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PRODUCTION PAPERS

Placement of UAN for Dryland Winter Wheat in the Central High Plains

^a Southwest Research-Extension Center, Kansas State Univ., Tribune, KS 67879
^b Dep. of Agricultural Economics, Kansas State Univ., Manhattan, KS 66506
^c Dep. of Soil Science, North Carolina State Univ., Raleigh, NC 27695

^* Corresponding author (schlegel{at}ksu.edu).

Received for publication November 19, 2002.

	ABSTRACT

TOP NOTES ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION CONCLUSIONS REFERENCES

 
Research was initiated in 1993 to determine the N fertilizer requirement for dryland winter wheat (Triticum aestivum L.) grown under reduced tillage systems in western Kansas. Six sites in west-central Kansas were selected each year for 4 yr in cooperation with area farmers. The typical cropping system was wheat-fallow with reduced tillage practices. All sites were on silt loam soil that ranged in residual soil nitrate-N content from 2 to 9 mg kg^-1 (0- to 60-cm sample). Crop residue cover at wheat planting averaged 28%. Fluid N (28% N as urea-ammonium nitrate solution, UAN) was injected in the fall and spring and surface broadcast during the winter and spring at five rates (22, 45, 67, 90, and 112 kg ha^-1) along with a zero N control. Typical production practices consisted of planting winter wheat in mid-September with a hoe-type drill. Grain protein increased linearly with increased N rates with greater than 130 g kg^-1 when 112 kg N ha^-1 was injected. Apparent fertilizer N recovery decreased with increased N rates, but was consistently higher with fall or spring injected rather than winter or spring broadcast UAN. The straw/yield ratio was greater than 2 across all N rates, which is greater than the commonly used value of 1.7. The soil N test was an indicator of yield response to N fertilization. Grain yields increased in 10 of 13 site-years with N fertilizer. Average grain yields were 8% greater from spring injected than broadcast UAN. The time of N application had little effect on grain yield. Economic analysis indicated that injecting UAN in the fall or spring was more profitable than topdressing UAN in the winter or spring because of improved yields and/or lower total N costs. These data suggest that N rate recommendations should vary with application method.

	INTRODUCTION

TOP NOTES ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION CONCLUSIONS REFERENCES

 
WINTER WHEAT is the predominant dryland crop grown in the central Great Plains. In Kansas, about 85% of the total wheat production occurs in the western 2/3 of the state. However, much of the productive land is highly erodible. Of the 4 to 5 million hectares of wheat in Kansas, approximately 70% of the land is classified as highly erodible (USDA-SCS, 1992). In some western Kansas counties, 100% of the cropland is considered highly erodible. To control erosion on these lands, over 50% of the NRCS (Natural Resources Conservation Service) conservation farm plans include at least 30% surface crop residue cover and in some counties as many as 95% of the farm plans include surface crop residues for erosion control.

Adoption of reduced tillage practices to maintain surface crop residue cover for erosion control will influence water balance and N management. Reduced tillage systems tend to increase precipitation capture and soil water storage, affect nutrient cycling by less residue incorporation into the soil, and enhance yield potential. Soil water at wheat planting was 28% greater and wheat yields were 12% greater with reduced tillage compared with conventional tillage in a wheat–fallow rotation in western Kansas (Norwood et al. 1990). Apparent fertilizer N recovery (AFNR) with broadcast N can be significantly reduced in high residue cropping systems. Research in eastern Kansas found that injected UAN applied to no-till grain sorghum [Sorghum bicolor (L.) Moench] increased AFNR and grain yield by 0.9 Mg ha^-1 compared with broadcast UAN (Lamond et al., 1991). Jacobsen and Westermann (1988) reported fall-broadcast urea N requirements for dryland winter wheat were 28 kg ha^-1 greater with no-till than with conventional tillage. Therefore, N fertilizer recommendations may need to be adjusted for reduced and no-till cropping systems. Nitrogen soil test calibration data collected several decades ago were based on clean-tillage cropping systems. Kolberg et al. (1996) reported that current N fertilizer recommendations for wheat and corn (Zea mays L.) were not adequate to ensure maximum production under no-till management in eastern Colorado.

