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ALFALFA

Yield, Quality, and Persistence of Grazing- and Hay-Type Alfalfa under Three Harvest Frequencies

Department of Agronomy, Univ. of Missouri, Columbia, MO 65211

* Corresponding author (kallenbachr{at}missouri.edu)

Received for publication October 1, 2001.

	ABSTRACT

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

 
Producers in the lower Midwest often plant grazing-type alfalfa (Medicago sativa L.) cultivars assuming they can withstand frequent hay harvests. However, little research has examined the long-term effects of frequent hay harvests on grazing-type compared with hay-type alfalfa. Our objective was to determine how cultivar-type and harvest frequency change long-term alfalfa yields, quality, and stand persistence. ‘Alfagraze’ (grazing-type), ‘Pioneer 5373’ (modern, multipest resistant hay-type), and ‘Cody’ (older hay-type) alfalfa were seeded on 1 Apr. 1994, near Mt. Vernon, MO. Cultivars were main plots, and four, five, or six harvests before 15 September (42, 34, and 28 d between harvests, respectively) were subplots in a randomized complete block in a split-plot arrangement. Cumulatively, over 5 yr, Pioneer 5373 produced 6% (2.8 Mg ha^-1) more forage than Alfagraze and 10% (5.0 Mg ha^-1) more than Cody. Alfalfa harvested four times yielded 7% (0.8 Mg ha^-1) more per year than when harvested five times, and 28% (3.1 Mg ha^-1) more than when harvested six times. Alfagraze and the hay-types yielded equally when harvested six times. Alfagraze usually had equal or lower detergent fiber, and equal or greater crude protein (CP) concentrations than other cultivars. Harvesting more frequently improved forage quality but had little impact on plant density. We concluded that a grazing-type, like Alfagraze, does not show a yield or persistence advantage over a modern hay-type under frequent hay harvest regimes in the lower Midwest. However, the grazing-type used in this study often had superior forage quality.

Abbreviations: ADF, acid detergent fiber • CP, crude protein • NDF, neutral detergent fiber • NIR, near infrared reflectance

	INTRODUCTION

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

 
THE IMPACT of cultivar selection and harvest frequency on yield, forage quality, and stand persistence of alfalfa has been widely studied (Graber and Sprague, 1928; Kust and Smith, 1961; Tesar and Yager, 1985; Brown et al., 1990; Sheaffer and Marten, 1990; Sheaffer et al., 2000). Studies conducted in the 1920s and 1930s showed significant reductions in yield when alfalfa was harvested too frequently during the growing season or when harvested within 6 wk of the first killing frost (Graber and Sprague, 1928; Silkett et al., 1937; Tysdal and Kiesselbach, 1939). Much of this early work was conducted with relatively unimproved cultivars such as ‘Grimm’, ‘Nebraska common’, and ‘Ladak’. As plant breeders developed alfalfa cultivars with rapid recovery, greater disease resistance, and improved winter hardiness, they found that more frequent harvests were possible. Kust and Smith (1961) reported that ‘Vernal’ alfalfa ideally would be harvested three times (at about 42-d intervals) before 1 September in Wisconsin as a compromise among forage yield, quality, and stand persistence. However, harvesting four or more times during the growing season or after 1 September reduced yields the following year by 30 to 78%. Subsequent studies by Matches et al. (1970), Brink and Marten (1989), Brown et al. (1990), and Sheaffer et al. (2000) have shown that alfalfa should be harvested every 30 to 35 d during the growing season to maximize forage yield, quality, and stand persistence.

Research from Georgia suggests that harvesting alfalfa frequently during the growing season may be less detrimental for grazing-type cultivars than for traditional hay-types (Brummer and Bouton, 1991, 1992). Brummer and Bouton (1991) found that Alfagraze, a cultivar selected under continuous grazing pressure, was morphologically different than modern hay-types, being more decumbent and having many, thin stems compared with modern hay-types. They suggested that these morphological traits made grazing-type alfalfa cultivars tolerant of frequent harvests. Subsequent research with Alfagraze showed that it tolerated weekly harvests in the greenhouse better than ‘Florida 77’ (Brummer and Bouton, 1992). An extension of this work in the field by Hoveland et al. (1996) showed that Alfagraze had equal yields when harvested every 4 wk vs. every 6 wk during the growing season. Based in part on the research of Hoveland et al. (1996), farmers in the lower Midwest often plant Alfagraze and other grazing-type alfalfas, expecting that more frequent harvests (and in turn better quality forage) are possible with these cultivars without decreasing yields or stand persistence.

