Illinois
Fertilizer Conference Proceedings
January 25-27, 1999
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E.C. Varsa, S.A. Ebelhar, P.R. Eberle, Erik Gerhard, and Terry
Wyciskalla1
Decisions concerning the management of nitrogen (N) in no-till corn production have a large impact on the agronomic performance of the crop. Surface application of urea-containing N fertilizers in the presence of previous crop residues can result in high volatilization losses of ammonia (Fenn and Hossner, 1985; Grant et al., 1996) and reduced crop N recovery and yield (Beyrouty et al., 1986; Mengel et al., 1982). Higher rates of N immobilization and denitrification losses of N are also known to occur in the presence of surface residues (Kitur et al., 1984; Rice and Smith, 1982; Rice and Smith, 1984).
The urease inhibitor AgrotaiN, commercially available since 1996 and marketed by IMC-Agrico, serves to reduce the rate of urea hydrolysis that results in the formation of ammonia (NH3). Beyrouty et al. (1988) measured NH3 losses of up to 30% of the N applied as urea, and other researchers have indirectly estimated that losses can be as high as 50% when no inhibitor is used. If a rainfall of 0.5-inch or more is received within a day or two following application, ammonia volatilization losses are greatly reduced. It is in situations where urea or other urea-containing N sources such as UAN are applied to a moist soil surface with residues and rapid drying conditions follow that high ammonia volatilization losses are likely to occur.
A number of researchers have reported no-till corn yield increases when using AgrotaiN with surface-applied urea N sources. Fox and Piekielek (1993) reported that AgrotaiN-amended urea resulted in an average yield increase of 14 bu per acre in a three-year study in Pennsylvania, and Murphy and Ferguson (1997) reported a yield benefit up to 56 bu per acre in one of three years under ridge-'till in Nebraska. In those studies, the greatest response to AgrotaiN was associated with conditions where ammonia volatilization losses were high following N application.
Wheat yield responses to AgrotaiN-amended urea tend to be much smaller. In two years of study, Varsa et al. (1998) reported that across three southern Illinois locations, AgrotaiN inclusion with urea resulted in wheat yield increases averaging 1-2 bu/acre above those of non-amended urea.
This report contains the results of AgrotaiN evaluation on no-till corn and wheat in 1998. Also included is a summary of results for no-till corn from 1995 to 1998 and for wheat from 1996 to 1998. An economic assessment of AgrotaiN use on no-till corn forms the conclusion.
Specific objectives of this research were as follows:
1. To determine the agronomic benefit of AgrotaiN-amended urea and UAN compared to non-amended N fertilizers managed optimally in no-till corn production.
2. To determine the effectiveness of AgrotaiN-amended N sources relative to non-amended N fertilizers in a continuous corn and corn-soybean rotation that is no-till managed.
3. To evaluate the improved yield and plant N use efficiency that is gained through the utilization of the urease inhibitor NBPT (AgrotaiN) compared to the efficiency of N use obtained with best N management practices.
4. To determine the responsiveness of NBPT-amended urea compared to non-treated urea and ammonium nitrate applied as a topdressing to wheat.
5. To make an economic assessment at the conclusion of the experiment of the costs and benefits of AgrotaiN use compared to the economic returns using best N management practices on no-till corn and wheat.
Studies were initiated in 1995 and continued in 1996, 1997, and 1998 at the Dixon Springs Agricultural Center (DSAC) of the University of Illinois and the Belleville Research Center (BRC) of Southern Illinois University to evaluate N sources, placement, timing and AgrotaiN inclusion on no-till corn. Nitrogen sources that were surface-applied included granular urea (without and with AgrotaiN at 0.14%), granular ammonium nitrate, and UAN solution (without and with AgrotaiN at 0.5 lb/acre) which was both broadcast sprayed and dribble placed. Injected N sources included UAN (knifed-in at DSAC and point injection-applied at BRC) and anhydrous ammonia. Split N treatments included a 40-lb N/acre application of UAN without AgrotaiN as a broadcast spray ("weed and feed") at corn planting followed by sidedressing of dribbled UAN (without and with AgrotaiN at 0.516/acre) and an injected UAN treatment.
