By Dusty Sonnenberg, CCA, Ohio Field Leader: a project of the Ohio Soybean Council and soybean checkoff
Soybean fertility studies, relative maturity, row width, seeding rates, and the benefits of adding wheat to the rotation were just a few of the topics covered by Laura Lindsey in a presentation given at the Conservation Tillage Conference in Ada last week.
“A study conducted from 2013-2015 with 199 farmers in Ohio looked at cultural practices, and measured soil fertility and
soil cyst nematode levels in 600 fields,” said Laura Lindsey, Ohio State University Extension soybean and small grains specialist. “The study investigated both the highest yielding areas of the field and lowest yielding areas of each field and compared them. Soil fertility was a primary factor that accounted for yield differences.”
When evaluating soil test phosphorus (P), 65% of the fields had at least a portion of the field that needed P fertilizer. Those areas of the field that were below the critical P levels yielded an average of 49.7 bushels per acre. The areas that were above the critical P level yielded an average of 57.1 bushel per acre. Of the 600 fields sampled, 21% had areas that fell below the critical level of P. The critical level is defined as below 20 ppm Mehlich-3. The maintenance range is between 20 to 40 ppm Mehlich-3.
Soil test potassium (K) was also evaluated in the study. In these fields, 23% of the samples were below the critical level. In fields below the critical K level, yields averaged 52.4 bushels per acre. In fields above soil K critical level, yields averaged 56.4 bushels per acre.
A study was conducted by Libby Dayton looking at soil test P trends from 1993-2015. This study was based on soil test results form a number of different soil labs, categorized by zip code. A majority of Ohio counties (53) have decreasing soil test P levels. Another 13 counites have increasing soil test P levels, however within those 13, only two of the counties have the average soil test P level above the maintenance range (20-40 ppm). The other 11 counties were below 40 ppm.
A one-year study evaluating the use of foliar fertilizer on soybeans was conducted with 20 trials across 13 states. Multiple nutrient packages were tested in the various states from a variety of companies, along with uniform controls in each. In all the trials, the yield differences were not statistically significant.
“Foliar fertilizer application on soybeans did not show a statistically significant yield difference,” Lindsey said. “This study will be repeated in 2020 across a larger area.”
Soybean relative maturity (RM) studies were conducted in 2017 and 2018 in Wood and Clark counties. Maturities tested ranged from .3 to 3.8 in the Wood county trial at the Northwestern Ag Research Station (NWARS). Anything between a 2.9 and a 3.8 RM did not show a statistical yield difference. The 2.9 bean did reach the R8 growth stage 7 days earlier relative to the 3.8 bean, which means there is an earlier harvest advantage to the 2.9 bean in terms of being able to plant cover crops or do field work following harvest.
In Clark county at the Western Ag Research Station (WARS), 16 cultivars were tested with maturities ranging from was 1.1 to 4.6 RM beans. Yield increases from 3.2 to 4.6 were not statistically significant. There is approximately a 15-day difference between when a 3.2 bean reaches R8 versus a 4.6 RM bean. This again can make a big difference in being able to plant cover crops or do field work following harvest.
A multi-state soybean row width study was conducted in 7,044 fields across the north central region. Row widths studied included 15-inch (narrow row) and 30-inch (wide row) beans. Past research has shown 7.5-inch and 15-inch row widths yielded nearly the same. The study was broken down by more specific geographic areas within the region. Ohio was in the middle region and saw a 1.6-bushel yield advantage for narrow rows over the wide rows. In northern regions, the yield advantage was 3.6 bushels per acre in narrow rows versus the wide rows. Much of the yield difference in the northern region is attributed to planting date, and the ability of the crop to canopy and capture sunlight more efficiently. In the southern region there was an 8-bushel per acre yield advantage to narrow row versus the wide row. That was largely attributed to the heat, with soybeans not favoring the hot weather. The narrow row beans canopied earlier and shaded the soil and reduced the evaporation losses.
A multi-state soybean seeding rate study was conducted across 211 fields. Ohio had both small plot and on-farm research included in this study. The research was grouped by growing environment conditions, and further grouped by yield potential. Low yield areas were defined as having a yield potential below 58 bushels per acre. The medium yield potential range was 58 to 71 bushel per acre. High yielding potential was considered greater than 71 bushels per acre. The agronomic optimum seeding rate for low yield potential was 170,000 seeds per acre. The agronomic optimum seeding rate for the medium yield environments was 146,000 seeds per acre. The high yield environment agronomic optimum seeding rate was 128,000 seeds per acre. Economic seeding rates would most likely be the same or lower for each of these environments.
When considering no-till and conventional tillage soybean seeding rates, specific research has not been done at Ohio State comparing the two practices. The previous study was conducted across tillage practices.
“Typically, the no-till soils are going to be cooler and wetter, and often times emergence can be reduced,” Lindsey said. “It would be advisable to possibly increase seeding rates to account for this. Most farmers know their fields and should adjust accordingly.”
For May planting dates, final stand counts should be 100,000 plants per acre. For June planting dates, a farmer should have 130,000 plants per acre. Double-crop soybeans should have a stand of 180,000 plants per acre.
“Final stand is a much better predictor of yield than seeding rate. The relation between seeding rate and yield is poor,” Lindsey said. “Soybeans have the ability to branch out and compensate for lower stands. Soybeans can also self-thin if populations are too high.”
A study looking at the benefits of adding wheat to a rotation was started in 2012. Results were not statistically significant. In 2018 at the Northwestern Ag Research Station (NWARS), there was a 3-bushel per acre yield advantage by adding wheat to the corn-soybean rotation, compared to only rotating corn and soybeans. That same year at the Western Ag Research Station (WARS) there was a 2-bushel per acre disadvantage (-2) to the addition of wheat in the rotation. In 2019 the NWARS showed a 7-bushel yield advantage to adding wheat to the rotation, and WARS showed a 4-bushel per acre advantage to the addition of wheat.
“Looking back at data from 2016 and 2017, typically the soybean yield is 3 to 5 bushels per acre better with wheat added to the corn-soybean rotation compared to a two year corn-soybeans rotation alone,” Lindsay said. “Additional data was also collected in this study evaluating both stand counts and root biomass. Improved final stands were observed in the fields with a three-year crop rotation, as well as increased soybean root biomass in those fields. Soil organic matter was also measured and increased in the three crop rotation fields over the 7-year period.