Winter wheat response to fall/ spring application of stabilized anhydrous ammonia fertilizer in Missouri (1).

Abstract

Soft red winter wheat (Triticum aestivum L) yields can be very responsive to nitrogen (N) fertility management. The objectives of this study were to evaluate fall application of anhydrous ammonia with or without nitrapyrin for soft red winter wheat yield in Missouri, and to relate crop yield to N[H.sub.4.sup.+] :N[O.sub.3.sup.-] soil ratios. A three-year study was conducted at Columbia on a Mexico silt loam (fine' montmorillonitic, Udollic Ochraqualf), at Novelty on a Putnam silt loam (fine' montmorillonitic, mesic Mollic Albaqualf), dand at Portageville on a Tiptonville silt loam (fine-silty, mixed, thermic, Typic Argiudoll). Anhydrous ammonia, with and without nitrapyrin (2-chloro-6-(trichloromethyl) pyridine) added, was injected into the soil in the fall at rates varying from 0 to 112 kg N [ha.sup.-1] in 28 kg N [ha.sup.-1] increments. Urea was surface applied to each plotin the spring to augment fall application for a total of 112 kg N [ha.sup.-1] per plot. Yields ranged from 753 kg [ha.sup.-1] to 5,852.2 kg [ha.sup.-1]. Lowest yields were observed in plots receiving 0 N at all three locations. Addition of N fertilizer almost doubled yields at all locations when compared with the unfertilized control. Nitrapyrin did not affect wheat yield at any location. Application of N increased the number of heads [m.sup.-2], but did not influence thousand kernel weights (TKW). Nitrogen use efficiency (NUE) increased as the amount of N applied in the spring increased. The highest NUE was observed by applying 50% of the total N preplant in the fall and 50% at Feekes growth stage 3 in the spring. High NUE also resulted from application of 25% of the N in the fall and 75% spring, and from application of all N in the spring. Use of nitrapyrin did not influence grain yield for soft red winter wheat production in Missouri.

1. Introduction

Management of soft red winter wheat in Missouri is based on a perception that wheat serves only as a minimum-input crop in rotation with higher valued commodities. Increasing soft red winter wheat yields in Missouri requires an increased emphasis on management of all aspects of production, including N fertility.

Nitrogen management for winter wheat production in the Midwest region of the United States has generally split then total into fall and spring applications (Huber et al., 1980). Use of nitrapyrin could allow farmers to adjust their application to where most or all of the N required for winter wheat production may be applied in the fall (Touchton et al., 1978), with less risk of N loss during winter months. Fall application of N allows farmers the opportunity to shift equipment and labor out of competition with spring crop activities, and to utilize anhydrous ammonia which is a cheaper source of N. In addition, fall application of N can often avoid inclement weather that can limit opportunities to topdress N during late winter and early spring. Application of the total N required for winter wheat production in the fall also has the potential to reduce soil compaction and crop injury incurred b to dressing (Liu et al., 1983). Using nitrapyrin with fall applied N[H.sub.3] to maintain higher N[H.sub.4.sup.+] levels in the soil may provide a better balance between N[H.sub.4.sup.+] and N[O.sub.3.sup.-] ratios for optimum wheat growth. (Goh and Young, 1974), as well as reducing the potential for nonpoint-source contamination of surface water (Walters and Malzer, 1989).

Several studies have demonstrated that nitrapyrin increased yields of wheat and numerous other crops (Gasser, 1965; Prasad et al., 1971; Christensen and Huffman,1992; Hendrickson et al., 1978a; Huber et al., 1980). In a study to evaluate response of winter wheat to the inhibited nitrification of fall-applied N, Huber et al. (1980) reported a yield increase in two of the three experiments when nitrapyrin was added to spring-applied N, compared with yields obtained from either fall-N plus nitrapyrin or the split application of N without nitrapyrin.

