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Corn+Soybean Digest

Ask The Experts

Q: What should I do about soil testing?

HARMS: A good soil test is important in determining what nutrients are in the soil warehouse for the plant to draw from.

There are many ways to soil test. How you soil test and what type you use depends on your situation. If you have a good fertility program and have good soil test records, you may only need a “check and see” approach. This could be as few as eight tests on an 80-acre field.

On the other hand, if you're starting from scratch on a new piece of ground, you may want at least 16 tests from an 80-acre field. In either case, you get the best results when tests are pulled according to management zones or soil types.

I like to see pH, buffer pH, OM, CEC, phosphorus, potassium and calcium ratings. In addition, yield history will help in determining what level of productivity the field should be fertilized to achieve.

NAREM: South Dakota has a long history of annual soil testing to 24" in order to make nitrogen recommendations based on residual soil nitrates. This has become less important with the change from small grain farming to a corn-bean rotation. While we still do a great deal of “whole field” soil testing, we're working toward creating management zones determined by soil electrical conductivity (EC) data indicating soil types. This, along with grid sampling on manured fields, has shown variability we never dreamed existed in fields.

Q: How would a warm, dry growing season affect nitrogen (N) fertility needs for ‘03?

HARMS: Since N is not stable in Illinois because of our rainfall pattern, it's difficult to guess what effect last year's warm, dry summer will have on N requirements this year.

First, I doubt we can count on any carryover. Denitrification and mineralization are constantly taking place in spring and fall when the soil temperature is above 50° F.

I would apply N this year based on expected crop needs in 2003. If you applied early last fall, you can expect to lose part of it. The closer to actual uptake that you apply nitrogen, the less loss you can expect.

NAREM: Residual soil nitrates vary greatly after a drought-shortened crop, usually carrying into the next year. Dry soil profiles will make leaching and denitrification less likely.

Soil nitrate has always been recommended in South Dakota as a guide to fertilization of the subsequent crop. Further east, spring nitrate tests would be worth consideration before sidedressing. If you're in an area that has good crops, or if fall/winter precipitation is sufficient to push nitrates through the profile, you're probably able to go with your traditional fertilizer program.

Q: What is the best method to choose soybean varieties?

HARMS: Over the years, I've found it very difficult to choose soybean varieties that work well on different farms — even if the farms appear to be alike.

The best method I know is to put experiments on each farm and compare results. For some reason corn can be moved around with more predictable results than soybeans. Some researchers feel soil microbes have more of an effect on beans than on corn.

NAREM: Each area has its own set of problems and each field has its own needs.

From white mold to cyst nematode, from iron chlorosis to phytophthora — each field or management zone usually has one or two primary challenges. Begin the screening process by using seed company research and then do your own.

Hopefully, you can find soybean varieties with defensive characteristics that still provide good yield potential. Know your ground and don't jump with both feet into new genetics until you've given them a good look.

Have a question? E-mail it to [email protected] and we'll address it in a future issue.

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