© 2011 Plant Management Network. Accepted for publication 12 October 2011. Published 23 December 2011.
Effects of Applying Nitrogen on Yield of Introduced Perennial Summer Grass Cultivars in Oklahoma Eddie R. Funderburg, Senior Consultant, Jon T. Biermacher, Associate Professor, Corey A. Moffet, Assistant Professor, Mohua Haque, Postdoctoral Researcher, and Jagadeesh Mosali, Staff Scientist, Agricultural Division, Samuel Roberts Noble Foundation, Ardmore, OK 73401 Corresponding author: Eddie R. Funderburg.
[email protected] Funderburg, E. R., Biermacher, J. T., Moffet, C. A., Haque, M., and Mosali, J. 2011. Effects of applying nitrogen on yield of introduced perennial summer grass cultivars in Oklahoma. Online. Forage and Grazinglands doi:10.1094/FG-2011-1223-01-RS.
Abstract A single-location, three-year study (2008-2010) was conducted near Ardmore, OK, to determine the effects of five nitrogen rates (0, 50, 100, 200 and 300 lb N/acre) on yield of seven varieties of bermudagrass and two varieties of old world bluestem (OWB). Four seeded and three vegetatively propagated (hybrid) bermudagrass varieties were tested. Forage yields were affected by N rate, variety, and year. The effect of N rate depended on year. B Dahl OWB outyielded Plains OWB at all N rates except 0 lb N/acre. Common, Cheyenne, and Wrangler had similar yields at all N rates except 300 lb N/acre. Blending Giant with Common increased yields over Common alone at all N rates except 50 lb N/acre. Tifton 85 yielded more than any other variety tested at all N rates. Midland 99 and Coastal had similar yield at all N rates. In general, all hybrid bermudagrass varieties tested and B Dahl OWB outyielded seeded bermudagrass varieties and Plains OWB when N rates of 100 lb/acre or more were applied, and hybrid bermudagrass varieties responded more to higher nitrogen rates than seeded bermudagrass varieties or OWB.
Purpose of the Study Introduced summer perennial grasses are used extensively in the southern Great Plains for grazing and hay (4,12). The primary introduced summer perennial grass species in south-central Oklahoma and north-central Texas are bermudagrass (Cynodon dactylon L.) and OWB [Bothriochloa ischaemum (L.) Keng and Bothriochloa bladhii (Retz)]. Much research has been conducted examining differences among cultivars of these species (4,5,7,8,15), but under a single N rate. By contrast, much work has compared N fertilizer rates, but usually on a single variety (1,2,6,7,10,13,14). Producers consider whether varieties that do best in trials with high N rates also do well with lower fertilizer inputs, and if lower yielding varieties produce comparable yields to higher yielding varieties if fertilized more heavily. The objectives of this study were to determine the effect of N rate on yield of each variety and determine the highest yielding varieties at each N rate. Site Description The test was conducted at the Samuel Roberts Noble Foundation Pasture Demonstration Farm, located five miles northwest of Ardmore, OK (34.22°N, 97.20°W). Soil series was Chickasha loam, 1 to 3% slope (fine-loamy, mixed, active, thermic Udic Argiustolls). The site was severely eroded from past management practices and very little original topsoil remains. This made the site representative of many locations in southern Oklahoma and north-central Texas where producers wish to plant summer perennial grasses for forage. Growing season rainfall was about average in 2010, considerably below average in 2008, and considerably above average in 2009 (Table 1).
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Table 1. Growing season rainfall (inches) data for the Noble Foundation Pasture Demonstration Farm near Ardmore, OK from 2008-2010 and the most recent 30 year average. Apr
May
Jun
Jul
Aug
Sep
Oct
Growing season total
30-year avg.
