It happens. A soybean grower has seed on hand that he meant to plant in May. Now it's the first of July, and he still has the seed. The grower wants to know if he can plant the seed and expect a good yield, or if he needs to use another variety.
University of Arkansas scientists wanted to know, too. In 1995 and 1996 they examined the performance of 50 soybean varieties planted on different dates at different Arkansas sites.
Cooperative Extension Service soybean agronomist Dr. Lanny Ashlock, says, "The varieties in this test are sold in Arkansas. They've appeared in the UofA soybean variety test and are the ones farmers have shown the most interest in."
Ashlock said the goals of this checkoff-funded study are to see how the different maturity groups respond when planted at different dates, to examine the response of varieties within each maturity group, and to see how the maturity groups responded at different sites.
"We looked at maturity group IVS, Vs and Vis planted very early, in April; from May 15 to June 15; and late, from mid-June to July 15," noted Ashlock. "In 1995, we had a dryland test at the UofA Cotton Branch Experiment Station at Marianna and an irrigated study at the Pine Tree Branch Experiment Station in St. Francis County.
"In 1996, we added dryland tests on a farm in Miller County and at the Northeast Research and Extension Center at Keiser. We wanted to see how the three maturity groups responded in different environments, to factors such as day length, soil types and rainfall patterns."
Preliminary results indicate that group IV varieties, as a group, performed better than group V and VI varieties when planted in April. Group IVS were competitive with group Vs and Vis when planted in May, but the group IVS generally didn't do as well when they were planted late.
Ashlock noted that Arkansas soybean producers plant group IV beans to take advantage of spring rains and reduce the number of irrigations. There's also the chance of a premium price for early harvested beans.
"Group V varieties offer soybean growers wider adaptability," said Ashlock. "There's not much difference in maturity between earlier and later maturing group Vs--about 10 days.
"In 1995, the group V varieties were solid performers, but they didn't excel regardless of planting date. That doesn't appear to be the case in '96."
In 1995, the group VI varieties did better than the group IVS and Vs when planted late, from mid-June to July 15, both in dryland and irrigated fields.
"There's a trend away from group Vis, and that may be a mistake," said Ashlock.
"Some group VI varieties have tremendous yield potential if you're planting from early May to early July. Of course, you can't wait too late and risk running into an early frost."
Ashlock warned growers not to "get overloaded with one maturity group. We need to use them all. And, there are superior varieties within each group."
Ashlock said that the 50 varieties in the trial include 10 group IVS, 20 group Vs and 20 group Vis--all varieties that are well adapted to Arkansas and are popular with growers.
"Among the group IVS in our test, some of the older varieties are still very competitive. Examples are Northrup King RA452 and Asgrow 4715. These were very strong when planted early.
"Two other group IV varieties, Hartz 4994 and Manokin, did well when planted late and irrigated, and even under dryland conditions. The one thing the two varieties have in common is that they are determinate, which means the plants complete their vegetative growth before they flower."
There was a lot of variation in the performance of group V varieties. The later maturing varieties in the 5.7-5.9 range did best. They included Pioneer 9592 and Northrup King S59-60.
"I was surprised," said Ashlock, "that some of the group VI varieties, including Pioneer 9641, did well planted early--almost as well as group IVS. Of course, the group VI varieties in general excelled when planted late.
"If you're going to plant beans after wheat on July 1, you need to look at early group VI varieties. They've been very consistent in our trials.
