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© 2005 Plant Management Network.
Accepted for publication 25 October 2005. Published 20 December 2005.

Nitrogen Rate and Source Effects on the Yield and Nutritive Value of Tall Fescue Stockpiled for Winter Grazing

Chris D. Teutsch, Assistant Professor, Southern Piedmont Agricultural Research and Extension Center, Virginia Polytechnic Institute and State University, Blackstone 23824; John H. Fike, Assistant Professor, Crop and Soil Environmental Sciences, Virginia Polytechnic Institute and State University, Blacksburg 24061; Gordon E. Groover, Extension Economist, Department of Agricultural and Applied Economics, Virginia Polytechnic Institute and State University, Blacksburg 24061; and Susanne Aref, Director, Statistical Consulting Center, Department of Statistics, Virginia Polytechnic Institute and State University, Blacksburg 24061

Corresponding author: Chris D. Teutsch. cteutsch@vt.edu

Teutsch, C. D., Fike, J. H., Groover, G. E., and Aref, S. 2005. Nitrogen rate and source effects on the yield and nutritive value of tall fescue stockpiled for winter grazing. Online. Forage and Grazinglands doi:10.1094/FG-2005-1220-01-RS.

Abstract

Late summer nitrogen fertilization is a primary factor affecting yield of cool-season pastures allowed to accumulate herbage for deferred grazing. Attention has been given to the quantity of N applied, but the source of N has not been investigated. This study evaluated the effects of N rate and source on yield and nutritive value of stockpiled tall fescue. Trials were conducted on two farms located near Amelia, VA in 2002 and 2003 and Blackstone, VA in 2004. Six N sources (ammonium nitrate, ammonium sulfate, broiler litter, complete fertilizer, urea, and urea-ammonium nitrate) were applied at 0, 40, 80, and 120 lb plant available N per acre in mid-August. Forage was allowed to accumulate until mid-December. Yield increased linearly with N rate for each N source, but the rate of increase varied from 5 to 13 lb DM/lb of N. Compared to the unfertilized control, yield at the highest N rate was increased 25 to 61% depending on nitrogen source. Ammonium nitrate and ammonium sulfate were the most effective N sources for stockpiling tall fescue. Urea-ammonium nitrate produced the lowest yield and would not be a suitable replacement for ammonium nitrate, even when applied at higher rates.

Tall fescue (Lolium arundinacea (Schreb.) S.J. Darbyshire) is grown on more than 24 million acres in the east-central and southeastern United States (5). It is the primary forage base for more than 9 million beef cows in this region (8). One of tall fescue’s strongest and most under-utilized attributes is its ability to be stockpiled for winter grazing (Fig. 1).

Fig. 1. Stockpiled tall fescue maintains forage quality better than other commonly used cool-season grasses making it well suited for stockpiling in the transition zone of the United States.

Agronomic factors that affect stockpiled tall fescue production were reviewed by Matches (7) more than 25 years ago and more recently by Poore et al. (10). A primary factor affecting yield was N fertilization. Response of tall fescue to autumn N applications is highly variable due to environmental conditions. In general, 10 to 20 lb of forage DM production per lb N can be achieved with moderate N inputs (55 to 110 lb of N per acre) (10). While a substantial amount of research has examined N rate effects on stockpiled tall fescue production, little research has evaluated the effect of N source. This study was designed to determine the effect of N source and rate on the yield and nutritive value of stockpiled tall fescue.

