I recently processed verification data from Arkansas, Louisiana and Mississippi for the past five years. Soybean verification programs have been in the Mid-South since 1983, when Arkansas initiated its program. Mississippi began its program in 1992, followed by Louisiana in 1994.
Over the years, 821 fields have been included in the verification programs. For the last five years (2000 through 2004), the tri-state verification fields out-yielded the three states' soybean yields by 14.4 bushels per acre.
What made these fields so much more successful than other fields throughout the three states? We know that these fields begin with proper fertility and are monitored once a week. They are also planted with recommended soybean varieties and use intense IPM strategies.
However, which maturity group, planting date, bed type, irrigation practice and row spacing have worked best in these verification fields?
Available varieties and cultural practices, verification fields from 2000 to 2004 in Arkansas, Louisiana and Mississippi were evaluated. This amounted to 292 fields encompassing over 15,000 acres. There was not enough data on maturity groups 3 and 6, so only groups 4 and 5 were analyzed.
Variables evaluated were yield, irrigation, bed type, planting date, maturity group, row spacing and plant population.
Across the tri-state area, irrigated fields out-yielded non-irrigated fields by 12.2 bushels per acre.
Mississippi realized the largest advantage to irrigation, followed by Arkansas, then Louisiana.
For the three states overall, irrigated raised beds outperformed flat irrigated beds, but in Mississippi alone, flat was better than raised when irrigated.
When comparing raised to flat beds, raised beds out-yielded flat beds by 1.4 bushels per acre.
Across the three states, Maturity Group 5 varieties yielded 4.6 bushels per acre higher than Maturity Group 4s. This could be explained in part to a breeding anomaly in that Group 5s still have a slightly better disease package overall than Group 4s, but the gap is closing rapidly.
Regarding planting date, some fascinating things surfaced from the data set. When group 4s and 5s were averaged together, the trend line that developed strongly suggests that the earlier you plant, the more you maximize yield.
How early is too early is the question. I can only attempt to answer that question for Louisiana producers with the data at hand. When Group 4s were evaluated separately, a gradual decrease in yield was noted for all three states when planting was delayed after April 30.
From the data, it appears that in Louisiana, to maximize yields with Group 4s, the time to plant them is the second and third week of April.
For Group 5s, a fascinating trend developed in that the trend line was much more steep in a negative direction when planting date was delayed past May 15 for Arkansas and slightly earlier for Mississippi and Louisiana.
What do the data mean? There is an opportunity to push the Maturity Group 5 planting date earlier than we have traditionally been planting. On most soils in Louisiana, if moisture is right and the soil is well-drained, some early Group 5s could be planted the last week of April, and yields would not be sacrificed.
Regarding plant population, both Mississippi and Louisiana yields were maximized when fields had final plant populations of 101,000 to 120,000 plants per acre. Arkansas maximized its soybean yields over a wider plant population of 101,000 to 140,000 plants to the acre.
Row spacing by bedding type and irrigation was analyzed also, but the bottom line on row spacing is that across the tri-state area, yields were maximized when row spacing ranged from 12 to 32 inches.
So what does all of this mean? This data set encouraged me in that most of our recommendations are on target, the ones that are outdated are being researched fully, and we should have more answers in the very near future.
The bottom line is this: irrigation, raised beds, and proper plant population, maturity group, planting date and variety will return monetary benefits.
David Y. Lanclos is the soybean, corn and grain sorghum specialist at LSU AgCenter. e-mail: firstname.lastname@example.org