DELAWARE NUTRIENT MANAGEMENT NOTES

"Nitrogen Management"

The goals and objectives of the Delaware Nutrient Management Act were described in the January edition of Nutrient Notes ("1999 Delaware Nutrient Management Act"). Subsequent Nutrient Notes (February and March 2000) addressed who is affected by the Act and the contents of Nutrient Management Plans. This issue will focus on nitrogen management in production agriculture. Next month's Nutrient Notes will address nutrient management issues on lawns.

WHY IS NITROGEN MANAGEMENT IMPORTANT?

· Nitrogen causes water-quality problems in many parts of Delaware. Nitrogen pollution comes from a variety of sources within the state; however, agriculture is a significant contributor in many areas. This contribution can be greatly reduced by establishing or improving nutrient management.

· An important goal of the Delaware Nutrient Management Program is to improve water quality while maintaining or enhancing agricultural profitability. One way to accomplish this goal is to balance the amounts, placement, and timing of nitrogen on cropland with crop needs.

· Management techniques that increase our ability to use the nitrogen from applications of organic materials (such as animal manure or litter) and inorganic fertilizers will protect water quality and can increase the profitability of farming operations.

WHAT ARE THE BASICS OF NITROGEN MANAGEMENT?

· The first step in managing nitrogen is determining the needs based on the crop type, yield goals, and soil characteristics. University of Delaware Cooperative Extension offers guidelines for all the major agronomic and vegetable crops in this state.

· The second step is predicting the availability of nitrogen from past and current applications of organic sources, such as poultry litter or animal manures. This step requires detailed information regarding nutrient content of the organic material, crop needs, and availability of nutrients after application. A manure analysis or a reliable history of analyses should be used whenever possible. In the absence of an analysis, Cooperative Extension has guidelines for estimating nutrient content and availability from organic sources.

· The third step is calculating application rates based on crops needs and predicted nitrogen availability from the organic material or fertilizer. These calculations are a relatively simple matter of dividing the amount of nitrogen required per acre by the amount of nitrogen available from a given application. For example, if a crop requires 150 pounds of nitrogen per acre, and the organic material is estimated to supply 50 pounds of plant-available nitrogen per ton, the recommended application rate would be 3 tons per acre. (150 pounds of nitrogen needed divided by 50 pounds of nitrogen available per ton applied equals 3 tons).

IMPROVING NITROGEN MANAGEMENT IN CORN

· One of the biggest challenges in nitrogen management is estimating such things as application rates, nutrient content of organic sources, and plant availability of organic nitrogen to crops. This is particularly difficult since nitrogen can be present in many forms in soils, and can be lost through various processes after application and before plant uptake. For example, poultry litter that is applied on the land surface and not incorporated can be expected to lose as much as 75 percent of the plant-available nitrogen before crop uptake.

· We can improve on basic nitrogen management for corn by improving our estimate of nitrogen availability to the crop. Two possibilities are discussed below: soil testing and use of a leaf chlorophyll meter. A complete nitrogen management program may also include tissue testing and end-of-season cornstalk testing. Information on these tools is available from University of Delaware Cooperative Extension.

WHAT IS THE PRE-SIDEDRESS SOIL NITRATE TEST (PSNT)?

· The Pre-Sidedress Soil Nitrate Test (PSNT) is a valuable tool for improving nitrogen management in corn. Specific guidelines for using this test are available from Cooperative Extension Soil Test Note 14: Pre-Sidedress Soil Nitrate Test for Corn. The PSNT is to determine the amount of plant available nitrogen that is in the soil just before corn plants begin rapid uptake of nitrogen. The PSNT is taken when corn plants are 10 to 12 inches tall, so any early losses of nitrogen can be detected. The timing of the test allows for early-season additions of nitrogen by sidedressing or fertigation. The County Conservation Districts and most private Nutrient Management Consultants offer PSNT testing for corn crops.

WHAT IS THE LEAF CHLOROPHYLL METER (LCM)?

· Another valuable tool for improving nitrogen management in corn is the leaf chlorophyll meter (LCM). The LCM allows the user to determine the nitrogen status of the corn plants relative to plants in that field that have been treated with rates of nitrogen that are positively adequate for plant needs. This tool is most useful for fields in which in-season additions of nitrogen are possible, primarily through fertigation. Instructions are available in Cooperative Extension bulletin ST-02: Use of the Leaf Chlorophyll Meter for Nitrogen Management of Corn.

SPECIAL CONSIDERATIONS

· In some situations, the amount of organic materials that can be applied will be limited by the amount of phosphorus in the material. In these situations, crop nitrogen-needs may not be met by organic sources, and fertilizer nitrogen may be needed to provide supplemental nitrogen.

WHERE CAN I GET MORE INFORMATION?

· Information on nitrogen management is available from University of Delaware Cooperative Extension offices or your County Conservation District.

Prepared by Dr. David Hansen, UD Cooperative Extension, specialist for water quality

Nutrient management plans, animal waste management plans, and records of implementation "..shall not be considered as public records under the Freedom of Information Act and shall not be disclosed for reasons other than compilation." These records, however, shall be available for inspection by the Delaware Department of Agriculture and the Delaware Nutrient Management Commission.

Cooperative Extension Education in Agriculture and Home Economics, University of Delaware, Delaware State University and the United States Department of Agriculture cooperating. John C. Nye, Dean and Director. Distributed in furtherance of Acts of Congress of May 8 and June 30, 1914. It is the policy of the Delaware Cooperative Extension System that no person shall be subjected to discrimination on the grounds of race, color, sex, disability, age or national origin.

Last Updated: Monday, 19-Mar-2007 09:37:32 EDT