The 2018 soybean crop got off to a slow start due to winter like conditions in April, but once the crop was up and running it turned into one of the best soybean seasons we’ve had in Illinois, with a predicted record yield of 66 bushels per acre. Dr. Nafziger sorts out weather and management factors that might have contributed to this turnaround as we prepare for the 2019 season.

A look at Illinois corn and soybean acreage [1990 – 2018]
  • Dependent on exports, prices
  • Equal acres of both crops are mutually beneficial
  • Experienced above-trend-line soybean yields for the past few years
    • Have seen increase in soybean yield: .64 bushels per acre per year
Soybean Trend Line – Straight line or upward curve?
  • • Predictive yield
    • o Applying a straight line over the last 10 years: 6.4-bushel increase
    • o Applying a curved line over last 10 years: 13.5-bushel yield increase
  • • Actual 2008 – 2018 yield difference: 64 bu/A – 47 bu/A =17 bushels increase
  • • There’s no question that we’ve seen strong yields over the last 10 years
Pod counts as a yield-indicator
  • Not always accurate representation/correlation
  • In 2018, assuming 2.5 beans/pod and 2,700 beans per lb., there were approximately 32 pods and 80 seeds per plant
NASS crop progress and condition – soybeans in Illinois, 2018
  • • Conditions were good this year, and they never really dropped
  • • Average yield in Illinois – 64 bu/A
  • • Accumulated precipitation July through August
  • • Drought monitor spiked in western Ill. early July and north central Ill. in mid-August
A look at high soybean yields (again) in 2018
  • Ideal weather
  • Planted crop earlier
  • Season was mostly stress-free for the crop
Soybean maturity x planting date – central Illinois 2018
  • Adding maturity actually added yield
  • Added .41 bushel for each day later in maturity in northern Illinois
  • In central and southern Illinois maturity really had no effect on yield
Lessons on Varieties, 2018 – 2019
  • Effect of maturity on yield varied by region
  • Selecting varieties based on protein content does not appear to be a path to higher profits
Planting Date
  • Early planting yielded better than late planting
  • No danger to planting in mid-April or early April
  • Can lose 20% of yield planting in June
Seeding Rate 2018
  • Stand consistency good with average >90% stand
  • Stands with highest yield range from 86K to 201K
    • Safe seeding rate in 140,000 to 150,000 range still supported
  • The less stress, the higher the yield – don’t create stress on purpose
  • Variety maturity does not correlate to yield potential
  • Planting early produces highest yields
  • Most fields with high yields did not receive fertilizer N
Q&A with Dr. Nafziger:

1. Can you recommend Biologicals, Biostimulants, PGR’s in managing stress or enhancing yield in soybeans?

While in principle some of these products might have some beneficial effects on soils and plants, we do not expect that to translate into higher yields in most Illinois fields, especially when weather conditions are good, and yields are (already) high. Most of these are promoted based on their ability to increase root growth and nutrient uptake, neither of which seems to be a limiting factor in most fields in most years. If they would happen to increase yields, the increase would in most cases be too small to be visible in strip trials. We would expect most of these to be harmless, but some classes of growth regulators may have the potential to decrease yields under some conditions.

2. How much did harvest delay cut yields in 2018?

Harvest delay had three possible effects: 1) increasing seed shatter at the combine header by allowing seed to get too dry (<10%); 2) weakening the pod “sutures” so that pods opened more readily when hit by the cutterbar and 3) allowing disease—mostly pod & stem blight—to continue to develop. Some of the latter also contributed to decreased test wt. and to higher damaged-kernel issues at the elevator. I know of no data-based estimate of yield and market value loss from delayed harvest but would estimate that it could have been in the range of 2-3 bushels per acre overall in Illinois, and higher in some other states. There is always some harvest-related loss, but in years with better conditions at harvest it could well be less than 1 bushel per acre.
3. How should one decide on how many or the best seed treatments to use?
It’s not easy, and there probably isn’t a lot of neutral information to inform us. More importantly, the need for these in a given field each year is unpredictable. SDS has been very sporadic; chances of it being a severe problem in each county in Illinois in 2019 are not very high. Cyst nematode is present in most fields but in good years like 2018 (in most areas) it likely causes little yield loss. Bacterial inoculum is unlikely to be needed for the development of fully-functioning nodules in fields where soybeans have been grown before. Even fungicides to improve emergence may not help stands when emergence conditions are as good as they were in 2018. Still, seed-applied fungicides are probably a good insurance investment, and seed-applied insecticide (almost always marketed along with fungicide these days) may improve stands in some cases, even though it’s not clear that are any insects for them to control (they seem to have a physiological effect in some cases.) I’d tend on principle to elect not to pay for treatments like micronutrients, growth regulators, or biological products, but if those are in packages with other things and don’t cost much, there’s no harm.
4. Besides rainfall amounts and any storm damage issues, what would be the most significant impact of climate change for soybeans?
It’s unclear to me whether higher temperatures would have an effect by themselves, unless of course they were tied to periods of low rainfall. Soybeans tend to be fairly tolerant of high daytime temperatures, as long as they have enough water.
5. What would be a good planting population for early planting in no-till, 15” row, fully treated soybeans?
135,000 to 140,000 per acre if planting into good conditions and with a weather forecast that looks like emergence will take place without cool, wet weather that could limit emergence. I might raise that by 10,000 if a cool front is on the way with some rain and might even wait to plant if a cool front is forecasted with a lot of rain.
6. Double crop soybean yields have been much higher recently and getting closer to full season yield in southern Illinois, what has changed?
High yields of DC soybeans haven’t been universal: if it doesn’t rain much in July and (especially) in August, yield scan still be low. Varieties are just better, though, which has improved their chances for growing a good root and plant even when conditions aren’t great. We’ve also tended to have good September weather to help yields of late-planted soybeans in most recent years.
7. What contributions did fungicides and insecticides make to yields in 2018? What is speaker’s choices for 2018 fungicide/insecticides?
I’ll defer this question to the UI the entomologist (Nick Seiter) and plant pathologist (Nathan Kleczewski). I will add, though, that we need to rethink the habit of adding a low-cost insecticide to fungicide sprays, when there aren’t any insect pests present. That does a lot more damage to predators in most fields than it does good by killing pests.
8. Can we further tweak MG selections to add more bushels per acre?
I don’t think so, given that we don’t know how the weather will interact with different maturities when we choose and plant varieties. Breeders are concentrating on improving varieties of the maturities that most farmers are planting, and small differences in maturity are almost irrelevant compared to proven ability (in wide testing) to yield well.
9. What is the next best production practice coming that will increase yields?
My vision might be somewhat limited, but I don’t see a big jump coming. If we can keep moving the high yields a little higher over time and bring some of the lower yields up to their potential, the overall results will be a continued upward move. That will, of course, be accompanied by ups and downs over years, due mostly to variable weather.
Click here for Nafziger’s slides. 

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