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Northeast North Dakota has seen a dramatic increase in soybean acreage in recent years especially counties along the Canadian border where the state’s coolest temperatures and shortest growing seasons occur. Choosing the right combination of seeding date and cultivar maturity group (MG) is an important decision producers make in obtaining optimum soybean production. The objective of this study was to provide research based data to assist farmers in determining the relationship between seeding date and MG for the NE region of the state.
Research was conducted at Langdon with five seeding dates and three MGs at each seeding date. Seeding dates were in approximate 10-day intervals ranging from May 15 to June 25. Maturity groups consisted of 00.5, 00.9 and 0.1 Roundup Ready cultivars. The target plant population was 180,000 plants per acre seeded in 6-inch rows. The June 25 seeding date failed to produce a harvestable crop because of a killing frost on September 29.
Agronomic trait data trends (not shown) indicated the number of days to mature decreased with later seeding dates while later MGs took more days to mature. Plant and pod height decreased with later seeding dates. No differences were observed in grain protein among seeding dates but oil content decreased at later seeding dates.
Yields were greatest at the earliest seeding date and decreased at each of the later subsequent dates (Figure 1). Yield decreases between the May 15 and June 14 seeding dates for the 00.5, 00.9 and 0.1 cultivars were 13.6, 21.4, and 23.7 bu/a, respectively. Yield response to seeding date varied by MG. Maturity group cultivars 00.9 and 0.1 had significant higher yields at the May 15 and May 24 seeding date, but at the June 14 seeding date the MG 00.5 cultivar had the highest yield. The 00.9 MG had the greatest yield on the June 4 seeding date. The further seeding date is delayed into June, the greater chance of a harvestable crop with the earliest MG. However, chances of a harvestable crop seeded the last ten days of June would be problematic with even the earliest MG and would be dependent on weather conditions and timing of the first fall freeze in any given year.