Some reports indicate that split N applications for winter wheat are superior to applying all N in the fall or in the spring (Boswell et al., 1975; Shaviv et al., 1987); however, a split application without a nitrification inhibitor may result in significant loss of fall-applied N (Huber et al., 1977). Boswell et al. (1975) found wheat yields of fall-applied N treatments were similar to the control on Cecil and Norfolk soils in Georgia. Split N treatments resulted in significantly greater wheat yields than nitrogenapplied in fall at either 28 kg N [ha.sup.-1] or 84 kg N [ha.sup.-1] without nitrapyrin. Use of nitrapyrin with fall-applied N maintains fertilizer N in the N[H.sub.4+] form for extended periods and reduces the risks of reduced NUE through enhanced N uptake and yield (Parr et al., 1971).

Previous work in Missouri has shown that soft red winter wheat yields are similar for either all-fall or all-spring applications of N under low-to-intermediate yield conditions (Buchholz and Schaeffer, 1990). They found that splitting the application of N between fall and spring growth periods improved winter wheat yields over all-fall and all-spring applications, particularly under intermediate to higher yield conditions.

The impact of or benefits from using N fertilizers treated with nitrapyrin under these conditions needs to be determined. The use of nitrapyrin with anhydrous ammonia has been shown to stabilize N[H.sub.4.sup.+] in the soil and reduce nitrification rates on clay-pan soil types common to Northern Missouri (Kidwaro and Kephart, 1997). This study was designed to evaluate fall-N applications of anhydrous ammonia, with or without nitrapyrin, to split and spring-N applications for soft red winter wheat in Missouri.

2. Materials and Methods

This study was initiated in the fall of 1990 at three different sites located near Columbia, Novelty, and Portageville, Missouri. Plots were established on a Mexico silt loam (fine' montmorillonitic, Udolic Ochraqualf) at Columbia, a Putnam silt loam (fine, montmorillonitic, mesic Mollic Albaqualf) at Novelty, and a Tiptonville silt loam (fine-silty, mixed, thermic, Typic Argiudoll) at Portageville. Phosphorus and potassium levels were determined in the surface 16 cm of the soil profile and amended to levels recommended by the University of Missouri Soil Testing Laboratory to achieve 6,700 kg [ha.sup.-1] yields of soft red winter wheat. Prior to planting anhydrous ammonia was applied in early September approximately 15 cm deep with a field applicator consisting of five shanks mounted 45 cm apart.

Anhydrous ammonia treated with and without nitrapyrin was applied at rates from 0 to 112 kg [ha.sup.-1] in 28 kg increments. Urea was surface applied during early spring growth (Feeke's Growth Stage 3) at rates augmenting the fall anhydrous ammonia applications to a total of 112 kg N [ha.sup.-1]. One set of control plots did not receive any fall or spring N applications. The nitrapyrin was combined with the anhydrous ammonia at a constant rate of 0.56 kg [ha.sup.-1]. 'Pioneer 2555' soft red winter wheat was seeded at 120 pure live seeds [m.sup.-1] of row, using a 19.00 cm row spacing in plots measuring 2.4 x 10.6 meters. Plots were planted immediately following anhydrous ammonia applications at all three locations.

Treatments at each location were replicated four times in a randomized complete block design. Stand density, plant height, grain yield, tissue-N and grain-N were measured. Yield components (heads [m.sup.-2], number of seeds [head.sup.-1] and thousand kernnel weight TKW were measured to ascertain the impact of the treatments on grain yield. The harvest index (HI) was calculated from a subsample of wheat that was cut at soil level weighed and threshed from each plot just prior to grain harvest. Grain and straw components were analyzed for N content. All plots were subsequently harvested to determine grain moisture and yield. Reported grain yields are adjusted to 13% moisture content. The study was repeated at Columbia, Novelty and Portageville in the fall of 1991, 1992 and 1993.

Straw and grain-N content were determined using a LECO analyzer at the University of Missouri. Nitrogen use efficiency was calculated according to Mercedes et al. (1993):

NUE (%) = (N uptake in N-treated plot-N uptake in control) x 100/Fertilizer N applied

Data were analyzed by analysis of variance (ANOVA) (SAS Inst., 1990) to determine significant treatment effects. Means were separated by Fisher's protected least significant difference (LSD) at the 0.05 probability level.

