2013, 2014, and 2015, with funding from Ohio Soybean Council and help from county extension educators, we measured soybean yield limiting factors on 199 farms across the state. Data collected included management practices (i.e., crop rotation, variety, row width, etc), soil fertility status, soybean cyst nematode (SCN) egg counts, and soybean yield. These were the top yield-reducers in our research:
1.) Planting Date: On average, soybean fields planted before May 16 were associated with yields 4 bu/acre greater compared to fields planted on or after May 16. The greatest benefit of planting during the first half of May is early canopy closure which increases light interception, improves weed control by shading out weeds, and helps retain soil moisture. However, make sure soil temperature is at least 50°F at planting. Planting before field conditions are adequate comes with the risk of damping-off, bean leaf beetle, and late spring freeze damage.
2.) Soil fertility: A grain yield reduction of 7 bu/acre was associated with soil phosphorus levels less than the state established critical level while a grain yield reduction of 4 bu/acre was associated with potassium levels less than the state established critical level. However, there was no yield benefit to having soil phosphorus and potassium levels above the state established critical levels (i.e., If you’re field is not below the soil phosphorus and potassium critical level, you’re very unlikely to see a yield increase with additional fertilizer applications.)
3.) Soybean cyst nematode: Fields with over 200 eggs/100 cc of soil were associated with yields that were 6 bu/acre lower compared to fields with less than 200 eggs/100 cc soil. With as few as 1,600 eggs/100 cc soil, yield losses of 25% have been reported in Ohio. In our research, 80% of the fields sampled had detectable levels of soybean cyst nematode. Furthermore, many of the participants were unaware of any soybean cyst nematode problems in their field. (Often times, soybean cyst nematode infection causes no visible above-ground symptoms.) If you’ve never tested your fields for soybean cyst nematode, we suggest doing so.
There are many other factors that can influence soybean yield, so our soybean yield limitation research is on-going with funding from the North Central Soybean Research Program. If you are interested in participating, see our online survey tool at: https://www.surveymonkey.com/r/ohiosoybean.