To examine the planting date effect on yield and agronomic performance for soybean cultivars in Northwestern Montana


This experiment utilized a split-plot design with planting date as the main block and varieties (maturity group) as subplots replicated three times. The three planting dates (PD) were 5/15, 5/29 and 6/12. The five relative maturity groups (MG) were 002, 005, 006, and 008. Harvest time was determined by observation when all the pods turned brown (i.e., 10/1 for PD 5/15 and 10/10 for the other two PDs).

Inoculant was inadvertently omitted during the seed preparation, so urea was added as rescue nitrogen (N). To minimize N loss of the applied urea, irrigation was applied immediately after urea broadcast. Table 1 is the detailed management information.

All MG (002-008) yielded similarly with planting date. The yield of PD May 15 averaged 28.8 bu/A. Delaying PD decreased yield. The PD May 29 yielded, on average, only 16.0 bu/A, and the latest PD (June 12) had near zero yield (Figure 1). This experiment was planted with 30-inch row spacing and narrower rows will be tried in 2019 with wider MG and PD ranges.

Table 1. Management information   

Seeding date: May 15, May 29, June 12 Harvest date: October 1, October 10
Julian date: 135, 150, 166 Julian date: 274, 283
Seeding rate: About 115,000 plants/A Soil nutrient residual (lbs/A): 93-7-84 (Fall, 2017)
Previous crop: Spring wheat Nutrient fertilizer applied (lbs/A): 120-50-0
Tillage: conventional Fungicide: Priaxor (at begin pod stage – R3)
Irrigation: 0.5 inches Inoculant None
Soil type: Silt loam Seed treatment: Cruiser 5FS, Apron Maxx RTA



Graph showing the relationship between the yield and respective planting dates May15th, May 29th, and June 12th.

Figure 1

Average yield of soybean varieties in 2018 with respective planting dates May 15, May 29, and June 12 planted on silt-loam soil.