3. Results and Discussion

a. Grain Yield

Grain yields were variable among the environments, averaging from 752 to 5,852 kg [ha.sup.-1] among the seven site years (Table 1). Scab (Fusarium graminearum) severely depressed grain yield at the Novelty and Portageville locations in 1991. In 1992, the Columbia and Novelty sites suffered extensive winter-kill, nearly 100% stand loss at Novelty so plots were not harvested. The Portageville site did not experience winter injury in 1992, and was the highest yielding environment during the course of the study. The Portageville site was not established in fall, 1992 due to excessive moisture during the planting period.

Yields were lowest at all sites in unfertilized plots, varying from 342 kg [ha.sup.-1] in 1991 to 4132 kg [ha.sup.-1] in 1992 at Portageville (Table 1). Nitrogen application resulted in a yield increase over unfertilized treatments at all harvested sites due to an increase in the number of tillers and subsequently, the number of heads per plant (Table 2). There was a 41%, 47%, and 22% percent increase in heads [m.sup.-2] from N application at Columbia in 1991, 1992 and 1993 respectively. Portageville, the highest yielding environment in 1992 had 55% increase in heads [m.sup.-2] where N was applied compared to unfertilized treatments. This is consistent with studies by Richardson and Fricke (1931) and Hobbs (1953) who reported that winter wheat yield increase with N fertilization treatments resulted mainly from an increase in number of tillers, number of heads per plant, and number of kernels per head.

Although use of nitrapyrin has been shown to retain N[H.sub.4.sup.+] N in the soil profile for extended periods under an established wheat crop (Kidwaro and Kephart, 1997), no difference in winter wheat grain yield was detected from applying nitrapyrin with the anhydrous ammonia in any of the split N treatments (Table 1). No difference in grain yield occurred when all the N was applied in the fall with and without nitrapyrin at all seven harvested sites. Applying all of the N in the spring resulted in lower yields at Columbia in 1991, and Portageville in 1992. There was a 907 kg [ha.sup.-1] yield advantage from applying all of the N in the spring compared to applying all of the N in the fall with nitrapyrin at Novelty during the 1993 study. Splitting fertilizer N application between fall and spring at 50% fall and 50% spring or at 25% fall and 75% spring regardless of nitrapyrin treatment, resulted in higher (P = 0.05) grain yield compared to the unfertilized treatment and average of the all the spring N applications. Applying all N fertilizer in the fall, regardless of nitrapyrin treatments, resulted in higher grain yields compared to applying all of the N in the spring at the Novelty site in 1993. Buchholz and Schaeffer (1990) reported similar winter wheat yields by using either all-fall or all-spring applications of N. Liu et al. (1983) found that wheat yields were equal or slightly higher with fall-applied N plus nitrapyrin than in treatments receiving only spring N.

Lack of winter wheat yield response to nitrapyrin may be due to disproportionate N[H.sub.4.sup.+]:N[O.sub.3.sup.-] soil ratios caused by the higher levels of N[H.sub.4.sup.+] that are retained in the soil profile compared with no nitrapyrin. Wheat plants preferentially absorb N in the N[O.sub.3.sup-] form (Marschner, 1995). During the second week of the soil sampling period of 1991 -1992, 288 mg N [kg.sup.-1] as N[H.sub.4.sup.+] and 3.4 mg N [kg.sup.-1] as N[O.sub.3.sup.-] (N[H.sub.4.sup.+]-N:N[O.sub.3.sup.-] -N ratio of 85:1) were retained in the anhydrous ammonia injection zone from plots treated with nitrapyrin (Kidwaro and Kephart, 1997). This high N[H.sub.4.sup.+]:N[O.sub.3.sup.-] ratio in plots treated with nitrapyrin persisted throughout both the 1991-92 and 1992-93 sampling periods. Shaviv et al., (1987) reported that applying N[H.sub.4.sup.+]-N:N[O.sub.3.sup.-] -N ratios of 50:50 and 25:75 were optimal for winter wheat during the early vegetative period, with the 25:75 N[H.sub.4.sup.+]-N: N[O.sub.3.sup.-] -N ratio producing the highest yields.

b. Yield Components and Harvest Index

The influence of the split N treatment on number of heads [m.sup.-2], seeds [head.sub.-1] and weight [seed.sub.-1] was not consistent among years and sites at the three sites (Table 2). Applying N increased (19 = 0.05) the number of heads [m.sup.-2] across sites regardless of nitrapyrin treatments. Nitrogen application also increased (p = 0.05) the number of seeds [head.sup.-1] in three of the five site years at Columbia in 1992, 1993 and at Novelty in 1993. The N fertilizer or inclusion of nitrapyrin with the N did not influence Thousand Kernel Weight (TKW). These results indicate that applied N consistently improved the number of tillers initiated per plant, resulting in more heads [m.sup.-2]. Number of seeds [head.sup.-1] was increased by N in three of the five site years, but the response may have been limited by other environmental factors.

