By early June 2024, more than 75% of soybeans had been planted, and more than half of all soybeans had emerged in Kansas (USDA Kansas Crop Progress and Report Condition, June 10, 2024).
Figure 1. Soybeans planted late (early June) into adequate soil temperature and moisture conditions. Photo by Ignacio A. Ciampitti, K-State Research and Extension.
Planting progress overview
Kansas farmers have been planting soybeans slightly earlier in recent years -- at the rate of about one-third day earlier every year (Figure 2). Statewide, in the past five growing seasons (2017-21), the “50% planting date” mark was achieved between the end of May (for the most recent decade) and the first of June (in the 1980s). The earliest date achieving half of the beans planted was May 12 in 2014, while the largest delay was June 28 in 1982.
Following the latest USDA Crop Progress and Condition report (June 10, 2024), soybean planting progress is above the 71% 5-year average (2019-2023); while emergence (60%) is also ahead of the 53% average.
Figure 2. Trend in the date at which 50% of planting progress was achieved for soybean from 1980 to 2023 in Kansas (the last four decades of soybean progress in Kansas). Source: USDA-NASS.
Considerations for Late Planting
Where soybean planting has been delayed (or in double-crop soybean systems), producers should consider a few key management practices. Planting soybeans in the right soil conditions is essential for establishing an adequate soybean canopy and improving the chances of increasing the yield potential.
Planting date and maturity group
By planting in early June, soybeans are expected to bloom and fill seed from mid-August to mid-September, when nights are cooler, and the worst of heat and drought stress is usually over.
From mid-April to mid-July, we may expect maximum soybean yield in Kansas to be reduced by about 0.3 bu/a per day of delay past mid-April, from yield levels of about 80-90 bu/a to ~50 bu/a (Figure 3). On the other hand, the yield variability range is expected to narrow as the planting date is delayed, which may result in improved yield “stability” for late-planted soybeans (although achieving a lower maximum yield). More information related to this topic available at https://eupdate.agronomy.ksu.edu/article/soybean-planting-date-and-maturity-group-selection-585-6
Figure 3. Soybean seed yields as a function of planting date from Early (mid-April to mid-May) to Medium (mid-May to mid-June) to Late (mid-June to mid-July) for a diverse set of maturity groups (from Maturity Group 2 to 6).
Seeding rate and plant density
Increasing the seeding rate of late-planted soybeans by 10-20% compared to the optimal seeding rate can help compensate for the shortened growing conditions. Under normal conditions, the same soybean cultivar planted early in the planting window will develop nearly 50% more productive nodes than when planted in late June: 19-25 nodes when planted early vs. 13-16 nodes when planted late.
Soybean emergence could be delayed or compromised where there has been an excessive amount of rainfall in recent weeks. Replanting soybeans should be reserved only for exceptional cases where the stand counts and the uniformity look seriously affected. Otherwise, the cost of replanting is unlikely to pay off. Initial assessments should be done by the cotyledon stage (VC) and a week or so after the initial damage to assess the overall condition of plants and potential issues related to lack of uniformity, which could be a problem when stands are severely reduced.
Ensuring final plant populations are not too far from the optimal levels is crucial. In medium and high-yield environments, yields begin to decline at stands of less than ~100,000 plants per acre. In low-yield environments, however, yields may begin to decline at stands of less than ~125,000 plants per acre. At optimal planting dates, yields can be reduced by up to 15% with a stand of 80,000 plants per acre. This may be exacerbated under late planting dates due to the reduced capacity of the plants to produce compensatory yield growth, for example via branches.
For more on this topic, check this our eUpdate article on “Adjusting seeding rates for soybeans”
Figure 4. Expected soybean relative yield (%) with respect to the optimal plant density by yield environment. Vertical lines indicate expected optimal plant densities (Low: 127,000 plants/a; Medium: 96,000 plants/a; High: 97,000 plants/a) and their corresponding uncertainty (95% intervals). Adapted from Carciochi et al. (2018).
Row spacing
Information on late-planted soybeans across multiple row spacing suggests that narrow rows (e.g. 7” or 15” vs. 30”) can hasten canopy closure, increasing season-long light interception, weed suppression, and potentially improving biomass and final yield. The likelihood of a positive yield response to narrow rows increases as the yield environment lowers (Figure 5), for example with delayed planting. For more details on this topic, check our eUpdate article on soybean row spacing.
Figure 5. On-farm experiments on soybean row spacing comparing conventional (30-inch) vs. narrow rows (15-inch). Collaborators: Kansas State University, United Soybean Board, North Central Soybean Research Program.
Finally, properly identifying soybean growth stages can make a difference in yield. Consult our soybean growth and development chart at:
https://www.bookstore.ksre.ksu.edu/pubs/MF3339.pdf
Ignacio Ciampitti, Farming Systems Specialist
ciampitti@ksu.edu
Victor Gimenez, Postdoctoral Fellow
vgimenez@ksu.edu