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Soybean Planting Date (6/04/20)

Soybean cultivars have different maturity ratings based on the number of days it takes the plant to reach physiological maturity.

Soybean cultivars have different maturity ratings based on the number of days it takes the plant to reach physiological maturity. In North Dakota, most growers will choose a cultivar in group 000, 00, 0, or group 1 due to the ability of these maturity groups to perform well given the short growing season in North Dakota. These groups are divided by decimal places to indicate the maturity ratings within a group. For example, a 0.3 maturity rating is an early group 0 cultivar, whereas a 0.9 is a later group 0 cultivar, and will take more days to reach physiological maturity. Early seeding dates are recommended for growers across all regions in North Dakota. However, due to the late season not all soybean fields have been seeded at this time.

A study was conducted (Sweep and Johnson, 2017) to determine the influence of cultivar maturity rating on soybean yield when planted from May to late into July and how many calendar dates were needed to get to V4 (four trifoliolate growth stage) and first bloom. Experiments were conducted at Prosper and Lisbon for two seasons, and Carrington during one season. Three cultivars were used with maturity ratings of 00.9, 0.7 and 1.4.

Beginning of bloom (R1) is defined as the presence of at least one flower on the plant at any node on the main stem.  With the later than normal planting dates this year there may be questions about when the first flowers will appear. Flower initiation is based on heat units (accumulated GGD) as well as the photoperiod (the lengthening of the nights after June 21).

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Figure 1 indicates that the plants will need to produce nodes and leaves before they can flower. The soybean first flower initiates on the third to sixth node on the main stem. In this study, flowering stared on July 10 for soybean planted on May 23 and on August 13 for soybean planted on July 9. The later planted soybean plants typically grow in warmer conditions than earlier planted beans and develop quickly. In addition, the plant will start flowering after fewer accumulated GDD when planting is delayed. Figure 1 indicates that fewer calendar days were needed to reach V4 and R1 when planting is delayed.

Typically when a crop has fewer total growing days in the field, the yields decline. Figure 2 provides the relative yield of three cultivars with different maturity ratings and six planting dates, expressed in percent. The average yield for the three cultivars for the first planting date was set at 100 percent and all other yields are expressed as a percent based on the average yield when planted on May 23. Not surprising, yields declined with later planting of soybean. The latest maturing cultivar had the highest yield when planted early. After the June 11 planting the late maturing cultivar yielded lower than earlier maturing cultivars.

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Soybean is an oil seed crop. When planting is delayed the oil content of the soybean seed declined (Figure 3).

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Conclusion

The interaction of planting date by maturity rating of cultivars indicated that yield decreased as planting was delayed further into the growing season with yields becoming less than economical in soybean planted after June 22. Soybean with maturity ratings 00.9 and 0.7 were better suited for delayed planting in North Dakota, while a later maturing cultivar (rating 1.4) rapidly lost yield with delayed planting.

Source: Research by E. Sweep and B. Johnson [Seeding Date, Maturity Rating, and Location Influence on Soybean (Glycine max. L. (Merr)) Performance and Phenology in Eastern North Dakota].

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 Hans Kandel

Extension Agronomist Broadleaf Crops

 

Burton Johnson

NDSU Professor and Agronomist

This site is supported in part by the Crop Protection and Pest Management Program [grant no. 2017-70006-27144/accession 1013592] from the USDA National Institute of Food and Agriculture. Any opinions, findings, conclusions, or recommendations expressed are those of the website author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture.

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