The harvest index (HI) ranged from a low of 11 to 41 among site years (Table 3), but no difference was detected among N treatments. Harvest index also was not influenced by nitrapyrin (Table 3).

c. Nitrogen Use Efficiency

Except for 1991 in Columbia, apparent NUE increased with increasing proportion of N applied in the spring among locations and years regardless of nitrapyrin (Table 4). Based on all data, there was a 10% advantage in NUE from applying all the N in the spring compared to applying all the N in the fall. Nitrogen applied in the fall may have been lost via leaching, denitrification, or immobilization. Nitrapyrin should have retained N in the soil profile and thus improved NUE, however, the low organic matter content of these soils may have reduced nitrapyrin's persistence. Soil organic matter recorded was 1.2%, 1.1% and 1.9% at Columbia, Portageville and Novelty respectively. Hendrickson et al. (1978b) reported that nitrapyrin's persistence was limited by it's volatilization, that was promoted by low organic matter content on a Plainfield loamy sand in Wisconsin. Hendrickson and Keeney (1979) found that nitrification was slower in a sandy loam soil with 5% organic matter than in one with 2% organic matter due to sorption of nitrapyrin by organic matter. Splitting the fertilizer N at 50% fall and 50% spring or 25% fall and 75% spring resulted in higher NUE compared to applying all the fertilizer in the fall or 75% in fall and 25% spring split application when averaged across locations. Applying all of the N fertilizer in the spring also resulted in higher NUE compared to applying all of the N in the fall or 75% fall and 25% spring application when averaged across locations.

The highest NUE was recorded at Portageville in 1992 (Table 4), the same year and location where the best yields were recorded. When averaged across split N rates with and without nitrapyrin, 34% of the N applied at Portageville in 1992 was utilized by the crop, 25% at Columbia in 1993 and 22% at Novelty in 1993. Higher NUE did not result in higher grain yields across environments suggesting higher grain yields will not necessarily result from a higher NUE. Relative grain protein content is also a component of NUE, therefore it is possible to obtain low yields at high NUE. Attaining high yields is important in N fertility management, therefore farmers will not sacrifice high yields for a higher NUE. These results show that split fall/spring application of N at 50% fall and 50% spring or 25% fall and 75% spring, and applying all the N in the spring improved NUE for winter wheat production. These findings are consistent with Sowers et al. (1994) who reported that splitting N between fall and spring or supplying all the fertilizer N in the spring improved NUE over comparable all-fall applications for soft white winter wheat. The findings are also consistent with Mercedes et al. (1993) who reported higher NUE with split N-applications for winter wheat. Despite the fact that the three years during which the study was conducted were among the poorest years for winter wheat production in Missouri, split and all-spring application of N improved NUE.

4. Summary and Conclusion

The use of nitrapyrin did not influence soft red winter wheat grain yield in Missouri during the three year study. Increase in grain yield in response to specific split N application treatments ranged from 753 kg [ha.sup.-1] to 5852 kg [ha.sup.-1] across sites during the three year study. Grain yields were similar at Columbia in 1992, at Novelty in 1993 and at Portageville in 1991 when anhydrous ammonia was applied at 112 kg N [ha.sup.-1] regardless of nitrapyrin. There was a yield advantage to applying all of the N in the fall at Columbia in 1991 and Portageviile in 1992 compared with applying all of the N in the spring. On the contrary, a 907 kg [ha.sup.-1] yield advantage was achieved at Novelty in 1993 from applying all of the N in the spring compared to applying in fall with nitrapyrin. Winter wheat responded to N application at all harvested sites regardless of the variation in yield between sites. The N fertilization increased number of heads [m.sup.-2] but the increase in the number of seeds [head-.sup.-1] appeared to be dependent upon other environmental factors. Nitrogen fertilization did not affect the TKW and HI across sites during the three year study. These results suggest that most of the applied N was utilized in increasing the number of tillers and heads [m.sup.2] and in development of dry matter, especially the biological yield, indicative of the low HI values during the three year study.

