Fertilizer Conference Proceedings
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E.C. Varsa, S.A. Ebelhar, P.R. Eberle and Dennis Klockenga1
Commercial availability of the urease inhibitor NBPT [N-(n-butyl) thiophosphoric triamide] will become a reality in 1996. This product, to be sold under the trade name of Agrotain and marketed by IMC-Agrico Group, serves to decrease the rate of conversion of urea to ammonia and carbon dioxide thereby reducing the potential for ammonia volatilization. Such a product will have the greatest benefit in reducing ammonia volatilization losses when urea or urea-ammonium nitrate solution (UAN) is surface-applied in the presence of residues or where limited or no soil incorporation occurs. Therefore the greatest probability of obtaining a meaningful response to the use of Agrotain is in no-tillage situations where the fertilizer is surface-applied and when little or no rainfall occurs for several days following application.
Considerable research has been conducted in which yield increases from NBPT use have been reported (Fox and Piekielek, 1993; Hendrickson, 1992; Varsa, et al., 1993). Most studies report of comparisons in which NBPT is added to either urea or UAN solutions. In most instances benefits of the inhibitor are the greatest when it is added to urea and lesser benefits are obtained when it is added to UAN. This observation is theoretically predictable because only about one-half of the nitrogen in UAN occurs as urea-N and the remainder is ammonium nitrate-N. Very little research has been reported in which NBPTtreated N sources were evaluated relative to best N management practices that include injected N sources and split N treatments.
For this research a comprehensive evaluation of NBPT (Agrotain) was undertaken in which its employment will be evaluated relative to best N management practices for notill corn production. At the culmination of the study an economic evaluation of its costeffectiveness will be presented. The efficacy of Agrotain treatment of N sources applied to wheat will also be evaluated and presented in later reports.
The objectives of this research are as follows:
Experiments were initiated at the Dixon Springs Agricultural Center (DSAC) of the University of Illinois and the Belleville Research Center (BRC) of Southern Illinois University in April of 1995 to evaluate N sources, placement, timing, and Agrotain inclusion on no-till corn. Nitrogen sources that were surface-applied include: granular urea (without and with Agrotain at 0.14%), granular ammonium nitrate, and UAN solution (without and with Agrotain at 0.5 lb/Ac) which included both broadcast spray and dribble placements. Injected N sources include UAN (knifed-in at DSAC and point injection-applied at BRC) and anhydrous ammonia. Split N treatments included a 40 lb N/Ac application of UAN without Agrotain as a broadcast spray ("weed and feed") prior to corn planting followed by sidedressing of dribbled UAN (without and with Agrotain at 0.5 lb/Ac) and an injected UAN treatment.
A total of 12 N fertilizer treatments were evaluated, along with a O-N control,
on both a corn following corn (CC) and a corn following soybean (CS) rotation
at each of the two locations. At the DSAC site the N treatments were established
for each rotation in different fields and were analyzed as separate experiments
with respect to rotation. At the BRC, rotation was established as a part of
the experimental design and was evaluated to determine if N fertilizer treatments
performed similarly or differently on the two rotations. A randomized complete
block design was used at each location and N treatments were replicated 4 times
at the BRC and 5 and 6 times, respectively, for the CS and CC rotations at the
DSAC. The N rate for all fertilizer treatments at both locations was 180 lb
N/Ac for the CC rotation and 140 lb N/Ac for the CS rotation. The N rate was
decreased by 40 lb N/Ac for the CS rotation to reflect a N credit allowable
for soybeans. More complete details of the site and experimental conditions
at both locations in 1995 are given in Table
The 1995 growing season was characterized as one being excessively wet from late April through early June followed by mid and late summer dryness that cut into the yield potential. An example of the wetness was the fact that at the Belleville location rainfall in May was over 13 inches above normal. The late spring wetness resulted in late planting especially at the BRC (June 8). The crop developed rapidly but temperatures that were above normal in August coupled with the dryness resulted in yields (especially at Belleville) that were below normal.
