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September 2000 |
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New Nitrogen Test to Fine Tune Corn Nitrogen Fertility |
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Nitrogen Test & Jim Jarman |
Nitrate concentration in corn stalks is most often seen as a problem when the corn is used as green chop or silage. Now the University of Missouri's nutrient testing laboratory can use nitrate levels to "fine tune" nitrogen fertilizer applications. The amount of left over nitrates left in the corn stalk right after maturity is an indicator of the amount available to and used by the corn plant. Experimental tests have shown three responses to increased amounts of nitrogen fertilizer applied to corn. The first is an increased yield with no increase in corn stalk nitrates. Second is increase in corn stalk nitrogen with no increase in yield. In the first case the amount of nitrogen applied was not meeting the nutritional needs of the corn plant to produce the optimum yield. In the second case there were sufficient nutrients to meet the yield potential and additional nitrogen fertilizer is a waste of money. In the test, there is a point where the amount of stalk nitrates begins to increase along with a decreased in yield response. When this occurs, the amount of applied nitrogen fertilizer is at optimum or ideal level. The variation in rainfall is a big factor. An optimum level of nitrogen fertilizer in a wet year is too high for a dry year. Still, the use of this test can help determine the optimum levels for typical years (if there is such a thing in Missouri). Also, nitrogen fertilizer running of into streams and rivers is important in water quality issues like hypoxia in the Gulf of Mexico. Tests are relatively easy but must be done within a certain time period. Samples of corn stalk need to be taken within one to three weeks after the corn reaches maturity. Cut 15 8-inch sections of corn stalk between 6 and 14 inches above the soil surface. Only put the stalk in to a PAPER bag and submit it to the University of Missouri Soil Testing Laboratory through the Callaway County Extension Center or your local extension center.
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