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PRODUCTION PAPER

Agronomic Consequences of Dormant–Nondormant Alfalfa Mixtures

Agron. Dep., Iowa State Univ., Ames, IA 50011

* Corresponding author (brummer{at}iastate.edu)

Received for publication April 23, 2001.

	ABSTRACT

TOP NOTES ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION REFERENCES

 
The yield of alfalfa (Medicago sativa L.) during the establishment year is typically less than that from fully established stands. Because nondormant cultivars produce more growth during autumn than dormant cultivars, a mechanism to increase yield during the establishment year in northern areas of the USA could be to mix seed of nondormant and adapted cultivars at planting. The objective of this experiment was to determine if establishment year yield could be improved by seeding dormant–nondormant mixtures without adversely affecting yield in the succeeding year. Two dormant–nondormant mixtures (‘Vernal’–'Mecca II' and ‘5454’–‘5939’) with 10, 30, or 50% of the nondormant cultivar and pure stands of all four cultivars were seeded in field studies near Ames, Nashua, and Castana, IA, in April 1998. Four forage harvests were taken in 1998, including one in late October, and in 1999. Plants were counted in May and October 1998 and in June 1999. Plant numbers among treatments were similar during 1998. Stand mortality in spring 1999 increased as the nondormant percentage increased, except that 10% nondormant plots had slightly more plants than 0% plots. In 1998, total forage yield increased linearly with increasing percentage of nondormant seed, but nutritive value in October 1998 declined slightly with increasing percentages of nondormant seed. In 1999, yield declined linearly as the percentage of nondormant seed increased; plots with 10% nondormant seed yielded less than the pure stands of dormant cultivars. We do not recommend mixing any nondormant seed with adapted dormant cultivars at planting.

Abbreviations: CP, crude protein • FD, fall dormancy • IVDMD, in vitro dry matter digestibility • NDF, neutral detergent fiber

	INTRODUCTION

TOP NOTES ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION REFERENCES

 
THE ECONOMIC RETURNS of alfalfa production are unfavorable in the establishment year when yields typically range from 40 to 60% of established stands (Brummer and Smith, 1999; Tesar and Jackobs, 1972) and when seed costs must be included. Yields can be maximized by clear-seeding alfalfa with a herbicide (Tesar and Marble, 1988) and harvesting three or four times beginning 60 d after planting (Sheaffer, 1983), but they never reach the level of fully established stands.

Dormancy classes of alfalfa cultivars are determined by the amount of regrowth produced in the fall following a late-season harvest, with a fall dormancy (FD) score = 1 representing very fall dormant and FD = 11 representing extremely nondormant (Teuber et al., 1998). Alfalfa cultivars adapted to the upper midwestern USA are classified as dormant or moderately dormant, with FD scores of 2 to 4. In general, more dormant cultivars are also more winter hardy. In the upper Midwest, FD = 1 cultivars produce too little yield, and FD 5 cultivars suffer too much winter injury to be productively grown. Nondormant cultivars (FD 8) can produce higher yields in the establishment year, but they tend to die over winter (Brummer, unpublished, 1999).

Yield depends on stand density. The minimum number of plants per square meter needed for optimum yields declines from 140 in the year after seeding to 50 to 60 in mature stands as the survivors grow larger to fill gaps left as plants die (Tesar and Marble, 1988). Commonly recommended seeding rates of alfalfa (15–18 kg ha^-1) result in about 800 seeds m^-2, and stands at the end of the seeding year are generally between 200 to 400 plants m^-2, considerably above the required 140 needed for maximum yield in the following year.

A means of improving the first-year yield may be to include a portion of nondormant seed with the adapted cultivar at the time of seeding. Although this may seem counterintuitive, the idea could work if the nondormant plants produced higher yield than the adapted cultivar and if the loss of these plants over winter did not adversely affect stand life or yield in subsequent years. Given that most established alfalfa stands have excess plants after the first year, the loss of nondormant plants over winter may not be a serious problem. The stands will be less affected in years with mild winters because not all of the nondormant plants will die (Ryerson and Brummer, unpublished, 2000). The percentage of nondormant seed that may be included without adversely affecting future performance but still providing some first-year yield boost needs to be determined.

Another consideration in using nondormant alfalfa cultivars is a possible negative effect on nutritional value. Nondormant cultivars typically have fewer but thicker stems than dormant and semidormant cultivars (Brummer and Bouton, 1991). Stems and, in particular, stem bases represent the least digestible part of an alfalfa plant (Marten et al., 1988). Though alfalfa forage from any cultivar likely will be of high nutritional value relative to most other forage species, some deleterious effects on nutritional value may be observed due to the presence of nondormant plants.

The objective of this experiment was to test the hypothesis that mixtures of dormant and nondormant alfalfa cultivars would result in improved establishment year yields without adversely affecting nutritional value or compromising yield and stand density in the subsequent year.