Trials Comparing Nitrogen Rates and Sources in 2002-2004

Trials were conducted on two farms, one located near Amelia, VA (37.3°N, 78.0°W) (2002 and 2003) and the other located near Blackstone, VA (37.1°N, 78.0°W) (2004). Soil series were an Appling sandy loam (fine, kaolinitic, thermic Typic Kanhapludults) and a Vance sandy loam (fine, mixed, semiactive, thermic Typic Hapludults) for the Amelia and Blackstotne locations, respectively. Initial soil nutrient levels are shown in Table 1. The Amelia location had received intermittent applications of broiler litter in the past with the most recent application occurring at a rate of 2 tons of broiler litter per acre in 2000. Organic N sources had never been applied at the Blackstone location. At this location, 50 lb of N per acre was applied in the spring of 2003. Swards at each location were dominated by tall fescue with small amounts of Kentucky bluegrass (Poa pratensis L.) and white clover (Trifolium repens L.).

Table 1. Soil characteristics of the experimental sites.

 ^x Mehlich I extract was utilized.

 ^y Soil Test Recommendations for Virginia, 1994.

The experiment was a randomized complete block design containing four replications of each treatment. Within this design N rate (3) and sources (6) were factorially arranged. Plot size was 8 × 25 ft. Nitrogen was applied on 12 August 2002, 16 August 2003, and 9 September 2004 at 0, 40, 80, and 120 lb plant-available N per acre as ammonium nitrate, ammonium sulfate, a complete fertilizer (18-9-9-12S), urea-ammonium nitrate, and urea (Table 2) (Fig. 2). Broiler litter was applied at 1, 2, and 3 ton/acre on an as-is basis. The actual amount of PAN applied varied between years due to differences in the moisture and N concentrations of the broiler litter (Table 2). The quantity of PAN applied in each year was used in the development of regression equations. Plots were allowed to accumulate herbage until mid-December (Fig. 3).

Fig. 2. Nitrogen treatments were applied in mid-August. In this photograph urea-ammonium nitrate is being applied to tall fescue plots at the Blackstone location in 2004.		Fig. 3. After nitrogen treatments were applied, cattle were excluded from the experimental area and forage growth was allowed to accumulate until plots were harvested in mid-December.

Table 2. Description of the nitrogen sources utilized in this experiment.

 ^x Plant-available Nitrogen, PAN = NH₃-N × 0.90 + Organic-N × 0.60 (16). This calculation was used for the broiler litter treatment only.

Plots were harvested on 18 December 2002, 22 December 2003, and 21 December 2004 by clipping a 4-ft-wide strip through the center of each plot using a self-propelled sickle bar-type forage harvester. Forage subsamples were randomly collected from the clipped forage from each plot for determination of dry matter and nutritive value. Neutral detergent fiber (NDF), acid detergent fiber (ADF), and crude protein (CP) were predicted using near infrared spectroscopy (Foss North America, Eden Prairie, MN). Total digestible nutrients (TDN) were calculated using the following equation: TDN = 100.32 – 0.4810 × ADF.

Data were analyzed across the three environments (year-location) using the general linear model procedure from SAS (SAS Institute Inc., Cary, NC). Main effects and interactions included in the model were environment, replication within environment, N rate, N source, N rate × environment, N source × environment, N rate × N source, and N rate × N source × environment. Regression analysis was used to examine the yield response to N rate for each of the six N sources using Sigma Plot 9.0 (Systat, Point Richmond, CA). The slopes of the regressions lines were then analyzed in a mixed model where the N-source (excluding the control) was a fixed effect and both replication and environment as well as their interaction were random effects.  The comparisons of the mean slopes were done using Tukey’s HSD (0.05) (SAS).

No environment × treatment interactions occurred (P > 0.05). Therefore, data are presented averaged across environments. A significant N rate × N source interaction occurred for yield but not for nutritive value data. Interaction means are thus presented for yield and main effects are presented for the nutritive value data.

Rainfall and Temperature Data

In 2002, rainfall was below the 30-year average for most of the growing season (Fig. 1). In all years of this study, rainfall that should have been sufficient to incorporate all N sources (> 0.1 inch) (4) occurred within 5 days of N application. Temperature data is shown in Table 3. Killing frosts (28°F) occurred on 27 November 2002, 10 November 2003, and 15 December 2004.