Overall, NUE increased when an increasing proportion of the N was applied as Urea in the spring at Feekes GS 3. Splitting the fertilizer N application between anhydrous ammonia in fall and urea in spring at 50% fall and 50% spring or 25% fall and 75% spring, regardless of nitrapyrin treatment and applying all of the N in the spring resulted in higher NUE compared to all-fall or 75% fall and 25% spring application when averaged across locations. Nitrogen use efficiency was improved even in environments where grain yields were limited by other factors. It is important to mention that striving for higher NUE will not necessarily result in higher yields, and farmers would rather have high profitable yields regardless of NUE. Splitting N application can improve grain yield and NUE over a total allocation in fall. Improvement of NUE at the cost of yield is of little concern in N fertility management. Lack of yield response to nitrapyrin does not justify its use in soft red winter wheat production in Missouri based on the conditions experienced in this study. It should also be noted that during the three years this study was conducted, conditions in Missouri for soft red winter wheat production were particularly severe (floods, winterkill, and scab), possibly masking the wheat yield response to nitrapyrin applications.

Literature Cited

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Buchholz, D. D. and J. A. Schaeffer. 1990. Nitrogen rates and timing for winter wheat in Missouri. Missouri Soil Fertility Research Update Rep. No. 90-01. University of Missouri, Columbia.

Christensen, R. H. and J. R. Huffman. 1992. Response of corn to preplant applications of nitrogen and to nitrogen plus nitrapyrin. J. Prod. Agric. 5:353-357.

Gasser, J. K. R. 1965. Effects of 2-Chloro-(trichloromethyl)-pyridine on the nitrification of ammonium sulphate and its recovery by rye-grass. J. Agri. Sci. 64:299-303.

Goh, K. M. and A. W. Young. 1974. Effects of fertilizer nitrogen and 2-Chloro-6-(trichloromethyl)-pyridine and nitrogen uptake of 'Arawa' and 'Hilgendorf' wheat. New Zealand J. of Agric. Res. 18:215-225.

Hendrickson, L. L., D. R. Keeney, L. M Walsh and E. A. Liegel. 1978b. Evaluation of nitrapyrin as a means of improving N efficiency in irrigated sands. Agron. J. 70:699-703.

Hendrickson, L. L. and D. R. Keeney. 1979. Effect of some physical and chemical factors on the rate of hydrolysis of nitrapyrin (N-SERVE). Soil Biol. Biochem. 11:47-50.

Hendrickson, L. L., L. M. Walsh and D. R. Keeney. 1978a. Effectiveness of nitrapyrin in controlling of fall and spring-applied anhydrous ammonia. Agron. J. 70:704-708.

Hobbs, J. A. 1953. The effect of spring nitrogen fertilization on plant characteristics of winter wheat. Soil Sci. Soc. Am. Proc. 17:39-42.

Huber, D. M., H. L. Warren, D. W. Nelson, and C. Y. Tsai. 1977. Nitrification inhibitors - new tools for food production. Bioscience 27:523-529.

Huber, D. M., H. L. Warren, D. W. Nelson, C. Y. Tsai and G. E. Shaner. 1980. Response of winter wheat to inhibiting nitrification of fall-applied nitrogen. Agron. J. 72:632-636.

Kidwaro, F. M. and K. D. Kephart. 1997. Retention of nitrogen from stabilized anhydrous ammonia in the soil profile during winter wheat production in Missouri. Commun. Soil Sci. Plant Anal J. 29:481-499

Liu, S. L., E. C. Varsa, G. Kapusta and D. N. Mburu. 1983. Effect of etridiazol and nitrapyrin treated N fertilizers on soil mineral N status and wheat yields. Agron. J. 76:265-270.

Marschner, Horst. 1995. Mineral Nutrition of Higher Plants. Academic Press, London.

Mercedes, M. A., F. M. Hons and V. A. Haby. 1993. Nitrogen fertilization timing effect on wheat production, nitrogen uptake efficiency, and residual soil nitrogen. Agron. J. 85:1198-1203.

