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 dribbled on 30" spacings, 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) site includes both conventional tillage (CT) and no-tillage (NT) systems, but fertilizer sources did not include incorporation with the NT system.
An ammonia volatilization test was conducted on most of the N sources used in this study by Willis Thornsberry, Jr., Ph.D., a consultant in Sturgis, KY. The N sources were incubated on soil provided by DSAC over a 21 day period under controlled conditions in order to determine the amount of release of ammonia gas from the soil surface. After 21 days, approximately 55% of the ammonia-N was lost from urea and UAN (Figures 1 and 2). Adding agrotain (NBPT) to urea or adding CaTs to UAN reduced the ammonia-N loss to just over 30%. Adding agrotain or agrotainplus to UAN reduced the loss to about 21% and ammonia loss from ESN was just over 10%. This data shows that most of the N sources are reducing ammonia volatilization losses to some degree compared to untreated urea or UAN.
Unfortunately volatilization losses may not have been very large in 2006 at any of the locations. Yields associated with the incorporation of N sources was not significantly different than when the N sources were left on the surface (Table 2). Only at DSAC with CT was there a significant yield loss associated with urea left on the surface compared to incorporated urea. Because there was no effect of incorporation, data was averaged over the incorporation and surface treatments.
Four out of the six study sites showed a significant response to N sources (Table 2). Three of the four responding sites (Massac Co., DSAC-CT, and DSAC-NT) had significantly higher rainfall than the non-responding sites (St. Clair Co. and DeKalb) (Figure 3). There was significant yield increases as N rates increased for each location (Table 3). DeKalb showed the least responsiveness, with check yields of 81-82% of maximum yields. The Massac Co. site showed the most responsiveness to N, with check plots only 36-37% of maximum yield.
In simplistic terms the yield responses associated with N sources can 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 4. 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 (Table 4). 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 were no significant differences among N sources when compared over the “dry” locations (Figure 5). 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.
It is too early to draw any definite conclusions at this point, especially in regards to economics associated with each of the N sources. More information on economics will be forthcoming. It appears that many of the N sources in this study may provide significant improvements in N use efficiency, especially during wet years.
Table 1. Site information for each location, 2006.
Table 2. Effects of N source and incorporation on corn yields at each location, 2006.
Table 3. Effects of N rates on corn yields at each location, 2006.
Figure 1. Ammonia volatilization from dry N sources, DSAC, 2006.
Figure 2. Ammonia volatilization from liquid N sources, DSAC, 2006.
Figure 3. Rainfall at each location for first 15 weeks after fertilizer application, 2006.
Figure 4. Effects of N sources on corn yields averaged over wet locations, 2006.
Figure 5. Effects of N sources on corn yields averaged over dry locations, 2006.
1S. A. Ebelhar and L. E. Paul are agronomists, Dept. of Crop Sciences, University of Illinois, at 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, at Dixon Springs and Urbana, respectively.