Fig. 4. Rainfall data for the 2002, 2003, and 2004 growing seasons.

Table 3. Average temperature and deviation from 30-year average (°F).

 ^x Deviation from 30-year average.

Nitrogen Rate and Source Effects on the Yield of Stockpiled Tall Fescue

Yield increased linearly with N rate for all N sources (Fig. 2). However, rates of increase varied between N sources and ranged from 5.0 to 13.3 lb DM/lb of N. This variation resulted in a yield difference of more than 925 lb/acre at the highest N rate when ammonium nitrate was applied versus urea-ammonium nitrate (Fig. 2). Yields at the highest N rate with urea-ammonium nitrate, urea, broiler litter, complete fertilizer, ammonium sulfate, and ammonium nitrate, were 25, 36, 40, 49, 51, and 61% greater than yields of unfertilized controls. Relative yield differences among sources were smaller at the lower N rates (Fig. 2).

Fig. 5. Nitrogen rate and source effects on the herbage yield of tall fescue harvested in mid-December. The slopes of the regression lines followed by the same letter are not significantly different according to Tukey’s HSD (0.05).

In grasslands, N losses occur via three principal pathways: volatilization of NH₃, leaching of NO₃, and the conversion of nitrates to NO or N₂ gas through denitrification (17). Environmental conditions present in late summer and abundant organic residues on pasture surfaces provide ideal conditions for N losses via volatilization (4). In contrast, the dry conditions often encountered in late summer are not conducive to N losses via denitrification or leaching (14,17). In addition, the acid soil conditions present in most pastures found in the southeastern United States (1) limit denitrification of ammonium compounds (4).

In this study, urea and urea-ammonium nitrate were the two N sources most susceptible to volatilization (11). These sources elicited the smallest yield response suggesting that N losses to the environment were likely occurring (Fig. 2). Urea-ammonium nitrate, which stimulated the least growth, was applied in solution and a relatively small quantity of spray solution was utilized (20 gal/acre). These factors coupled with ideal conditions for volatilization (large quantities of residue and warm temperatures) may have resulted in high losses of urea from the urea-ammonium nitrate fertilizer.

In addition, several days after N application, leaf burning was observed in the urea-ammonium nitrate plots. Application of spray solutions containing > 1 to 3% urea can cause severe leaf burn (6). Spray solution used in this study contained approximately 21% urea and leaf burn temporarily reduced the photosynthetic capacity of tall fescue, shortening the period of herbage accumulation. This factor, combined with N losses due to volatilization, probably caused the lower dry matter yields for this treatment.

Yield response to broiler litter was similar to urea (Fig. 2). Nitrogen in broiler litter is in an organic form and it is estimated that approximately 60% of this N is released through mineralization in the first growing season (16). Lower yields with the broiler litter likely occurred given that not all N from the broiler litter is immediately available at application. Past research indicates that approximately one-half of the plant-available N in poultry litter was available early in the growing season (2,12). Even a relatively short delay in N availability could negatively impact stockpile yield by shortening the period of dry matter accumulation (10).

Ammonium nitrate, ammonium sulfate, and the complete fertilizer (N as ammonium sulfate) produced the highest yields (Fig. 2). These compounds were also the least likely to volatize under the pasture conditions in this experiment (11). The application of S in ammonium sulfate and the complete fertilizer did not appear to increase yield and may indicate that pastures at these sites are not limited by S. The similar yield response of ammonium sulfate and complete fertilizer (N as ammonium sulfate) indicate that the additional cost of P and K in complete fertilizer is not justified when soil test values for P and K are in the high range (Table 1).

