inch row spaced plants will intercept a good portion of sunlight (for example see photo 1). However, although the canopy cover percentage is only a visual observation, it is obvious that some sunlight struck bare ground with less canopy cover. In a warmer year the crop should have been more advanced and covered the soil. Based on the data presented in Table 1, we conclude that in 2009 at the observed locations the narrower rows for soybean, Natto bean, and dry bean had a higher canopy closure percentage during the first week of August and plants were therefore intercepting more sunlight.

Table 1. Average percent canopy closure in soybean, Natto soybean and dry bean experiments in different row
spacings, measured the first week of August 2009.

 

Percent canopy closure

 

Carrington

Prosper

 

7 inch

14 inch

28 inch

7 inch

14 inch

28 inch

Soybean

98

70

96

71

Natto soybean

98

93

67

83

74

65

 

Carrington

Hatton

 

12 inch

18 inch

30 inch

12 inch

18 inch

30 inch

Dry bean

78

69

66

79

69

65


Photo 1: Farmer Field on August 5th 2009.
Soybean rows are not closed and sunlight
is reaching the soil surface


Photo 2. Soybean on 14 inch row spacing
at Carrington ND, August 4th 2009.


Photo 3. Soybean on 28 inch row spacing
at Carrington ND, August 4th 2009

Hans Kandel
NDSU Extension Agronomist, Broadleaf crops
hans.kandel@ndsu.edu

 

TIME TO PREPARE FOR WINTER WHEAT PLANTING

Winter wheat has grown in importance in North Dakota. But, why should anyone grow winter wheat in North Dakota given the risk associated with the loss of stand during the winter? Including some winter wheat in the farm does offer some potential advantages. Winter wheat typically is higher yielding than spring wheat. Furthermore, since it is planted in the fall, it more efficiently uses spring moisture and precipitation, and it spreads out labor requirements on the farm. It also establishes a fall cover, and offers an improved habitat for wildlife. Moreover, this year there is interest in planting winter wheat on land that was not planted in the spring due to excess moisture in order to better utilize land that was idle during the summer. The following are some general guidelines to help in establishing a successful winter wheat crop.

Field selection. Winter wheat survives our cold winters best when planted no-till into crop residue. Crop residues catch snow during the winter that insulates the winter wheat plants from the extremes in temperatures of the air. Tall erect stubble works best, but any erect stubble that will retain snow is recommended. For fields that were fallowed and tilled this year, conditions will not be ideal for winter wheat, since snow catch will be minimal. Nevertheless, this does not mean that a winter wheat crop cannot be produced on these fields. It does mean, however that there will be more risk of winter kill. Certainly in these type of situations, the most winter-hardy varieties should be grown, and all other practices that favor winter survival should be adopted. Planting wheat into a wheat stubble is not ideal for disease reasons, but as long as disease management is planned, wheat stubble can be an acceptable residue for winter wheat planting.

Variety selection. Use a winter hardy variety, especially if you are not planting into residue. The varieties released by NDSU (i.e. Jerry) as well as those developed in Canada are among the most winter hardy. Data on the winter survival during 2003/2004 of many of the currently grown varieties can be found at http://www.ag.ndsu.nodak.edu/aginfo/smgrains/WWsurvial.htm. Jerry, CDC Buteo and CDC Falcon are varieties for which seed is available in the state and that consistently have shown good winter survival. Accipiter and Peregrine are new varieties from Canada that also have good winter hardiness, although there is probably limited seed available currently in the state. Only plant varieties originating from SD and Nebraska if planting into a good residue. Yield data from the 2009 season will be posted on the Small Grains Page http://www.ag.ndsu.edu/smgrains/ when they become available (data are coming slowly this year due to the cool summer). Yield data from last year are available at http://www.ag.ndsu.edu/pubs/plantsci/smgrains/a574.pdf.

P fertilization. Apply phosphorus at or prior to planting. About 10-15 lbs of P with the seed can improve winter hardiness. Excessive N prior to winter freeze-up, however, can reduce winter survival.

Planting date. The optimum planting date for the northern half of the state is September 1-15 and for the southern half September 15-30. The last date that winter wheat can be planted will depend on the weather. The seed must germinate so that the crop will be vernalized by the spring. A larger plant will over winter better than a small seedling. Target the earlier portion of the recommended planting date range if planting into bare, fallow ground.

Planting depth. Adequate moisture for establishing winter wheat is often a concern as the soil profile is usually depleted of moisture in the fall. If there is little or no moisture in the soils surface, planting shallow (1 to 1.5 inches deep) and waiting for rain is recommended.

Seeding rates. Generally a seeding rate of 900,000 to 1 million viable seed per acre is adequate. Higher seeding rates may be appropriate if planting late or when planting into poor seedbeds. Since winter wheat tends to tiller more profusely than spring wheat, 1.2 million seeds per acre is the upper end of the seeding rate I recommend.

Avoid the green bridge. This will be discussed in more detail in the next crop and pest report.

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


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