Influence of Seeding Rate on Wheat Yield Potential

Henry Mascagni, Bell, Robert L., Harrison, Stephen A., Padgett, Guy B.  |  10/30/2006 11:20:55 PM

Henry J. “Rick” Mascagni, Stephen A. Harrison, Boyd Padgett and Bubba Bell

Wheat is a versatile crop that easily fits into several cropping systems. Additionally, harvest and marketing in the late spring provide producers much needed cash flow to support summer farming activities. Wheat acreage in Louisiana fluctuates yearly depending on grain prices and weather patterns. In 1985, when prices were high, Louisiana growers planted about 500,000 acres of wheat. Acreage has dropped to as low as 100,000 acres, however, during years when prices and weather patterns were not favorable. Yields range from low to relatively high, depending on factors such as stand establishment, weather, disease pressure and harvest conditions. Cultural practices, including seeding rate and nitrogen rate, also influence yield potential and profitability.

The LSU AgCenter’s recommended seeding rate for wheat is 60-90 pounds per acre of high quality seed planted into a good seedbed with adequate moisture. This rate should be increased if the seed is broadcast-planted, planted late or planted into a poorly prepared seedbed with poor moisture. Even when an optimum seeding rate is used, poor emergence is common, and growers often must decide whether the stand is worth keeping or should be abandoned.

Field Trials
To help answer these questions, a field trial was developed to provide producers with more information for making management decisions based on yield potential when stands are less than desired. Two wheat varieties were planted in 2004, and three varieties were planted in 2005 at the Macon Ridge Research Station in Winnsboro. Seeding rates were 4, 8, 16, 24 and 32 seeds per square foot, which correspond to approximately 17, 33, 66, 100 and 133 percent of the Ag Center’s recommended rate of 90 pounds per acre. In these trials, seed distribution within plots was uniform, fertility levels were optimum, and the plots were maintained weed-free, which promoted tillering (development of multiple stems per plant).

Yields were excellent in both years, averaging 81 bushels per acre in 2004 and 87.6 bushels per acre in 2005 (Tables 1 and 2). The second lowest seeding rate of 8 seeds per square foot produced yields equal to the highest yields for each variety each year. Even for the lowest seeding rate of 4 seeds per square foot, grain yields ranged from 72.1 to 76.1 bushels per acre for the two years.

The minimum number of plants required for maximum yield was 8 to 9 plants per square foot. Based on seed weight, the 8-seeds-per-square-foot rate is equivalent to a planting rate of about 30 pounds per acre. The 16- and 24- seeds-per-square-foot rates are equivalent to about 60 and 90 pounds per acre – the AgCenter-recommended rate under ideal conditions.

More Tillers  
The relatively high grain yields at the lower seeding rates were primarily due to increased tillering. On average, the plants at the low seeding rate produced five times as many tillers as those at the high seeding rate. In 2004, the tillering response of varieties was not as consistent across the seeding rates, and some varieties were better able to respond to low seeding rate than others. As a result of the differences in tillering, the total number of seed heads per acre was about the same for all seeding rates, except the lowest.

Producers often have to make management decisions about poor and nonuniform wheat stands. Management decisions affecting weed control and fertilization may need to be modified. In the worst cases, the wheat crop may need to be terminated so other crops such as soybeans or rice can be planted.

Uniform Spacing
In our wheat trials, plants were relatively uniformly spaced. In producer fields, the spacing is much more random, and in many cases, fields have large barren areas. If large portions of a field have poor stands, then it is an easy call to terminate the crop. When smaller areas within the field have low stands, then it is a more difficult decision. In these cases, it may be wise to keep the crop but decrease the total nitrogen fertilizer applied, knowing that the yield potential will probably be lower than the areas of the field with adequate stands.

Wheat varieties have a tremendous ability to compensate for low stands by producing tillers. Wheat stands as low as 8 to 9 plants per square foot produced maximum grain yields, while stands as low as 4 to 5 plants per square foot produced 85 percent of maximum yield. For maximum yield and profit, these stands need to be relatively uniform. Otherwise, yield will be lost, and weeds will thrive because of the lack of competition from the wheat crop. It is important with less than optimum stands to ensure that weed competition is minimized, and fertility and drainage are adequate during the late fall and winter. This will allow wheat plants to tiller at maximum rates and produce good yields. Heavy weed competition, waterlogged conditions or inadequate fertility will reduce the ability of wheat to compensate for poor stands and result in substantially lowered yields.
 
(This article was published in the fall 2006 issue of Louisiana Agriculture.)
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