An Evaluation Of Urease Inhibitor Technology As A Nitrogen Management Tool In No-Till Corn And Wheat Production

Illinois Fertilizer Conference Proceedings
January 27-29, 1997

1997 Index

An Evaluation Of Urease Inhibitor Technology As A Nitrogen Management Tool In No-Till Corn And Wheat Production

E.C. Varsa, S.A. Ebelhar, P.R. Eberle, Dennis Klockenga and Amy Mann¹ spacer

Introduction

Limited commercial availability of the urease inhibitor NBPT [N-(n-butyl) thiophosphoric triamide] became a reality in 1996. This compound is the active ingredient in AgrotaiN which is being marketed by the IMC-Agrico Group. AgrotaiN will be the most beneficial to producers who use urea or urea-ammonium nitrate (UAN) solution in surface application environments where incorporation is not possible (such as in no-till corn production) or where irrigation is not practiced. AgrotaiN can serve to enhance greater crop use of the N applied as urea or UAN because the rate of urea hydrolysis (breakdown) to form ammonia is reduced. A greater window of opportunity is thereby created by the inhibitor for a rain event to occur and move the dissolved urea into the soil where it is protected against ammonia volatilization loss.

Early results reported by Hendrickson (1992) over a wide range of conditions of NBPT (AgrotaiN) employment throughout the USA revealed an average corn yield increase of 4.6 and 1.6 bu/Ac when added to urea and UAN respectively. Fox and Piekielek (1993), in a Pennsylvania study, reported no-till corn yield increases of 14 bu/Ac when NBPT was included with surface-broadcast urea. In southern Illinois studies, Varsa et al. (1993 and 1996) reported no-till corn yield increases with NBPT (AgrotaiN) treated urea ranged from no response to 30 bu/Ac when evaluated over a 10-year period. No or small yield increases usually occurred when a significant rain event (> 0.5 inch) followed soon after application. Yield increases with NBPT addition to UAN were usually smaller than with granular urea because only the urea portion of the UAN is susceptible to significant ammonia volatilization loss.

In this report NBPT (AgrotaiN) treated urea and UAN are being evaluated with other N management options including injected N sources and split N applications on no-till corn. Little information is available where the urease inhibitor is being evaluated, agronomically and economically, with best N management practices for no-till corn. Likewise, very little research has been reported on the benefits that may accrue with AgrotaiN amendment of urea that is applied as a topdressing to wheat.

The objectives of this research are as follows:

l. To determine the agronomic benefit of AgrotaiN-amended urea and UAN solution compared to non-amended N fertilizers managed optimally in no-till corn production.

2. To determined the effectiveness of AgrotaiN-amended N sources relative to non-amended N fertilizers in a continuous corn and a 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 nontreated urea and ammonium nitrate applied as a topdressing to wheat.

5. At the conclusion of the experiment make an economic assessment of the costs and benefits of AgrotaiN use compared to the economic returns using best N management practices to no-till corn and wheat.

Materials and Methods

Experiments with No-Till Corn

Studies were initiated in 1995 and continued in 1996 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 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 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/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, in both a corn following corn and a corn following soybeans rotation at each of the two locations. A split-plot experimental design was used with rotations being main plots and the N fertilizer treatments being subplots. The experiment is replicated 4 times at the BRC and 5 times at the DSAC. For the corn following corn (CC) rotation the N rate was 1801b N/Ac and for the corn following soybean (CS) rotation the N rate was 140 lb N/Ac. The N rate was decreased by 401b N/Ac for the CS rotation to reflect a N credit allowable for a previous crop of soybeans. More complete details of the site and experimental conditions at both locations in 1996 are given in Table 1. Only the 1996 data will be presented and discussed in this report.