In western Kansas, approximately 68% of the wheat acreage in 1995 was fertilized with N before seeding and 15% after seeding (Cress, 1996). A prior survey in 1991 found 67% of the wheat fertilized before seeding and 10% after seeding (Cress, 1992). Broadcast N applications accounted for 10% of the fertilized wheat acreage in western Kansas in 1991, but increased to 32% by 1995. In other areas of the state, the proportion of broadcast N was higher with 69% in central Kansas and 90% in eastern Kansas in 1995. These surveys suggest that topdress N fertilization practices are becoming increasingly more common. There are potential benefits from delayed N applications. In Colorado, 10 to 25% additional fall broadcast N was required to optimize grain yield compared with spring topdress N; however, this study was conducted under clean-tillage systems (Vaughan et al., 1990). McInnes et al. (1986) found that ammonia volatilization losses were 7.6 to 16.6% from UAN broadcast applied to soil with wheat straw residue cover in eastern Kansas.

Nielsen and Halvorson (1991) reported that N fertilizer increased grain yield, above-ground biomass, rooting depth, and water use efficiency of dryland winter wheat in eastern Colorado. However, they found that high N fertility levels could be detrimental to wheat yields under conditions of severe water-stress. Kolberg et al. (1996) showed that with more available water in the soil for wheat, more grain was produced per unit of N uptake (physiological efficiency). Wagger et al. (1979) increased physiological N efficiency of dryland wheat by supplemental irrigation in western Kansas. Campbell et al. (1993) showed lower NUE with spring wheat in years of severe water stress and greater NUE in years having more favorable moisture conditions.

Development of the point-injection fertilizer applicator has provided an additional fluid fertilizer placement option in reduced tillage cropping systems (Baker et al., 1989). The advantage of point-injection is that it allows fertilizer placement in the root zone with minimal soil disturbance where it is readily available for crop uptake and increases the time period for N applications with N application after crop establishment. Another benefit from all injected methods compared with surface broadcast is that precipitation is not needed to move the N into the root zone. Point-injected N was as good or slightly better than knife applications in corn (Baker et al., 1989). In Alberta, Canada, Janzen et al. (1991) compared N timing and application method in no-till winter wheat and obtained maximum fertilizer N recovery with early spring point-injected N compared with N broadcast in early spring or late fall. Few N management studies comparing point injection with other placement methods have been conducted in the central Great Plains.

Information is needed to improve N fertilizer recommendations for dryland winter wheat grown under conservation tillage systems in the central Great Plains. The objectives of this research were to (i) quantify the relationship between winter wheat grain yield, residual soil nitrate, fertilizer N rate, and residue cover; (ii) relate the impact of fertilizer placement and time of application on grain yield, grain protein, and economic optimum N rate; and (iii) determine whether current N fertilizer recommendation models are adequate for wheat grown under conservation tillage systems.

	MATERIALS AND METHODS

TOP NOTES ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION CONCLUSIONS REFERENCES

 
Field experiments were conducted continuously from 1993 to 1997 in western Kansas in cooperation with area farmers. All sites had silt loam soils that are representative of about 1.6 million hectares in the central High Plains (Table 1). Soil samples (0- to 15- and 15- to 60-cm depth) were collected in the control treatments when making the initial fertilizer applications with values reported for each site. Soil pH (7.4–8.2) and organic matter (14–22 g kg^-1) at all sites were typical of soils in this region. Residual soil NO₃–N content (0- to 60-cm depth) at planting averaged 43 kg ha^-1 and ranged from 18 to 74 kg ha^-1 (2–9 mg kg^-1). Soil test P levels were above the critical level at all sites. Surface residue cover was measured using the line-transect method after wheat planting and averaged about 28%, ranging from less than 10% to greater than 60%. The typical cropping system was wheat-fallow using reduced tillage practices.