	MATERIALS AND METHODS

TOP NOTES ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION REFERENCES

 
Two nondormant cultivars, 5939 and Mecca II (FD = 9), and two commonly grown midwestern cultivars, Vernal (FD = 2) and 5454 (FD = 4), were used in the experiment. Vernal represents a standard check cultivar, and 5454 is an elite cultivar with excellent yields in Iowa (Brummer and Smith, 1999). For convenience, we refer to both Vernal and 5454 as dormant cultivars in the following discussion. All cultivars were grown as pure stands. In addition, a series of mixtures of 5939 with 5454 and of Mecca II with Vernal were included such that 10, 30, or 50% (on a weight basis) of the total seed planted was the nondormant cultivar. Germination of all cultivars was >90%.

Field experiments were planted in three Iowa locations representing diverse soil and climatic conditions: the Agronomy and Agricultural Engineering Research Farm west of Ames, IA, in a Nicollet loam soil (fine-loamy, mixed, superactive, mesic Aquic Hapludolls) on 14 Apr. 1998; the Northeast Research Farm south of Nashua, IA, in a Readlyn loam soil (fine-loamy, mixed, mesic Aquic Hapludolls) on 23 Apr. 1998; and the Western Research Farm east of Castana, IA, in a Monona silt loam (fine-silty, mixed, superactive, mesic Typic Hapludolls) on 22 Apr. 1998. The mean air temperature and precipitation for the three locations during the experiment, together with a mean value for the past 50 yr, are listed in Table 1. The experiment at each location consisted of 0.9- by 3.7-m plots arranged in a randomized complete block design with four replications. Seed was drilled at 17 kg ha^-1 in plots consisting of five rows spaced 15 cm apart. The mixtures had 10, 30 or 50% of the 17 kg ha^-1 as the nondormant component. All seed was treated with the correct Sinorhizobium species. The entire plot area was bordered by alfalfa. The selective herbicide EPTC (s-ethyl dipropylthiocarbamate) was applied at 4.67 L ha^-1 for pre-emergent weed control at Ames and Nashua; no herbicides were applied at Castana. Fertility was maintained throughout the study at recommended rates. Potato leafhoppers (Empoasca fabae Harris) were controlled at Ames and Nashua by spraying permethrin (Pounce) [3-(phenoxyphenyl)methyl (±)-cis,trans-3-(2,2-dichloroethenyl)-2,2-dimethyl cyclopropanecarboxylate (approximately 60% trans, 40% cis isomers)] twice in 1998 and 1999. No insecticides were used at Castana.

Nutritional value was assessed at the first and fourth harvests in 1998 by analyzing in vitro dry matter digestibility (IVDMD), crude protein (CP), and neutral detergent fiber (NDF) using near-infrared reflectance spectroscopy (NIRS) calibrated with wet laboratory analyses (Windham et al., 1989). In brief, samples were dried at 60°C for 4 d, after which they were ground to pass a 1-mm screen and scanned from 1100 to 2500 nm with a NIRS Systems (Silver Spring, MD) Model 6500 spectrophotometer. After collection of near-infrared spectral data, a representative set of samples was selected using the SUBSET program for chemical analysis to develop calibration equations for the instrument. Chemical analyses of the calibration subset was conducted in duplicate for each trait as previously described (Moore et al., 1995).

Calibration equations were developed by modified partial least squares regression (Shenk and Westerhaus, 1991). The coefficients of determination (R²) and standard errors of calibration and cross validation were, respectively, 0.99, 0.50, and 1.08 for IVDMD; 0.99, 0.22, and 0.48 for CP; and 0.99, 0.42, and 0.87 for NDF.

Data were analyzed with the SAS statistical software package (SAS Inst., 1990) using PROC GLM. The four degrees of freedom for percentage of nondormant seed in the seeding mixture were decomposed into four nonorthogonal contrasts testing linear effects, quadratic effects, dormant vs. nondormant cultivars (i.e., 0 vs. 100% nondormant seed), and 0 vs. 10% nondormant seed. Statistical significance was assessed at the 5% probability level unless otherwise indicated.

	RESULTS AND DISCUSSION

TOP NOTES ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION REFERENCES

 
In general, both mixtures responded similarly, so the two mixtures were pooled and all results are presented in terms of the percentage of nondormant seed in the planting mixture. Locations differed for most traits, and location x percentage nondormant seed interactions were present in some cases. However, because the interactions reflected magnitude differences rather than changes in rank, we pooled the three locations for analysis.

All cultivars and their mixtures established well, as demonstrated by the high plant numbers in May 1998, approximately 1 mo after planting (Table 2). The nondormant cultivars had slightly fewer plants than the dormant cultivars, primarily due to a weaker stand of Mecca II (data not shown). However, by the end of the establishment year, no differences among the cultivar types was evident. Even though the 1998–1999 winter was mild for Iowa (Table 1), stands declined in plots with increasing percentages of nondormant seed although plots with 10% nondormant seed had more plants than the dormant cultivars. Thus, plant numbers may not be affected if a small percentage of the seed planted is a nondormant cultivar, but more substantial amounts of nondormant seed included in the seeding mix will likely depress plant numbers after winter.

