Where are you on soybean planting?  All beans up and growing?  Finished, but some not yet emerged?  Barely started with planting and rained out again?  Beans still in the bag because corn planting is not yet finished?  While that covers the territory, most of the Cornbelt is concerned more with beans than corn at this point, since that may be the default crop when fields are dry enough to plant in the Eastern Cornbelt.  With that in mind, let’s look at the issues involved.

Undoubtedly you tuned up your planter early this year with the intention of timely planting of soybeans, possibly some in April, but at least the bulk of them in the first half of May.  That allows them to form a good canopy, capture every bit of possible sunlight both before and after the summer solstice, and you are on your way to a record yield and record market prices.  Unfortunately, you woke up from that dream when lightning and thunder shook your bed and you looked out to see water running out of the fields.  Spring turned into a nightmare and now you are several weeks behind where you wanted to be with your soybean operation.

Soybean specialist Shaun Casteel at Purdue offers some encouragement when he says that yield potential can be reduced as planting is delayed, but it is not a guarantee that yields will be lower.  He says late planting contributed to yields below trend in 2002 and 2008, but 2009 beans were also planted late and their yield was above the trend line.  Casteel says the latter was due to a favorable seed fill period which allowed larger beans to over compensate for fewer nodes. 

Casteel’s data on soybean planting was based on the date that half of the acreage was planted in his state of Indiana, and he says 33% of the yield departures were slightly more than the yield departures for corn in relation to its half-planted date.  The consensus reason is that soybean flowering is keyed when the length of the day shortens.  For delayed planting, that comes earlier in the life of the plant, compared to corn, and that is the reason for the differences in yield for corn and beans in comparison to the trend line.

Since you cannot do anything about the weather, and are forced to do as best you can with planting, Casteel says your focus should be on making the best decision to maximize revenue.  His suggestions include:

1) Planting in the first weeks of June require 10 to 20% increase in seeding rates to facilitate quicker row closure and higher pod height with fewer days to flowering.

2) Increased seeding rates will also be needed in those fields that have heavy corn residue and weed biomass.

3) Late-planted soybeans should also be planted in narrow rows to hasten the time to row closure.

4) 30-inch rows take nearly 25 days longer than 15-inch rows and 40 days longer than 7.5-inch rows to develop a canopy.  This delay will certainly decrease the yield potential as canopy closure would occur well after reproductive initiation.

5) Full-season varieties for your respective regions should be planted until June 15 for the northern quarter, June 20 for the central half, and June 25 for the southern quarter of Indiana.  (Compare the latitude lines for Indiana to reconcile that recommendation for your state.

6) Varieties should be dropped a half maturity group after these dates and planted for another two weeks before we consider other alternatives.

Summary:
While late planted soybeans may yield less, that is not for certain, based on other weather phenomena during the balance of the growing season.  Light is a significant issue, and the more light soybeans can absorb, the better the yield.  Light will trigger reproductive development, and that means flowering may occur while beans are at a shorter height and with fewer nodes than earlier planted beans that may be taller.  Late planted beans will benefit from an increased seeding rate and narrower rows, all in an effort to increase vegetative growth that will capture more sunlight.

Source: Farmgateblog.com