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Corn+Soybean Digest

Nitrogen Strategies For A Wet Spring

This true or false quiz comes from the Iowa Soybean On-Farm Network. It’s a part of their Nitrogen management handbook, which can be accessed in full online at

True or False:
1. All you need to know about nitrogen management in corn is the anticipated yield level and previous crop.
False. Several factors influence nitrogen availability and supply to the crop, to the extent that most Midwestern states have dropped yield goal from their nitrogen recommendations.

2. Although soybeans can fix nitrogen, the real reason corn after soybeans needs less nitrogen is the lack of corn residue tying up nitrogen.
True. First, soybeans tend to use more nitrogen than they fix. And second, as soil bacteria break down crop residues, they tie up nitrogen. The more crop residue to be processed (as in the case of a corn crop vs. a soybean crop), the more nitrogen the soil bacteria need.

3. Higher yielding corn environments will always require more nitrogen fertilizer than lower yielding environments.
False. The amount of nitrogen fertilizer needed depends on the amount of residual nitrogen released from organic matter and how much nitrogen is lost. Often, soils higher in organic matter are more biologically active and can produce higher yields with less nitrogen fertilizer than low organic matter soils.

4.Almost all the nitrogen a corn plant uses to make grain comes from the fertilizer applied.
False. Only about half of the nitrogen a typical corn crop utilizes is from fertilizer, the rest is from soil organic matter.

5.Soil pH can have a major impact on nitrogen management.
True. In Iowa State University and Iowa Soybean Association studies, high-pH soils increase the rate of nitrification from applied anhydrous ammonia, which results in more nitrate available for loss earlier.

6. Fields typically have some nitrogen variability within an 80-acre area, but the differences within a field are generally minor compared to nitrogen differences between fields.
False. Nitrogen availability across most fields varies considerably.

7. Manure management is very similar to managing nitrogen fertilizer.
False. Manure contains nitrogen as urea, nitrate, and ammonia, in very different concentrations and with varying quantities of organic matter. Depending on form (liquid, dry, amount of bedding, etc.), manure is more difficult to manage than nitrogen fertilizer.

8. Variable-rate application of nitrogen is well established and should be done by everyone.
False. Most variable rate recommendations are based on outdated yield goals and fail to account for other factors that affect nitrogen loss and availability.
9. Minimizing the amount of time that nitrate is present in the soil before it can be taken up is a good way of reducing the risk of nitrogen loss from leaching rainfall.

10.From a management perspective, a pound of nitrogen is a pound of nitrogen regardless of form it is applied as.
False. While this may be true for nitrogen in its purest form, nitrogen fertilizer for crop production varies in forms such as nitrate ammonium and urea. These forms vary in risk of loss and availability, which can have a huge impact on the nitrogen availability.

11. Because of the high price of grain and the financial incentive to over-apply nitrogen, there are seldom nitrogen stresses observed in the fields.
False. Even when nitrogen is over-applied, there are still likely to be locations within individual fields where nitrogen is not available in sufficient quantities.

12. If every farmer dropped his application rate by 50 lbs./acre, the average yield loss would be expected to be about 42 bu./acre (50 lb./1.2 lb./bu.).
False. Many Iowa Soybean Association On-Farm Network nitrogen study participants have been able to drop nitrogen use rates by 50 lbs. per acre or more with no significant reduction in per acre profits. This is especially true when rate reductions are combined with injected sidedressed applications.

13. It is easy to tell when you have a nitrogen-related yield loss because the corn will turn yellow and is easy to see from a truck cab.
False. While the yellowing of severe nitrogen deficiency may be noticeable from the ground, yield losses occur before symptoms can be seen while walking or driving by the field. An aerial image of the field, however, makes color gradations more easily detectible.

14. After sidedressing, there are no options available for detecting or correcting a nitrogen deficiency.
False. Aerial imagery can show problem areas in the field. With the right equipment, it’s possible to apply – even inject– corrective nitrogen up to tasseling.

15. Despite all the new technology and improved equipment, we still frequently see application errors.
True. Autosteer and GPS can improve the field efficiency of equipment, but they are not infallible. And application equipment can plug or otherwise malfunction. Aerial imagery
can detect problems before they become yield losses.

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