Nitrogen rates were 22, 45, 67, 90, and 112 kg ha^-1 along with a zero N control. The point-inject applicator had eight spokewheels (manufactured by Spoke Injector Systems, Inc., Lemberg, SK) on 38-cm spacing (total width of 3 m) with 15-cm spacing between spokes on the wheels. Janzen and Lindwall (1989) reported an optimum injection interval of 40 cm. Fluid N was delivered by a compressed air system mounted on the applicator. Flow rate was controlled by use of individual flow regulators (Spraying Systems Co., Wheaton, IL) placed in the fertilizer delivery line to each spokewheel. The various N rates were obtained by varying pressure, solution N concentration, and application speed. The spokewheels placed fluid N 6 to 8 cm into the soil with minimal soil disturbance. The injection depth was slightly less than the optimal injection depth of 10 cm (Janzen and Lindwall, 1989). The broadcast applications were made with a 3-m spray boom with eight XR flat spray tips (Spraying Systems Co.) at 38-cm spacing on a tractor-mounted applicator. Fluid N was delivered to the spray boom by compressed air. Similar to the spokewheel applicator, the various broadcast N rates were obtained by varying pressure, solution N concentration, and application speed. Both applicators were calibrated to deliver the same N rates by collecting output and determining flow rate before field applications. All applications were made perpendicular to the direction of the wheat rows to minimize interference with the planted rows. Plot size was 3.0 by 12.2 m. The experimental design was a randomized complete block with four replications in all site-years.

The farmer cooperators performed all tillage and planting operations. Typical production practices consisted of reduced tillage with a sweep plow to control weeds during the fallow period. Wheat was generally seeded in mid-September with a hoe drill on 30-cm row spacing. The wheat cultivars were TAM 107 and Larned seeded at about 50 kg ha^-1.

The center of each plot (harvest width of 1.8 m) was combine-harvested with grain yields adjusted to 125 g kg^-1 moisture. The wheat at several sites was damaged by adverse weather (hail and spring freeze damage), thus only 13 site-years (out of 24 established) are included in the analysis. While these weather perils can have a significant impact on the economic optimal fertilizer strategy because they occur after the spring application of N they are not particularly relevant to the wheat fertilizer decision-making process. Thus, it is appropriate to exclude them from the analysis. Furthermore, N fertilizer applied in these years, either in the fall or spring, would at least partially be utilized by the next crop in the event wheat freezes out. Aboveground biomass (0.3-m² area) of straw and grain was collected from each plot at harvest, oven-dried, and weighed. Straw was calculated as aboveground biomass minus grain yield (determined by combine harvest). The straw/yield ratio was calculated as straw (kg ha^-1) divided by grain yield (kg ha^-1). Grain samples collected at harvest were dried, ground to pass a 1-mm screen, and digested by a sulfuric acid and hydrogen peroxide digest (Isaac, 1977). Grain N was determined with a Technicon Autoanalyzer using Technicon Industrial Method 334-74 W/B (Technicon Industrial Systems, 1977). Grain protein was calculated as grain N times 5.7 (Association of Official Analytical Chemists, 1984). Apparent fertilizer N recovery was calculated as the increase in grain N in treatments receiving fertilizer N over that of the control treatment divided by the fertilizer N rate (Boman et al., 1995).

Analysis of variance was performed to evaluate treatment effects on grain yield and grain protein by the GLM routine of SAS (SAS Institute, 1996). Single degree of freedom contrasts were used to compare spring broadcast vs. spring inject, broadcast winter vs. spring, and injected fall vs. spring. The main effect of N rate was partitioned into linear and quadratic relationships.