Alfalfa producers in the lower Midwest need stands to last at least 5 yr and expect them to last 6 or 7 yr (Moore et al., 1991). Despite extensive research on alfalfa cultivar selection and harvest frequency, especially in the north central states, most studies have been conducted for 3 yr and, therefore, do not fully address long-term effects. Many researchers note that older alfalfa stands respond differently to harvest management regimes than younger stands (Sheaffer and Marten, 1990; Horrocks and Zaifnejad, 1997). Cumulative effects that influence alfalfa yield or quality in the fourth year or beyond might not have been detected in previous experiments. Given the trend of alfalfa producers in the lower Midwest to plant a grazing-type of alfalfa and to harvest it up to six times during the growing season, long-term studies examining the influence of this management are needed. Our objective was to determine the influence of cultivar-type and harvest frequency on long-term alfalfa yield, forage quality, and stand persistence.

	MATERIALS AND METHODS

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

 
Alfagraze, Pioneer 5373, and Cody alfalfa were seeded on 1 Apr. 1994, at the Southwest Missouri Research Center, near Mt. Vernon, MO, on a Huntington silt loam (fine-silty, mixed, mesic Fluventic Hapludoll). These cultivars represent three distinct types: a grazing-type (Alfagraze), a modern multipest resistant hay-type (Pioneer 5373), and an older, commonly planted hay-type (Cody). At planting, Alfagraze was the only commercially available grazing type, Pioneer 5373 was representative of a modern hay-type and Cody was the most widely planted hay-type in the lower Midwest. A summary of the other differences between these cultivars, including fall dormancy and disease resistance ratings, is shown in Table 1. Before planting, the plot area was sprayed with 3.9 kg ha^-1 a.i. of EPTC (S-ethyl dipropylthiocarbamate) to control weeds during establishment. Seed was inoculated with Rhizobium meliloti, and then broadcast seeded at a rate of 17 kg ha^-1. After seeding, the soil was firmed with a cultipacker.

View this table: [in this window] [in a new window]   Table 1. Fall dormancy and disease resistance ratings of Alfagraze, Cody, and Pioneer 5373 alfalfa.

Weeds were controlled with an annual dormant season application of 840 g ha^-1 a.i. hexazione (3-cyclohexyl-6-(dimethylamino)-1-methyl-1,3,5,triazine-2,4(1H,3H)-dione). Additional weeds (mainly summer annual grasses) were controlled by applications of paraquat dichloride (1,1'-dimethyl-4,4'-bipryidinium dichloride) at 263 g ha^-1 a.i., clethodim {(E)-2-[1-[[(3-chloro-2-propenyl)oxy]imino]propyl-5-[2-(ethylthio)propyl]-3-hydroxy-2-cyclohexen-1-one} at 175 g ha^-1 a.i., or sethoxydim(2-[1-(ethoxyimino)butyl]-5-[2-(ethylthio)-propyl]-3-hydroxy-2-cyclohexen-1-one) at 420 g ha^-1 a.i. Carbofuran (2,3-dihydro-2,2-dimethyl-7-benzofuranol methylcarbamate) was applied at 1121 g ha^-1 a.i. each year in early April to control alfalfa weevil (Hypera postica Gyllenhal). Other insect pests, mainly potato leafhopper (Empoasca fabae Harris), were controlled as needed with carbofuran at 1120 g ha^-1 a.i. or carbaryl (1-napthyl N-methylcarbamate) applied at 1350 g ha^-1 a.i.

Treatments
There were nine treatments consisting of three alfalfa cultivars as main plots and three harvest frequencies (four, five, or six harvests before 15 September; Table 2) as subplots. These harvest frequencies provided approximately 42 d between cuttings when harvested four times, 34 d between cuttings when harvested five times, and 28 d between cuttings when harvested six times. During the establishment year (1994), all plots were harvested three times. Harvest frequency treatments began in spring 1995 and continued through the 1999 growing season.

Forage Quality Analyses
Crude protein, acid detergent fiber (ADF), and neutral detergent fiber (NDF) were determined for all samples collected in 1995, 1997, 1998, and 1999 using near infrared reflectance (NIR) spectroscopy. Forage samples from 1996 were accidentally discarded. The NIR spectrophotometer was a Pacific Scientific 6250 scanning monochromator (NIRSystems, Silver Spring, MD) operating with software developed by Infrasoft International (Port Matilda, PA). The spectrophotometer was calibrated for CP, ADF, and NDF by regressing chemically derived data against spectral data using modified partial least squares regression (Shenk and Westerhaus, 1991). The NIR calibration and validation statistics are presented in Table 3.