A total of 12 N fertilizer treatments were evaluated, along with a 0-N control, in both a corn following corn and a corn following soybean rotation at each of the two locations. A split-plot design was used with rotations being the main plots and N fertilizer treatments being subplots.
This experiment was replicated four times at the BRC and five times at the DSAC. For the corn following corn (CC) rotation, the N rate was 180 lb N/acre, and for the corn following soybean (CS) rotation, the rate was 140 lb N/acre. The N rate was decreased by 40 lb N/acre for the CS rotation to reflect an N credit allowable for a previous crop of soybean. More complete details of the site and experimental conditions at both locations in 1998 are given in Table 1. The 1998 data will be presented and discussed, as well as a summary of the 1995-1998 results. Reports of results for individual year (1995, 1996, and 1997) experiments were presented earlier in the Proceedings of the 1996, 1997, and 1998 Illinois Fertilizer Conferences.
Third year experiments with AgrotaiN on wheat were conducted in 1998 at three southern Illinois locations: Dixon Springs, Carbondale, and Belleville. The variables evaluated were three N sources: granular urea, AgrotaiN-amended urea, and ammonium nitrate. Each was applied at 40, 80, and 120 lb N/acre and on three topdressing dates: mid-February, early march and late March. AgrotaiN was coated on urea at 0.14 percent. At each site, the experiment was a 3 x 3 x 3 factorial design with six replications. A zero N treatment was included as a control, giving a total of 28 plots per experimental block. Pioneer brand 2540 was seeded at 120 lbs/acre at all locations between October 8 and October 10, 1997. Soybeans were the previous crop at all locations. Flag leaf tissue samples were collected for N composition determination at the late boot stage, but the analysis of that data is incomplete at this time. Wheat harvest was completed by the end of June 1998 and the grain yield results will be given in this report. Results of the 1996 and 1997 experiments with wheat were presented earlier in the Proceedings of the 1997 and 1998 Illinois Fertilizer Conferences.
General Comments
The 1998 growing season got off to an early start, but excessive April rainfall delayed planting until mid-May for both the Belleville and Dixon Springs locations. Much-above-normal June rainfall caused waterlogged soils in many areas of southern Illinois, but the two experimental sites were on better drained soils and no loss in stand was observed. July and August had nearnormal rainfall that was favorable for corn growth, and no extended periods of heat or drought were experienced at either location. As a result, above-average corn yields were obtained at both locations.
The experimental treatments were applied in a timely manner and no major pest problems were observed. At both location,s there was a seven-day period without rainfall following the surface N applications of urea and UAN that included AgrotaiN (Table 1). That seven-day period would have been conducive for ammonia volatilization to occur. The split N treatments that included dribbled UAN without and with AgrotaiN were applied just three days prior to a significant rain event at both locations. That rainfall may have negated any benefit of AgrotaiN addition to the UAN for that particular treatment comparison. A dry September and October favored rapid crop maturity and early dry-down of the stalks and grain.
Ear leaf N composition
Ear leaf N composition in 1998 was influenced by N treatment applications but not by rotations at both Belleville (Table 2) and Dixon Springs (Table 3). There was no significant interaction between rotations and treatments, which meant that N treatment effects on ear leaf N were not different for the CC and CS rotations. Generally, higher leaf N concentrations were observed at Dixon Springs than at Belleville.
