S. A. Ebelhar, C. D. Hart, J. D. Hernandez, L. E. Paul, and J. J. Warren 1
Farmers today are faced with escalating fertilizer prices, especially for nitrogen. In addition, new state and federal regulations are reducing the availability of some products such as anhydrous ammonia and ammonium nitrate. It appears that urea is going to the primary replacement for these products. But urea requires a higher level of management to prevent N losses and inefficient N use.
The current nitrogen recommendation numbers for corn in Illinois ranges from 0.8 to 1.2 lb N/bu based on yield goal, previous crop, manure credits and other incidentals. But corn has a nitrogen use efficiency (NUE) of less than 50% on average. Fertilizer N losses can occur from leaching, volatilization, denitrification, and immobilization. Several new N technologies have recently appeared on the market in Illinois to reduce N loss potentials. Many of these products are being evaluated in this study.
The objectives of this study are to 1) evaluate the effects of new nitrogen fertilizer technologies on corn yields under conventional tillage for corn after corn systems, 2) use buried “teabags” to trace N release curves from slow release N products, and 3) determine the N use efficiencies for new nitrogen fertilizer technologies.
Nine different N sources were utilized at five locations across the state of Illinois. These sources included 1) liquid urea-ammonium nitrate (UAN) sidedress injected, 2) urea surface broadcast, 3) UAN surface broadcast, 4) urea + agrotain® (Agrotain International) surface broadcast, 5) UAN + agrotain surface broadcast, 6) UAN + agrotainplus® (agrotain plus a nitrification inhibitor, Agrotain Intl.) surface broadcast, 7) UAN + 10% v/v CaTs® (calcium thiosulfate, Tessenderlo Kerley) surface broadcast, 8) SuperU® (urea with agrotain and a nitrification inhibitor, Agrotain Intl.) surface broadcast, and 9) ESN® (a polymer coated urea, Agrium US, Inc.) surface broadcast. All of the above treatments were applied at planting, except for the sidedress UAN injected treatment. Treatments also included each of the N sources above either incorporated into the soil with a final tillage pass (disk or field cultivator) or left on the surface. There were also four nitrogen rates associated with each of the above N source/ placement treatments, plus a check plot which received no fertilizer N. The nitrogen rates used were 60, 120, 180 and 240 lb N/acre.
The five locations are listed in Table 1 below along with soil type, drainage class and fertilizer application dates associated with each location. The Dixon Springs (DSAC) and Belleville sites includes both conventional tillage (CT) and no-tillage (NT) systems, but fertilizer sources did not include incorporation with the NT system. The NT sites also included urea coated with Nutrisphere-N (NSN, Specialty Fertilizer Products) at a rate of 2 qt/ton (Urea+NSN), UAN plus 2 qt/99.5 gal NSN (UAN+NSN), and UAN plus agrotainDF (UAN+AgroDF). With NT, all of the UAN treatments were applied dribbled on 30" spacings.
In 2006 (see Ebelhar, et al., 2007), the yield responses associated with N sources could be broken into wet locations (those with >12" rainfall over the 15 week period after fertilizer application) and dry locations (<12"). Comparisons among N sources averaged across “wet” locations are shown in Figure 1. In general the sidedress injection of N provided the highest corn yields with ESN second. These treatments appear to be reducing N losses most likely due to denitrification. These two treatments also had the best nitrogen use efficiencies (NUE) as determined by the lb N per bu of corn at the optimum economic N rate. Urea + agrotain, superU, and UAN +agrotainplus were all about the same and significantly better than urea applied alone, but less efficient than the ESN and sidedress injected UAN treatments. There was no significant differences among N sources when compared over the “dry” locations in 2006 (Figure 2). At these locations the sidedress treatment seemed to be a detriment, perhaps due to the dry conditions at time of sidedress application preventing corn roots from taking up the N when needed.
In 2007, most locations would be considered dry compared to 2006, except perhaps the DeKalb location which became wet very late in the season (Figure 3). The Massac Co. site was irrigated with approximately 3.6" of water applied between the dates of July 28 and August 27 (weeks 11-15).