Stand Density Measurements
Stand density was determined by counting the number of plants in four, randomly placed, 0.1 m² quadrats within each plot. Stand density was measured in June (after the first harvest) and in December of the establishment year (1994). Thereafter, stand density was measured after the first harvest (May) and last harvest (September) of each year.

Experimental Design
The experimental design was a randomized complete block in a split-plot arrangement of treatments with four replications. Analysis of variance was conducted on cultivars (main plots), harvest frequencies (subplots), years (sub-subplots), and all possible interactions using the model outlined by Steele and Torrie (1980). Main effects and all interactions were considered significant when P < 0.05. When the F-test was significant (P < 0.05), means were separated using Fisher's protected LSD (alpha = 0.05) (Steele and Torrie, 1980).

	RESULTS AND DISCUSSION

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

 
Forage Yield
The main effects of cultivars and harvest frequencies were significant. Cultivar x year and harvest frequency x year interactions were significant. Due to the significant interactions with year, data are presented by year. However, interactions between cultivars and harvest frequency were not significant for any year and the three-way interaction of cultivar, harvest frequency, and year was not significant. Thus, data for cultivars were combined across harvest frequencies and in turn, data for harvest frequencies were combined over cultivars.

Cultivar Response
In total, from 1995 through the end of 1999, Pioneer 5373 produced 6% more dry matter than Alfagraze and 10% more than Cody (Table 4). Much of this difference occurred in 1995 and 1996 when Pioneer 5373 annually produced 0.8 Mg ha^-1 more dry matter than Alfagraze, and 1.4 and 1.3 Mg ha^-1 more, respectively, than Cody. The cultivar-types did not differ in 1997. In 1998, Pioneer 5373 yielded 0.5 Mg ha^-1 more than Alfagraze and 0.6 Mg ha^-1 more than Cody while in 1999, Pioneer 5373 yielded 0.8 Mg ha^-1 more than Alfagraze and 1.2 Mg ha^-1 more than Cody. These data suggest that Pioneer 5373, a modern hay-type, was better suited to the harvest regimes used in this study than was Alfagraze, a grazing-type, or Cody, an older, but commonly planted hay-type.

Harvest Frequency Response
From 1995 through 1999, alfalfa harvested four times yielded an average of 0.8 Mg ha^-1 more per year than alfalfa harvested five times (Fig. 1) . However, there were significant interactions among years. For instance, in 1995, the first full production year, alfalfa harvested five times annually yielded 1.3 Mg ha^-1 more than when harvested four times. But in 1996, 1997, and 1999, alfalfa harvested four times produced an average of 1.8 Mg ha^-1 more than when harvested five times. Annual yields for plots harvested four or five times were similar in 1998, a high yielding year for all treatments.

View larger version (31K): [in this window] [in a new window]   Fig. 1. Yield at each harvest for alfalfa harvested four, five, or six times before 15 September for 5 yr in southern Missouri. Data are averaged over three cultivars. Bars indicate standard errors at individual harvests. Total annual yield and LSD values are presented in tabular format within each panel. Lines connecting harvest dates are included only to clarify treatments and do not indicate a linear response between harvest dates.

The seasonal pattern of forage production was roughly similar among treatments within a year (Fig. 1). However, seasonal trends between years varied widely. Precipitation appeared to have a major influence on the pattern of seasonal forage yield. For instance, in 1995 and 1999, the first harvest produced the highest yield of the season for all treatments and then subsequent harvests yielded less. Precipitation in 1995 and 1999 was above average in April, May, and June followed by below average rainfall for the rest of the growing season (Fig. 2) . Under typical conditions in Missouri, the first harvest produces approximately 30% of the annual yield in a four-harvest system (Joost et al., 1998). The below average rainfall in the summer of 1995 and 1999 reduced summer production and indirectly increased the relative contribution of the first harvest to nearly 40%.

View larger version (49K): [in this window] [in a new window]   Fig. 2. Monthly precipitation from January 1995 through December 1999 and the 39-yr monthly average precipitation at the Southwest Missouri Research Center near Mt. Vernon, MO.

Forage Quality
Cultivars and harvest frequencies differed in ADF, NDF, and CP, and cultivar x year interactions were significant. Due to the significant interactions with year, data are presented by year. However, interactions between cultivar and harvest frequency were not significant for any year and the three-way interaction of cultivar, harvest frequency, and year was not significant. Thus, data for cultivars were combined across harvest frequencies and data for harvest frequency responses were combined over cultivars.

