By Dusty Sonnenberg, CCA (Adapted from Crop & Soils Magazine, July-August 2021)
Names like Kip Cullers of Stark City, MO, or Randy Dowdy of Pravo, GA are legends in soybean yield contests. In 2010, Cullers harvested 160.6 bushels per acre of soybeans. In 2019, Dowdy harvested 190 bushels per acre of contest soybeans. While many sales agronomists have worked alongside Cullers, Dowdy and other major soybean growers across the country, academia has not thoroughly evaluated production until recently.
A review of high yield practices was undertaken by Larry Purcell, a soybean physiologist at the University of Arkansas, professor emeritus of crop physiology and holder of the Altheimer Chair for Soybean Research. Also in 2020, Shawn Conley, University of Wisconsin-Madison professor and Soybean and Small Grains Extension Specialist and North Central Soybean Research Program agronomist, and 12 other academic agronomists participated in a large SOYA collaborative research project to study high intake. the impact of the system on soybean yield and profitability. So what has the research shown?
Agronomic practices were tested in 20 field locations in 9 states. The results revealed that 90% of high-yield practices were unprofitable, even at $15 per bushel of soybeans producing 75 bushels per acre. High-yield practices increased yield in 6 of 9 Midwestern states, 3 states did not observe an increase in yield.
Soybean nodules fix enough atmospheric nitrogen to produce about 80 to 85 bushels per acre of soybeans according to Purcell’s research.
“If you apply N, it stops N binding from soybeans,” Purcell said. “I don’t know of any way to apply N without stopping the fixation of N.”
Other research shows that there is no economic support for applying nitrogen. With the current price of N, it would take a very large yield response to break even.
It is essential to find the best varieties for the environmental conditions of each farm.
“Generally, the top performers produce between 20% and 40% higher yields than the bottom ones,” Purcell said.
Farmers achieving record yields identified the best performing varieties on their farms.
Number and weight of seeds
The yield of soybeans is determined by the number of seeds and the weight. Purcell says seed number is determined during growth stages R1 through R5. Seed weight is determined by the length of steps R5 to R7. All practices should work to achieve optimal growing conditions of R1 to R7 to maximize sugar production from photosynthesis during seed formation and lengthen the seed fill period to maximize yield. This means achieving complete canopy closure by flowering and reducing stress.
“You want to increase the bloom time, capture that extended photoperiod at the summer solstice, which results from planting early,” Purcell said.
Optimize seeding rates
The most profitable seeding rates vary by region and agronomic productivity class and are determined by variations in seed costs, grain prices, use of seed treatment and environmental productivity. In a seeding rate study, researchers found that soybeans can adapt to a wide range of planting populations. Growers should increase seeding rates in less productive growing areas and decrease rates to approach the optimum seeding rate in more productive areas.
Soil test results
Soybeans can generally utilize the residual P and K from a well-fertilized corn crop. High applications of P and K to achieve record yields are unaffordable practices for traditional farmers. High application rates of N, P and K on soybeans are prohibitively expensive and could also have negative environmental impacts.
Plant early and regularly
Getting soybeans planted early and with rapid emergence (within 24 hours) is a factor in achieving high yields.
Good seed-to-soil contact is important, especially when following a high-residue corn crop.
“The soybean should be planted in the ground, not the residue,” Purcell said.
Reduce plant stress
Water stress, weeds and disease pressure all negatively impact soybean yield. Those with high-yielding contest soybeans usually irrigate. Weed control starts early.
“Two-inch amaranth takes far too long to wait before spraying,” Purcell said.
Weed control programs should include both pre-emergence and post-emergence herbicide application. Various modes of action should also be incorporated.
There are still a lot of things that are largely unknown about inputs. Timing of application and doses to be used are not yet an exact science. Slow-release fertilizers, micronutrients, and organics are all used at different rates and times by many high-yielding soybean growers. According to Purcell, inoculants for soybeans are not necessary if soybeans are planted at least every 3 years.
Asking questions and being willing to try new things are key factors in achieving higher returns.
“Curiosity and a focus on soybeans tends to serve high-yielding soybean contest growers well,” Purcell said.