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60 Ways Farmers Can Protect  Surface Water
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30. Apply Nitrogen In The Spring

N losses with Fall Application

Your best bet is to apply nitrogen as close as possible to when your crop needs it most. Fall application of nitrogen increases the loss of nitrogen through denitrification. It also gives nitrogen time to leach through the root zone and into groundwater or subsurface drainage tile.

Researchers estimate that with fall application, nitrogen losses from denitrification and leaching can range from 10 to 20 percent on fine- and medium-textured soils, and 20 to 50 percent on coarse-textured soils. University of Illinois research has also shown that it can take 120 pounds of fall-applied nitrogen to produce the same yield increase as 100 pounds applied in the spring.

Sidedressing a Field The increased risk of leaching on sandy soil may call for sidedressing—applying nitrogen right before the peak demand of the plant. But timing is critical with sidedressing. The period in which corn takes up nitrogen most rapidly is from about three to twelve weeks after planting. If the weather is too wet and you have trouble getting application equipment on the field in time, the benefits of sidedressing are greatly reduced.
Irrigating a field If you irrigate your sandy soil, one option is to apply a small amount of nitrogen at planting time (30 to 40 pounds per acre), one-third of it through the irrigation system no later than two weeks after tasseling, and the remainder as a sidedress application before corn is 8 inches tall. If you do not irrigate, you can split your nitrogen applications by applying one-third preplant and the other two-thirds sidedress.
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