Best Management Practices for Late Planted Soybeans

A wet spring has delayed soybean planting for many Ontario growers. See picture #1.

Picture #1. No-till field ready for soybean planting in Perth County. May 27,2024.

Timely planting is important for maximum yield, but soybeans are more tolerant to late planting than other crops. Although late April or early May planting is ideal weather in August and September often has more influence on final yield than early planting. June planted soybeans can do extremely well if the rest of the growing season is favorable. When planting is delayed, fewer days are required to reach maturity in the fall because of the plants ability to adjust to the season. A 3-week delay in spring planting results in a one-week delay in maturity in the fall due to the photoperiod effect. One of the problems associated with late planting is that it reduces the vegetative growth period. This results in physically shorter plants with fewer nodes and pods closer to the ground. 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 together reduce overall yield potential, but early June planted soybeans still have over 90% yield potential compared to early May planted fields. See table #1. Soybean management does not need to change until planting is delayed into June.

Table 1:   Effect of Planting Date on Yield
  Planting Date  Yield* (bu/acre)  Percent of Full Yield
April 15 – May 563.8100  
May 6 – 2063.3  99  
May 21 – June 5  58.5  92  
*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 physically 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. The exact seeding rate depends on the soil type, row width, growing area, and variety. Heavy clay soils need even more plants per acre as do northern counties. More plants per acre increases the height of the lowest pods as well as the number of pods per acre. Keep in mind that seeding rates should not be increased if the field has a history of white mold. Even late planted fields can get white mold if conditions are favorable for the disease.
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 into 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
The decision to switch to a shorter maturing variety will depend on what maturity was chosen in the first place. If a recommended full season variety for a given area was initially purchased than switching varieties is not necessary unless planting is delayed into July. Full season soybean maturity recommendations are conservative in Ontario and allow for later planting. The main reason to avoid switching to shorter maturing varieties is that shorter maturing varieties have lower yield potential. A reduction of one full maturity group (1.0 MG) will drop yield potential by about 5 bu/ac. If the field is intended for winter wheat a shorter maturing variety has likely already been selected to facilitate timely wheat seeding. If seeding wheat this fall is an absolute priority a further reduction may be warranted if soybean planting is delayed past June 15th. In the relative maturity grouping system used for soybeans each decimal place represents a 1-day delay in maturity in the fall. For example, a 1.5 MG variety will mature 4 days earlier than a 1.9 MG when seeded on the same day at the same location. Weather conditions will influence the exact difference in maturity but generally speaking a variety that is 0.5 MG shorter than a full season is considered adequate for timely wheat seeding. On heavy textured clay soils, selecting a very early maturing variety is not a good idea. Planting an early maturing variety late in the season will result in physically short plants with few pods close to the ground on clay soils.