Under the conditions of this experiment, these data illustrate that ammonium nitrate is the best N source for stockpiling tall fescue. However, the future availability of this source is uncertain. Global use of ammonium nitrate has decreased since 1985 and this N source has been banned in some countries due to security concerns (4). In all likelihood the availability and increased price may limit the use of this N source in the future. Ammonium sulfate may be an acceptable alternative for late-summer N applications, especially if sulfur is needed. A disadvantage of this source is its acid-forming characteristics, requiring over two times as much lime per unit of N (11). Urea could be used for stockpiling; however, results from the current study indicate that approximately 65% more N would need to be applied to obtain a yield similar to 60 lb of N per acre as ammonium nitrate.

Nitrogen Rate and Source Effects on the Nutritive Value of Stockpiled Tall Fescue

Nitrogen rate and source did not affect ADF, NDF, or TDN (Table 4 and 5). Crude protein increased with N rate, but the range was small and likely biologically insignificant (Table 4). Nitrogen source also had limited effects on CP (Table 5). Although treatment differences were small, these data clearly indicate the high nutritive value of stockpiled tall fescue. Compared to average grass hay in Virginia, stockpiled tall fescue in this study contained 23% more energy and 36% more CP (13) and would meet the nutritional requirements of all classes of beef cattle (9). The nutritive value range observed for stockpiled tall fescue in the current study is similar to observations made on a commercial farm in south-central Virginia over a 5-year period (10).

Table 4. Nitrogen rate effects on ADF, NDF, CP, and TDN
concentrations (%) of stockpiled tall fescue.

Table 5. Nitrogen source effects on ADF, NDF, CP, and TDN
concentrations (%) of stockpiled tall fescue.

Influence of Nitrogen Costs and Hay Value on Stockpiling Economics

Yield response to two nitrogen sources (ammonium nitrate – high yield and urea ammonium nitrate – low yield) at three prices per source are presented in Table 6. The results depicted in Table 6 are based on the following assumptions: (i) the value of hay or stockpiled fescue used in the calculation range from $40 to $160/ton and are not adjusted for relative differences in forage quality; (ii) farmers have established fescue pastures and the capacity to stockpile fescue; (iii) N application costs are $6.00/acre; (iv) the value of no-N control yield (1,860 lbs/acre) is $37, $56, $74, $93, $112, $130, and $149 based on hay values of $40, $60, $80, $100, $120, $140, and $160; and (v) farmers will accept a no-N stockpile regime to achieve 1,860 lb/acre of available forage.

Table 6. Net additional returns ($/acre) above the value of the control yields at various prices of hay and N for ammonium nitrate (AN) and urea-ammonium nitrate (UAN)^w.

 ^w All yields are based on a utilization rate of 65% or approximately a 3-to-4-day strip grazing regime and are adjusted to 12% moisture.

 ^x Feeding and storage losses can vary greatly. The range of hay values will allow the reader to make their own comparison based on individual losses, e.g., for hay valued at $100/ton with a 40% feeding and storage losses would yield a feeding value of $167/ton or a table value in the table of around $160/ton for comparison.

 ^y Ammonium nitrate yield equation, y = 1859 + 9.83x.

 ^z Urea-ammonium nitrate yield equation, y = 1911 + 3.69x.

Under conditions of the current study, N should not be applied for stockpiling when N prices are high (Table 6). Even under moderate N prices, N would be applied as ammonium nitrate only if the hay cost more than $60 per ton. Only when N prices are low and hay values are $60 or more/ton does stockpiling with additional N become a profitable decision. These results are directly influenced by the high yield of the no-N control in this study (1,860 lb/acre of available forage). Although this yield is high, it may not be unrealistic (3,15) for well-managed pastures that contain some legumes, have grazing livestock, and receive organic N sources on an annual or semiannual basis. Producers who fall into this category should determine the yield of no-N stockpile on their farms in order to make prudent and profitable stockpiling decisions.

Conclusion

The yield of stockpiled tall fescue is influenced by the choice of N source. Results from this study clearly indicate that ammonium nitrate is the best source for stockpiling tall fescue, but its future availability may be limited. In addition, the high cost of N fertilizer may force producers to look for alternative sources. One alternative is to increase the use of readily available organic N sources such as broiler litter or biosolids. More work is needed to better define the N release characteristics of these sources in order to optimize application timing for stockpiling cool-season grasses.

