Illinois
Fertilizer Conference Proceedings
January 26-28, 1998
| Home | 1998 Index | Search |
| Home | 1998 Index | Search |
E.C. Varsa, S.A. Ebelhar, P.R. Eberle, Dennis Klockenga and
Amy Mann1
Commercial availability of the urease inhibitor NBPT [N-(n-butyl) thiophosphoric triamide] became more widespread in the retail fertilizer trade in 1997. NBPT is the active compound in AgrotaiN which is marketed by IMC-Agrico Group. It is formulated for use at the retail level for either coating onto dry urea or addition to urea-ammonium nitrate (UAN) solutions. Agronomic benefits will most likely accrue from its inclusion with urea and urea-containing N fertilizers when applied to residue-covered soil surfaces or when incorporation into the soil is not possible, such as in no-tillage.
AgrotaiN serves to block the urea hydrolysis reaction that converts urea to ammonia. Beyrouty et al. (1988) reported that up to 30 percent of the ammonia formed from urea hydrolysis can be voltailized into the air and lost from the soil in high residue situations. If rainfall greater than 0.5 inch is received within one to two days following urea application, ammonia volatilization losses are greatly reduced. It is in situations where urea and UAN are applied to moist soil surfaces that are undergoing rapid drying, and when no rain is received for several days following application, that ammonia losses are the highest. AgrotaiN serves to block urea from hydrolyzing to ammonia for up to 14 days following application thereby allowing a rain event to "wash" the fertilizer into the soil.
Corn yield responses to AgrotaiN can be quite variable. Hendrickson (1992), when summarizing research results across the midwestern USA, reported average yield increases of 4.6 bu/acre from the addition of AgrotaiN to urea and 1.5 bu/acre when the inhibitor was added to UAN. Under high ammonia loss conditions, responses to AgrotaiN can be very large. Murphy and Ferguson (1997) in studies on ridge till reported a 56 bu/acre yield increase with AgrotaiN-amended urea in one of three years of study but no response to its use the other two years because rains soon after application precluded ammonia loss. Fox and Piekielek (1993), reported average yield increases of 14 bu/acre from AgrotaiN addition to urea in a three year study in Pennsylvania. Under southern Illinois conditions, during evaluation of AgrotaiN on no-till corn from 1986-1996, Varsa et al. (1993; 1996) reported yield responses to the inhibitor addition to urea and UAN to average from 0 to 30 bu/acre. Highest responses were usually obtained with urea and were associated with conditions conducive to high ammonia volatilization losses.
This report contains the results of AgrotaiN evaluations on no-till corn and wheat obtained in 1997. No-till corn responses to N timing, placement and source were evaluated under two crop management sequences (continuous corn and a corn-soybean rotation) and at two locations (Belleville and Dixon Springs). Wheat studies were conducted with AgrotaiN at Belleville, Carbondale, and Dixon Springs in which N sources, N rates, and timing of application were evaluated.
Specific objectives of this research are as follows:
Studies were initiated in 1995 and continued in 1996 and 1997 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 AgrotraiN 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") prior to corn planting followed by sidedressing of dribbled UAN (without and with AgrotaiN at 0.5 lb/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.
The 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 a N credit allowable for a previous crop of soybean. More complete details of the site and experimental conditions at both locations in 1997 are given in Table 1. Only the 1997 data will be presented and discussed in this report. Reports of results of the 1995 and 1996 experiments are contained in the Proceedings of the 1996 and 1997 Illinois Fertilizer Conferences.
Second-year experiments with AgrotaiN on wheat were conducted in 1997 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 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 2571 was seeded at 100 lbs/acre at all locations between October 10 and October 17, 1996. Soybeans were the previous crop at all locations. Flag leaf tissue samples were collected for N analysis 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 1997 and the grain yield results will be given in this report. Results of the 1996 (first year) experiments with wheat are given in the Proceeding of the 1997 Illinois Fertilizer Conference.
General comments
The 1997 growing season was characterized by normal to above normal rainfall in April and May that delayed planting until mid May. The wetness that extended into June delayed some of the sidedress N treatment applications and resulted in high denitrification losses of the surface N treatments, especially at Dixon Springs. As seen in Table 1 nearly 2.5 inches of rain was received at the DSAC site within a 7-day period following application of the surface N treatments. These rains precluded any response opportunity for AgrotaiN but also set up environmental conditions for large denitrification losses of the surface-applied N treatments. Excessive rainfall was not a serious problem at Belleville where a 1-inch rain was not received until 4 days following surface N treatment application. A wet period (>2 inches of rain received within 7 days after N application) following the sidedress N treatment application at Dixon Springs also resulted in no response to AgrotraiN but also contributed to high denitrification losses of the surface sidedress treatments.
The precipitation received for the main growing season months of July and August was below average at Dixon Springs but very near to normal at Belleville. This resulted in reduced yield potential at Dixon Springs but above average growing conditions for Belleville. Seasonal temperatures were very close to normal for June, July, and August at both locations which prevented any prolonged heat stress conditions from damaging the corn crop.
Ear leaf N composition
The nitrogen composition of ear leaf tissue was significantly affected by N fertilizer treatments at Belleville (Table 2 and Figure 1). There was no difference in average N composition of leaf tissue between the rotations but some N treatments resulted in higher ear leaf N percentages being observed in the CC rotation while other N treatments resulted in higher N contents in the CS rotation (a significant N fertilizer by rotation interaction). There was no clear pattern to explain the inconsistency. The highest ear leaf N was obtained with the at-planting and sidedress (injected) UAN treatments while the lowest ear leaf N composition, excluding the control, was observed with granular urea. AgrotaiN addition to the fertilizers significantly increased ear leaf N in the urea and dribbled UAN treatments but had no influence on broadcast UAN or sidedress (dribbled) UAN. Ear leaf N for the ammonium nitrate and anhydrous ammonia treatments was similar but significantly below the ear leaf N composition for the injected UAN treatments.