Parr, J. F., B. R. Carroll, and S. Smith. 1971. Nitrification inhibition in soil: I. A comparison of 2-Chloro-6-(trichloromethyl)-pyridine and potassium Azide formulated with anhydrous ammonia. Soil Sci. Soc. Am. Proc. 35:469-473.

Prasad, R., G. B. Rajale, and B. A. Lakhdive. 1971. Nitrification retarders and slow-release nitrogen fertilizers. Adv. Agron. 23:337-383.

Richardson, A. E. V., and E. F. Fricke. 1931. Effect of nitrogenous fertilizer on the growth and yield of wheat and barley. J. Dept. Agric. So. Aust. 35:57-86.

Shaviv, A., J. Hagin and P. M. Neumann. 1987. Effects of a nitrification inhibitor on efficiency of nitrogen utilization by wheat and millet. Comm. in Soil Sci. and Plant Analysis 18:815-833.

Sowers, K. E., W. L. Pan, B. C. Miller and J. L. Smith. 1994. Nitrogen use efficiency of split nitrogen applications in soft white winter wheat. Agron. J. 86:942-948.

Touchton, J. T., R. G. Hoeft and L. F. Welch. 1978. Effect of nitrapyrin on nitrification of fall and spring-applied anhydrous ammonia. Agron. J. 70:805-810.

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Fanson M. Kidwaro (2), and Kenneth D. Kephart

(1) This paper is a contribution from the Missouri Agriculture Experiment Station, Journal Series No. 12 ,457.

(2) Corresponding author Dept. of Agriculture, College of Applied Science and Technology, Central Missouri State University. 126 Grinstead Hall, Warrenburg, Missouri 64093.

Table 1. Grain yield of soft red winter wheat at Columbia, Novelty
and Portageville, Missouri, from 1991 to 1993 at various split fall/
spring applications totaling 112 kg N [ha.sup.-1]. Anhydrous ammonia
was applied in fall with and without nitrapyrin. W/ = With nitrapyrin
and W/O = Without nitrapyrin.

                       Columbia             Novelty      Portageville
 Fall/Spring
  ([dagger])     1991    1992    1993    1991    1993    1991    1992
   Nitrogen
 Application

     kg N
 [ha.sup.-1]                     kg [ha.sup.-1]

W/ Nitrapyrin
    112/0        2,559   2,049   4,327    651    2,170   1,115   5,670
    84/28        2,492   2,237   4,427    745    2,600   1,222   5,838
    56/56        2,385   2,385   4,380    752    2,687   1,377   6,215
    28/84        2,486   2,103   4,280    853    2,989   1,417   6,303

W/O Nitrapyrin
    112/0        2,425   1,968   4,125    732    2,358   1,431   5,838
    84/28        2,633   1,921   4,138    678    2,103   1,216   6,369
    56/56        2,580   2,284   4,609    826    2,593   1,518   6,302
    28/84        2,445   2,224   4,394    913    2,889   1,437   6,060
    0/112        2,176   2,049   4,280    766    3,077   1,222   4,132
     0/0         1,404    826    3,554    483    1,148    342    4,132

Mean             2,358   2,008   4,253    752    2,391   1,229   5,852
LSD (0.05)        282     336     530     282     389     235     705

([dagger]) Nitrapyrin used with fall applications of anhydrous ammonia.
Spring nitrogen as urea was surface topdressed at initial greenup
(Feeke's GS 3).

Table 2. Yield components for soft red winter wheat at Columbia,
Novelty and Portageville, Missouri from 1991 to 1993 at various
split fall/spring applications of 112 kg N [ha.sup.-1] as
anhydrous ammonia with and without nitrapyrin. W/ = with
nitrapyrin and W/O = without nitrapyrin.