Acknowledgments

The authors would like to thank Danny and Grace Royster and Whit and Jennifer Morris for allowing us to conduct this study on their farms. We would also like to than J. B. Daniel, former agricultural extension agent in Amelia County, for his technical assistance with this research. Lastly, we would like to recognize Rainbow Plant Food for supplying the nitrogen fertilizer used in this study.

Literature Cited

1. Ball, D. M., Hoveland, C. S., and Lacefield, G. D. 2002. Southern Forages, 3th ed. Potash and Phosphate Inst. and Found. for Agron. Res., Norcross, GA.

2. Bitzer, C. C., and Sims, J. T. 1988. Estimating the availability of nitrogen in poultry manure through lab and field studies. J. Environ. Qual. 17:47-54.

3. Gerrish, J. R., Peterson, P. R., Roberts, C. A., and Brown, J. R. 1994. Nitrogen fertilization of stockpiled tall fescue in the Midwestern USA. J. Prod. Agric. 7:98-104.

4. Havlin, J. L, Beaton, J. D., Tisdale, S. L., and Nelson, W. L. 2005. Soil Fertility and Fertilizers: An Introduction to Nutrient Management, 7th ed. Pearson-Prentice Hall, Upper Saddle River, NJ.

5. Hoveland, C. S. 1993. Importance and economic significance of the Acremonium endophytes to performance of animals and grass plant. Agric. Ecosyst. Environ. 44:3-12.

6. Kenney, D. R. 1982. Nitrogen management for maximum efficiency and minimum pollution. Pages 635-636 in: Nitrogen in Agricultural Soils. F. J. Stevenson, ed. Agron. Mongr. 23. ASA, CSSA, SSSA, Madison, WI.

7. Matches, A. G. 1979. Management. Pages 171-199 in: Tall Fescue. R. C. Buckner and L. P. Bush, eds. Agron. Mongr. 20. ASA, CSSA, and SSSA, Madison, WI.

8. NASS. 2005. U.S. and state level data for cattle and calves. Online. USDA-NASS, Washington, D.C.

9. National Research Council. 1996. Nutrient requirements of beef cattle, 7th rev. ed. (updated 2000). Nat. Acad. Press, Washington, D.C.

10. Poore, M. H., Benson, G. A., Scott, M. E., and Green, J. T. 2000. Production and use of stockpiled fescue to reduce beef cattle production costs. Online. Proc. Amer. Soc. Anim. Sci., Savoy, IL.

11. Potash and Phosphate Institute. 2003. Soil Fertility Manual. Norcross, GA.

12. Reddy, K. R., Khaeleel, R., Overcash, M. R., and Westerman, P. W . 1979. A nonpoint source model for land areas receiving animal wastes: I. Mineralization of organic nitrogen. Trans. ASAE 22:863-872.

13. Stallings, C. C. 2005. Test available for measuring forage quality. VCE Publication 404-124, VPI & SU, Blacksburg.

14. Stevenson, F. J. 1982. Origin and distribution of nitrogen in soil. Pages 1-39 in: Nitrogen in Agricultural Soils. F. J. Stevenson, ed. Agron. Mongr. 23. ASA, CSSA, SSSA, Madison, WI.

15. Taylor, T. H., and Templeton, W. C. 1976. Stockpiling Kentucky bluegrass and tall fescue forage for winter pasturage. Agron. J. 68:235-239.

16. Virginia Department of Conservation and Recreation. 1995. Virginia nutrient management standards and criteria. Division of Soil and Water Conservation, Richmond.

17. Whitehead, D. C. 2000. Nutrient Elements in Grassland: Soil-Plant-Animal Relationships. CABI Publishing, New York, NY.