To evaluate the effect of planting date and maturity group on soybean grain yield and quality in northwestern Montana


J.A. Torrion, E. Nafi


Five different maturity groups (MG) of soybeans were planted on different dates, starting from late-April to late-May (Table 2) dryland conditions. Damage due to vegetative consumption by deer was observed in the late part of the season (prior to harvest, primarily) but did not contribute to the variability in yields.  There was minimal lodging and shattering in the trial.

No significant interaction between planting date and MG was recorded for soybean measured traits except seed oil content. The average grain yield across the trail was 36.6 bu/A. the highest yield (42.9 bu/A) was observed when soybean was planted in May 6th and the lowest (33.6 bu/A) was recorded with delayed planting (Figure 1). The MG 0.08 had higher yields (39.0 bu/A) and increasing MG beyond 0.08 did increase yield any further (Figure 2). The caveat is that for longer MG beyond 0.08, drying down time of the pods and stems is a major concern for timely harvesting.

The highest seed protein content was observed under the delayed-planted and early maturing soybean varieties (Table 3). As planting was delayed, thousand kernel weight (TKW) and test weight (TWT) increased (Table 3). The lowest TKW (34.5 g) and TWT (57.3 lbs/bu) was found for early-planted soybean. The average TKW and TWT were 35.8 g and 57.7 lbs/bu, respectively. Late maturing soybean varieties also showed the greatest TKW (except 0.4) and TWT compared with the early maturing ones (Table 4). Seed oil content topped out at 22.1% for early-planted soybean, and decreased as planting was delayed. Oil content was inconsistent with the maturity groups, ranging from 20.7% to 21.9%.


Table 1. Management information

Seeding rate (plants/acre): 150,000 Field location: X1
Previous crop: Corn Soil type: Creston silt loam
Herbicide: 6/3: Basagran Tillage: Conventional
Insecticide: None

Soil residual nutrient:

(NO3-, P, K lb/A): 190-12-258
Fungicide: None Nutrient fertilizer applied: (N, P2O5, K20 lb/A): 0-30-0
Inoculant: Verdesian N-Dure    


Table 2. Harvesting dates of the respective soybean planting dates

Planting dates Harvesting dates
27-Apr 2-Oct
6-May 2-Oct
18-May 8-Oct
29-May 8-Oct


Table 3. Planting date (individual) effects on soybean quality

Planting dates Protein TKW TWT Oil
  (%) (g.) (lbs/bu) (%)
27-Apr 37.1b 34.5b 57.3b 22.1a
6-May 36.9b 35.5b 57.8ab 21.2b
18-May 38.2a 34.9b 58.2a 20.7c
29-May 38.3a 36.6a 58.0a 20.6c
Mean 37.6 35.6 57.8 21.2
CV% 4.8 11.9 1.9 4.8
Pr > F 0.006 0.04 0.02 <0.001

TWT= test weight, TKW = thousand kernel weight

Table 4. Maturity group (individual) effects on soybean quality

Maturity groups Protein TKW TWT Oil
(%) (g.) (lbs/bu) (%)
0.02 39.9a 33.8bc 57.4ab 20.7c
0.06 37.9b 36ab 57.3b 21.9a
0.08 37.2bc 35.9ab 57.9a 21.1bc
0.2 36.8bc 38.7a 57.8ab 21.3b
0.4 37.1c 32.4c 58.4a 20.7c
Mean 37.8 35.4 57.7 21.3
CV% 4.5 10.8 1.8 4.7
Pr > F <0.001 <0.001 0.02 0.0008

TWT= test weight, TKW = thousand kernel weight


Bar graph showing the soybean seed yield with planting dates

Figure 1.

Soybean seed yield with planting dates. Same letter assignment denotes no statistical difference (α = 0.05).


Bar graph showing the soybean seed yield with maturity groups

Figure 2.

Soybean seed yield with maturity groups. Same letter assignment denotes no statistical difference (α = 0.05).