Cultivar Response
Cultivars showed small differences in forage quality at individual harvests, so the data are summarized as annual averages (weighted by yield) (Table 5). In 1995, there was no difference in ADF among cultivars (Table 5). In 1997, 1998, and 1999, Alfagraze had 9 to 16 g kg^-1 less ADF than Cody while Pioneer 5373 was often intermediate to the other two cultivars. Neutral detergent fiber responded similarly to ADF. Except for 1997, Alfagraze had less NDF than either of the other two cultivars. In 1997, Alfagraze and Pioneer 5373 had similar NDF concentrations while Cody had 12 g kg^-1 more NDF than Pioneer 5373 and 16 g kg^-1 more than Alfagraze (Table 5). In all years except 1999, CP for Pioneer 5373 and Cody was similar, but both cultivars had less CP than Alfagraze (Table 5). In 1999, Alfagraze had the most CP, Pioneer 5273 was intermediate, and Cody had the least CP. Based on all years, Alfagraze averaged 8 g kg^-1 more CP than the other cultivars.

Harvest Frequency Response
In each year tested, the annual average ADF and NDF was highest when harvested four times, intermediate when harvested five times, and lowest when harvested six times (Fig. 3 and 4) . Averaged over years, ADF for alfalfa harvested four times was approximately 36 g kg^-1 higher than when harvested five times, and ADF for alfalfa harvested five times was 23 g kg^-1 higher than when harvested six times (Fig. 3). Patterns for NDF were similar to those for ADF but the differences were about 46 g kg^-1 between harvesting four or five times, and about 28 g kg^-1 between harvesting five and six times (Fig. 4). In a consistent manner, CP was highest when harvested six times (4-yr avg. of 250 g kg^-1), intermediate when harvested five times (4-yr avg. of 227 g kg^-1) and lowest when harvested four times (4-yr avg. of 195 g kg^-1) (Fig. 5) .

View larger version (30K): [in this window] [in a new window]   Fig. 3. Acid detergent fiber concentration at each harvest for alfalfa harvested four, five, or six times before 15 September in southern Missouri. Data are averaged over three cultivars. Bars indicate standard errors. Annual weighted averages and LSD values are presented in tabular format. Lines connecting harvest dates are included only to clarify treatments and do not indicate a linear response between harvest dates.

View larger version (31K): [in this window] [in a new window]   Fig. 4. Neutral detergent fiber concentration at each harvest for alfalfa harvested four, five, or six times before 15 September in southern Missouri. Data are averaged over three cultivars. Bars indicate standard errors. Annual weighted averages and LSD values are presented in tabular format. Lines connecting harvest dates are included only to clarify treatments and do not indicate a linear response between harvest dates.

View larger version (29K): [in this window] [in a new window]   Fig. 5. Crude protein concentration at each harvest for alfalfa harvested four, five, or six times before 15 September in southern Missouri. Data are averaged over three cultivars. Bars indicate standard errors. Annual weighted averages and LSD values are presented in tabular format. Lines connecting harvest dates are included only to clarify treatments and do not indicate a linear response between harvest dates.

In 1995, within a harvest frequency, ADF and NDF fluctuated in a 40 g kg^-1 range from April through August, but both ADF and NDF were much lower at the final harvest in mid-September (Fig. 3 and 4). Although there were some exceptions in 1997, 1998, and 1999, ADF and NDF within a treatment tended to be low early in the season, higher during mid-summer, and low again in autumn. The trends for CP were, appropriately, nearly the opposite of that for ADF and NDF.

The forage quality data suggest two things. First, harvest frequency has a large effect on forage quality and a greater effect than cultivar selection. Few other management practices influence forage quality more than does harvest frequency. Producers wishing to produce higher quality hay for a given cultivar will have to harvest more frequently, although there are biological and economic limits. Second, environmental conditions greatly influence potential forage quality. For instance, forage quality tends to be greatest (low in ADF and NDF; high in CP) at the first and last harvest of the season when temperatures in the lower Midwest are cooler, daylengths shorter, and soil moisture is likely to be adequate. In a review, Marten et al. (1988) concluded the size of alfalfa stems was larger and forage quality was lower when daylengths were long vs. short. In addition, they suggested quality of alfalfa grown under field conditions was often superior when ambient temperatures during the growing season were cool compared with warm. Thus, while second, third, and later harvests of alfalfa often demand a premium in the marketplace (Moore et al., 1991), our data, along with that of previous research, suggest that alfalfa harvested in mid-summer is potentially the lowest quality hay of the season.

