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Soil test can answer nitrogen question

May 08, 2007|by HEATHER HUTCHINSON

The weather is finally warming and agricultural activity in Washington County is bustling.

Now that corn is in the ground, efforts are being focused on soybeans. Next up is side-dressing nitrogen onto the corn crop

Or, is it????

In the coming weeks, farmers may be faced with the decision of whether or not to apply side-dress nitrogen to their corn crops.

It is a question of economics. Nitrogen prices are soaring and while it is true that corn prices are reaching levels never seen before, is it enough to offset $490/ton urea?

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Now, look at it another way. What would your net profit be if you eliminated the side-dress nitrogen application and still claimed $4.00/bu for your corn grain?

The question that needs to be answered is, "Can you minimize nitrogen inputs without compromising yield?"

There is a soil test that can help you answer this question.

The Pre-Side-dress Soil Nitrate Test (PSNT) isn't new. It was developed at the University of Vermont and has subsequently been tested and modified at numerous other USDA and state agricultural experiment stations. It has been available in Maryland since 1991.

Farmers in Washington County have used it and are pleased with the results.

How do we know? Repeat customers! The Maryland Cooperative Extension nutrient management advisors have been running PSNT every year for some farmers.

PSNT is designed for use on corn fields that have received organic applications - manure or biosolids - in the past or that have grown a forage legume such as alfalfa or clover in the year prior to planting corn.

The test measures the amount of nitrate-nitrogen available in the soil at the time when the crop is most likely to start using it. This nitrogen is a byproduct of the mineralization of manure and/or last year's forage legume crop, and its availability is influenced by soil temperature and moisture.

The PSNT should be run when corn is between 6 and 12 inches tall. This is the time period when corn is getting ready for a rapid growth spurt and will require nitrogen to fuel this growth.

If the PSNT shows enough nitrogen is present, save yourself some time and money and forego the application. If the test shows nitrogen is low, you may consider side-dressing additional nitrogen to avoid any potential compromise in yield.

PSNT is applicable on fields where corn for silage or grain is being grown, and fewer than 50 pounds of commercial fertilizer nitrogen was applied per acre before side-dress.

It's applicable on fields where a forage legume was grown last year and/or where manure or biosolids have been applied this year or in the past two years.

PSNT should not to be used on fields where:

· More than 50 pounds of commercial fertilizer nitrogen per acre have been applied prior to sidedress;

· Commercial fertilizer has historically been the only nutrient source; or

· Irrigation is used.

Please note that fields with commercial fertilizer as the only nutrient source and irrigated fields were not included in the PSNT calibration studies in Maryland. Therefore, the PSNT is not appropriate in these situations.

If you want to use the test to help decide whether or not to side-dress nitrogen, you will have to collect soil samples.

Here's what you should do: Randomly collect 30 to 40 soil cores at a depth of 12 inches when corn plants are between 6 and 12 inches tall. Take the soil cores from between the rows of corn to avoid the planter's fertilizer bands. Mix the sample very well and take a sub-sample (approximately 1 cup). Then, air-dry quickly and completely.

The sub-sample(s) can be tested by Washington County Nutrient Management Advisors Kenlin Martin and Richard Spoonire. Ken and Rich work out of the Maryland Cooperative Extension office off Sharpsburg Pike and can be reached at 301-791-1304.

PSNT season is a busy time for the advisors, so be sure to call and check their availability before dropping off samples. They will test the samples and get back to you with the results within a few days so that you have time to make plans to side-dress, if necessary.

If you are interested in having an advisor come to your farm to collect samples, please call to schedule a visit before the corn is 6 inches tall. PSNT is very time-sensitive and there is a short window of opportunity for collecting soil samples.

For more comprehensive information on the PSNT, please see Making Decisions for Nitrogen Fertilization of Corn Using the Pre-Sidedress Soil Nitrate Test (Soil Fertility Management-2) available on our Web site at www.agnr.umd.edu/agron/nutrient/Pubs/SFM-2.pdf

You can also contact the program office at 301-405-1319 and ask for a free copy.

Heather Hutchinson is a nutrient management specialist at the Western Maryland Research and Education Center near Keedysville. She can be reached weekdays at 301-432-2767, ext. 339.

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