Soybeans are incredibly adaptive and can yield well when planted late. Although early May planting is ideal weather in August and September often has more influence on final yield than early planting. When planting is delayed, fewer days are required to reach maturity because of the plants ability to adjust to the season. A one month delay in planting results in a 9 day delay at maturity. One of the problems associated with late planting is that it will reduce the vegetative growth period. This results in shorter plants with lower pods. Late planting also reduces the number of pods per plant because of the shorter flowering period. Planting date also has an effect on the duration of the pod-filling period. These factors reduce overall yield potential somewhat but early June planted beans still yield over 90% compared to early May planted fields. See Table 1. Soybean management does not need to change unless planting is delayed well into June.
|Table 1: Effect of Planting Date on Yield
|Percent of Full Yield
|April 15 – May 5
|May 6 – 20
|May 21 – June 5
|*Average of 22 trials across Ontario from 2010 – 2012, OMAFRA, U of G, and Monsanto.
Increase Seeding Rates
Soybean yield is largely determined by the number of pods per acre. Since later planting will result in plants with fewer pods the only way to compensate is to increase the number of plants per acre. Since the plants will be shorter more plants can be sustained per acre. If planting is delayed into June start to increase seeding rates. By the 15th of June increase seeding rates by at least 10% for a minimum of 200 000 seeds/acre in narrow rows. This will increase the height of the lowest pods as well as the number of pods per acre.
Decrease Row Width
Using wide rows (30″) when planting late will lead to reduced yield potential. Too much sunlight is wasted on bare ground because the rows do not close before early pod set. Ideally 7.5″ rows should be used when seeding is delayed past the middle of June. Narrow rows discourage branching and the plants from setting pods closer to the ground. A combination of narrow rows and increased seeding rates can make a significant impact on yield.
Switching to Shorter Season Varieties
Generally speaking changing varieties is not necessary because the photoperiod effect will speed up maturity in the fall. However, if the field is intended for winter wheat choosing a shorter maturity variety is worth considering if planting is delayed past June 15th. On heavy textured soils, select an adapted variety. Planting a short-day variety late in the season will result in extremely short plants with few pods on heavy soils. An early frost may cause dark hilums to “bleed” into the soybean. Select a light hilum variety if this is a concern. It is also possible to improve the vegetative growth of late plantings by selecting taller varieties.