Ask an Agronomist
Does Uniformity of Wheat Emergence Matter?
May 08, 2012
Question: We farm in the Willamette Valley of western Oregon, about an hour south of Portland. We run a complex rotation of irrigated vegetables (sweet corn, snap beans and cauliflower), grass seed (turf-type tall fescue and perennial ryegrass) and wheat. Some years we grow sugar beet seed. Our wheat is soft white, mainly public varieties from breeding programs at Oregon State University and Washington State University. Wheat is often planted following a vegetable crop, using a small amount of conventional tillage (no moldboard plowing). Varieties such as Goetze, Tubbs06 and Stephens yield from 100-140 bu/a, depending on the year and the ground (if everything comes together on a good piece of dirt, 175 bu/a is possible).
Traditionally, we plant in a pretty rough seedbed, in early to mid-October, using an end wheel drill with double disk openers on 6" centers. University recommendations would have us using 75-100 pounds of seed per acre, but most growers bump that to 120-140 "for insurance."
A few growers (especially those with large acreages) have been broadcasting seed, at 160-200 lb/a, then incorporating it with a field cultivator or disc harrow. As you can imagine, emergence is not very uniform, but if the spreader does a good job with the seed, and the tillage tool is set right, some of these fields look pretty good!
My question: Besides the extra seed cost, what are these growers giving up? Winter wheat here tends to just come up and then just sit there through the winter. Does uniformity of emergence matter? Is it time to park my 12' end wheel drill, and start seeding wheat 50' at a pass? If you'd care to comment, I'd welcome hearing from you.
Answer: Consistent depth control and uniform emergence are both very important for creating high wheat yields, in fact replicated research work from Canada found that wheat plants which emerge 7-9 days after initial emerging plants yielded 3.2 times less at harvest (data averaged over 2 years). Uneven emergence becomes an even greater yield limiting factor later in the season, especially when trying to apply a foliar fungicide. For example, early emerging plants are likely to flower ahead of later emerging plants, so when trying to time the fusarium fungicide at flowering, the standards of control are reduced on account of variation in timing.
You mentioned seeding by pounds per acre. My suggestion is to seed by live seed population per acre (not pounds), simply because the size of the seed can vary significantly between growing seasons, different seed lots and even varieties. For example I have often seen varieties with 18,000 seeds per pound and others with 9,500. Seeding both varieties at 120 lb/a for example, would result in seed populations ranging from 1.1 million all the way up to 2.16 million per acre. The seed population actually planted needs to be adjusted up or down, according to seeding date, fertility practices and seedbed conditions.
If everything hits just right, it’s certainly possible to broadcast wheat and make top yields, but year in and year out I’m afraid there are often yield limiting problems which arise from broadcasting wheat. Two of the biggest challenges include spinner spreaders which don’t spread the wheat evenly across the fields (air-trucks are usually much better) and inconsistent incorporation depth across the fields, especially within the wheel tracks of the tractor pulling the tillage equipment.
Without conducting stand counts after seeding, it’s not possible to comment on the performance of your end wheel drills. However, if you find the stand counts are consistent across all rows and the depth control is uniform, then keeping what you have might be OK. However, older drills (especially those with worn parts) often don’t provide the standards of stand uniformity required for high yields, so in these examples it could be costing you more money to seed with older drills than to spend the money on newer ones which provide better emergence standards.