On the basis of the analysis of variance results, economic optimum N rates were calculated by a quadratic production function with grain yield as a function of residual soil NO₃–N, surface residue cover at planting, rate of fertilizer N, method of N placement, and year.

The yield response function was specified as

[1]

where Y = grain yield of winter wheat, Mg ha^-1; SN = residual soil NO₃–N, kg ha^-1; IN = injected fertilizer N, kg ha^-1; BN = broadcast fertilizer N, kg ha^-1; RES = surface residue, %; Y94 = year effect for 1994; Y95 = year effect for 1995; Y96 = year effect for 1996; e = error term; and ß = parameters to be estimated.

The model was estimated by ordinary least squares techniques (SAS, 1996). The year variables were used to account for the yield variation among years. Although other functional relationships are possible, a quadratic function was used because yields increased at a decreasing rate across the range of N rates. Quadratic production functions have been used by others to estimate yields (Mjelde et al., 1991; Arce-Diaz et al., 1993; Vanotti and Bundy, 1994). The N rate of broadcast and injected fertilizer N required for maximum grain yield, at selected residual soil NO₃–N contents, were found by equating the first derivative of the production function to zero and solving for N.

Once the production function was estimated, net returns (NR) to N fertilizer were calculated by the following Eq. [2].

[2]

where Y = grain yield of winter wheat in Mg ha^-1 from the production function in Eq. [1]; P_w = price of winter wheat, $ Mg^-1; N = N rate, kg ha^-1; P_n = price of N, $ kg^-1; AC = application costs, $ ha^-1.

Production expenses, other than N fertilizer and application costs, were considered constant for all fertilizer treatments and thus are not included in the analysis. Price and cost assumptions were based on typical values in the region during the study period and were N at $0.49 kg^-1, winter wheat at $119 Mg^-1, application cost for injected N at $13.86 ha^-1, and application cost for broadcast N at $8.72 ha^-1. The economic optimal injected and broadcast N rates were calculated by setting the first derivative of the profit function (Eq. [2]) to zero and solving for N (note—this is mathematically equivalent to taking the derivative of the yield function (Eq. [1]) and setting it equal to the N/wheat price ratio and solving for N).

	RESULTS AND DISCUSSION

TOP NOTES ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION CONCLUSIONS REFERENCES

 
Maximum grain yield with fertilizer N treatments ranged from 2.5 to 4.2 Mg ha^-1 across all site-years while grain yield in the control treatments ranged from 0.9 to 3.1 Mg ha^-1 (Table 2). Grain yield was increased in 10 out of 13 site-years by N fertilization. There was no yield response to N fertilizer at two site-years and at one site-year N fertilizer linearly decreased grain yield. At all sites with increased yields, there was a highly significant (P > F = 0.001) linear grain yield response to N rate. In eight out of 10 positive response sites, there was also a significant (P > F = 0.05 or less) quadratic response. Grain yield response varied across site-years from a negative 0.4 to a positive 1.8 Mg ha^-1 and generally increased with decreased levels of residual soil NO₃–N. When residual soil NO₃–N was <20 kg ha^-1, grain yield of the control treatment was <50% of the yield of the highest yielding treatment in two out of three site years. Of the three site-years where yields were not increased by N fertilizer, residual soil NO₃–N was >50 kg ha^-1, although there were also two site-years with >50 kg ha^-1 residual soil NO₃–N where yields did improve with fertilizer N.

When fertilizer N was point-injected in positive responsive site-years, the time of application was significant 60% of the time (6 of 10 site-years). In four of the six site-years, greater yields were obtained with fall than spring point-inject and the reverse was true in the other two site-years. Janzen et al. (1991) reported no difference in grain yield of winter wheat from varying application times of point-injected UAN, broadcast urea, and broadcast ammonium nitrate from seeding to late spring. When averaged across all responsive site-years and N rates, there was no difference in yield between fall and spring injected treatments. This indicates that there was little over-winter loss from fall N applications. For broadcast applications, there were yield differences between winter and spring applications at only two site-years. At one site-year, grain yields were higher with winter broadcast while at the other site-year yields were higher with the spring application. Christensen and Meints (1982) reported greater fertilizer N uptake and winter wheat yields from spring compared with fall broadcast urea. When averaged across all responsive site-years, grain yields were the same for winter and spring broadcast treatments, which indicates that there is a considerable time period for topdress N application with minimal impact on grain yield.