Experiments with Wheat

First year experiments with wheat were initiated with granular urea, AgrotaiN-amended urea, and ammonium nitrate each applied at 40, 80, and 120 lb N/Ac on three dates of topdressing: mid-February, early March, and late March. AgrotaiN was coated to urea at a concentration of 0.14 percent. The experiments were conducted at three southern Illinois locations: Dixon Springs, Carbondale, and Belleville. At each site the experiment was a 3x3x3 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 2571 was seeded at 100 lbs/Ac in mid October 1995. Soybeans were the previous crop at all locations. Flag leaf samples were collected for analysis of the total N concentration in the tissue at the boot stage, but the analyses are incomplete at this time. Wheat harvest was completed at all three locations by the end of June.

Results and Discussion

Experiments with No-Till Corn

General Comments. The growing season in 1996 was characterized as one being much wetter than normal in April and May but drier than normal in the important summer months of June, July, and August (Table 1). At Belleville, April rainfall was 3-fold greater than normal while at Dixon Springs, April rainfall was 1.1 inches greater than normal. May rainfall was only slightly above normal and planting of the no-till corn occurred on May 22 and 23 at the two locations. The June, July, and August total rainfall at Belleville was only slightly below normal and the distribution was near ideal. At Dixon Springs the distribution was poor. June and July rainfall was near normal but only 0.55 inch was received throughout August. The crucial grain fill and ear development stages were seriously affected by the August dryness and lower than normal yields were obtained at that location. At Belleville, where the summer rainfall was near normal and evenly distributed, excellent yields were obtained despite the later-than-normal planting date. The crop was helped at both location because summer temperatures were somewhat cooler than normal.

Rainfall received after the N fertilizer treatments were applied probably had an important impact on the responses that were observed with AgrotaiN. At Dixon Springs a total of 1.85 inches of rain was received within 72 hours after the fertilizers were applied, while at Belleville a total of 0.57 inches was received during the same period (Table 1). The heavy rains at Dixon Springs probably served to leach the surface applied N fertilizers into the soil, precluding much benefit from the urease inhibitor. At Belleville, rainfall after N application was less and significant responses to AgrotaiN-amended urea and UAN were observed.

Ear Leaf N Composition. Ear leaf N was significantly affected by N sources, AgrotaiN, and rotation at Belleville (Figure 1) but not at Dixon Springs (Figure 2). At Belleville, the highest ear leaf N was observed with the two injected N treatments (anhydrous ammonia and UAN) and the sidedressed UAN treatment that was injected. Leaf N was significantly higher in those treatments than any of the other N treatments. The N concentrations in the leaf tissue of the AgrotaiN-amended urea and broadcast UAN treatments were significantly greater than in the tissue of the non-amended N sources. However, AgrotaiN addition to dribbled UAN had no effect on ear leaf N. The higher leaf N values with urea and broadcast UAN that was amended with AgrotaiN were probably a reflection of the greater ammonia volatilization loss that likely occurred when the urease inhibitor was not present. The lack of a significant response to AgrotaiN when UAN was dribbled was probably a result of the UAN being concentrated in bands and the decreased urease activity that is usually found when UAN is placed in localized zones in the soil. The leaf N for the ammonium nitrate treatment was significantly greater than for urea but was similar to that of the AgrotaiN-amended urea. Sidedressed UAN application was not improved by AgrotaiN. However, both were significantly below the leaf N of the injected sidedressed UAN treatment. When averaged over all N sources where comparisons of without and with AgrotaiN were possible, ear leaf N was significantly increased by 0.15 percent.

A significant interaction between fertilizer N treatments and rotation was observed (Table 2). For all N treatments the ear leaf concentrations were greater in the CC rotation than the CS rotation. The only exception was for the O-N control where the opposite response to rotation was observed (and was the explanation for the significant interaction). The lower ear leaf N concentrations in treatments receiving N for the CS rotation were probably a result of the reduced N application rate (401b N/Ac) for that rotation relative to the CC rotation. It was apparent that in 1996 at this location the 40 lb N /Ac credit given for the previous crop of soybeans was too generous and actually a full 180 lb N/Ac probably was necessary to give leaf N concentrations equivalent to those of CC.

