August 25, 2006

Use seeds/acre to calibrate winter wheat seeder

Table 1. Seeding rate for winter wheat with 18 seeds/foot of row.   Row spacing (inches) Feet of row/acre ------------------ Wheat seeds/lb ------------- 12,000 13,000 14,000 15,000 16,000 17,000 18,000     ------------------ lb/acre of seed ------------- 6 87,120 131 121 112 105 98 92 87 8 65,340 98 90 84 78 76 69 65 10 52,272 78 72 67 63 59 55 52 12 43,560 65 60 56 52 49 46 44 14 37,337 56 52 48 45 42 39 37

If we examine the seed size for 2006 in the UNL Extension Fall Seed Guide 2007 (EC103), the smallest winter wheat seed had 24,790 seeds/lb and the largest had 13,440 seeds/lb. Some years the largest seeds will have fewer than 10,000 seeds/lb. All seed should be cleaned and the small and cracked seeds eliminated. Shriveled seed can reduce yields because germination is slower and emergence is reduced.

Winter wheat will respond to a limited range of seeding rates without affecting yields. Using seeding rates below that range can lead to excessive tillering. It also may delay maturity, increase weed competition and fail to make use of full yield potential; however, rates above that limited range may increase costs, increase lodging and possibly reduce yields.

Too much competition, even among the small grain plants, may lead to fewer kernels per head and lower kernel weight. The key is an optimum plant population with uniform distribution for efficient use of available resources.

A review of how seeding rate affects yield potential is helpful. On the average, there are 22 seeds per head and 5 heads per plant, or 110 seeds per plant. With an average seed size of 15,000 seeds per pound or 900,000 seeds per bushel, a pound of average sized seed with 80% germination and emergence has a yield potential of approximately 1.5 bushels per acre. Seeding 40 pounds of seed with a weight of 15,000 seeds per pound has a yield potential of 60 bushels.

Seed cleaning and sizing is essential to remove straw, chaff, dirt, stones, weed seeds, and broken, diseased or small shriveled kernels. Generally, seed cleaning will add 1 to 2 pounds to the seedlot's test weight by removing the small kernels. Taking a germination test is essential to determine the seed viability. After seed germinability has been determined, the seeding rate can be determined. Seed for planting should be above 85% germination.

There are several views on how many winter wheat seeds the grower should plant per acre. Floyd E. Bolton, crop scientist at Oregon State University, says 18 seeds per foot of row seems to be the point of diminishing yield increases, no matter what row spacing from 6 to 18 inches. For dryland winter wheat in western Nebraska row spacings of 10 to 14 inches are recommended. Narrow row spacing offers an advantage for weed competition. For irrigation, row spacings of 6 to 8 inches are preferred. If a narrow row drill is not available for seeding irrigated wheat, seed the field twice – the second time at a slight angle to the first seeding. Use one-half the seeding rate each time. Following is a table on the pounds of seed/acre for 6- to 14-inch row spacings and seed sizes of 12,000 to 18,000 seeds/lb based on 18 seeds per foot of row. If planting is delayed, increase seeding rates up to 50% on dryland fields and up to 2.7 million seeds per acre on irrigated fields to offset the reduction in tillering that occurs with cooler temperatures.