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Rock and Roll Agronomy Growing Soybeans on Soybeans It’s “Guns and Butter” Economics: You Get More of Something Only By Giving Up Something Else By Jason Hanson, Certified Crop Advisor, You don’t need me telling you that the interest in soybeans Increasing acres at large rates can sometimes mean that sooner or later the rotation gets to be soybeans on soybeans. Economics is pushing the rotation shorter as other crops have not brought increased net return to the farm. In fact, some farmers are making a conscious decision to grow beans on beans, and I have received some calls on this as well. There are short range and long range considerations with this. It reminds me of the old “guns and butter” analogy, a fundamental concept in every college economics classroom, including that of the late Dr. Thor Hertsgaard at North Dakota State University. Many of you who went to NDSU back when and are considering beans on beans now may recall Thor’s classic “guns and butter” theory which demonstrates that: 1) There is a limit to what you can achieve, given existing resources and technology. 2) Every choice you make has an opportunity cost. You can get more of something only by giving up something else. In applying the theory to soybeans, most people are probably limited in resources (land, capital) and by putting in soybeans on last year’s soybean ground, you believe you will get a better net return with that crop, getting a better market price and spending less on nitrogen. But remember, as we go back to our guns and butter example, you can get more of something only by giving up something else. Most research data shows that a rotation that breaks up a monoculture is better than running with a continuous crop year after year. Even running with a rotation of corn-corn-soybeans-corn has benefits over a continuous corn planting. In many areas of North Dakota, the crops of sunflowers or canola broke up small grain rotations nicely this year and did make a difference in yield for the next year’s wheat or barley crop. Long term rotation studies have proven that continuous soybeans are a trip down a yield robbing road. But most of those studies are done in eight or nine year blocks of soybeans on soybeans. What about putting soybeans on soybeans for only one to three years? Are the dangers as real with that rotation? Table 1. The effect of crop rotations on soybean yields, Ridgetown, Ontario, Brookston clay. Average 1997-1999.
Some work done in Wisconsin has shown that second-year soybeans often yielded quite well relative to first-year soybeans and certainly better than beans in the third consecutive year. Probably the biggest threats to two years of soybeans are reduced soil structure and increased soybean cyst nematodes. Results would indicate that low populations of soybean cysts can multiply rapidly in that second year of soybeans and cause real problems with soybean yield potential. Now soybean cyst nematode has not been a problem in this area of the world in the past as it has in Minnesota, South Dakota or Wisconsin, but it has been documented in Richland County this year. That could play a large part of how and if we shorten soybean in the rotation. Same goes for soybean aphids. Rotation is so important due to the breaking up of disease cycles within a certain crop. Weather can enhance certain diseases in a given year, but putting soybeans two or three years on top of one another could make a soil population of phytophthora (root rot) explode. Granted, there are certain defensive genes built into some varieties, but why build up a population of disease for future attacks on soybeans? Some data out of Plant Health Progress, a professional plant health publication, shows an increase of yield loss in soybeans due to Fusarium root rot, Phytophthora rot and seedling diseases for both North Dakota and Minnesota from 1999-2002. I have talked to people that have already grown soybeans on soybeans and have felt they have gotten a yield kick in some situations from this. I would suspect that this has more to do with things like nitrogen management or inoculation than anything, especially if these were the first two years this ground has ever seen soybeans. What I have seen in the field is that in a corn-soybean or even a soybean-wheat-corn rotation, the second year of soybeans on soybeans is a little less in yield but not enough to matter. It’s the third year of beans or more is when the hurting (including increased pest and disease risks) starts. Back to guns and butter, there is lost opportunity to consider too, and that is the rotation effect for your grass crops. Wheat or corn tends to yield better following this legume. There is the nitrogen benefit, and possibly cleaner fields if the beans were Roundup-Ready. If you are unwavering in planting beans on beans, then at least consider the following: • Move away from the same variety or class of soybean on that ground as last year. Planting offensive bean varieties year in and year out might help increase the chance of letting disease be the main yield cause in that certain variety. Plant a more defensive or combination of offensive/defensive soybean. Check with your seed dealer about the disease package the variety carries. • Going into the first year of soybeans following soybeans, it would be wise to have those seeds treated with a fungicide. Products like Warden RTA or Apron Maxx will help protect against pythium, fusarium root rot, phytophthora, rhizoctonia root rot and other seedling diseases. Consider it a preventative investment for this and future crops of soybeans. • Soil test to get a good handle on the background nitrogen and phosphate content of the field. Even with relatively high nitrogen prices, it might be better to convert that acre to wheat or some other crop. • Be observant of areas in last year’s fields that could be iron cholorosis hot spots, possible soybean cyst nematode activity or soybean aphid colonies. These could really be spoilers for your beans-on-beans next year. Finally, even if you’re going to plant beans on beans next year, don’t turn it into a long-term venture. Beans-on-beans may gain you a few extra dollars in the short-term, but good rotation is the key for long-term crop production health and economic sustainability. Once again, the guns and butter concept rules the day. Here’s to you Thor. Hanson is a certified crop advisor near Devils Lake, N.D. |
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has grown
tremendously in the Northern Plains over the last three years. Early indications for next year are that soybean acres will increase again, fueled by a current bullish
market. Supply of seed varieties is either tight or gone at the end of November, so that should be a good bench mark for seeing more acres next summer.