When it comes to understanding yield loss in Oklahoma soybean fields, Oklahoma State University Cropping Systems Specialist Chad Godsey recommends looking at saving yields as opposed to gaining yields.
With help from the Oklahoma Soybean Board, Godsey recently collected data in a project that looked at field-scale yield loss.
“There is a lot to look at when it comes to potential yield loss through the year, including soil fertility factors, weeds, insects and rainfall,” he told producers at the recent Oklahoma Soybean Expo in Stillwater, Oklahoma. “The overall objective of this study was to evaluate the variability of soybean yields across the landscape.”
The project, according to Godsey, featured two components, grid soil sampling/EC mapping and deep core samples.
The fields in the study had been no-till for the last four years and featured a variety of soils ranging from Kirkland silt loam, Port silty clay loam and Tablet silt loam, each varying in slope.
“The data was collected in the spring of 2010 and fall of 2010 and yield monitor data was used to summarize the yield data,” he said. “Soil samples were taken every 2 1/2 acres and deep cores from zero to four foot were taken to characterize soil depth and texture. Elevation was also looked at.”
When comparing pH to yield, the field ranged in pH from a low of 5 to a high of 7.5, making it highly variable and not explaining yield change.
Godsey also compared potassium vs. yield and did find the higher the soil test P the higher the yields but results, once again, according to him, were variable.
“In conclusions, small things add up. There was a poor correlation with single variable versus yield,” he explained. “This basically means if you correct a single problem it probably will result in little effect on yield.”
The second point, according to Godsey, was that soil conservation proved to be important.
“Anywhere we tested where the field had hillsides, slopes or erosion, yield decreased due to the lack of topsoil,” he explained. “The key here is to maintain what you have to help slow down yield loss and soil conservation should be a top priority.”
In summary, Godsey told producers that intensive management will pay off in increased yield and decrease in inputs on occasion.
The last part of the study looked at planting dates. Research was conducted using early season MG III with an April planting date, full-season MG IV or V with a late May, early June planting date and double-crop.
“We looked at six planting dates with the different maturity groups using top performing varieties, as well as looking at yield components like pods per foot and seeds per foot,” he explained.
According to him, the results were consistent. The trend was that those planted in April to early June showed no difference in yield potential. However, late June and July plantings showed decreased yield potential.
“Planting after June 15 is when we saw a drop off in yield potential,” he said.
When looking at increasing yield in late-planted soybeans the specialist recommended increasing the number of pods and seeds per square meter. Additionally, he recommended increasing population, decreasing row spacing and adding a small amount of starter fertilizer.
In the end, Godsey reminded producers to pay attention to important management strategies, which include, fertility, plant population, seed bed and planting depths.
“The small things add up. Moisture often decides our final yield potential but we need to be ready to capture a high yield when we have the moisture,” he concluded.