Effect of N Treatments on the N composition of Ear Leaf Tissue and Corn Grain
Ear leaf N composition was significantly affected by N sources, placement, and Agrotain when applied to corn following corn (Figure 1) and corn following soybeans (Figure 2) at Dixon Springs in 1995. Ear leaf N composition was not any different for urea compared to the O-N control in either rotation, but Agrotain amendment of urea increased ear leaf N in both rotations compared to urea. Agrotain inclusion with broadcast UAN significantly increased ear leaf N compared to no-amended UAN for the CS rotation (Figure 2) but a significant reduction occurred for the CC rotation (Figure 1). No clear reason can be given to explain the N composition reduction in the presence of Agrotain. Addition of Agrotain to dribble-placed UAN was significant in increasing ear leaf N only when the fertilizer was applied as a split N treatment in the CC rotation. The highest ear leaf N composition was observed with anhydrous ammonia for the CC rotation and with ammonium nitrate in the CS rotation. When averaged over both urea and UAN and over the two placement methods for the UAN, Agrotain increased ear leaf N composition by 0.11 percent for corn following corn and 0.16 percent for corn following soybeans. At Belleville (data not shown), ear leaf N composition was not affected differently by any of the N fertilizer treatments but all N treatments were significantly higher than the O-N control.
Grain N composition was significantly affected by N treatments at Belleville
(Figure 3) but was not influenced by N
treatments at Dixon Springs, regardless of rotation (Table
2). At Belleville, among the fertilized N treatments, grain N composition
was the lowest in the urea-N treatment and the highest in the anhydrous ammonia
treatment. Grain N was not affected to any degree by Agrotain inclusion with
UAN but it was significantly increased by Agrotain addition to urea. Grain N
composition was increased by 0.05 percent by Agrotain when averaged over all
comparisons that included the inhibitor. A higher grain N composition was observed
in the CC rotation compared to the CS rotation at the Belleville location.
Effect of N Treatments on Corn Grain Yield
Grain yield was significantly affected by N sources and Agrotain in the corn following corn rotation at Dixon Springs (Figure 4) and by N Sources, placement, and Agrotain in the companion study of corn following soybeans (Figure 5) at the same location. For the CC rotation experiment (Figure 4) the highest yield was obtained with anhydrous ammonia (141 bu/Ac) and the lowest fertilized yield was with granular urea (119 bu/Ac). The O-N control had a yield of 73 bu/Ac. Agrotain addition to urea resulted in an increase of 9 bu/Ac but inclusion of the inhibitor with UAN resulted in only small, non-significant yield increases. Ammonium nitrate in this experiment gave a further yield increase of 11 bu/Ac over Agrotain-treated urea reflecting the occurrence of some N loss even in the presence of Agrotain. Addition of Agrotain to dribbled UAN did not result in any yield differences whether applied at plant emergence or as a split application at the sidedressing stage. Anhydrous ammonia was superior to injected UAN and, when the inhibitor was evaluated over all treatments, Agrotain use gave a non-significant 4 bu/Ac yield increase.
Agrotain inclusion with N sources in the corn following soybeans study at Dixon Springs (Figure 5) had a larger effect on yield than it did for corn following corn. Yield was increased by 30 bu/Ac with Agrotain addition to urea and by 19 and 14 bu/Ac when added to UAN that was broadcast and dribbled, respectively, at plant emergence. Addition of the inhibitor to the sidedressed UAN treatment resulted in a yield increase of 13 bu/Ac in this study. Clearly urease activity was greater in the soybean residues as reflected in the large yield differences that were observed. The highest yield in this study was with granular ammonium nitrate (157 bu/Ac) and the lowest yield of a fertilized treatment was 103 bu/Ac from granular urea. Yield from anhydrous ammonia treated corn was greater than with injected UAN probably because of some plant root injury that occurred when the UAN was knifed-in. Averaged over all N treatments that included Agrotain, inhibitor inclusion resulted in a yield increase of 18 bu/Ac.
At Belleville, smaller but significant yield benefits from Agrotain use were
observed (Figure 6) even though yield
was significantly reduced because of the late summer drought. The N treatment
response data in Figure 6 were averaged
across both the CC and CS rotations in the study because there was no difference
in the behavior of the N treatments whether applied to a previous crop residues
of corn or soybeans. The greatest yield increase from Agrotain was with its
addition to urea (9 bu/Ac) followed by its addition to broadcast UAN (6 bu/Ac)
and to dribbled UAN (5 bu/Ac). These yield increases from Agrotain were observed
despite the 1-inch rain that was received 2 days following application of the
surface N treatments (Table 1). The highest
yield observed in this experiment was 141 bu/Ac from injected UAN at sidedressing
and the lowest yield was 125 bu/Ac from granular urea. Overall Agrotain increased
corn yield by 5 bu/Ac in this experiment and the average rotation benefit of
corn following soybeans compared to corn following corn was 13 bu/Ac, despite
40 lb N/Ac less fertilizer that was applied.