At Dixon Springs, no significant ear leaf N concentration differences were observed among the treatments receiving nitrogen (Figure 2). Only the O-N control was significantly lower. The lack of ear leaf N concentrations to respond differently among the various N treatments including AgrotaiN was probably a result of the nearly 2 inches of rainfall that occurred within 3 days following application. AgrotaiN had no significant effect on ear leaf N concentrations but there was a trend for AgrotaiN to increase N levels. Although not significant, the leaf N of plots in the CC rotation were greater than those of the CS rotation, reflecting the 401b N/Ac credit given for soybeans was likely too generous in 1996.

Grain Yields. At Belleville excellent yields were obtained and numerous significant treatment effects were observed (Figure 3). In general, yields paralleled the responses observed with ear leaf N concentrations. The best yields were observed with the injected N sources with the highest yield observed with injected UAN (200 bu/Ac). This compares with the lowest yields observed (among the fertilized plots) for the broadcast UAN (151 bu/Ac) and urea (154 bu/Ac) treatments. AgrotaiN amendment of the N sources led to significant yield increases for all the N fertilizers except for the UAN that was dribbled. For urea and broadcast UAN, these yield increases were 16 and 19 bu/Ac, respectively. Yield from ammonium nitrate, although less than for the injected UAN treatments, was significantly greater than those obtained from any of the urea or other UAN treatments, regardless of the employment of AgrotaiN. The inclusion of AgrotaiN to UAN dribbled in the sidedress treatments significantly increased yield over its non-amended comparison but was significantly below the yield obtained when the UAN was injected. The excellent growing conditions throughout the season at this location obviously created an environment for maximum expression of yield differences. Over all comparisons where AgrotaiN was included as an amendment, its inclusion led to an average yield increase of 12 bu/Ac.

Yield did not behave similarly at Belleville for all N treatments across the two rotations (Table 2). In general, higher yields were always observed in the CC rotation rather than the CS rotation. The only exceptions were the AgrotaiN amended UAN (dribble) treatment and the O-N control. Overall, the yield from the CC rotation was 8 bu/Ac greater than the CS rotation and followed the pattern observed with ear leaf N. It was apparent that the additional 40 lb N/Ac applied to the CC rotation was of greater importance than the 401b N/Ac credit allowed from the previous crops of soybeans.

At Dixon Springs, yields were much lower than those obtained at Belleville and very few significant treatment responses were observed (Figure 4). The very dry conditions at that location in August seriously eroded yield potential and very few significant treatment effects were obtained.

Experiments with Wheat

General Comments. The wheat crop got off to a slow start in the fall of 1995 because of dry soil conditions at seeding. A colder than normal November did not allow for adequate seedling development and the crop entered the winter in a less-than-desired state of development. Wide swings in winter temperatures caused some heaving problems but it also caused severe stress on the crop. Consequently, winter-kill was widespread throughout the wheat producing region of southern Illinois. The wheat at the three experiment sites came through the winter in only fair condition with stand reductions the greatest at Dixon Springs. As a result yields were (at best) only average across the three sites.

Effect of Nitrogen Sources, Rates, and Timing on Wheat Yield. All three sites were responsive to the applied N fertilizers. As seen in Table 3 yield increases were obtained with each 40-pound increment of nitrogen but in a decreasing manner. The greatest yield increase over the control treatment was obtained at Belleville (29 bu/Ac) with 120 lb N/Ac. At both Dixon Springs and Carbondale the highest yields were obtained with last date of N application (approximately March 3 1). At Belleville the highest yield was obtained with the March 10 date of N application. At Dixon Springs, the highest yield was obtained with the 80 lb N/Ac rate of application on the third date of application which accounts for the significant interaction that was observed.