3.19
5.08
4.25
2.47
2.47
4.16
4.36
25.98
2007
1.44
7.74
6.09
2.93
1.42
1.52
2.59
23.73
2008
2.24
3.20
1.79
1.09
3.88
1.59
2.51
16.30
2009
7.36
8.51
1.94
3.92
1.96
7.21
7.64
38.54
2010
3.11
4.03
2.72
2.11
3.70
6.44
1.65
23.76
Year
Methodology Nine introduced perennial summer grass varieties were fertilized with five N rates and replicated three times in a randomized complete block design. There were four seeded bermudagrass varieties (Common, Common/Giant blend, Cheyenne, and Wrangler), three hybrid bermudagrass varieties (Coastal, Midland 99, and Tifton 85) and two OWB varieties (Plains and B Dahl). Plots were 5 × 10 ft with 5-ft alleys completely around each plot. The test was planted in the spring of 2006 and no stand was obtained on any variety or species due to extreme drought. No fertilizer or herbicide was applied in 2006. The test was replanted in 2007, maintaining plot integrity from the 2006 planting, and excellent stands were obtained. Midland 99 was planted 12 March 2007. Coastal and Tifton 85 were planted 16 March 2007. These three hybrid varieties were treated with 1 lb/acre diuron (1 qt/acre Diuron 80) herbicide after sprigging on 16 March 2007, for weed control. Post-emergence herbicides were applied on all varieties for broadleaf weed control when needed after the forages were large enough to tolerate the herbicides. Common, Common/Giant, Wrangler, Cheyenne, Plains, and B Dahl were planted 16 April 2007. No fertilizer treatments were applied in 2007, and no harvest data were collected. The plots were mown to a uniform 5-inch plant height in late October. Fertilization and harvests began in 2008. Four harvests per year were obtained from 2008-2010. Five N rates (0, 50, 100, 200, and 300 lb N/acre) were applied by hand to each variety each year of the test using ammonium nitrate as the N source. Treatments with 50 or 100 lb N/acre received all their fertilizer in a single application in late April or early May. Treatments with 200 or 300 lb N/acre received 100 lb N/acre initially, and an additional 100 lb N/acre after first harvest. An additional 100 lb N/acre was applied to the 300 lb N/acre plots after the second harvest. Phosphorus and potassium were blanket applied to the entire study at rates high enough that deficiencies of those elements would be very unlikely to limit yield, usually 0-60-180 per acre per year. Plots were harvested with a Hege forage combine. A subsample was collected from each plot to determine moisture content. Yields are reported in pounds of dry matter per acre. Statistical Analysis Yield response and N rate data for each year and variety were plotted in scatter plots. Appropriate functional forms for each variety were selected from visual inspection of the plots. Yield responses of Plains, Cheyenne, Common/Giant, Tifton 85, Coastal, Midland 99, and Wrangler varieties were consistent with a linear functional form (LR), while yield response of Common variety was consistent with a quadratic form (QR). The B Dahl yield response plot indicated a linear response plateau (LRP) form was most appropriate. The Likelihood Dominance Criterion was used to compare the fit of a linear, quadratic, and linear response plateau model and indicated the linear response plateau functional form best fit the B Dahl yield response data (10). For each variety, the effects of N, year, and the N × year interaction were estimated using mixed modeling procedures in SAS version 9.2. In each model, N rate, year, and
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N rate by year interaction were treated as fixed effects, while replication (block) and its interactions were treated as random. In addition, the statistical models applied the autoregressive (AR1) covariance structure to account for autocorrelation among years in cases where the AR1 model significantly improved the model over an independent errors model. Plots were treated as subjects in all analyses, as they represented the experimental units in the study. Fisher’s Protected Least Significance Difference (LSD) tests were conducted to compare yields among N treatment levels for each variety and to compare yields across varieties for a given N level. Findings Regressions for yield response to N, year, and N × year interaction for each variety are reported in Table 2. Yield can be calculated for each variety, N rate, and year from these equations. In general, the solution is: Yield = Intercept + Yr2009*(Yr=2009) + Yr2010*(Yr=2010) + (N*N applied) + [N2009*N applied* (Yr=2009)] + [N2010*N applied*(Yr = 2010)] + [N²*(N applied)²]. This is expressed symbolically as: YYR = a + b(Yr=2009) + c(Yr=2010) + dN + eN(Yr = 2009) + fN(Yr = 2010) + gN², where a through g are the parameters in Table 2, N is the amount of N applied in lb/acre, and Yr=2009 and Yr=2010 are conditions that evaluate to 1 when true and 0 when false. For example, common bermudagrass fertilized with 150 lb/acre of N is predicted in year 2010 to yield 1389 + 2014*0 + 3695*1 + 20.46*150 +7.77*150*0 + (-0.90)*150*1 + (-0.05) *150², or 6893 lb DM/acre.
Fig. 1. Response of two old world bluestem varieties to five nitrogen rates in south-central Oklahoma (20082010). Yields denoted as a point for a N rate of a particular variety that are followed by the same letter are not statistically different (α = 0.05).
