Anhydrous vs Urea -- An Introduction to the Discussion
Apr 26, 2013
With the spring season off to a slow start, those growers who had a chance to knife in anhydrous last fall are glad they did. Soil temperatures were too warm in much of the Corn Belt to allow for anhydrous ammonia applications until very late in the season, and some growers missed the fall anhydrous window altogether.
Anhydrous ammonia has been the nitrogen source of choice for many Midwestern growers, but that trend may be due for a change. Anhydrous pricing has been stuck at the top of its retail pricing range for a good long time now -- long enough anyway, that some are looking for an alternative source of N.
Urea is the world's most popular nitrogen fertilizer, and while urea has a strong foothold in areas like Oklahoma and Ohio, the northern Belt has been resistant to making the switch. But some new research from Purdue University Extension suggests that a split application of nitrogen may be required, as modern hybrids developed after 1990 demonstrate a 27% increase in N uptake during the flowering stage compared to pre-1990 hybrids.
Along with this shift comes a necessary examination of how nitrogen is applied most effectively, and which form of N will produce the best yields. This discussion will look at the major differences between urea and anhydrous ammonia for corn. We all know there is much more to growing corn than burying seeds and going to church. A targeted, intentional approach to nitrogen application requires forethought, soil testing and research -- it wouldn't hurt to go to church no matter what your preferred N source.
Anhydrous ammonia --
Anhydrous ammonia (AA) is a gas that is transported and handled as a liquid under pressure. This can be a fickle form of N as product can easily be lost if, when knifed in, the soil is damp and clumpy or very sandy as the knife openings may not fully close, allowing AA to escape into the air. This risk is mitigated to a degree by AA's nearly 85% nitrogen content, which is potent enough to withstand some winter losses while leaving plenty behind for the following spring.
There are inherent dangers to humans with anhydrous application and with the product itself. AA moves toward water and when accidental exposure occurs, injuries can range from skin irritation, to organ failure and death. Special equipment and expertise is required and often adds to the expense. Commercial applications take the danger out of the grower's hands, but can be expensive.
Urea is an equally respected form of N -- the most widely used worldwide -- and is much less hazardous to humans. But the corn carries the risk. Growers who prefer AA find it works on their timetable, and produces the most nitrogen bang for the buck. But as sidedress applications become more popular, UAN solutions -- urea ammonium nitrate -- will likely become more popular.
Urea is available in either granular, prilled or liquid form making it user-friendly to growers, requiring very little special equipment. Dry granular urea has a nitrogen content of 46% and currently runs roughly a dime per pound of N above anhydrous. In its granular form, urea can be surfaced applied, but must be incorporated to avoid N loss. Losses of up to 50% have been observed when dry urea has been spread over moist ground, allowing premature nitrification. But surface applied urea under the right conditions can pack some real benefits.
Fall applications of urea have been shown to be a bad idea as significant losses typically occur. Given the right soil conditions, dry urea is most effective when applied to the surface and either tilled in or rained in. Just 1/4 to 1/2 inch of rain within a few days of application has been shown to get urea's N where it needs to be. Liquid urea (UAN) can be easily sidedressed post-emerge, when corn plants need it most. Surface applications of urea are not recommended for a no-till approach as crop residue may block urea from making it to the soil.
There are positives and negatives on each side of this issue and this is only an introduction to what I expect will be a great debate in the minds of many growers. I urge you to stick with your program this year -- don't change horses midstream. But as technology changes how plants consume nitrogen, growers will follow proven success. Talk to your agronomist or CCA and fellow farmers. There is a wealth of experience and knowledge there, so take some time to compare anhydrous ammonia and urea as you look ahead to next year... we, here at the Monitor will do the same, and keep you posted.