No significant responses of wheat yields to N sources (including AgrotaiN) were obtained at either Dixon Springs or Carbondale (Table 4). However, a small but statistically significant 2 bu/Ac increase was observed at Belleville for ammonium nitrate compared to urea. AgrotaiN-coated urea was no different than non-treated urea at each of the three . locations in 1996. The lack of any meaningful differences in yield among the various N sources is probably a reflection of the very low ammonia volatilization loss potential to which non-treated urea is susceptible in the cold soils during February and March. If the overall yield levels across sites would have been higher then there would have been a greater likelihood of more meaningful differences among N sources.

Summary

In experiments with no-till corn at the Belleville location, ear leaf nitrogen composition and grain yields were among the highest when the N fertilizers were injected. Yields obtained with the injected N sources were significantly higher than any of the surface applied urea or UAN treatments regardless of the inclusion of AgrotaiN with those fertilizers. AgrotaiN treatment of urea or UAN, however, gave significant yield increases over the'non-amended N sources in most all comparisons. The yield increase for AgrotaiN use was 12 bu/Ac. Yield obtained with ammonium nitrate was usually equal to or greater than those obtained with the AgrotaiN amended N sources, but less than the yield from injected N sources. It appears that AgrotaiN addition to urea or UAN will increase its effectiveness to that of ammonium nitrate but be less effective than injected N sources. The 401b N/Ac credit allowed for soybeans in the corn-soybean rotation was not as effective in 1996 as that same 40 lb of N/Ac applied in the corn following corn rotation.

At Dixon Springs, heavy rains following N fertilizer treatment application and a subsequent very dry August resulted in no significant responses being observed in ear leaf N composition or no-till corn grain yield.

In the wheat experiments for 1996, no significant yield differences were observed with ammonium nitrate, urea, or AgrotaiN-amended urea at the three experimental locations of study. It appeared that ammonia volatilization losses from non-treated urea were not a serious problem in these studies where the N fertilizers were applied to cool soil environments.

Tables and Figures

Table 1: Experimental conditions and details at the Dixon Springs Agricultural Center and Belleville Research Center for No-Till Corn Experiments in 1996

Table 2: No-Till Corn Ear Leaf N Composition and Yield as Affected by Rotation, N Fertilizers, and Agrotain at the Belleville Research Center in 1996

Table 3: Wheat Yield as Influenced by Nitrogen Rate and Date of Sidedress N Application at Dixon Springs, Carbondale, and Belleville in 1996. (Averaged Across Three N Rates: 40, 80, and 120 lb N/Ac).

Table 4: Wheat Yield as Influenced by Nitrogen Rate and Date of Sidedress N Application at Dixon Springs, Carbondale, and Belleville in 1996. (Averaged Across Three N Sources: Ammonia Nitrate, Urea, and Urea with Agrotain).

Figure 1. Nitrogen Composition of Corn Ear Leaf Tissue as Affected by N Fertilizers, Agrotain, and Rotation at the Belleville Research Center in 1996

Figure 2. Nitrogen Composition of Corn Ear Leaf Tissue as Affected by N Fertilizers, Agrotain, and Rotation at the Dixon Springs Agricultural Center in 1996

Figure 3. No-Till Corn Yield as Affected by N Fertilizers, Agrotain, and Rotation at the Belleville Research Center in 1996

Figure 4. No-Till Corn Yield as Affected by N Fertilizers, Agrotain, and Rotation at the Dixon Springs Agricultural Center in 1996

Footnotes and References

¹ Associate Professor, Plant and Soil Science Dept., SIUC, Agronomist, Dixon Springs Agricultural Center, University of Illinois, Associate Professor, Agribusiness Economics Dept., SIUC, and Graduate Assistants, 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., S.A. Ebelhar, P.R. Eberle, and Dennis Klockenga. 1996. An evaluation of Urease Inhibitor Technology as a Nitrogen Management Tool in No-Till Corn Production. In R.G. Hoeft (ed). 1996 Illinois Fertilizer Conference Proceedings. pp. 105-119.

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.

Back to Table of Contents