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Table 2. Regression parameter estimates for yield response to nitrogen, year, and nitrogen by year interactions for nine warm season perennial forage varieties. Seeded bermudagrass Cheyenne
Wrangler
Common
Common/Giant
Intercept (a)
2237
1948
1389
4310
Yr2009 (b)
3413
1253
2014
2703
Yr2010 (c)
2619
1944
3695
301
N (d)
9.09
6.66
20.46
10.01
N2009 (e)
−
16.34
7.77
−
N2010 (f)
−
9.77
-0.90
−
N² (g)
−
−
-0.05
−
Parameter
Hybrid (sprigged) bermudagrass Coastal
Midland 99
Tifton 85
Intercept (a)
3969
5112
7522
Yr2009 (b)
2150
−
2944
Yr2010 (c)
1375
−
-121
N (d)
19.43
15.44
21.47
N2009 (e)
−
−
-3.44
N2010 (f)
−
−
-10.69
Parameter
Old World Bluestem Parameter
B Dahl
Plains
Intercept (a)
4213
3278
Yr2009 (b)
6332
3708
Yr2010 (c)
7063
3927
N (d)
41.82
−
Nmax
68.3
−
Variety Response to N Rate and Year A linear response plateau best fit the B Dahl old world bluestem yield to N response (Fig. 1). B Dahl was significantly more productive in 2009 and 2010, compared with the drier-than-normal 2008 at all N application rates, but the effect of applying N was the same among all three years (Table 2). The minimum N application rate that achieved maximum yield was 68 lb N/acre. B Dahl yield increased 41.8 lb/acre for each lb N/acre applied between 0 and 68 lb N/acre, but yield was unresponsive to N application above 68 lb/acre. Plains OWB did not respond to N application in the range studied (α = 0.05). The response of Cheyenne bermudagrass to N was best fit to a linear model (Table 2). Mean yields did not increase significantly above 100 lb N/acre. Cheyenne had a negative year effect in the drier-than-average year 2008 compared with 2009 and 2010. Wrangler responded to N in a linear manner and produced the greatest mean yield at 300 lb N/acre. Wrangler yield under N fertilization was not significantly greater than unfertilized unless 200 or 300 lb N/acre were applied. Compared with 2009 and 2010, wet and nearnormal years, respectively, Wrangler had significantly less yield in 2008 and responded less to each pound of N applied (Fig. 2).
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Fig. 2. Response of four seeded bermudagrass varieties to five nitrogen rates in south-central Oklahoma with regression equations listed for the three-year average (2008-2010). Yields denoted as a point for a N rate of a particular variety that are followed by the same letter are not statistically different (α = 0.05).
Common responded to N in a quadratic manner and the minimum N rate to achieve maximum mean yield was 100 lb N/acre. Common bermudagrass showed positive year effects in both the wetter-than-average year 2009 and the near-average precipitation year 2010. The yield increase per pound of N applied was greater in 2009 than in either 2008 or 2010. Common/Giant blend responded to N in a linear manner and the minimum N rate to achieve maximum mean yield was 100 lb N/acre. In the wetter-than-average year 2009, the Common/Giant blend yielded 2703 lb DM/acre more forage than in 2008 and 2402 lb DM/acre more forage than in 2010, irrespective of N application rate (Table 2). Coastal and Midland 99 both showed a linear response to N. Coastal yield depended on year, with the dryer-than-normal year the least productive and the wetter-than-average year being most productive, but the increase in yield for each lb N/acre applied was the same among years. In general, Midland 99 yield was insensitive to year and yield increased linearly with increasing N fertilization. Both Coastal and Midland 99 yields were greatest at 300 lb N/acre (Fig. 3).
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Fig. 3. Response of three hybrid bermudagrass varieties to five nitrogen rates in south-central Oklahoma with regression equations listed for the three year average (2008-2010). *Yields denoted as a point for a N rate of a particular variety that are followed by the same letter are not statistically different (α = 0.05).
Tifton 85 was the highest, or tied for the highest, yielding variety at all N rates tested. Tifton 85 yield had a linear response to N application. Tifton 85 yield, at a given N application rate, depended on year. The greatest Tifton 85 yield was in the wetter-than-average 2009, but yields were similar between 2008 and 2010 (Table 2). Highest mean yield for Tifton 85 was obtained with 300 lb N/acre (Fig. 3). Overall, the hybrid varieties response to N application was greater than in OWB or seeded bermudagrass varieties. Comparisons Between Varieties Plains and B Dahl had similar yields at the 0 N/acre rate. However, B Dahl significantly outyielded Plains at all other N rates tested. B Dahl outyielded Plains by more than one ton DM forage/acre when N fertilizer was used (Table 3). Among the seeded bermudagrass varieties, there were no significant yield differences between Common, Cheyenne, and Wrangler at any N rate except 300 lb N/acre, where Wrangler outyielded Common (Table 3). It is customary for producers to blend Giant seed with Common, even though Giant has poor winter hardiness (11). In our study, the addition of Giant to Common resulted in significantly more forage than Common alone at the 0, 100, 200, and 300 lb N/acre rates. Yield increases ranged from 1904 to 2465 lb DM forage per acre (Table 2). This indicates that adding Giant to Common is a good practice even if Giant is lost to winter kill in 2 to 3 years. In our test, Giant was not injured during the winters of 2007-2008 or 2008-2009, but suffered severe injury from the winter of 2009-2010. Stands of Giant were very poor in the growing season of 2010.