Where volatilization losses may not have been very large in 2006 at any of the locations (Ebelhar, et al., 2007), 2007 proved to be quite different. If the incorporation of urea is used to judge volatilization losses, the Urbana, Belleville and Massac county locations all appear to have some volatilization losses, resulting in 3-5 bu/acre corn yield loss when surface applied and not incorporated (Table 2). Adding agrotain to the surface applied urea at these locations increased yield by 4-9 bu/acre. ESN and superU treatments had similar results. However, the effects of adding either agrotain, agrotainplus or CaTs to UAN on the surface had mixed results and were inconsistent compared to the observations with urea. When averaged over all locations for surface applications, the agrotain, ESN and superU treatments contributed 2.6, 0.9 and 4.7 bu/acre yield increases over the urea treatment (Table 2 and Figure 4). Surprisingly, there was only a one-to-two bu/acre yield difference between the surface applications and the incorporated treatments, except at DSAC where the incorporated treatments outyielded the surface treatments by about 8 bu/acre. It could be possible at this location that the surface application treatments left a portion of the N unavailable for uptake as this was a fairly dry year and roots were not as active in the surface layers as they would have been further down in the profile. At both the Urbana and Massac county locations, the dry fertilizers outyielded the liquid formulations. This was also an observation at several sites in 2006.
There was significant yield increases as N rates increased for each location (Table 3). DeKalb showed the most responsiveness, with check yields only 47-48% of maximum yields. The Massac Co. site showed the least responsiveness to N, with check plots of 67-70% of maximum yield.
The no-till (NT) portion of this study had mixed results as well. The upland site at Dixon Springs was very wet early and dry late which produced both poor stands and reduced yields compared to the CT site (Table 4). The site at Belleville had both good stands and good yields. At Belleville some of the treatments were misapplied causing us to lose the UAN sidedress, UAN surface dribbled, and UAN+AgroDF treatments. At both locations the N sources and N rates were both highly significant. At DSAC the poor stands and dry weather made it very difficult to evaluate N source differences. However, the Belleville site showed, on average, higher yields with the dry fertilizer products compared to UAN. The losses of N were much more evident with NT at Belleville, with urea yielding over 20 bu/acre less than urea+agrotain, ESN and superU. These three products resulted in similar yields and were about equal to the UAN+agrotainplus treatment. The other products were equal to or not significantly different than the urea treatment.
The nitrogen use efficiencies (NUE) were not all that different in 2007 among the N sources in the CT study (Table 5). Most of the sources fell in the 0.9-1.2 lb N/bu range. There was no difference in efficiency based on whether or not the N was incorporated. With NT, the urea and urea+NSN were significantly worse than the other N sources. Overall, it would also appear that the dry sources were slightly more efficient than the UAN sources.
There is some indication that higher yields and increased NUE were achieved over tile lines compared to areas between tile lines in small plot research in 2005, but not 2006. It is still too early to speculate on the advantage of tile drainage on a whole field basis. Monthly soil sampling identified periods when moisture and soil test K levels were different above the tiles versus between tiles, but these differences are small and infrequent. This study will continue for several more years.
Table 1. Site information for each location, 2007.
Table 2. Effects of N source and incorporation on CT corn yields at each location, 2007.
Table 3. Effects of N rates on corn yields at each location, 2007.
Table 4. Effects of N source and incorporation on NT corn yields at each locaiton, 2007.
Figure 1. Effects of N sources on corn yields averaged over wet locations, 2006.
Figure 2. Effects of N sources on corn yields averaged over dry locations, 2006.
Figure 3. Rainfall at each location for first 15 weeks after fertilizer application, 2007.
Figure 4. Effects of N sources on CT corn yields averaged over locaitons, 2007.
Figure 5. Effects of N sources on NT corn yields at Belleville, 2007.
1S. A. Ebelhar and L. E. Paul are agronomists, Dept. of Crop Sciences, University of Illinois, Dixon Springs and DeKalb, respectively. J. D. Hernandez is an assistant professor, Southern Illinois University, Carbondale. C. D. Hart and J. J. Warren are research specialist and senior research specialist, Dept. of Crop Sciences, University of Illinois, Dixon Springs and Urbana, respectively.
Ebelhar, S. A., C. D. Hart, J. D. Hernandez, L. E. Paul, and J. J. Warren. 2007. Evaluation of new nitrogen fertilizer technologies for corn. In E. D. Nafziger (Ed.) 2007 Illinois Fertilizer Conf. Proc., pp 64-71.