The results from estimating Eq. [2] with ordinary least squares (OLS) regression are reported in Table 3. All fertility variables were statistically significant with the exception of soil NO₃–N squared and broadcast N squared. Also, all variables had signs consistent with diminishing returns (i.e., positive linear term and negative quadratic term). Since averaged across all N rates and site-years, there was no yield difference between injecting UAN in the fall or spring or broadcasting UAN in the winter or spring, the time of application variable was not included in the model. Residue positively affected yields up to a residue cover level of 47% at which point increased levels of residue negatively affected yields. The projected yields from injected and broadcast UAN varied with N rate and residual soil N content (Fig. 1) . The difference in yield from injected vs. broadcast N was greater at lower residual soil N levels. For example, at a low soil N content (24 kg ha^-1 residual soil NO₃–N) injection of 70 kg ha^-1 of UAN produced 2.98 Mg ha^-1 of wheat compared with 2.66 Mg ha^-1 when broadcast, a difference of 0.32 Mg ha^-1. The yield difference between application methods at a higher residual soil N level (62 kg ha^-1 residual soil NO₃–N) with the same 70 kg ha^-1 application was 0.19 Mg ha^-1 (3.41 vs. 3.22 Mg ha^-1).

View larger version (21K): [in this window] [in a new window]   Fig. 1. Projected wheat yield response to fertilizer N rate and application method at two residual soil N levels. The time of application was fall and spring for injected and winter and spring for broadcast applications.

View larger version (17K): [in this window] [in a new window]   Fig. 2. Estimated economic optimal fertilizer N rate for fall or spring injected and winter or spring broadcast UAN to winter wheat.

The current Kansas State University N recommendation model (revised 2002) uses yield goal, residual soil N, and soil organic matter content to estimate N fertilizer recommendations, along with credits for previous legume crops or manure applications, if applicable. The general form of the model is

[3]

where N_rec = fertilizer N recommendation, kg ha^-1; YG = yield goal, Mg ha^-1; OM = organic matter, g kg^-1; PN = profile (0- to 60-cm depth) soil NO₃–N, kg ha^-1.

On the basis of this model and the average soil organic matter from this study (18 g kg^-1), the total amount of fertilizer and residual soil N required to obtain the average optimal yield for injected N (about 3.3 mg ha^-1) would be 112 kg ha^-1. Since yield goals are often set 5 to 10% higher than average yields, the KSU recommendation model adequately predicts N needs in this study of 128 kg ha^-1 total available N (fertilizer plus residual soil N) when N is injected. However, with winter and spring broadcast UAN, the KSU model considerably under-recommends N fertilizer requirements, particularly at lower residual soil N levels, because it does not account for lower efficiency from late broadcast N applications.

Grain protein increased with increased N rate at all site-years (Table 4), even in those site-years where yields did not increase with N application. Averaged across all site-years, grain protein increased 15 g kg^-1 by application of 112 kg N ha^-1. In about half of the site years the time/method of application had a significant effect on grain protein; however, the magnitude of the response was much less than the effect from N rate. For example, averaged across all site-years, the difference in grain protein between spring injected and spring broadcast UAN was significant but only 2 g kg^-1. Similarly, the difference between time of application for injected and broadcast UAN was only 1 g kg^-1.

