Friday, August 10, 2012

Down The Back Stretch

I posted a while back about our planting date trial in soybeans.  I thought it was time to update our observations.  There is a lot we can learn about growth stages of soybeans and the effect of weather during the later development stages of the crop.

For a refresher these are the reproductive stages of a soybean plant.  The stages seem complicated, but you just have to look at the top of the plant to make the assessment.

R3 - Beginning pod, short pods visible in top 4 nodes of the plant.

R4 - Full Pod, pods 2 cm long at top 4 nodes of the plant.

R5 - Beginning Seed, seed .3 cm long at top 4 nodes of the plant. 

R6 - Full Seed, seed in upper pods fills the cavity.

The R5 stage is the most critical for yield development. The soybean plant can shake off earlier problems and still produce high yields if weather co-operates during this stage. It is why Horst Bohner will say it does not matter what happens to the crop until August.  He is right.  What is sometimes not mentioned however, is the effect of maturity in the yield equation.  That is why we are looking at full season soybeans planted early, May 11 and late (for this year), May 26. 

Pioneer variety 92Y12 is an early group 2 bean.  Early group 2 is approxmately 3050 CHU.  A lot of you would not consider plantring a bean this late.  Some of you do not want to plant corn hybrids in this maturity range either.  That is ok.  Very full season crops are not for everyone.  You have to feel comfortable with your maturity choice. 
The reason we looked at 92Y12 is purely yield.  This is one of the highest yielding group 2 varieties on the market.  Last year in our strip plot it yielded 72 bu/acre harvested on October 12.  We would not be doing our job as a Pioneer rep if we did not push the edge of maturity to see if it makes sense for some of us to try it on a larger scale. 

The May 11 planted 92Y12 were still producing a few flowers at the top pf the plant last week.  This is the late stages of R4.  The upper pods are forming.
Further down in the canopy the pods are flat.
The 92Y12 planted on May 26 is in the R3 stage of early pod formation.  A long way to go, but the growing season is not over. 

The other variety that is being evaluated in the planting date trial is 91Y61.  It is a mid group I variety which is  approximately 2900 CHU.  This is closer to the maturity that, at least in corn, many of you are comfortable with.
The May 11 planting date is just entering the R5 stage.   
The 91Y61 planted May 26 is close to the same maturity stage, late R4, as the May 11 planted 92Y12. 

For comparison we also have late group 0 soybeans planted on May 11.  A late group 0 variety is approximately 2750 CHU.
90Y90 is an example of this maturity. 
Soybeans in this maturity are well along in R5 and approaching R6.  These beans have had extreme heat and drought stress to contend with.  The R5 and R6 stages are both about 2-3 weeks in duration under normal circumstances.  Where the drought is worse it appears the early varieties have rushed through the R5 period quicker than normal.  What effect will this have on yield?  Probably negative. 
It is way too early to make many predictions.  August and September weather will decide who wins the gold in this race.

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