Agronomy Update  

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Late Planted Soybeans

By James D’Aoust CCA

 

As August quickly comes to a close, many growers are wondering what they can expect from their late planted soybean fields.

 

Here are a few considerations to keep in mind

 

·For every 3 day delay in planting beyond the optimum planting date for soybeans in Ontario (say May 20^th), you can expect a 1 day delay in maturity in the fall.  So, planting soybeans on June 15^th vs May 20^th will result in soybeans reaching maturity 8 days later. 

·Regardless of what you are planting, late planted beans are not going to get very big or very tall. Driven by day length and heat accumulation, beans will have a shortened vegetative period and quickly enter into flowering stage.  Beans will be short and pods will be close to the ground.

·Don't have any elusions as to if these beans are going to be your best beans.  Expect 10-20% lower yield than if you planted end of May or first part of June.

 

Ontario Planting Date Experience  

Planting Date	Yield bu/acre
May 23	36.5
May 29	37.4
June 6	34.1
June 15	31.8

Table 1: Yield for various planting dates Kemptville College, University of Guelph 1967-70

 

 

Planting Date	Yield bu/acre
May 8	54.6
May 16	52.4
May 28	50.3
June 8 (2yrs)	44.4

Table 3: Yield fo Various Planting Dates, Kemptville College, University of Guelph, 1990-93

 

Reproductive Growth Stages in Soybeans

 

There are 8 stages that are divided into 4 parts:  R1 and R2 describe flowering; R3 and R4 pod development; R5 and R6 seed development;  R7 and R8 plant maturation.

 

Plants at R4 are called full pod and are 40 to 45 days to maturity. Soybeans at R5 are beginning to form seed and are 30 to 35 days to maturity. R6 is full seed where green seeds fill the pod and are 18 to 22 days to maturity. At R6 soybeans have accumulated 80% to 85% of yield potential. R7 is when leaves and pods start to yellow. Maturity is 10 days away and 95 % of yield potential is set. At R8 the plant is fully mature and the seed will take 7 to 10 days to dry down to 14% moisture.

Most fields planted by June 15^th are at the R5 to R6 stage at this point.  Fields planted at the end of June or the first part of July, are just nicely finishing flowering and into pod development.

At this point, all we can do is hope for a wide open September for these later planted fields.