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Table 3. Yields (lb dry matter/acre) of nine different varieties of introduced summer perennial grass varieties obtained with five nitrogen rates in southcentral Oklahoma in 2008-2010. N rate (lb/acre) 0x Variety
50
100
200
300
Yield (lb dry matter/acre)
Plains
5399 bc
5602 c
6557 cde
5807 c
5750 e
B Dahl
5822 b
7913 b
8638 ab
8355 b
9042 bc
Cheyenne
3993 cd
4630 cd
5586 def
6159 c
6784 de
Wrangler
3305 d
3793 d
4087 f
6106 c
7760 cd
Common
3237 d
4367 cd
5083 ef
5682 c
5464 e
Com/Giant
5141 bc
5023 cd
7002 bcd
7986 b
7929 cd
Coastal
4753 bcd
6036 c
7675 bc
9226 b
Midland 99
4974 bc
5472 cd
7366 bc
8216 b
Tifton 85
7889 a
10121 a
10158 a
11452 a
13592 a
P>F
0.0001
0.0001
0.0001
0.0001
0.0001
x
10660 b 9563 bc
Yields in a column (within a given N application rate) followed by the same letter are not statistically different (α = 0.05).
In the hybrid varieties (Coastal, Midland 99, and Tifton 85), there was no yield difference between Coastal and Midland 99 at any N rate tested (Table 3). Tifton 85 was the highest yielding, or tied for the highest yielding variety, at all N rates tested (Table 3). Tifton 85 showed visual injury symptoms from the winter of 2009-2010, as evidenced by late emergence from dormancy and visual tip burn, but recovered completely during the growing season of 2010. All hybrid varieties outyielded Common, Cheyenne, or Wrangler when 100 lb N/acre or more was applied. If a producer is willing to fertilize with at least 100 lb N/acre, our study shows that a hybrid variety of bermudagrass is likely to outyield a seeded variety of bermudagrass, with the exception of Giant. Conclusions Based on the results of this study, if a rancher does not intend to fertilize with N, Plains, B Dahl, Common/Giant blend, Coastal, or Midland 99 should all produce about the same yield. Common, Cheyenne, and Wrangler should yield less than other varieties with no N fertilizer used, and Tifton 85 should yield more than any other variety with no fertilization. Anecdotal and scientific evidence show that not fertilizing bermudagrass for long periods of time can lead to stand decline (3). If a rancher plans to use moderate rates of N, such as 50 lb N/acre, B Dahl and Tifton 85 are excellent choices. If a producer is willing to use higher rates of N, such as 100 to 300 lb N/acre, Common/Giant, Coastal, Midland 99, and Tifton 85 are preferred. Tifton 85 was the highest yielding variety in the test at every fertilizer rate tested. It is an excellent choice, regardless of N management, in climates where severe winter injury is uncommon, but Tifton 85 is the least cold-tolerant hybrid variety we tested (7). An examination of how varieties responded to N showed Plains OWB did not respond to N. Many producers in our area do not fertilize Plains due to perceived lack of response to N. Our study validates that decision. B Dahl responded well to 68 lb N/acre, but did not respond to higher N rates. The minimum N rate to achieve maximum yield for Common and Common/Giant blend was 100 lb N/acre. Cheyenne and Wrangler did not respond to N until the rate reached 200 lb N/acre. Even though high N rates increased yields of Cheyenne and Wrangler, the seeded varieties did not yield as well as hybrid bermudagrass varieties at lower N rates. Coastal and Midland 99 responded positively to N at rates of 100 lb/acre or more. This study shows that increasing N rates can increase yields of seeded varieties, but they still are not as high yielding as hybrid varieties.