                                   Columbia

                                     1991
Fall/Spring
([dagger])                                           1,000
Nitrogen             Heads           Seeds          Kernel
Application       [m.sup.-2]     [Head.sup.-1]      Weight

     kg N
 [ha.sup.-1]                                           g

W/ Nitrapyrin
    112/0            777.4           28.7            24.6
    84/28            696.7           31.1            26.3
    56/56            734.3           30.9            28.0
    28/84            723.6           28.4            28.0

W/O Nitrapyrin
    112/0            766.6           29.8            24.5
    84/28            677.9           27.4            26.0
    56/56            745.1           26.6            24.1
    28/84            707.4           25.8            27.0
    0/112            677.9           28.0            30.4
     0/0             419.6           25.8            28.2

Mean                 692.6           28.5            26.7
LSD (0.05)           139.8            6.2             3.4

                                   Columbia

                                     1992
Fall/Spring
([dagger])                                           1,000
Nitrogen             Heads           Seeds          Kernel
Application       [m.sup.-2]     [Head.sup.-1]      Weight

     kg N
 [ha.sup.-1]                                           g

W/ Nitrapyrin
    112/0            404.2           53.5            23.5
    84/28            356.5           61.1            23.8
    56/56            395.6           49.6            32.1
    28/84            384.9           55.0            22.9

W/O Nitrapyrin
    112/0            276.0           48.9            33.8
    84/28            325.6           54.4            32.2
    56/56            419.1           49.9            27.1
    28/84            416.1           53.3            23.6
    0/112            383.5           57.0            16.8
     0/0             197.4           42.1            11.9

Mean                 355.9           52.5            24.8
LSD (0.05)           62.2            10.4            12.9

                            Columbia

                              1993
Fall/Spring
([dagger])
Nitrogen             Heads           Seeds
Application       [m.sup.-2]     [Head.sup.-1]

     kg N
 [ha.sup.-1]

W/ Nitrapyrin
    112/0            421.0           33.6
    84/28            445.5           36.1
    56/56            446.5           33.7
    28/84            339.0           34.6

W/O Nitrapyrin
    112/0            459.5           34.0
    84/28            431.0           33.0
    56/56            463.5           32.7
    28/84            477.5           34.2
    0/112            499.5           38.5
     0/0             344.5           25.7

Mean                 441.5           33.6
LSD (0.05)           69.0             4.4

                                    Novelty

                     1991                   1993
Fall/Spring
([dagger])
Nitrogen             Heads           Heads           Seeds
Application       [m.sup.-2]      [m.sup.-2]     [Head.sup.-1]

     kg N
 [ha.sup.-1]

W/ Nitrapyrin
    112/0            170.4           423.5           23.5
    84/28            201.0           406.5           26.3
    56/56            192.0           534.5           26.1
    28/84            183.9           427.5           26.0

W/O Nitrapyrin
    112/0            187.5           377.5           19.5
    84/28            168.0           528.0           23.3
    56/56            204.0           443.5           27.1
    28/84            195.0           453.5           26.2
    0/112            175.5           462.5           29.3
     0/0             102.0           321.5           19.5

Mean                 177.9           438.5           24.7
LSD (0.05)           41.1            105.0            3.1

                                 Portageville

                                     1992
Fall/Spring
([dagger])                                           1,000
Nitrogen             Heads           Seeds          Kernel
Application       [m.sup.-2]     [Head.sup.-1]      Weight

     kg N
 [ha.sup.-1]                                           g

W/ Nitrapyrin
    112/0            438.5           41.1            35.5
    84/28            536.3           39.9            34.0
    56/56            632.8           42.9            34.5
    28/84            488.3           39.9            34.0

W/O Nitrapyrin
    112/0            447.1           41.1            34.5
    84/28            560.9           40.2            33.9
    56/56            568.9           41.6            32.9
    28/84            559.7           42.3            32.9
    0/112            559.7           38.3            35.3
     0/0             356.7           39.1            35.3

Mean                 514.9           40.6            34.3
LSD (0.05)           132.7            4.8             2.9

([dagger]) Nitrapyrin only used with fall applications of anhydrous
ammonia. Spring nitrogen applied in the form of urea surface topdressed
at initial greenup.

Table 3 Harvest index and total nitrogen in stem and grain tissue
of soft red winter wheat at Columbia, Novelty and Portageville,
Missouri from 1991 to 1993 at various split fall/spring applications
of 112 kg N [ha.sup.-1] as anhydrous ammonia with and without
nitrapyrin. W/ = with nitrapyrin and W/O = without nitrapyrin.
Total N = Straw N + Grain N.

