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50 Ways Farmers Can Protect Their Groundwater
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3. Credit Other Nitrogen Sources

Recommended nitrogen application rates Recommended nitrogen application rates should be adjusted to account for nitrogen supplied by previous legume crops, manure, other organic wastes, or residual soil nitrate. If you do not credit other sources of N, you may end up applying more nitrogen than is agronomically necessary or environmentally wise.

Charts are available to estimate the amount of nitrogen supplied by legume crops during the previous year, as well as the amount of nitrogen and other nutrients in manure.
manure However, the most accurate way to gauge the nutrient content of manure is to have a laboratory analyze samples for your specific farm.
spraying field Based on research at the Northern Illinois Research Center, Illinois agronomists also suggest that for each week of delay in planting after the optimum date for the area, you can reduce the nitrogen rate 20 pounds per acre. The minimum rate would be 80 to 90 pounds per acre for very late planting in a corn-soybean cropping system.
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