From Agronomists of the
Potash & Phosphate Institute
655 Engineering Drive, Suite 110
Norcross, Georgia 30092-2837
Phone (770) 447-0335

Summer 2000, No. 6


Agriculture is being increasingly blamed for algal blooms, low dissolved oxygen, and a host of other fresh water and marine problems supposedly related to elevated nitrogen and phosphorus in the water.

Most practicing agronomists are aware of the improvements agriculture has made in soil conservation and in nutrient and pesticide use-efficiency.
Regrettably, the urban public is unaware and seemingly does not appreciate the recent accomplishments and continuing improvements. According to the National Agricultural Statistics Service, fertilizer nitrogen use-efficiency by corn has improved by 32 percent since the early 1980s: 0.76 bushels of corn produced per pound of nitrogen then, versus one bushel of corn produced per pound of nitrogen now. This is the result of many factors, including crop genetics, better management capability among farmers, and best management practices, which contribute to agronomic efficiency and environmental stewardship.

Farmers are generally doing a fairly good job of managing nutrients in their fields.
Research data indicate that on the average, about 4 pounds of nitrogen per acre and less than 1 pound of phosphorus per acre escape fields in surface runoff. Without the implementation of new best management practices, we lose the equivalent of about 12 percent of the applied nitrogen and about 8 percent of the applied phosphorus. In other words, about 88 percent of the applied nitrogen and about 92 percent of the applied phosphorus typically remain in the field. According to published research, some of the remaining nitrogen can be lost as nitrate-nitrogen in tile drainage in a wet year which follows a dry year. The amount of loss from drained fields can exceed 20 lb/A in some states.

Analyses of river discharge data in the Mississippi River drainage basin by the U.S. Geological Survey
indicate that nitrate-nitrogen discharge to the Gulf of Mexico via the Mississippi River tripled from 1970 to 1983, but has been relatively constant since. The discharge of phosphorus to the Gulf of Mexico has not changed since the early 1970s. These numbers suggest that agriculture is doing a better job of getting applied nutrients into crops and maintaining them at crop-recoverable soil depths in fields.

Many believe that we can, and must, improve on these recent trends in nutrient use efficiency and nutrient stewardship.
There are a host of best management practices which might be considered by farmers, in consultation with their Certified Crop Adviser, fertilizer dealer, and conservation specialist, to make further agronomic and environmental improvements. Some of these practices require no additional direct costs to the farmer while others require some investment to establish and maintain. Several are likely to increase farm profits. Examples include: site-specific soil testing, balanced fertilization for realistic yield goals, conservation tillage, appropriate application timing to avoid runoff-producing and leaching rainstorms, appropriate nutrient placement, consideration of nitrification inhibitors and urease inhibitors where research has shown them to be beneficial, site-specific nutrient management planning and application, vegetative buffers and improved riparian zone management, appropriate fall application of nitrogen at soil temperatures below 55o F (particularly for spring planted crops), and improved irrigation water management.

An excellent choice for many farmers will be to raise soil test phosphorus and potassium to agronomically optimum levels.
The benefits have been proven. Long-term corn research in Kansas, for example, has shown that residual soil profile nitrate-nitrogen levels were decreased by 66 percent with appropriate phosphorus fertilization, with virtually no change in the optimum nitrogen fertilization rate. Ohio research showed that raising soil test potassium levels to the optimum range increased the recovery of nitrogen in the standing corn crop and in the top three feet of soil. With more of the nitrogen recovered in the standing crop, yield potential is increased and the potential for off-site movement of nitrogen is minimized.


For more information, contact Dr. Cliff S. Snyder, Midsouth Director, PPI, P.O. Drawer 2440, Conway, AR 72033-2440. Phone: (501) 336-8110. E-mail:

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