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December 23, 2004 Getting the Most Out of Nitrogen Fertilizer With nitrogen prices higher than last year and crop prices lower, the need for better use of nitrogen fertilizer never has been greater. As the nitrogen source most used, anhydrous ammonia still holds a slight lead over urea in North Dakota. “To get the most out of applied anhydrous, the application should be made at least 4 inches deep,” according to Dave Franzen, North Dakota State University Extension soil specialist. “Shallow application often helps save a trip and uses less fuel, but because of volatilization, it should only be considered 90 percent as efficient as a deeper application. Growers should consider the trade-offs between deeper versus shallow application.” Behind anhydrous ammonia, urea is the next most common nitrogen fertilizer source in the state. There is economic pressure on urea suppliers to empty their storage bins at least twice a year, once in the fall or winter and once in the spring. Urea is easy to have applied. One phone call and someone will come out and spread the fertilizer and it’s done. But is it? “This winter there is little snow on the ground and prices are probably going to be higher next spring while fertilizer warehouses are full, so there is great temptation to have urea applied under winter conditions,” Franzen says. “If urea lays on the soil surface for very long, enzymes in the soil convert it to free ammonia, which can volatilize and be lost to the crop. The conversion is slower in winter, but it proceeds at a slow rate for a long time.” Since the soil soon will be frozen deeply, any melt will not carry dissolved urea into the soil, but will move it sideways somewhere. A study at the Carrington Research Extension Center showed that winter application resulted in about 20 bushels per acre less wheat and 1 percent to 2 percent less protein than a late-fall application before a rain or a spring application. Studies of surface application of urea in South Dakota also show large yield differences compared to incorporated treatments. “Regardless of what prices do between now and spring, it would not be wise to surface apply urea in the winter,” Franzen says. “As we near spring and the snow melts, there also will be pressure to apply urea as soon as possible. Again, the longer the urea stays at the surface, the more urea will volatilize.” In very dry conditions, the urea pellets can stay on the surface for a long time. As long as the pellets are visible, nothing is happening. But, urea has a high attraction for water and dissolves easily. Fog, high nighttime humidity or a light shower will dissolve the urea pellets, but not move it into the soil. At this point, the urea is subject to attack by soil enzymes that result in volatilization of nitrogen. The rate of attack depends on temperature and the amount of residue in the soil. Soils with a lot of residue, such as no-till, contain hundreds of times the concentration of harmful enzymes as tilled soil, yet it is the no-till farmers who seem to apply the most surface-applied urea. No-till farmers should consider various methods of applying urea under the soil surface, safely distant from the seed, rather than applying urea on the surface. If they are lucky, surface appliers will get at least a half-inch of rain within a few days of application, which will move the urea safely below the soil in most cases. However, most will not be that lucky. Without significant rain, the urea may sit for a week or more, resulting in large losses of nitrogen. The addition of a urea enzyme inhibitor such as Agrotain will provide about 10 days of safety, but further dry weather will begin the volatilization process. These efficiency drags on nitrogen application have always existed. However, this year’s economics make these efficiency drags more important than ever to consider. ### Source:
Dave Franzen, (701) 231-8884, david.franzen@ndsu.nodak.edu |
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North Dakota State University |