At Dixon Springs, the ear leaf N composition differences among the N treatments dramatically illustrated the high denitrification N losses that occurred following the surface N treatment applications (Table 3 and Figure 2). Clearly the injected N treatments (UAN and anhydrous ammonia) were much higher in ear leaf N composition than any of the surface applied treatments. These results illustrate the importance of injection of N sources below the active sites of denitrification which occur at or in the surface 1 inch of soil below the crop residues. Also, it is most apparent that AgrotaiN does not serve a role as a nitrification inhibitor since no differences in ear leaf N were observed with its addition to the surface-applied N sources (urea or UAN).
Grain yield
No-till corn yield at Belleville was significantly affected by N fertilizer treatments, rotation and AgrotaiN inclusion with N sources (Table 2 and Figure 3). The highest yield (166 bu/acre) was obtained with injected UAN (at-planting or sidedress-applied) and the lowest yield (83 bu/acre) was observed with broadcast urea. AgrotaiN additions resulted in significant yield increases when added to urea (38 bu/acre increase) and UAN that was dribble-applied at planting (14 bu/acre increase) or dribbled at sidedressing (11 bu/acre increase). AgrotaiN addition to broadcast UAN at planting had no effect. Both the anhydrous ammonia and ammonium nitrate treatments resulted in the same yields but were some 30 bu/acre less than the yield obtained with injected UAN. The lower yield with anhydrous ammonia compared to injected UAN may have been a result of N loss from the anhydrous ammonia treatment that was applied some 40 days prior to the application date for the injected UAN treatment. For all N sources that included AgrotaiN, its inclusion resulted in a 16 bu/acre average yield increase. Corn yields averaged some 12 bu/acre greater on the CS plots compared to the CC plots even though less N was applied (a total of 140 lb N/acre was applied to the CS rotation and 180 lb N/acre was applied to the CC rotation).
At Dixon Springs, corn yields were dramatically affected by the high denitrification losses of surface applied N that occurred (Table 3 and Figure 4). Corn yield from the injected N treatments (anhydrous ammonia and UAN) ranged from 109 to 112 bu/acre while all the surface N treatments that were applied at planting averaged in the 70 to 80 bu/acre range. Even the surface dribbled UAN treatments (without or with AgrotaiN) that were applied at sidedressing averaged some 20 to 25 bu/acre less than injected N sources. Clearly these data show the importance of injection of N when high denitrification conditions prevail. Also, it is readily apparent from these data that AgrotaiN does not serve any role in decreasing denitrification losses.
General comments
The 1997 growing season for wheat in southern Illinois was much improved over the 1996 growing season, which was very severe and resulted in heavy winterkill. At the high N rate, yields at Belleville averaged over 90 bu/acre for all three dates of application. No serious disease outbreaks affected the crop at any of the locations in 1997. However, yields at Carbondale were considerably below the other two locations because of deer and geese feeding during the winter.
Effect of nitrogen rates, sources, and timing on wheat
The crop was responsive to N rates at all three locations across the three dates of application (Table 3). At all three locations the highest yields were obtained from topdressing the wheat in late March. Application of N to the wet soils earlier in the season may have resulted in greater losses and less efficient use of the N by the wheat crop.
The yield response pattern was similar on all three dates of application for
the three N sources at Dixon Springs and Carbondale but not at Belleville (Table
4). At those two locations, yield from ammonium nitrate and urea plus AgrotaiN
was about three to four bu/acre greater than non-amended urea when averaged
over the three application dates. At Belleville, there was no consistent pattern
of yield response to the three N sources such that no significant differences
were observed. It was likely that some ammonia volatilization loss did occur
from the non-treated urea at Dixon Springs and Carbondale but little if any
loss likely occurred at Belleville.
Addition of AgrotaiN to urea and UAN that was surface applied to no-till corn in 1997 at Belleville resulted in significant increases in ear leaf N composition and yield compared to non-amened N sources. Yield increases from the amendment of AgrotaiN to urea and dribbled UAN averaged 38 and 14 bu/acre, respectively. Yield was not significantly increased when AgrotaiN was added to UAN that was broadcast applied. Highest corn yields at Belleville were obtained with injected UAN, averaging some 40 bu/acre greater than AgrotaiN-treated urea that was surface broadcasted and some 30 bu/acre greater than AgrotaiN-treated UAN that was surface dribbled. These results illustrate the importance of injection of N sources compared to surface application of N to achieve maximum N use efficiency, for no-till corn, regardless of the employment of a urease inhibitor.
At Dixon Springs, high denitrification losses in 1997 of all surface applied treatments resulted in ear leaf N composition values and grain yields that were much less than those obtained with anhydrous ammonia or injected UAN. Yields were some 35 to 40 bu/acre less with the surface applied N treatments compared to the injected N sources. AgrotaiN addition to the urea or UAN fertilizers had no effect on increasing corn yield or decreasing dentrification losses.
Wheat yields at two of three locations were increased an average of three
to four bu/acre when urea was amended with AgrotaiN. At the other location
AgrotaiN use had no influence on yield. Ammonium nitrate and AgrotaiN treated
urea were equally effective in optimizing yield at all three locations.
1 E.C. Varsa is an Associate Professor, Plant, Soil and General Agriculture Dept., SIUC; S.A. Ebelhar is an Agronomist, Dixon Springs Agricultural Center, University of Illinois; P.R. Eberle is an Associate Professor, Agribusiness Economics Dept., SIUC; Dennis Klockenga and Amy Mann are Graduate Assistants, Plant, Soil and General Agriculture Dept., SIUC.
