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Start Safe, Build Yield, And Finish Strong – Managing Your Nitrogen
DR. JOHN D. BAILEY
SPRINGERTON, ILL.
Nitrogen management continues to be difficult due to the transformations of nitrogen when fertilizers are applied to soil. Uncertainties about weather, temperature and moisture make nitrogen management one of the most difficult jobs to do right on the farm.
Form of nitrogen partly determines the risk of loss
Urea forms of fertilizer are subject to ammonia volatilization because of the activity of an enzyme called urease, which is found in all soils and even in crop residues. The activity of urease increases with warm soil temperatures, high crop residues (i.e., no-till), soils that are moist but drying, soils that are sandy, and in soils with low buffering capacity and(or) high pH. Risk of loss with urea forms of fertilizers are highest when it is applied and left on the soil surface and one or more of these factors are at play.
Ammonium forms of fertilizers are relatively stable because they have a positive charge and can be fixed to the soil colloids. However, ammonium will eventually be transformed to nitrate through the activities of specific soil bacteria (Nitrosomonas and Nitrobacter), which exposes the fertilizer to other potential loss pathways associated with nitrate (see next paragraph).
Nitrate containing fertilizers, (or ammonium that has been transformed to nitrate) are subject to additional below-ground losses, known as denitrification and leaching. Ammonium nitrate and UAN are two fertilizers of concern because they of their soluble nitrate content. The below-ground pathways of nitrogen loss are dependent upon temperatute, water content and movement of water through the soil. In heavier soils, water tends to pond after large rain events. This can result in anaerobic conditions that favor higher denitrification rates. In lighter soils, water moves easily through the soil profile, and since nitrate can not bind to the soil colloid, higher nitrogen loss due to leaching can occur.
Because there are many ways that nitrogen is transformed and moved around in soil, all all synthetic fertilizers can eventually be converted to nitrate, nitrogen loss is always a consideration and nitrogen use efficiency is usually low.
Urease and Nitrification Inhibitors
To decrease nitrogen losses, increase nitrogen use efficiency, and increase the capture of more yield potential, a number of products have been developed to delay fertilizer nitrogen transformations. By delaying transformation, stabilizers can help ensure that the fertilizer is available for uptake when the crop needs to take up a large amount of nitrogen. Stabilizers can be classified as either urease inhibitors or nitrification inhibitors. Urease inhibitors block the activity of urease in the soil, which slows the transformation of urea into ammonium. Nitrification inhibitors slow the transformation of ammonium into nitrate, thus giving the fertilizer nitrogen a better chance of being used by the developing crop and a reduced chance of loss due to denitrification and(or) leaching.
The compound that has been most utilized to decrease urea volatilization in granulated urea or UAN solutions is NBPT (n-butyl thiophosphoric acid triamide). The two nitrification inhibitors that have been used most in commercial formulations are nitrapyrin and dicyandiamide (DCD). Nitrapyrin is most often used in anhydrous ammonia whereas DCD is more often used in urea or UAN. Nitrification inhibitors inhibit the transformation of ammonium to nitrate by inhibiting the bacteria that are involved with this process, namely, Nitrosomonas and Nitrobacter.
The world’s first stabilizer with a patented root biostimulant – Excelis Maxx
Timac Agro USA formulated Excelis Maxx with both NBPT and DCD because these compounds are proven to be very effective in reducing lost yield potential when conditions are conducive to poor nitrogen efficiency. The innovation that Timac Agro USA bring to the stabilizer market is our patented root biostimulant, Rhizovit. Rhizovit comes from our parent company, the Roullier Group, whose large R&D effort found that the Rhizovit compound results in higher root uptake of water and nutrients; this has a beneficial effect on root growth and microbial activity in the rhizosphere (see https://patents.google.com/patent/US20070173409A1/en for information). Recent research by North Carolina State University found that Excelis Maxx improved nitrogen use efficiency of UAN by around 25% in corn (see http://www.us.timacagro.com/fileadmin/contributions/products/PDF_Research/29_-_Excelis_Maxx__UAN_-_Corn_-_NCSU_-_2017_-_NC.pdf for write-up), suggesting a clear benefit to adding supportive technology to improve nitrogen uptake in a nitrogen stabilizer.
Unproven Technologies
Although other formulations that lack NBPT and(or) DCD (e.g., Nutrisphere-N®, NZONE®, etc.) have been cleverly marketed to have urease or nitrification inhibitory properties, these products have failed to show such effects at the university level and have lead many scientists, retailers, and farmers to question the practical benefits of these unproven technologies (see https://dl.sciencesocieties.org/publications/aj/abstracts/106/2/423 and https://www.ndsu.edu/fileadmin/soils/pdfs/goos-franzen-meeting-2.pdf for review). With commodity prices the way they are and thin margins on the farm, it doesn’t make good sense for farmers to gamble on technology that might not bring value, especially when there are proven formulations readily available.
Conclusions
I am often asked, “Do stabilizers really pay off?” My answer is, “It depends.” If conditions are right for nitrogen loss and this loss reduces yield, then, yes, the proven chemistries will probably help. I further advise farmers to look at their soil tests. They need to evaluate their CEC and get a good feel for how much nitrogen they can put out at one time. A very rough measure is to take the CEC and multiply it by 10…that’s roughly how much nitrogen one can feel comfortable about putting out at one time. Let’s say the CEC is 7…that’s about 70 lb N/ac I am comfortable putting out at one time. Can a farmer raise a 250 bu/ac corn crop on 70 lb N/ac? Probably not. So, it’s probably better to split apply the nitrogen and use a stabilizer to slow the transformations down in order to maximize the amount that will be available for uptake, reproduction, and final grain fill. This approach seems to strike a balance between protecting the pocketbook, protecting the environment, and protecting yield. ∆
DR. JOHN D. BAILEY: National Product Manager – Row Crops, Timac Agro USA
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