Averaged across all site-years and N rates (excluding the control), AFNR was 25% for injected (average of fall and spring) compared with 17% for broadcast (average of winter and spring) UAN (Fig. 3) . There was no significant difference in AFNR between fall and spring injected UAN (24 vs. 26%) indicating there was little over-winter loss. In contrast, Janzen et al. (1991) reported greater fertilizer N recovery with early spring compared with fall applications in Alberta presumably because of over-winter N losses with fall applications. They also reported higher fertilizer N recovery from early spring applications of point-injected UAN compared with broadcast ammonium nitrate or urea. There was no difference in AFNR between winter and spring broadcast UAN (17% for both times). While AFNR for broadcast UAN remained constant across N rates, the AFNR for injected UAN decreased with increased N rates from 28% at the lowest N rate to 21% at the highest N rate. Similarly, Boman et al. (1995) reported that AFNR in wheat decreased from 29 to 25% when N rates increased from 33 to 101 kg ha^-1.

View larger version (11K): [in this window] [in a new window]   Fig. 3. Apparent fertilizer N recovery by wheat as affected by UAN broadcasted (winter and spring) and injected (fall and spring), average of 13 site-years, west-central Kansas.

View larger version (9K): [in this window] [in a new window]   Fig. 4. The ratio of straw production to grain yield as affected by N fertilization, average of 13 site-years, west-central Kansas.

	CONCLUSIONS

TOP NOTES ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION CONCLUSIONS REFERENCES

	NOTES

TOP NOTES ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION CONCLUSIONS REFERENCES

 
Contribution no. 03-173 of the Kansas Agric. Exp. Stn. Support for this research was provided by the Kansas Fertilizer Research Fund. Mention of a trade name is for identification only and does not imply endorsement or preference to other products not mentioned.

	REFERENCES

TOP NOTES ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION CONCLUSIONS REFERENCES

 

