Will's Windmill Column: Nitrogen best management practices will reduce contamination
Nitrogen is an essential plant nutrient that is applied to our crops in greater quantity than any other fertilizer. With the current cost of nitrogen fertilizer, it is more important then ever that producers use care and caution, and yet get the best bang for their nitrogen buck.
Vast quantities of nitrogen are contained in the ecosystem, including in soil organic matter, the air and all living organisms. Biological processes that convert nitrogen to its mobile form, nitrate (NO3), occur continuously in the soil system.
Unfortunately, nitrates can be leached from the rooting part of the soil. To minimize losses to surface and groundwater, management guidelines have been developed.
Best Management Practices (BMPs) for nitrogen are broadly defined as "economically sound, voluntary practices that are capable of minimizing nutrient contamination of surface and groundwater."
The BMPs recommended are based upon research, particularly at the University of Minnesota and other land-grant universities, and upon practical considerations. The BMPs are based, in part, upon the concept of total nitrogen management, which accounts for all forms of on-farm nitrogen in the development of crop management plans.
BMPs are applicable to all crops and farming practices. They are based upon the concept that accurate determination of crop nitrogen needs is essential for profitable and environmentally sound nitrogen management decisions.
These BMPs include:
n Set realistic yield goals;
n Develop and use a comprehensive record-keeping system for field-specific information;
n Adjust nitrogen rate according to soil organic matter content and previous crop and manure applications;
n Use a soil nitrate test where appropriate;
n Use prudent manure management to optimize nitrogen credit;
n Test manure for nutrient content;
n Calibrate manure application equipment;
n Apply manure uniformly throughout a field -- injection of manure is preferable, especially on strongly sloping soils;
n Avoid manure application to sloping, frozen soils;
n Incorporate broadcast applications whenever possible;
n Credit second-year nitrogen contributions from alfalfa and manure;
n Do not apply nitrogen above recommended rates;
n Plan nitrogen application timing to achieve high efficiency of nitrogen use;
n Do not apply fertilizer nitrogen in the fall to coarse-textured (sandy) soils; When soils have a high leaching potential -- application of nitrogen in a side-dress or split application program is preferred;
n Use a nitrification inhibitor with early side-dressed nitrogen on labeled crops.
Get started on composting
If the snow would just go away, April would be a great time of the year to review your composting program. Gardening plans should include both the selection of plants and a soil fertility program that will meet the needs of those plants. Composting should be part of those plans.
Composting is primarily a microbial process that converts plant materials such as grass clippings and leaves to a more useful soil amendment. Gardeners have used compost for centuries to increase soil organic matter, improve soil physical properties, and supply some of the essential nutrients for plant growth.
We need to put organic materials into a pile 36 to 44 inches tall. This gives the amount of vertical height needed to heat up the piles. Next we need to provide the composting microorganisms with the correct amount of air, water and food to heat up to 131 degrees to 150 degrees. These temperatures reduce weed seed viability and pathogens.
Aerobic microorganisms need oxygen to live. Free air space inside the pile should be between 55 percent and 70 percent when the pile is built and will help assure that oxygen can get into all parts of the pile. Course particle size and small twigs can help increase airspace in a compost pile.
The moisture content in the compost pile should be kept between 46 percent and 61 percent. This is "moist" but never "wet." A "wrung-out sponge" feeling is just about the right amount of water. To maintain this level of moisture may require weekly or more frequent watering of the pile, especially in hot windy weather.
Compost microorganisms thrive with a carbon (C) to nitrogen (N) ratio of 25:1 to 35:1. Whenever possible adjust feed stock mixtures to get into this range. Fall tree leaves have a carbon:nitrogen (C:N) ratio of about 90:1. To get into the proper C:N ratio, you will need to add 2 cups of urea (46 percent nitrogen); or 5 cups of a 22-01-14 fertilizer or an equivalent amount of nitrogen from other sources for each 100 pounds of leaves in the pile.
Turn the pile two to five times to mix the cooler outsides into the hotter inside of the pile in order to get faster and more uniform composting. If you start composting now, you should have some very nice compost material ready to apply to the garden next October, at a rate of one-half inch to 1 inch and worked into the soil 6 inches deep. Using finished compost to grow new plants completes the cycle.
For more information about composting, such as how to purchase or make a structure for backyard composting, visit extension.umn.edu/gardeninfo and click on "soils and composting." April is a great time to begin your compost program for 2008!