Figure 1 gives the ear leaf N composition as an average across the two rotations at Belleville. Ear leaf N was significantly higher for ammonium nitrate (2.64%o) compared to urea (1.84%). AgrotaiN addition to urea resulted in an ear leaf N composition of 2.28%, intermediate between the two dry N sources. AgrotaiN addition to UAN, whether surface broadcast or dribbled, had no significant influence on ear leaf N. Ear leaf N values for all the surface UAN treatments (without or with AgrotaiN) were significantly higher than granular urea but significantly lower than dry ammonium nitrate. There was basically no difference in leaf N between the dribbled UAN treatments that were applied at planting and those that were applied as a sidedressing. The highest ear leaf N compositions were obtained with injected UAN (either at planting or at the sidedressing stage) and anhydrous ammonia. Obviously, much greater amounts of applied N were plant-useable with the injected treatments than with any of the surface applied treatments, including those that contained AgrotaiN. For those treatments containing AgrotaiN (urea and UAN), the inclusion of the urease inhibitor resulted in a 0.14% greater N concentration in the ear leaf tissue compared to treatments containing no AgrotaiN.
At Dixon Springs, ear leaf N composition differences among applied N treatments were much smaller (Figure 2). The control (0-N) treatment at 2.31 % N was much higher than at Belleville (1.41 % N), which probably reflected more soil N mineralization occurring at Dixon Springs than at Belleville. The high release rate of N from the soil probably explained the small N composition differences among treatments. However, the granular urea treatment had the lowest ear leaf N (2.69%) among all the treatments and was significantly lower than granular urea with AgrotaiN at 3.03%o N, which was the highest among all treatments, including the injected N treatments. The N composition increase in leaf tissue observed with AgrotaiN, as an average over all direct comparisons of treatments without AgrotaiN, was 0.09% N.
Grain yield
At both Belleville (Table 2) and Dixon Springs (Table 3), grain yield was significantly influenced by N treatments and rotation. At Dixon Springs, the grain yield for all N treatments to corn following soybean was higher than those treatments applied to corn following corn (147 versus 138 bu/acre). This occurred despite the N rate for the CC rotation being 180 lb N/acre compared to 140 lb N/acre for CS. At Belleville, there was a significant interaction in that the corn yields of most N treatments applied to corn in the CS rotation were higher than comparable treatments to the CC rotation. However, some were lower, notably the two injected UAN treatments and the sidedressed dribbled UAN treatment that received AgrotaiN.
Widely differing corn yields were observed at Belleville as a result of the different N treatment applications (Figure 3). When the yields across the two rotations were averaged, the injected UAN treatment at planting had a yield of 192 bu/acre compared to granular urea at 92 bu/acre. Other high-yielding treatments were anhydrous ammonia (181 bu/acre), injected UAN at sidedressing (180 bu/acre), and ammonium nitrate (159 bu/acre). AgrotaiN addition to urea gave a yield increase of 28 bu/acre, and its addition to dribbled UAN resulted in a 16 bu/acre increase. No yield benefit was observed with AgrotaiN addition to broadcast UAN. Injected N sources were clearly superior to any N treatments that were surface-applied to the no-till corn. Losses associated with ammonia volatilization or immobilization of N were probably the major factors resulting in the lower yields relative to those obtained with injected N sources.
At Dixon Springs, the effect of N treatments on corn yield averaged across the two rotations clearly showed the beneficial effects of AgrotaiN inclusion with the N sources (Figure 4). For the urea, broadcast UAN, and dribbled UAN treatments, the yield increase with AgrotaiN was 26, 11, and 13 bu/acre. The apparent ammonia volatilization loss at this location must have been very high following surface application of those N sources in 1998. The highest yield obtained, 151 bu/acre with anhydrous ammonia, was no different than the yield obtained with urea plus AgrotaiN (148 bu/acre), ammonia nitrate (147 bu/acre), UAN broadcast plus AgrotaiN (147 bu/acre), or UAN dribbled plus AgrotaiN (151 bu/acre). Neither the UAN application method (inject versus dribble) nor AgrotaiN addition had any impact on the corn yield obtained with the split N treatments.