• Association of Official Analytical Chemists. 1984. Method 14.067. p. 259. In Official Methods of Analysis. Assoc. Official Analytical Chemists, Inc., Arlington, VA.
• Arce-Diaz, E., A.M. Featherstone, J.R. Williams, and D.L. Tanaka. 1993. Substitutability of fertilizer and rainfall for erosion in spring wheat production. J. Prod. Agric. 6:72–76.
• Baker, J.L., T.S. Colvin, S.J. Marley, and M. Dawelbeit. 1989. A point-injection applicator to improve fertilizer management. Appl. Eng. Agric. 5:334–338.
• Boman, R.K., R.L. Westerman, W.R. Raun, and M.E. Jojola. 1995. Spring-applied nitrogen fertilizer influence on winter wheat and residual soil nitrate. J. Prod. Agric. 8:584–589.
• Campbell, C.A., R.P. Zentner, F. Selles, B.G. McConkey, and F.B. Dyck. 1993. Nitrogen management for spring wheat grown annually on zero tillage: Yields and nitrogen use efficiency. Agron. J. 85:107–114.[Abstract/Free Full Text]
• Christensen, N.W., and V.W. Meints. 1982. Evaluating N fertilizer sources and timing for winter wheat. Agron. J. 74:840–844.[Abstract/Free Full Text]
• Cress, D.C. 1992. Kansas Agricultural Chemical Usage–1991 Sorghum and wheat summary. Kansas State University Cooperative Extension, Manhattan, KS. MF-1045.
• Cress, D.C. 1996. Kansas agricultural chemical usage–1995 wheat pesticide summary. MF-2215, Kansas State University Cooperative Extension, Manhattan, KS
• Daigger, L.A., D.H. Sander, and G.A. Peterson. 1976. Nitrogen content of winter wheat during growth and maturation. Agron. J. 68:815–818.[Abstract/Free Full Text]
• Goos, R.J., D.G. Westfall, A.E. Ludwick, and J.E. Goris. 1982. Grain protein content as an indicator of N sufficiency for winter wheat. Agron. J. 74:130–133.[Abstract/Free Full Text]
• Isaac, R.A. 1977. Total N determination in plant tissue. p. 65. In R.A. Isaac (ed.) Laboratory procedures for soil and plant analysis. Georgia Exp. Stn., Athens, GA.
• Jacobsen, J.S., and R.L. Westermann. 1988. Nitrogen fertilization in winter wheat tillage systems. J. Prod. Agric. 1:235–239.
• Janzen, H.H., and C.W. Lindwall. 1989. Optimum application parameters for point injection of nitrogen in winter wheat. Soil Sci. Soc. Am. J. 53:1878–1883.[Abstract/Free Full Text]
• Janzen, H.H., T.L. Roberts, and C.W. Lindall. 1991. Uptake of point-injected nitrogen by winter wheat as influenced by time of application. Soil Sci. Soc. Am. J. 55:259–264.[Abstract/Free Full Text]
• Karlen, D.L., and D.A. Whitney. 1980. Dry matter accumulation, mineral concentrations, and nutrient distribution in winter wheat. Agron. J. 72:281–288.[Abstract/Free Full Text]
• Kolberg, R.L., N.R. Kitchen, D.G. Westfall, and G.A. Peterson. 1996. Cropping intensity and nitrogen management impact of dryland no-till rotations in the semi-arid Western Great Plains. J. Prod. Agric. 9:517–522.
• Lamond, R.E., D.A. Whitney, J.S. Hickman, and L.C. Bonczkowski. 1991. Nitrogen rate and placement for grain sorghum production in no-tillage systems. J. Prod. Agric. 4:531–535.
• McInnes, K.J., R.B. Ferguson, D.E. Kissel, and E.T. Kanemasu. 1986. Ammonia loss from applications of urea-ammonium nitrate solution to straw residue. Soil Sci. Soc. Am. J. 50:969–974.[Abstract/Free Full Text]
• Mengel, D.B., D.W. Nelson, and D.M. Huber. 1982. Placement of nitrogen fertilizers for no-till and conventional till corn. Agron. J. 74:515–518.[Abstract/Free Full Text]
• Mjelde, J.W., J.T. Cothren, M.E. Rister, F.M. Hons, C.G. Coffman, C.R. Shumway, and R.G. Lemon. 1991. Integrating data from various field experiments: The case of corn in Texas. J. Prod. Agric. 4:139–147.
• Nielsen, D.C., and A.D. Halvorson. 1991. Nitrogen fertility influence on water stress and yield of winter wheat. Agron. J. 83:1065–1070.[Abstract/Free Full Text]
• Norwood, C.A., A.J. Schlegel, D.W. Morishita, and R.E. Gwin. 1990. Cropping system and tillage effects on available soil water and yield of grain sorghum and winter wheat. J. Prod. Agric. 3:356–362.
• SAS Institute. 1996. SAS user's guide: Statistics. Version 6.12 ed. SAS Inst., Cary, NC.
• Technicon Industrial Systems. 1977. Individual simultaneous determination of N and/or P in acid digests. p. 1–7 In Industrial Method No. 334–74 W/B. Technicon Industrial Systems, Tarrytown, NY.
• Vanotti, M.B., and L.G. Bundy. 1994. An alternative rationale for corn nitrogen fertilizer recommendations. J. Prod. Agric. 7:243–249.
• Varvel, G.E., J.L. Havlin, and T.A. Peterson. 1989. Nitrogen placement evaluation for winter wheat in three fallow tillage systems. Soil Sci. Soc. Am. J. 53:288–292.[Abstract/Free Full Text]
• Vaughan, B., D.G. Westfall, and K.A. Barbarick. 1990. Nitrogen rate and timing effects on winter wheat grain yield, grain protein, and economics. J. Prod. Agric. 3:324–328.
• Wagger, M., P. Galleger, R. Gwin, and D.E. Kissel. 1979. Water-nitrogen availability in winter wheat. In D.E. Kissel (ed.) Kansas fertilizer research report of progress. p. 47–49. Agric. Exp. Stn., Kansas State Univ., Manhattan, KS.

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