Soybean High Yield Checklist

Chad Lee, Extension Agronomist, University of Kentucky

These soybeans went 90 bu/A
and hit every point on the checklist.

Based on the responses to the Corn High Yield Checklist we decided to define the key parameters to getting high soybean yields. You will see a lot of similar points between this checklist and the one for corn. Both of these checklists are intended to be a framework for where high yields start.

Soybean High Yield Checklist

1. Productive soils (deep, proper pH, adequate fertility, no compaction, excellent drainage)
2. Adequate, timely rainfall (or irrigation)
3. Using good genetics (high yielding and appropriate disease packages)
4. Rotating soybean with other crops
5. Planting on time or possibly early (soil conditions and favorable forecasts may be more important than the calendar)
6. Planting in narrow rows (20 inches or less)
7. Nitrogen fixed from Bradyrhizobium japonicum 
8. Capturing 95% sunlight at by about the time the first flower appears (R1 growth stage)
9. Getting excellent weed control (no trophy-hunting; this usually means removing in-crop weeds before they get to 6 inches in height)
10. Scouting for diseases and insects (a calendar application is not a good substitute for scouting, forecasts and taking appropriate action at threshold levels)

Just like the corn checklist,  the soybean checklist suggests that all of these things must be working for excellent yields. As with any list, there are caveats. A) For the nitrogen, if the B. japonicum is not effective (for example, from a failure of an inoculant), then a higher yield of soybean will need at least 250 to 300 lbs N/acre; B) For weed removal, if Palmer amaranth plants are in the field, then they must be removed before they are about 3 inches tall. If a field has Palmer amaranth, then all other management decisions become secondary to weed removal. C) Narrow rows - there will be occasional fields when soybeans in 30-inch rows yield well, but over time, soybeans in narrow rows will yield more than soybeans in wide rows. If our neighbors to the north are fighting with white mold, then that's another story. D) Soybean populations - I didn't include this one above because final populations from about 100,000 to 170,000 plants per acre will result in good yields for full season soybeans. If maximum yields are desired, then err on the higher side (the economics are close to paying).

In my opinion, there are several key reasons why we lose yield in our environment. In order of what I have observed, the most common yield limitations are:

• lack of water during seed fill - we normally have a dry spell during seed fill and our soils run out of water...right when soybeans need it the most. The timing and duration of water shortage is the single biggest factor on our yields, in my opinion.
• soil compaction - more common in tilled fields, but sidewall compaction has been a problem in no-tillage as well
• potassium (K) deficiency - usually where not enough K was applied before soybean; also a result from soil compaction
• weeds getting too big before being removed
• second fiddle to corn - if both corn and soybeans needs something done the same day, most farmers will take care of the corn, first
• SCN - a bigger problem when soybeans are not rotated
• Palmer amaranth - we already mentioned weeds in general, but this one is an increasing problem on its own and may be climbing up this list.

As the season progresses, we will expound on the checklist. If you have an idea about what else may result in high yields or want clarification of these points, please send me an email with your thoughts.