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Delayed planting coupled with wet early season growing conditions across much of Wisconsin has dampened grower enthusiasm to enter the 2013 WI Soybean Yield Contest. Excellent growing conditions over the last several weeks has renewed grower interest. To facilitate this interest we are extending the entry due date to September 1st to enter the contest.  Below please find links for entry forms and rules. Good Luck!!!

2013 Wisconsin Soybean Yield Contest Rules

 2013Wisconsin Soybean Yield Contest Entry Form

The WI soybean crop ranges anywhere from just planted (JP) to beginning flower (R1). As we enter the soybean reproductive growth phase there are a few things to keep in mind. The first is that soybean will produce flowers for ~3 to five weeks, depending upon planting date and environment. During that time soybean will abort anywhere from 20 to 80% of the flowers that they produce. Generally it is the first and last flush of flowers produced that are most likely to be aborted.

Mike Bertram a WSA board member reminded me to add the category almost planted (AP).  That’s the treated seed that’s in the drill that will hopefully gets planted if the field dries out this week.  It might end up as forage.

R1 soybean growth stage

Next, the timing window for glyphosate applications in our early planted soybean is quickly closing. Glyphosate labels indicate that applications can be made through R2 or full flower. The R3 growth stage begins when one of the four top nodes with a fully developed leaf has a 3/16 inch long pod. Applications made after the R3 stage begins are off-label applications. On average it takes ~ 4 days to move from R1 (beginning flower) to R2 (full flower) and ~10 days from R2 to the start of R3 (beginning pod).

Last but not least, wheel track damage made from ground applications may start to reduce yield. Sprayer wheel traffic from first flower (R1) through harvest can damage soybean plants and reduce yield (Hanna et al. 2008). Our research suggests that an adequate soybean stand (more than 100,000 plants per acre) planted in late April though mid-May can compensate for wheel tracks made when a field is sprayed at R1. Yield loss can occur, however, when wheel tracks are made at R1 or later in thin soybean stands (less than 100,000 plants per acre) or late planted soybeans. Regardless of stand, plants could not compensate for wheel tracks made at R3 (early pod development) or R5 (early seed development). The average yield loss per acre is based on sprayer boom width (distance between wheel track passes). In our trials yield losses averaged 2.5, 1.9, and 1.3% when sprayer boom widths measured 60, 90, and 120 foot, respectively. Multiple trips along the same wheel tracks did not increase yield loss over the first trip.

Spraying soybean at the R1 crop growth stage

Wheel track damage to drilled soybean at R1

Hanna, S., Conley, S. P., Shaner, G., and Santini, J.  2008.  Fungicide application timing and row spacing effect on soybean canopy penetration and grain yield.  Agronomy Journal: 100:1488-1492. 

Scouting our field trials today we noticed an area presenting phytophthora symptoms. Further scouting showed plants were actually dying due to excessive flood injury and soil saturation. These fields have been subjected to nearly 5 inches of rain this week. This specific pocket has been anaerobic for 48 to 76 hours. Couple that with the heat, humidity, and larger crop growth stage (R1) plants are going downhill quickly. For more information on flood damage to soybean please visit www.coolbean.info.

Instead of complaining right off the bat let me be a glass half full kinda guy….well it looks like the drought of 2012 appears to be over! Ok…with that being said lets talk facts. We have already discussed maturity switch dates for corn grain, corn silage and soybean cultivars. What about switching corn ground to soybean.

1. Check your herbicide label. Several burn-down or early pre-plant programs have labels for both crops. However tankmix partners or rates may differ between the two. Maker sure you verify rates, timings, and plant back restrictions before you make the switch. Even with the intense rainfall we have experienced don’t bank on these products being gone.   

2. Fall applied anhydrous or spring applied urea. How much N is too much to not even consider the switch?  Biologically I don’t think that number really exists. Economically that number is a moving target given yield penalty, corn drying costs, etc. What I can surmise and you would likely agree with is that over the last 6 weeks the amount of N readily available to the late planted corn crop or in this case the soybean crop has declined, though some N is still readily in the soil profile. We were somewhat prepared for this question given the likelihood of residual N following last years drought stricken corn and the drought impact on rhizobia populations. In that article I stated:

In excess situations soybean will generally utilize the background nitrogen prior to initiating maximum N fixation. This may lead to luxurious early season growth, which in fields with a history of white mold, may cause problems if weather conditions are conducive. High soil N reserves may also lead to increased lodging. In either case, manage your soybean crop accordingly to minimize risk of white mold or lodging. This can be accomplished through variety selection (e.g. white mold tolerance, short statured soybean cultivars or good lodging tolerance), decreasing seeding rates, and proper scouting to time fungicide applications if needed.    

The only change I would make to this paragraph would be to increase seeding rates to compensate for delayed planting. Remember when I wrote this I was under the assumption that soybean would be planted the first week in May not the first week in June.

3. Should I use an inoculant with these late planted soybeans. The simple answer is yes and here is why.

• Background populations are likley diminished: Drought impact on rhizobia populations
• Excess N limits N fixation (Lit review excerpt quoted with permission from Eric Wilson; M.S. Thesis; Shaun Casteel Adviser; Purdue University)

Nitrate uptake of soybean plants did not appear to directly damage the BNF capacity (Streeter, 1985; Arrese-Igor et. al, 1997). Streeter (1985) concluded that carbohydrate deprivation and nitrate toxicity did not inhibit BNF. It is hypothesized that additional nitrate increased the oxygen diffusion barrier of the nodule, which limited oxygen supply and restricted nitrogenase activity and nodule respiration (Vessey and Waterer, 1992). This hypothesis was supported by Arrese-Igor et al., 1997. However, additional oxygen supplied to the nodules did not markedly increase BNF (Heckmann et al., 1989; Serraj et al., 1992).

• Frankly speaking the cost:risk/benefit ratio for 2013 suggests the usage.

Literature cited: