Tuesday, May 12, 2015

Last Night's Cold Temperatures Had No Impact on Emerged Soybean or Your Wheat Crop

Coauthored by Dr. Shawn P. Conley (15%) and Dr. Jim Specht (85%)

Last nights cold temperature has led to an influx of questions regarding the potential impact on either the wheat crop or emerged soybean seedlings. In short there is nothing to worry about in either crop. In the case of wheat, which is still in the jointing growth stage, cold temperature would need to reach 24 degrees F or less for 2 plus hours before injury occurred (Please see Recent Cold Temperatures will have Little Impact on WI Winter Wheat Crop for more details). 

In the case of soybean I was fortunate enough to be copied on this email from Dr. James Specht (please see below) which saved me a few hours of library time today so thank you Jim.

First of all 34F will not impact above-ground tissue.  Second, tissue freezing does not even take place at 32F because cell cytoplasm has solutes in it – like a modest anti-freeze, which depresses freezing point of the tissue a degree or two less than 32F - thus air temps surrounding the tissue have to get to below 31 or 30F before tissue freezing can occur.  Third, the soil surface is typically warmer than the air temperature (particularly when the soil is wet) and does not give up heat acquired during a sunny day as fast as the air does after sunset.  In actuality, the interface between soil surface temp and the air temp near that soil surface will be closer to the soil temp than to the air temp which most peopled measure on thermometers viewable at their height (not at ground level).  Biophysically, control of the soil temp over the air temp this is called the “boundary layer effect”).  So don’t trust air temperatures read on thermometers unless you know what the air temperature near the soil surface was (put a thermometer on the soil surface tonight where the cotyledons are and check it just before dawn (when the soil surface temp reaches its nadir for a 24-hour temperature cycle) and send out an e-mail blog to your producer colleagues early the next day.   Fourth, the cotyledons are a huge mass of tissue that are about 95% water.  That big amount of water-filled tissue is hard to freeze unless the exposure to temps of 30F at the soil-air interface is many, many hours.  Cotyledons will freeze faster (in fewer hours) but only if the soil surface temps get well below 30F (say 25F).  The only concern I would have is when cotyledons are no longer closed and protecting the young stem tip.  However, if that is in fact frozen off, the nodes to which the cotyledons are attached will regenerate TWO main stem tips.  Not an ideal way to start the growing season, but better than having to replant (0.5 bu/ac loss per each day that soybeans are NOT in the ground on May 1).

Thursday, April 16, 2015

Soybean Planting Date by Maturity Group Considerations for 2015

Article coauthored by Dr. Shawn P. Conley and Adam Gaspar

Early May planting in Wisconsin has been documented to increase soybean seed yield due to increased light interception (Gaspar and Conley, 2015).  In theory, earlier planting can potentially intercept greater amounts of solar radiation due to a longer growing season and therefore longer maturity group (MG) soybean varieties may be better suited to maximize yield if they can mature before a hard fall frost.  Unlike 2013 and 2014, 2015 may provide growers with an opportunity to plant their soybean crop earlier than ever before. Yet, in some instances (weather or logistical problems) planting will be delayed or replanting may be needed. Therefore, investigating the effect of different MG’s at multiple planting dates across the state would provide WI growers with BMP’s for soybean establishment regardless of planting timing.

To answer this question field trials were initiated at Arlington, Hancock, and Spooner, WI in spring of 2014.  The five planting dates at each location were planting roughly on: (1) May 7th, (2) May 20th, (3) June 1st, (4) June 10th, and (5) June 20th.  Planting after June 20th is not recommended in WI.  Two varieties within each MG from a 2.5 all the way down to a 00.5 were tested depending upon the location and planting date and are displayed in Table 1.


Table 1. Maturity Group’s tested within each location and planting date.
Planting Date

Arlington
Hancock
Spooner
1 (May 7th)

2.5, 2.0, 1.5
2.5, 2.0, 1.5
1.5, 1.0, 0.5
2 (May 20th)

2.5, 2.0, 1.5
2.5, 2.0, 1.5
1.5, 1.0, 0.5
3 (June 1st)

2.0, 1.5, 1.0
2.0, 1.5, 1.0
1.0, 0.5, 0.0
4 (June 10th)

2.0, 1.5, 1.0
2.0, 1.5, 1.0
1.0, 0.5, 0.0
5 (June 20th)

1.5, 1.0, 0.5
1.5, 1.0, 0.5
0.5, 0.0, 00.5













Let's start with the easy and redundant part, get your soybeans in the ground ASAP to maximize yield.  This is evident again in this trial, where Figure 1 shows the effect of planting date across all MG’s (varieties) tested in 2014.  If the soil is fit, soil temps are near 50 ˚F, and the forecast is favorable….. get the planter rolling!

Figure 1. Dots represent the mean yield within each planting date for each location.  The average yield loss per day for delaying planting past May 7th is presented in the legend.
However, the question still remains for many producers, should I use a longer maturity variety in early planting situations (very possible in 2015) and should I switch to an earlier maturing variety when planting is delayed?  

Table 2. Effect of Maturity Group on Yield tested within each location and planting date.
Planting Date

Arlington
Hancock
Spooner
1 (May 7th)

NS
NS
NS
2 (May 20th)

NS
NS
NS
3 (May 30th)

NS
**
NS
4 (June 10th)

NS
NS
NS
5 (June 20th)

**
NS
NS
** MG had a significant effect on yield at the  P ≤ 0.05 level














Based upon the 2014 data, only 2 out of 15 location x planting date combinations displayed a significant effect of MG on yield (Table 2).  So the moral of the story is that within a realistic MG range for your region and planting date, variety selection should be based heavily upon the varieties past local and regional performance, disease package, and etc.  Variety selection heavily based upon the MG is not a silver bullet to frequently increasing yields.

However, there are always caveats…… Growers may consider trying a slightly longer maturing soybean on a portion of their acres because there is a “potential”, but not guarantee, for higher yields with no additional dollars spent.  Within planting date 1, there was no significant MG effect, but MG 2.5 did yield the highest numerically in Arlington and Hancock with no fall frost damage, while the same is true for MG 1.5 in Spooner.  The longest MG tested within each planting date in our study numerically yielded the highest through June 10th (planting date 4). 

On the back end of the planting season, the inverse was seen.  Within planting date 5 at Arlington and Hancock, MG 1.5 did not mature before the first fall frost and was the lowest yielding.  Therefore, growers may consider switching to an earlier maturing variety as planting is delayed into June.  If switching to an earlier maturing variety, don’t use a variety less than 0.5 MG earlier than a full season variety (2.5 in southern WI) in early June.  However, if planting is delayed into mid to late June then a variety that is greater than or equal to a full MG earlier should be considered.

Acknowledgements: The authors would like to thank the Wisconsin Soybean Marketing Board and DuPont Pioneer for supporting this research.

References:
Gaspar, A.P. and S.P. Conley. 2015. Responses of canopy reflectance, light interception, and soybean seed yield to replanting suboptimal stands. Crop Sci. 55:377-385.