Yield in the second production year is the key to the successful use of dormant–nondormant mixtures. Despite the mild winter, large yield reductions were observed in the nondormant cultivars relative to dormant cultivars (Table 3). Importantly, even though plant numbers were higher for the 10% nondormant plots compared with the dormant plots (Table 2), the former produced less forage than the dormant pure stands in 1999, primarily due to a large reduction in first-harvest yield (Table 3). From these results, we suggest that including even small amounts of nondormant seed in the mixture can have serious implications for postestablishment year yields. As the 1999 season progressed, the yield differential between the dormant and nondormant cultivars lessened, but this was partially the result of dandelion (Taraxacum officinale L.) encroachment in the nondormant plots. Although we did not quantify the amount of dandelion present, dandelion was only present in the plots with significant open areas, typical of plots with large amounts of nondormant seed.

Crude protein and NDF were similar for all treatments at the first harvest in 1998, but IVDMD declined linearly as the percentage of nondormant seed increased (Table 4). At the final harvest, the nondormant cultivars had lower nutritive value, in terms of all three parameters measured (i.e., lower IVDMD, lower CP, and higher NDF), than the dormant cultivars, and both linear and quadratic effects were noted across all treatments. The higher yields observed due to the inclusion of nondormant seed, then, was offset by lower quality. Nevertheless, the quality of all entries was excellent, so this slight quality decline is probably immaterial when considering the overall dietary needs of the livestock.

	ACKNOWLEDGMENTS

 
We thank Mike Peterson, W-L Seeds, for an interesting discussion that led to this study and Mark Smith and Trish Patrick for technical assistance. Partial funding of this research was generously provided by the Leopold Center for Sustainable Agriculture at Iowa State University, Grant no. 2000-47.

	NOTES

TOP NOTES ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION REFERENCES

 
Journal Paper no. J-19234 of the Iowa Agric. Home Econ. Exp. Stn., Ames, IA, Project no. 2569, supported by Hatch Act and State of Iowa Funds.

	REFERENCES

TOP NOTES ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION REFERENCES

 

• Brummer, E.C., and J.H. Bouton. 1991. Plant traits associated with grazing-tolerant alfalfa. Agron. J. 83:996–1000.[Abstract/Free Full Text]
• Brummer, E.C., and M. Smith. 1999. The 1999 Iowa crop performance test—alfalfa. Ext. Bull. AG-84. Iowa State Univ. Ext., Ames.
• Marten, G.C., D.R. Buxton, and R.F Barnes. 1988. Feeding value (forage quality). p. 463–491. In A.A. Hanson et al. (ed.) Alfalfa and alfalfa improvement. Agron. Monogr. 29. ASA, CSSA, and SSSA, Madison, WI.
• Moore, K.J., K.P. Vogel, T.J. Klopfenstein, R.A. Masters, and B.E. Anderson. 1995. Evaluation of four intermediate wheatgrass populations under grazing. Agron. J. 87:744–747.[Abstract/Free Full Text]
• SAS Institute. 1990. SAS/STAT user's guide. Version 6. 4th ed. SAS Inst., Cary, NC.
• Sheaffer, C.C. 1983. Seeding year harvest management of alfalfa. Agron. J. 75:115–119.[Abstract/Free Full Text]
• Shenk, J.S., and M.O. Westerhaus. 1991. Population structure of near infrared spectra and modified partial least squares regression. Crop Sci. 31:1548–1555.[Abstract/Free Full Text]
• Tesar, M.B., and J.A. Jackobs. 1972. Establishing the stand. p. 415–435. In C.H. Hanson (ed.) Alfalfa science and technology. Agron. Monogr. 15. ASA, CSSA, and SSSA, Madison, WI.
• Tesar, M.B., and V.L. Marble. 1988. Alfalfa establishment. p. 303–332. In A.A. Hanson et al. (ed.) Alfalfa and alfalfa improvement. Agron. Monogr. 29. ASA, CSSA, and SSSA, Madison, WI.
• Teuber, L.R., K.L. Taggard, L.K. Gibbs, M.H. McCaslin, M.A. Peterson, and D.K. Barnes. 1998. Fall dormancy. In Standard tests to characterize alfalfa cultivars. 3rd ed. (Amended 1998). North Am. Alfalfa Improvement Conf., Beltsville, MD. (Available online at http://www.naaic.org/stdtests/Dormancy2.html). (Verified 25 Mar. 2002.)
• Windham, W.R., D.R. Mertens, and F.E. Barton II. 1989. Protocol for NIRS calibration: Sample selection and equation development and validation. p. 97–103. In G.C. Marten et al. (ed.) Near infrared reflectance spectroscopy (NIRS): Analysis of forage quality. USDA, Washington, DC.

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