Yield
At Belleville (Figure 5), the four highest-yielding treatments over the four years of study and averaged across the two rotations were injected UAN (174 bu/acre), injected UAN at sidedressing (170 bu/acre), anhydrous ammonia (163 bu/acre), and ammonium nitrate (153 bu/acre). The two lowest-yielding treatments were granular urea (114 bu/acre) and broadcast UAN (130 bu/acre). AgrotaiN addition to urea resulted in a yield increase of 25 bu/acre, its addition to broadcast UAN increased yield by 7 bu/acre, and its inclusion with dribbled UAN gave a yield increase of 10 bu/acre. AgrotaiN treatment of UAN that was dribbled at sidedressing resulted in an 8 bu/acre increase. Over the four years, nitrogen applied to the CC rotation (180 lb N/acre) resulted in an average yield across N treatments of 139 bu/acre, whereas 140 lb N/acre applied in N treatments to the CS rotation resulted in an overall yield of 147 bu/acre.
At Dixon Springs, yield responses to N sources, AgrotaiN, and placement were smaller (Figure 6). The smaller differences in yield responses to treatments were related to poor yields obtained in the 1996 and 1997 crop years. Despite the lower overall yields at Dixon Springs, the four highest-yielding treatments were the same ones as occurred at Belleville, although the ranking was different. Clearly, the injected N sources were the ones that resulted in the highest yields. AgrotaiN addition to urea resulted in a 13 bu/acre increase, while its inclusion with dribbled or broadcast UAN resulted in yield increases of 4 to 6 bu/acre. The overall yield difference between the CC and CS rotations was 4 bu/acre, favoring the CS rotation.
Ear leaf N composition
The ear leaf composition, averaged over the four years of study and across the two rotations, for Belleville and Dixon Springs is shown in Figures 7 and 8. There was a clear parallel between those treatments that resulted in the highest grain yield and those that had the highest ear leaf N composition. The highest ear leaf N was observed with the following N treatments, both at Belleville and Dixon Springs: anhydrous ammonia, injected UAN (at planting and as a sidedressing), and ammonium nitrate. Surface dribbled UAN with AgrotaiN gave nearly the same ear leaf N values as ammonium nitrate. For the most part, those treatments with high ear leaf N concentrations also resulted in the highest grain yields observed in the study.
General comments
The 1997-1998 growing season for wheat in southern Illinois was not very favorable. The mild winter resulted in very little frost heaving or winterkill, and crop dormancy never fully set in. In early March, a very severe cold outbreak (the coldest weather of the winter) occurred after the wheat had fully tillered, and significant injury was widely reported, even to the extent that some fields were destroyed and planted to another crop. These seasonal conditions impacted the final yield results to a large degree.
Effects of nitrogen rates, sources, and timing on wheat yield
At all three locations (Dixon Springs, Carbondale, and Belleville), the effect of N rate was significant on yield (Table 4). However, most all yield increases due to the N treatments of 40, 80, and 120 lb N/acre were small. At Belleville, a yield decrease was observed at the 120 lb N/acre rate compared to the lower two N rates. This yield decrease was a result of severe lodging that occurred at the highest N rate. Lodging was also a problem at the highest N rate at Dixon Springs, but yield was not reduced.
Nitrogen sources and the addition of AgrotaiN to urea had no influence on wheat yields at any of the three locations in 1998 (Table 5). Less than 1 bu/acre difference in yield was noted among N sources at Dixon Springs and Carbondale. The later timing of N applications generally resulted in the highest overall yields, but at Belleville the latest application date (March 26) resulted in significantly lower yields. The lush plant growth promoted by the late N application and the ensuing lodging that occurred probably accounted for the lower yield.
