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Issue No. 7, Article 3/May 18, 2012

Nitrogen Applications for the 2012 Corn Crop

While soil temperatures were warmer than normal last winter, this spring’s dry soil conditions have resulted in very little nitrogen loss. We began the fall with dry soils in Illinois, and only during November and December did we start to accumulate some above-average precipitation in the state (Table 1). As I have mentioned in earlier articles, the risk of N loss would increase only if the spring became too wet. Precipitation in Illinois so far this year is below average overall. While Table 1 does not show precipitation for May, the first half of the month has also been dry for most of the state. The weather data thus indicates very low probability for N loss so far this year.

Table 1. Mean monthly precipitation for a 20-year period (1991-2010), precipitation in fall 2011 and spring 2012 (11-12), and the departure (Diff.) from the mean for six Illinois locations.

Month

Brownstown*

Champaign

DeKalb

20-yr

11-12

Diff.

20-yr

11-12

Diff.

20-yr

11-12

Diff.

January

1.5

0.8

-0.7

3.0

3.7

0.8

2.4

3.5

1.1

February

1.6

1.9

0.3

2.1

1.9

-0.2

1.9

1.4

-0.5

March

2.1

2.0

-0.1

2.9

2.6

-0.3

2.8

1.9

-0.9

April

3.1

2.2

-0.9

3.5

5.1

1.6

3.4

1.4

-2.0

May

4.0

 

 

4.6

 

 

4.7

 

 

June

4.1

 

 

3.8

 

 

3.9

 

 

July

3.3

 

 

3.1

 

 

4.7

 

 

August

3.3

 

 

2.5

 

 

3.8

 

 

September

3.1

 

 

2.6

 

 

3.0

 

 

October

2.4

0.8

-1.6

3.0

2.6

-0.4

3.1

2.6

-0.4

November

2.3

5.6

3.2

3.5

4.4

0.9

3.4

5.1

1.7

December

1.7

3.9

2.2

2.3

4.1

1.8

2.3

3.2

0.9

 

Month

Monmouth

Perry

Rend Lake*

20-yr

11-12

Diff.

20-yr

11-12

Diff.

20-yr

11-12

Diff.

January

1.52

0.82

-0.7

1.6

1.0

-0.6

2.0

0.6

-1.3

February

1.58

1.9

0.3

1.6

1.8

0.2

1.9

1.3

-0.6

March

2.13

2.04

-0.1

1.9

1.8

-0.1

2.1

1.7

-0.4

April

3.13

2.23

-0.9

2.9

2.7

-0.3

3.0

5.3

2.2

May

3.97

 

 

3.5

 

 

3.7

 

 

June

4.06

 

 

3.9

 

 

3.5

 

 

July

3.35

 

 

3.4

 

 

3.3

 

 

August

3.33

 

 

3.7

 

 

3.1

 

 

September

3.12

 

 

3.2

 

 

2.8

 

 

October

2.38

0.8

-1.6

2.6

1.5

-1.1

2.7

1.0

-1.7

November

2.33

5.57

3.2

2.1

4.5

2.3

2.5

5.2

2.7

December

1.7

3.88

2.2

1.7

3.4

1.6

1.8

3.3

1.5

Source: www.sws.uiuc.edu/warm.
*Fall nitrogen applications are not recommended at this location due to high risk of loss because of warm-winter soil temperatures.

Taking a look at soil N also provides evidence that applied N remains in the soil. As shown in Figure 1, nitrification has proceeded quickly this spring. As ammonium was transformed to nitrate, ammonium concentrations declined over time, and nitrate concentrations increased. Note that ammonium concentrations are still high, probably because not all of the ammonium has been nitrified and because organic N in the soil is being mineralized to ammonium.


Figure 1. Soil ammonium and nitrate concentrations over time during spring 2012. Values represent average concentrations for the top 12 inches of soil (averaged across knife and between-knife tracks) for a field receiving 150 lb N/acre with a nitrification inhibitor (NServe) at the end of November 2011. These data were graciously provided by the Illinois Council on Best Management Practices.

Last week, during the last sampling shown in Figure 1, additional samples were collected for the 12-to-24–inch depth. As expected, since there has not been sufficient water to move nitrate down the profile, N concentrations were low: soil nitrate was only 9 ppm, and soil ammonium 3 ppm.

Most corn is now rapidly growing and starting to take up N. If the full amount was already applied, I do not anticipate any need to apply more for this crop. If no N or only a portion was applied, now is the time to start applying the balance.

The corn plant’s nitrogen needs are low during the early vegetative development stages, until about V5 (5th-leaf stage). The V8 to VT (tassel) stages are when most N is taken up. Soon after pollination, N uptake is essentially complete. Because the potential for N loss by leaching or denitrification at this time of the growing season is very low, and because corn plants will soon enter a phase of rapid N uptake, I recommend not delaying any needed application. But don’t despair if you aren’t quite ready; research has shown that the chance for yield loss due to N stress is very low for applications done as late as the V6 development stage. This is true because most soils in Illinois provide ample N for early crop demands through mineralization of soil organic N.

In addition, if a portion of the total N was already applied, a delay in applying the remainder is not likely to cause plants N stress. Where soil N-supplying power is low (soils low in organic matter) or where no N has yet been applied, make it a priority to try to apply early (preferably before V6 stage) to avoid loss of yield potential. Finally, the dry conditions this year underscore one of the main reasons I recommend not delaying N applications; the sooner N is applied, the greater chance it will have to be moved into the root zone by rain.

I consider injecting into the soil or dribbling between rows to be the best options to sidedress N. If anhydrous ammonia is used, make sure the knife track gets properly sealed to avoid crop injury from free ammonia escaping to the atmosphere. While most fields look very dry on the surface, adequate moisture is still present below the surface to retain the ammonia. I expect there should be no problems with ammonia volatilization if the application is done at least 6 inches below the surface in fine-textured soils or at least 8 inches below in coarse-textured soils. The benefit of dribbling nitrogen between crop rows compared with broadcast applications is that dribbling reduces the potential for volatilization of urea-containing fertilizers (urea and UAN) and reduces fertilizer contact with the foliage, thus protecting against foliar damage.

If injection or dribbling options are not available, I would recommend broadcast urea, as this product has the least impact on leaf burn compared with UAN, ammonium nitrate, or ammonium sulfate. If the canopy is wet early in the morning, it is best to wait until it dries out to minimize adhesion of dry fertilizer to the leaves. If there is not a good chance for rain in the forecast, I suggest applying urea with a urease inhibitor (like Agrotain) to minimize volatilization of N from urea. When urea is broadcast on the soil surface without a urease inhibitor, N loss starts to increase 3 to 4 days after the application if there is no rain to incorporate it. One can stand to lose as much as 30% of the application if rain does not incorporate urea into the soil within 10 days of the application. On the other hand, ammonium sulfate and ammonium nitrate are not subject to volatilization loss if left on the soil surface.

The least desirable option is to broadcast UAN solution, as this application has the greatest potential for crop injury. If this is the only option available, do it as soon as possible, because the smaller the plant, the less chance there is for fertilizer to contact it. Some studies have found that there is no considerable damage if UAN solution is broadcast when plants are about 6 inches tall. For bigger plants (V4), an application of up to 100 lb N/acre is unlikely to cause substantial yield reduction. Also, if at all possible, do this kind of application within a few hours tahead of rain so the fertilizer can be washed off the leaves. Of course, this would not be advisable if herbicide is combined with the application--which you should not do without ensuring that the label allows for it. Also, be aware that including herbicide with UAN can intensify leaf burn damage.--Fabián G. Fernández

Author:
Fabián Fernández

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