As you begin planning for the 2008 growing season, take advantage of ways of reducing your dependency on fertilizer nitrogen for your crop. Some of these include:
If your field has a history of manure application, or if it is continuous corn with the previous year having a drought, residual nitrate nitrogen can be substantial. This residual nitrogen is used as efficiently as fertilizer nitrogen. The only way of determining this residual nitrogen is by a deep soil nitrate test. Suggested sampling increments are 0-8 inches, 8-24 inches, and 24-36 inches. Generally, there is not a lot of residual nitrogen for corn following soybeans.
Set realistic goals. Expected yields is one of the major factors in determining the nitrogen rates for corn. If you set your expected yields at 250 bushels/acre but the average for the past five years is 160 bushels per acre, you will be applying too much nitrogen for that field. Use a proven, five year corn yield plus five percent to account for hybrid and management improvements.
Nitrogen credits can also be given for previous crop residues particularly the legume crops. Soil tests will not show legume or crop residue credits as the residue or nodules must break down during the growing season. The nitrogen credit for alfalfa ranges from 80 to 150 pounds per acre and for soybeans is 45 pounds per acre.
Manure is an excellent nutrient source for nitrogen. It often produces higher yields than inorganic fertilizer alone. Manure and compost should be tested for nutrient content. Nitrogen availability in manure varies because nitrogen must be converted from organic to usable inorganic forms which is a microbial function. Microbial organisms work depends upon the temperature and moisture that is available in the field. For this reason, the crop should be monitored mid-summer to see if additional inorganic nitrogen should be applied to reach expected yields.
Timing of application can also play a roll in the efficiency of nitrogen application. Applying as close to the time that the crop needs the nitrogen will improve the efficiency of that nitrogen. This could include side-dressing or the application of nitrogen through a center pivot system in split applications.
Soil organic matter can play a role in determining the amount of nitrogen needed by the crop. Nitrogen released from organic matter is considered in the UNL recommendations for corn when a soil test is made.
For many years, it has been shown that not all fertilizer recommendations are the same. The University of Nebraska-Lincoln fertilizer recommendations tend to be lower than those suggested by many commercial labs. UNL suggestions are based on research and on-farm verification. They are generally the most economical rates, even for high yield environments.
There has in the past been considerable discussion regarding the rotation of corn and soybeans or other crops versus continuous corn. Continuous corn certainly has the greatest need for nitrogen of all of the crops. A rotation of corn and soybeans will effectively reduce nitrogen needs by half and will actually improve the corn yields in that rotation by ten to fifteen percent. Yes, corn prices are high, but so are soybeans. Take advantage of that and rotate your crops.