General comments
The cost and net benefit of each of the 12 alternative N management practices was compared. Partial budget analysis compared added costs and added benefits for each N management practice relative to the check plot. Yield (Table 6) and net benefit comparisons (Table 10) between treatments with and without AgrotaiN were also made. All cost and net benefit comparisons were on a per-acre basis. The economic evaluation was based on the corn-corn rotation because of few significant rotational differences and the common practice in southern Illinois of no-till corn following a previous corn crop. The only difference in net benefit/acre or cost/acre between the corn-corn and corn-soybean rotations was that the corn-soybean rotation costs less by the value of the 40 lb N/acre rate difference between the rotations.
Cost analysis
Costs for each N management treatment included the material costs (180 lb N and AgrotaiN) and application costs. The costs were calculated based upon typical application methods. A local fertilizer dealer was consulted. Prices were quoted in cost/ton, including any custom application charges and delivery charges (Twin County FS, Murphysboro, IL). Costs for labor and tractor services as reported by Lazarus (1997) were used for anhydrous ammonia and UAN (inj) applications because farmers typically provide these services.
Costs of materials per ton and per pound of N appear in Table 7. Anhydrous ammonia was the most cost-effective treatment, even though its cost per ton is the highest. This was due to the concentration of N in anhydrous ammonia, which is the highest at 82%, compared to the other treatments. Thus, the cost/Ib of N at $.198/lb N was less expensive for anhydrous ammonia than the other treatments. The next least expensive treatment was UAN (be) at $.258/lb N. The cost per acre of materials and application charges is presented in Table 8.
The costs of the alternative N management practices are summarized in Table 9. The N treatments are ranked from the least costly per acre to the most costly per acre. Anhydrous ammonia was the least costly N management practice. Anhydrous ammonia had a $19.60 advantage over UAN broadcast, which was the next least costly alternative. The UAN alternatives were then followed by urea. Ammonium nitrate was the most costly alternative other than the AgrotaiN treatments. Note that the broadcast UAN plus AgrotaiN treatment was $0.07 less expensive than the ammonium nitrate treatment.
Net benefit analysis
The net benefit of the alternative N management practices and the net benefit of the AgrotaiN treatments were calculated. The benefits were the value of the added yield per acre that resulted from the treatments. The increased yield was valued at $2.50 a bushel. The net benefit equaled benefit less material and application costs per acre. The results appear in Table 10. The UAN injected practice had the highest net benefit because of its 7.5 bushel yield advantage over the next best alternative, which was anhydrous ammonia. The UAN injected practice had an $8 advantage over anhydrous ammonia and a $33.00 advantage over ammonium nitrate. UAN injected, anhydrous ammonia, and ammonium nitrate had the three highest net benefits. The sidedressed UAN dribbled plus AgrotaiN had the fourth highest net benefit of all treatments. The AgrotaiN treatment resulted in a $6.00 per acre increase over sidedressed UAN dribbled alone.
AgrotaiN had positive net economic benefits for three of the four practices that included AgrotaiN, although AgrotaiN treatments resulted in a positive yield effect for all treatments. The greatest benefit for using AgrotaiN was with urea. AgrotaiN had a $42 per acre advantage over urea. For UAN dribbled, AgrotaiN resulted in a net loss of $2.00 per acre.
Overall economic assessment
The UAN injected practice had the greatest net economic benefit of the N management practices evaluated due to its higher yield advantage. UAN was followed by anhydrous ammonia and ammonium nitrate in terms of net economic benefit. The AgrotaiN treatments were more costly per acre. The net benefits of AgrotaiN were $12 to $68 lower than the top three N management practices. However, for farmers who prefer to use urea, AgrotaiN clearly had an advantage of $42 per acre. For UAN applications, the results were mixed. AgrotaiN had an advantage for UAN broadcast and sidedressed dribble applications but not for dribble alone.
