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Nitrogen Check

August 13, 2009

With corn silage harvest just around the corner, now is the time to check your corn to see how well you managed your nitrogen this year. Farmers are using many different methods to get nitrogen to their crops, manure, urea, UAN, etc . . . All these are good forms of N, but they all have the potential to “leak” out of the soil and into the environment, leaving the farmer with a shortage of the most important nutrient for a crop. A lot of farmers are utilizing newer technologies to monitor nitrogen in their corn fields. PSNT and Chlorphyll Meter are the two newer technologies used the most. PSNT or PreSidedress Nitrate Test is a pretty simple test do. One must take 10-20 12inch deep soil cores in a field, dry them down, and then send them to a soil-testing lab for Nitrate N analysis. Chlorphyll Meter test is a little more costly, because you have to purchase a Meter which can run into the thousand dollar range. This little meter is very easy to use. The meter reads the “greeness” of a corn plant. When using this method, one should read the fifth leaf on the corn plant. The meter can hold up to 30 readings, so you should take 30 readings per field and then calculate an average. This number is then run through a chart that will determine if you need to apply N or not. These tests do not work very well on corn fields that have had a lot of nitrogen fertilizer applied. If you don’t have the time, money, or desire to use one of these two tests to check your corn fields for nitrogen, there is another way to test and see how you’ve done for the year. The Late Season Stalk Nitrate Test is a great way to determine if you had to much N, enough N, or not enough N. This test is done by sampling approximately 15 corn plants in a field. To take a sample cut an 8in section of the corn stalk starting at 6in above the ground. Then cut this sample into 2in sections and place into a paper bag. (The paper bag will prevent molding) Send the samples to a Testing Lab. The results will come back in PPM:

0-750 = Low Nitrogen
750-2000 = Optimum Nitrogen
2000 and above = excessive Nitrogen

This test does not tell you what you need to change, but it does give you guidance on how you are doing. If you do this test every year and keep records, you can see how management changes nitrogen.

Nitrogen deficient Corn This picture shows classic sign of Nitrogen deficiency in corn.

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