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Teaming conventional and RR beans

Cheap seed planted as `weeds' boost Round Ready yields Turning the current commodity-price angst on its head, weed scientist Dick Oliver figured it might be worth a shot to see how cheap conventional soybean seed could benefit a Roundup Ready crop.

"We're always wanting to look at ways to increase yields and give advantages to soybeans. So we took conventional soybeans and essentially made them the weeds in a Roundup Ready soybean system."

A soybean competing with a soybean is more competitive than a weed competing with a soybean, says Oliver, a professor working out of the University of Arkansas in Fayetteville.

"What we wanted to do was fill up safe sites (the places within a canopy, in between a row, or other areas that hold a position open to weeds coming in)." The seeding rate was increased by putting conventional varieties and Roundup Ready varieties together. About four weeks later Oliver and colleagues sprayed Roundup. That killed the conventional varieties and the few weeds that were in the field. The Roundup Ready varieties were left in the field at the right density for production, says Oliver.

"The theory is that by using conventional varieties in such a way, the safe sites are filled, weeds are kept in check and the Roundup Ready varieties are stimulated to compete better and yields better. In truth, we weren't sure how yields would do, but we were hoping it would work out for the better."

Oliver looked at lower-cost production systems as well as several standard production methods. On the low-cost production system, he worked the soil seedbeds and broadcast mixtures on top of the soil. The seed were worked into the soil with a field cultivator and the field was then rolled. The beans were then allowed to emerge.

"We did that at different populations in 1998, 1999, and this year. This year's numbers should be in within a couple of months."

In the first two years, Oliver worked some fields in Kaiser (heavy clay soils) and in Little Rock and Pine Tree (both having light, silt-loam soils). The main thing learned from using the different locations was the broadcast method doesn't work well in heavy clay. The seed-to-soil contact just wasn't what was needed, says Oliver.

"It may work with a grain drill. We did some of that this year, but it wasn't given a fair shot due to the drought and heat.

"What we did find out on the silt loams was weed control really worked. Also, at certain ratios, we increased the yields. We had the test under irrigated and non-irrigated conditions. We went with 200,000 seeds per acre with the Roundup Ready varieties - a little high, but pretty close to recommendations. We added 200,000 conventional seed that were the same seed size. That way when mixed, the seed would distribute evenly. With 400,000 seed, we increased the yield 6.8 bushels on average over the two years."

Oliver not only got the yield bump, but including the cost of weed control and returns, he increased net profits some $35 per acre.

What about weed control? "At those rates, we were getting 60 to 80 percent weed control. It was much better than the regular system."

Was 400,000 the optimum seeding rate? "Yes. Starting out, for dryland conditions we had from zero - Roundup Ready varieties only - to 50,000 conventional seed. It went to 100,000; 200,000; 400,000; and 600,000. We went up to 800,000 seeds per acre for conventional varieties in irrigated tests.

But after seeing the data, the best ratio - whether dryland or irrigated - was 200,000 conventional seed."

The very high populations - 600,000 to 800,000 - were too dense, says Oliver. What happens is soybeans are more competitive than weeds and they fight each other if the populations are too high. Oliver lost yield by overloading the carrying capacity of the land.

"This really is a matter of timing. You've got to take the conventional varieties out before they start negatively affecting the Roundup Ready varieties. It can be done, but you have to pay close attention."

What varieties were used? "The first two years, we used Delta King RR5961 - a late Group V. The conventional variety, we didn't care about as long as it was the same size at the 5961. We just went to (Arkansas Extension soybean specialist) Lanny Ashlock and found some properly sized beans.

"Mixing them wasn't a big problem since we were on small plots. This year, we used a small grain drill and stirred them around, making sure they mixed well."

Using the grain drill, Oliver planted on 7-inch spacing.

"We went one direction and then turned around and crossed the field the other way to cut down on the safe sites. That worked fine."

The advantage of broadcasting is the closer spacing, says Oliver. However, there's some concern from crop insurance companies that seed needs to be drilled or put out with a planter.

"They don't want you just broadcasting. That's curious because we broadcast on light soils all the time and get good stands. It doesn't seem to make any difference. But the crop insurance folks don't like that, although I've heard they may be changing their views."

When was the Roundup sprayed? "We spray it at V5 to V6. That means about four or five weeks into the growing season. For top-notch weed control in normal production, we usually take the weeds out two to three weeks after emergence. (For the test) we delayed it for a couple of weeks after that just so the conventional soybeans could choke out the weeds as best they could. Then, when they were taken out, the Roundup Ready varieties were large enough to close the canopy quickly and keep the weeds down further."

Oliver has shown this system at several field days.

"There has been some interest in it. Some farmers may have thought we were a little crazy. But I thought, `Soybeans are so cheap, what could it hurt?' We wanted to see if we could turn the cheap beans to the farmers' advantage."

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