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Our study had similar results to those found by Corriher and Redmon (3) where Tifton 85 outyielded all other varieties. Their study agreed with ours in that Cheyenne and Common had similar yields in both studies. However, Wrangler was inferior to Common and Cheyenne in their test, where all three were similar in our test. Our findings differed slightly from those found by Guretzky (6). He found that there was no yield difference between Tifton 85, Midland 99, and Coastal when fertilized at 300 lb N/acre, whereas we found Tifton 85 was higher yielding than Coastal or Midland 99 at that N rate. Taliaferro et al. (13) found that Tifton 85 slightly outyielded Coastal, and greatly outyielded Common when fertilized at 80 lb N/acre. This agrees with our findings. Evers (5) found that Coastal responded to 179 lb N/acre, a finding similar to ours. Massey et al. (8) also found that an unnamed variety (probably Coastal) responded to 200 lb N/acre, and Osborne et al. (9) found that N recovery rate was maximized in Coastal at 200 lb N/acre. These findings were similar to ours. Exact comparisons with our study were difficult to locate due to differences in the ways the studies were designed. Literature Cited 1. Altom, W., and Rogers, J. L. 1975. The effects of various fertilizers and lime on Midland bermudagrass forage yields and soil test values of a Chickasha fine sandy loam. Noble Foundation report. Samuel Roberts Noble Foundation, Ardmore, OK. 2. Burns, J. C., Wagger, M. G., and Fisher, D. S. 2009. Animal and pasture productivity of Coastal and Tifton 44 bermudagrass at three nitrogen rates and associated soil nitrogen status. Agron. J. 101:32-40 3. Childs, D. 2006. Fertilizer economics 101: Can you afford to fertilize? May 2006, Ag. News and Views, Samuel Roberts Noble Foundation, Ardmore, OK. 4. Corriher, V., and Redmon, L. 2009. Bermudagrass varieties, hybrids and blends for Texas. Ext. Publ. SCS-2009-11, Texas A&M AgriLife, College Station, TX. 5. Edwards, N. C., Hovermale, C. H., Ivy, R., Lang, D., Elmore, R., Ingram, D. M., and Johnson, D. Mississippi forage crop variety trials, 1999. Info. Bull. 356, August 1999. Mississippi Agric. and Forestry Exp. Stn., Mississippi State, MS. 6. Evers, G. W. 1998. Comparison of broiler poultry litter and commercial fertilizer for Coastal bermudagrass production in the Southeastern US. J. Sustain. Agric. 12 (4):55-57 7. Guretzky, J. 2005. Forage yields from 2005 bermudagrass varieties and strains. Report NF-FO-06-01. Samuel Roberts Noble Foundation, Ardmore, OK. 8. Lee, R. D., Harris, G., and Murphy, T. R. 2002. Bermudagrasses in Georgia. Coop. Ext. Serv. Bull. 911, Univ. of Georgia, Tifton, GA. 9. Massey, C. G., Slaton, N. A., DeLong, R. E., Golden, B. R., and Maschmann, E. T. 2008. Bermudagrass forage response to nitrogen fertilization. Pages 7-17 in: Wayne E. Sabbe Arkansas Soil Fertility Studies 2007. Res. Ser. 558. N. A. Slaton, ed. Arkansas Agric. Exp. Stn.. Fayetteville, AR. 10. Osborne, S. L., Raun, W. R., Johnson, G. V., Rogers, J. L., and Altom, W. 1999. Bermudagrass response to high nitrogen rates, source and season of application. Agron. J. 91:438-444 11. Pollak, A. R., and Wales, T. J. 1991. The likelihood dominance criterion: a new approach to model selection. J. Econometrics 47:227-242. 12. Redfearn, D., Woods, B., and Wu, Y. Choosing, establishing and managing bermudagrass varieties in Oklahoma. Ext. Fact Sheet PSS-2583. Oklahoma State Univ., Stillwater, OK. 13. Seay, R., and Slaton, N. 2008. Bermudagrass yield response to nitrogen and potassium fertilization in northwest Arkansas. Online. Forage and Grazinglands doi:10.1094/FG-2008-0818-01-RS. 14. Slaton, N., DeLong, R., Golden, B., Massey, C., and Roberts, T. 2007. Bermudagrass forage response to nitrogen, phosphorus and potassium fertilization rate. Pages 52-57 in: Wayne E Sabbe Arkansas Soil Fertility Studies 2006. Res. Ser. 548. N. A. Slaton, ed. Arkansas Agric. Exp. Stn., Fayetteville, AR. 15. Taliaferro, C. M., Williams, G. L., Pickard, T. G., Hooper, D. W., and Kochenower, R. D. 2002. Performance of forage bermudagrass varieties in Oklahoma tests 1998-2000. PT 2002-3. Oklahoma State Univ., Stillwater, OK.
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