Interpretation of economic benefits is limited to the alternatives and application rates evaluated. In practice, the actual net economic benefits could be greater or less than those observed. If we were to assume that the injected UAN practice at 180 lb N reached the yield response plateau, then its net benefit could possibly be greater with less N applied. Further, the net economic benefits of UAN broadcast, UAN dribbled, or urea could be improved by increasing the rate of N application. This increase in N rate would imply greater cost but would narrow the differences in net economic benefits between the alternatives.
In 1998, no-till corn yields at Belleville at Dixon Springs were significantly affected by N sources, placement, and AgrotaiN. At both locations, granular urea application resulted in the lowest yields, while injected UAN (at Belleville) and anhydrous ammonia (at Dixon Springs) were the N sources that resulted in the highest yields. AgrotaiN, when added to urea, gave yield increases of 28 and 26 bu/acre over non-amended urea at Belleville and Dixon Springs, respectively. Inclusion of AgrotaiN to UAN resulted in much smaller yield increases, from 0 to 16 bu/acre, when either broadcast or dribble applied. At both locations, the highest overall yields were obtained in the corn-soybean rotation compared to corn following corn, even though less N (40 lb N/acre) was applied.
When grain yields were summarized over the four years of study (1995-98) at the two locations (Belleville and Dixon Springs), several common observations were made. The four highestyielding treatments at both locations were anhydrous ammonia, injected UAN at planting, injected UAN at sidedressing, and ammonium nitrate. The treatments with the lowest yield were granular urea followed by broadcast UAN. AgrotaiN gave the greatest benefit to yield when added to urea. The yield benefit that accrued from AgrotaiN addition to UAN was much less, and it was not clearly more beneficial for one placement method over the other. Ear leaf tissue N composition results followed the treatment trends observed with grain yield.
An economic assessment clearly showed that injected N sources gave the greatest net economic returns in no-till corn. However, for those growers who prefer to use urea, AgrotaiN use was very cost effective.
Wheat yield responses to N rates, AgrotaiN use with urea, and timing of N applications were small and inconsistent in 1998. Weather-related factors and lodging problems resulted in few significant treatment effects being observed at any of the three locations.
Table 5. Wheat Yield as Influenced by Nitrogen Rate and Date of Sidedress N Application at Dixon Springs, Carbondale, and Belleville in 1998 (Averaged Across Three N Rates: 40, 80, and 120 lb N/ac).
Table 7. Cost of AgrotaiN per Gallon and N Materials per Ton and per Pound of N.
Table 9. Cost of Applying 180 Pounds of N per Acre.
Figure 2. Nitrogen Composition of Corn Ear Leaf Tissue as Affected by N Fertilizers, AgrotaiN, and Rotation at the Dixon Springs Agricultural Center in 1998.
Figure 3. No-Till Corn Yield as Affected by N Fertilizers, AgrotaiN, and Rotation at the Belleville Research Center in 1998.
Figure 4. No-Till Corn Yield as Affected by N Fertilizers, AgrotaiN, and Rotation at the Dixon Springs Agricultural Center in 1998.
Figure 5. No-Till Corn Yield as Affected by N Fertilizers, AgrotaiN, and Rotation at the Belleville Research Center (Average 1995-1998).
Figure 6. No-Till Corn Yield as Affected by N Fertilizers, AgrotaiN, and Rotation at the Dixon Springs Agricultural Center (Average 1995-1998).
Figure 7. Nitrogen Composition of Corn Ear Leaf Tissue as Affected by N Fertilizers, AgrotaiN, and Rotation at the Belleville Research Center (Average 1995-1998).
Figure 8. Nitrogen Composition of Corn Ear Leaf Tissue as Affected by N Fertilizers, AgrotaiN, and Rotation at the Dixon Springs Agricultural Center (Average 1995-1998)
1 Associate Professor, Plant, Soil and General Agriculture Dept., SIUC; Agronomist, Dixon Springs Agricultural Center, University of Illinois; Professor, Agribusiness Economics Dept., SIUC; and Graduate Assistant and Researcher; Plant, Soil and General Agriculture Dept., SIUC.
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