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
Nine different N sources were utilized at five locations across the state of Illinois. These sources included
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 four 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 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"). In 2008, Urbana and DeKalb locations were “wet” and Belleville reached “wet” conditions late in the season (Figure 1). The DSAC CT and NT fields would have been “dry” under this scenario. All of the locations were planted later than usual due to wet weather early in the growing season.
Nitrogen source effects were highly significant at the wet locations in 2008 of DeKalb and Urbana (Table 2). They were also slightly significant at Dixon Springs. At Dixon Springs, ESN had a slight advantage (trend only) over the other treatments when incorporated, and the urea treatments had a slight advantage over the UAN treatments (Figure 2). At Belleville, the sidedress treatment tended to be lower yielding, probably due to the treatments being applied relatively late for sidedressing (Figure 3). At Urbana, the sidedress treatments could not be applied due to logistical problems. The dry products tended to do better than the liquid products, a phenomena seen frequently in the past years of study at several locations. The liquid is UAN based which has 25% of the material as nitrate which is easily leached or denitrified and can be lost quickly from the system. The dry base is urea which has to be converted to nitrate before it can be lost by leaching or denitrification. ESN did much better at Urbana when incorporated rather than left on the surface. This indicates that ESN may have been less available at this location when left on the surface. This may be due to dry weather not letting ESN release it’s urea as quickly or ESN was moved offsite by heavy rains. There was a fair amount of N loss from surface applied urea or UAN, indicating volatilization losses, which was reduced significantly by the application of agrotain or superU. The exception was with the application of agrotainplus, but why is uncertain. At DeKalb, the incorporated treatments did better in general than the surface treatments (Figure 5). As with Urbana, the dry products did better than the liquids and the surface ESN treatments did worse than the incorporated.
Increasing nitrogen rates significantly increased grain yields at all locations (Table 3). All of the locations had high check yields (93-101 bu/acre, 39-62% of highest yields).
Although Dixon Springs and Belleville had lower rainfall than normal after N application, these sites had much higher than normal rainfall prior to N application which caused problems with planting at optimal timing. At both locations, heavy losses of urea occurred from the surface applications (Table 4 and Figure 6). Products containing agrotain tended to significantly reduce these N losses, presumably from volatilization. Sidedressing injection of UAN or application of ESN also significantly reduced N losses and increased yields. UAN sources had less loss of N than urea.
Because all of the locations and tillage fields had significant quadratic responses to increasing N rates, economic optimum N rates, yields, and nitrogen use efficiencies (NUE, defined as lb N/bu yield) can be determined. In general the dry materials (urea based) had significantly lower NUE than liquids (UAN based, Table 5) with CT fields. With NT, the urea only treatment had a poor NUE, but the other dry treatments had significantly lower NUE than urea or the liquid sources.
It appears that many of the N sources in this study may provide significant improvements in N use efficiency, especially during wet years. These differences appear to more important with NT than CT systems, but more research is needed.
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.