Effect of N Treatments on Nitrogen Accumulation in the Grain
Uptake and accumulation of N in the grain as a function of N sources and Agrotain is shown in Figure 7 for the study at Belleville and given in Table 2 for the experiments at Dixon Springs. At Belleville the highest N uptake was observed in the 3 injected N treatments followed by Agrotain-amended UAN that was applied at corn emergence. Uptake of N in the grain from Agrotain treatment of urea was essentially equal to that obtained from ammonium nitrate. The lowest N accumulation in the grain was observed with granular urea (68 lb N/Ac) while the O-N control had a N accumulation of 23 lb N/Ac. Averaged over all N treatments that included Agrotain, use of the inhibitor resulted in about 71b/Ac additional N taken up in the grain. Only slightly more N (3 lb N/Ac) was taken up in grain on CS plots compared to uptake in the grain of the CC plots.
At Dixon Springs very few differences in grain N accumulation were observed
in the corn following corn rotation but numerous differences were observed in
the corn-soybean rotation (Table 2). For
the CC rotation the highest N uptake was obtained with anhydrous ammonia but
in the CS rotation the highest N accumulation in the grain was observed with
Agrotain-treated urea. Significant N uptake increases from Agrotain use with
N sources in the CS rotation were observed with urea (33.3 lb N/Ac), dribbled
UAN (13.4 lb N/Ac), and broadcast UAN (10.2 lb N/Ac). Uptake of N in the non-fertilized
control plots ranged from 43 to 45 lb N/Ac across rotations.
In studies of N sources, placement, and Agrotain addition to urea and UAN in
1995 at Dixon Springs and Belleville it was observed the highest yields were
usually found with anhydrous ammonia and injected UAN. In most all studies Agrotain
treatment of urea gave larger yield increases (ave. 14 bu/Ac) then did Agrotain
inclusion with UAN (ave. 7 bu/Ac). The greatest yield benefit from Agrotain
was observed with its addition to urea (30 bu/Ac) and when applied to corn grown
in a CS rotation. Enhanced uptake of N in the grain from Agrotain use generally
paralleled the increases observed in grain yield.
Figure 1. Effect of Nitrogen Sources, Placement, Timing, and Agrotain on Ear Leaf Nitrogen Composition of No-Till Corn Following Corn at Dixon Springs in 1995
Figure 2. Effect of Nitrogen Sources, Placement, Timing, and Agrotain on Ear Leaf Nitrogen Composition of No-Till Corn Following Soybeans at Dixon Springs in 1995
Figure 3. Nitrogen Composition of Corn Grain as Affected by N Fertilizers, Agrotain, and Rotation at the Belleville Research Center in 1995
Figure 4. Effect of Nitrogen Sources, Placement, Timing, and Agrotain on Yield of No-Till Corn Following Corn at Dixon Springs in 1995
Figure 5. Effect of Nitrogen Sources, Placement, Timing, and Agrotain on Yield of No-Till Corn Following Soybeans at Dixon Springs in 1995
Figure 6. No-Till Corn Yield as Affected by N Fertilizers, Agrotain, and Rotation at the Belleville Research Center in 1995
Figure 7. Nitrogen Accumulation in the Grain Per Acre as Affected by N Fertilizers, Agrotain, and Rotation at the Belleville Research Center in 1995
Table 1: Experimental Conditions and Details at the Dixon Springs Agricultural Center and Belleville Research Center in 1995
Table 2: Grain Nitrogen Composition and Uptake of N in the Grain as Affected by N Fertilizer Sources, Placement, Timing, and Agrotain at Dixon Springs in 1995
1Associate Professor, Plant and Soil Science Dept., SIUC, Agronomist, Dixon Springs Agricultural Center, University of Illinois, Associate Professor, Agribusiness Economics Dept., SIUC, and Graduate Assistant, Plant and Soil Science Dept., SIUC.
Fox, R.H., and W.P. Piekielek. 1993. Management and urease inhibitor effects on nitrogen use efficiency in no-till corn. J. Prod. Agric. 6:195-200.
Hendrickson, L.L., 1992. Corn yield response to the urease inhibitor NBPT: five year summary. J. Prod. Agric. 5:131-137.
Varsa, E.C., J.M. Jemison, M.W. Osborn, A.K. Leis, S.W. Hnetkovsky, and N. Jan. 1993. Effect of NBPT-amended urea and UAN on no-till corn in southern Illinois. Proceedings of the Twenty-Third North Central Extension-Industry Soil Fertility Conference. Vol. 9. pp. 72-80. Oct. 27-28, 1993. St. Louis, MO.
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