                                  Columbia
 Fall/Spring            1991                       1992
  ([dagger])
   Nitrogen      Harvest       Total        Harvest       Total
 Application      Index          N           Index          N

     kg N
 [ha.sup.-1]        %      kg [ha.sup.-1]      %      kg [ha.sup.-1]

W/ Nitrapyrin
    112/0         27.5         104.2         10.9          31.9
    84/28         27.2          86.2         10.3          39.9
    56/56         17.5          84.0          9.3          48.9
    28/84         25.9          86.2         11.4          45.1

W/O Nitrapyrin
    112/0         27.5          92.9          7.7          37.9
    84/28         26.9          90.7          9.1          38.8
    56/56         18.7          82.9         10.1          39.9
    28/84         27.8          71.7          9.4          45.4
    0/112         22.5          69.4         11.3          45.8
     0/0          27.8          40.3         17.6          15.6

Mean              24.8          80.6         10.7          38.9
LSD (0.05)         6.6          22.4          3.9          7.4

                      Columbia                  Novelty

 Fall/Spring            1993                       1993
  ([dagger])
   Nitrogen      Harvest       Total        Harvest       Total
 Application      Index          N           Index          N

     kg N
 [ha.sup.-1]        %      kg [ha.sup.-1]      %      kg [ha.sup.-1]

W/ Nitrapyrin
    112/0         33.2          89.7         23.7          51.6
    84/28         29.9          90.9         26.0          55.7
    56/56         30.3          92.3         25.2          56.6
    28/84         29.1          95.4         26.6          60.8

W/O Nitrapyrin
    112/0         31.8          75.9         24.6          40.0
    84/28         32.0          87.0         23.2          46.5
    56/56         32.1          91.7         25.8          51.9
    28/84         26.8          99.5         23.6          59.4
    0/112         28.0          98.3         26.4          62.7
     0/0          32.8          62.9         24.5          29.1

Mean              30.6          88.4         25.0          51.5
LSD (0.05)         4.4          12.1          2.8          10.4

                   Portageville

 Fall/Spring            1992
  ([dagger])
   Nitrogen      Harvest       Total
 Application      Index          N

     kg N
 [ha.sup.-1]        %      kg [ha.sup.-1]

W/ Nitrapyrin
    112/0         40.3          78.1
    84/28         41.9          87.2
    56/56         41.2          90.5
    28/84         39.9          94.4

W/O Nitrapyrin
    112/0         40.5          92.2
    84/28         40.6          97.8
    56/56         41.3          99.9
    28/84         39.9          97.6
    0/112         42.3          88.7
     0/0          42.1          53.4

Mean              41.0          88.0
LSD (0.05)         2.3          18.3

([dagger]) Nitrapyrin only used with fall applications of anhydrous
ammonia. Spring nitrogen applied in the form of urea surface topdressed
at initial greenup (Feeke's GS 3).

Table 4. Nitrogen Use Efficiency of soft red winter wheat at Columbia,
Novelty and Portageville, Missouri from 1991 to 1993 at various split
fall/spring applications of 112 kg N ha-1 as anhydrous ammonia with
and without nitrapyrin. W/ = with nitrapyrin and W/O = without
nitrapyrin.

  Fall/Spring            Nitrogen Use Efficiency
   ([dagger])
    Nitrogen          Columbia      Novelty   Portageville
  Application
kg N [ha.sup.-1]    1992     1993     1993         1992

W/ Nitrapyrin
     112/0          14.6     23.9     20.0         22.0
     84/28          21.7     25.0     23.7         30.2
     56/56          29.8     26.2     24.4         33.1
     28/84          26.4     29.0     28.2         36.6

W/O Nitrapyrin
     112/0          20.0     11.6      9.5         34.6
     84/28          20.7     21.5     15.4         39.6
     56/56          21.7     25.7     20.3         41.5
     28/84          26.6     32.7     26.9         39.4
     0/112          27.0     31.6     30.8         31.5
Mean                23.2     25.2     22.1         34.3
LSD (0.05)          NS       NS       NS           NS

([dagger]) Nitrapyrin only used with fall applications of anhydrous
ammonia. Spring nitrogen applied in the form of urea surface topdressed
at initial greenup (Feeke's GS 3).