The response of forage quality to harvest frequency is consistent with the work of other scientists. Kust and Smith (1961), Matches et al. (1970), Brink and Marten (1989), Sheaffer and Marten (1990), and Sheaffer et al. (2000) all showed that harvest frequency is a major factor influencing alfalfa quality in the north central USA. Our data, collected over a greater number of years, and at a more southern location, corroborate that conclusion and suggest that age of the stand does not influence the response to harvest frequency for forage quality.

Stand Persistence
Initially, plant density declined rapidly for all treatments, but then the rate slowed as the experiment progressed (Fig. 6) . At 85 d after planting, all treatments had a density of 265 plants m^-2. Then, regardless of harvest frequency or cultivar, all stands continued to thin rapidly over the next 12 to 18 mo, so that by the spring of 1996, there were only 60 plants m^-2. Thereafter, stands thinned at a much slower rate. Jackobs and Miller (1973) in Illinois and Hoveland et al. (1996) in Georgia reported similar rates of plant thinning for field-grown alfalfa. By the autumn of 1999, our plots still averaged 42 plants m^-2, which can still provide acceptable yields under good management (Jackobs and Miller, 1973; Mays and Evans, 1973; Tesar and Yeager, 1985).

View larger version (19K): [in this window] [in a new window]   Fig. 6. Stand density of alfalfa harvested four, five, or six times before September 15 for 5 yr in southern Missouri. Data are averaged for three cultivars. Bars indicate standard errors.

Although plant persistence is desirable, in this study, it was not always related to forage yield. Pioneer 5373 and Alfagraze had similar stand densities, yet Pioneer 5373 yielded more (Table 4). Under a typical hay-management regime in Iowa, Brummer and Moore (2000) found Alfagraze maintained equal stands but yielded less than most commercial hay-types. In addition, Bates et al. (1996) found that Alfagraze was more persistent under heavy grazing pressure, but that hay-types showed equal persistence when grazing pressure was reduced. Producers most interested in stand longevity might select a grazing-type like Alfagraze or a modern hay-type like Pioneer 5373 over an older hay-type like Cody. However, our data shows that greater plant persistence does not necessarily lead to increased forage yield, at least when stand density is >46 plants m^-2. In a review, Sheaffer et al. (1988) concluded that plant persistence and yield are not necessarily correlated because as stands thin, individual plants compensate for this loss by producing more stems per plant.

Harvest Frequency Response
In this study, stand density was not consistently influenced by harvest frequency. Plots harvested six times had fewer plants m^-2 in the autumn of 1995 and the spring and autumn of 1996 than plots harvested four or five times, but these differences did not last (Fig. 6). By the end of 1999, all treatments had similar density. This suggests that, with good soil fertility and pest control, plant persistence is affected less by harvest frequency than by cultivar selection in the lower Midwest. This is in contrast to research from Minnesota (Brink and Marten, 1989; Sheaffer and Marten, 1990), where alfalfa harvested four times during the growing season had lower persistence than when harvested three times. However, our data are similar to that collected in Georgia (Hoveland et al., 1996), where alfalfa harvested every 4 wk persisted as well as when harvested every 6 wk.

	CONCLUSIONS

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

 
1. Alfalfa should be harvested four times before 15 September in the lower Midwest if yield is the major consideration. Harvesting five times increases forage quality with only a slight reduction in yield. Producers should consider the premium assessed to higher quality hay before deciding to harvest five vs. four times. Harvesting six times gives the highest quality forage, but yields are markedly reduced.

2. Harvesting either four, five, or six times per year has less influence on stand persistence than does cultivar selection. Stand persistence in southern Missouri is greater for a grazing-type (Alfagraze) than for an older hay-type (Cody). Perhaps cultivars selected under grazing are inherently more persistent than those developed under a typical hay-harvesting regime.

3. In this study, the grazing-type of alfalfa, Alfagraze, did not show a yield or persistence advantage over a modern hay-type like Pioneer 5373 under frequent harvest regimes. However, the forage quality of the grazing-type was often superior to the hay-types. Further, a grazing-type of alfalfa would presumably provide more within-year management options (hay or grazing).

4. Forage quality is generally lowest in mid-summer. Second, third, and later harvests of alfalfa often demand a premium in the marketplace, but our data suggest that in harvest regimes with four to six cuttings per year, alfalfa harvested in spring or late summer has the potential to be the best quality hay of the season in the lower Midwest.

	NOTES

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

 
Contribution from the Missouri Agric. Exp. Stn. Journal Series no. 13,180. Mention of trade name or proprietary product does not constitute endorsement by the University of Missouri over products of other manufacturers that may also be suitable.

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

 

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