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a USDA-ARS, National Soil Tilth Lab., Ames, IA 50011
b Dep. of Agronomy, Iowa State Univ., Ames, IA 50011
* Corresponding author (singer{at}nstl.gov)
Received for publication February 3, 2006.
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ABSTRACT |
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 TOPNOTES ABSTRACT INTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSREFERENCES |
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Abbreviations: DM, dry matter • 4REB, four-row, early band treatment • 4RLB, four-row treatment with a late glyphosate band: 4RNB, four-row treatment without a glyphosate band • 2RB, two-row band treatment • 2RBNC, two-row band, no-chop treatment
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INTRODUCTION |
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TOPNOTESABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSREFERENCES |
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Innovative cover crop management systems are needed to reduce costs and maintain the same level of ecosystem benefits. Self-seeding legume cover crop systems are an example of an innovative approach relying on natural processes to reduce input costs and provide environmental protection from agricultural production. Ranells and Wagger (1992) reported that crimson clover (Trifolium incarnatum L.) successfully reseeded each year during their 3-yr study and that corn (Zea mays L.) grain yield was only marginally affected in 1 of 3 yr. They concluded that under adequate moisture conditions, a 50% dessicated strip can maximize clover N contribution, but a 75% strip-width can minimize potential competition with corn for water. Boquet and Dabney (1991) evaluated legume species for their effectiveness at reseeding and reported that crimson and subterranean (Trifolium subterraneum L.) clovers and big flower vetch (Vicia grandiflora Scop.) all reseeded before 21 April, berseem clover (Trifolium alexandrinum L.) reseeded before 13 May, and arrowleaf clover (Trifolium vesiculosum Savi.) did not reseed in a grain sorghum system in northeastern Louisiana.
Interest in legume reseeding systems was focused primarily on the N contribution from the legume to reduce N costs for subsequent crops with high N demand. Winter cereal cover crops do not offer the same potential for offsetting N costs, but do protect the soil, increase organic matter, and cycle nutrients (Hartwig and Ammon, 2002; Sarrantonio and Gallandt, 2003; Snapp et al., 2005). Successful self-seeding winter cereal cover crop systems must not excessively compete with the cash crop. Results from relay-intercropped soybean in winter wheat in Missouri found that soybean yield, averaged across 3 yr, was reduced 12% compared with a no-wheat full-season soybean planted in 80-cm row widths when wheat was at Feekes growth stage 10.3 and no N was added (Reinbott et al., 1987).
In self-seeding winter cereal systems where management of the cereal grain is not dependent on grain yield, it may be possible to reduce yield loss further. Singer and Kohler (2005) reported from 30 to 60% yield loss in soybean using mechanical control to suppress a rye cover crop at second node-, boot-, and anthesis growth stages. In their study, the four rows of rye planted between each 76-cm soybean row were highly competitive with soybean. Reducing the number of rows of cover crops spatially and temporally and using different winter cereals may provide more viable management options for producers, yet still provide the desirable ecosystem benefits. The objectives of this study were to: (i) compare growth and seed production of winter wheat, triticale, and rye cover crops using different planting configurations and management options while growing concurrently with soybean; (ii) quantify the competition effects on soybean yield and yield components; and (iii) determine the ability of the cover crops to self-seed.
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MATERIALS AND METHODS |
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TOPNOTESABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSREFERENCES |
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The experimental design was a randomized complete block with treatments arranged as a split-plot with four replicates. Cover crop species main plots were randomly assigned to winter rye (‘Rymin’), wheat (‘Karl 92’) and triticale (‘Décor’ in 2003 and ‘Kitaro’ in 2004). Décor seed was unavailable in 2004, therefore Kitaro was selected because it had a similar height and anthesis date. Cereals were selected for low height and an early anthesis date to minimize competition with soybean for light and to minimize delaying soybean planting. Cover crops were planted at 2 470 000 seeds ha–1 on 25 Sept. 2003 and 9 Oct. 2004 using a Marliss (Marliss Division/Sukup Manufacturing Co., Jonesboro, AR) grain drill with 19-cm row widths. Subplot treatments were cover crop management systems (Table 1) and a no-cover crop check. On 15 Oct. 2003 and 8 Nov. 2004 stand density was measured by counting all the plants in a 2.3-m2 area in each subplot.
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Mechanical control was applied on 11 May 2004 and 21 May 2005 using a Buffalo (Fleischer Manufacturing, Columbus, NE) rolling stalk chopper to all treatments except the check and 2RBNC. This operation reduced cover crop height from about 45 cm to approximately 15 cm. Feekes growth stages before this operation were 10.3, 10.1, and 8.0 for rye, triticale, and wheat, respectively. Our goal was to time the operation to produce regrowth to obtain seed production. Ashford and Reeves (2003) reported 81 and 74% control of wheat and rye using a roller-crimper at anthesis and 95% control at the soft dough growth stage. To avoid confounding with soybean planting date and regrowth of the cover crops, all species were controlled on the same day.
Asgrow Brand ‘AG2107’ soybean was planted no-tillage on 17 May 2004 and 24 May 2005 at 445 000 seeds ha–1 in 76-cm rows. A glyphosate band was applied to the 4RLB treatment on 3 June 2004 and 9 June 2005, while a second glyphosate band application was applied to the 4REB on 22 June 2004 and 20 June 2005. The two-row band (2RB) and 2RBNC treatments only received one glyphosate band application. On 18 July 2005, glyphosate was broadcast on all plots at a rate of 1.1 kg a.i. ha–1 in solution with 68 L ha–1 of water to minimize weed seed production. Check treatments were maintained weed free for the entire growing season with additional glyphosate and hand weeding as necessary.
Cover crop shoot dry matter (DM) was collected on 10 May 2004 and 20 May 2005 from one 0.5-m2 area (two rows, 0.38 m wide by 1.31 m long) in each subplot. All DM samples were clipped at the soil surface and dried at 70°C in a forced-air oven until a constant weight was achieved. On 17 May 2004 and 24 May 2005, gravimetric soil water was determined from the 0- to 30-cm soil depth by collecting four soil cores (18-mm diam.) from the row zone in each subplot. Soil samples from each subplot were combined, weighed wet, and dried in a forced-air oven at 100°C until dry. Weed density was determined by counting all the weeds in a 2.3-m2 area in each subplot on 4 June 2004 and 13 June 2005. Cover crop tiller density was determined by counting all tillers in a 0.5-m2 area (two rows, 0.38 m wide by 1.32 m long) in each subplot on 8 June 2004 and 14 June 2005. Cover crop height was determined after final height was attained by measuring the distance from the soil surface to the spike tip of the tallest tiller on 10 plants in each subplot.
At cover crop maturity, a 0.5-m2 sample (two rows, 0.38 m wide by 1.32 m long) was collected from each subplot to determine shoot DM, spike number, and seed number. All cover crop plant samples were collected from the two interior rows in each interrow. Samples were collected when cereal treatments reached Feekes growth stage 11.4. At the R8 growth stage (Ritchie et al., 1994) of soybean, plant height from the soil surface to main stem tip was measured on 10 plants in each subplot and soybean plant population density was measured by counting all plants in 6.1 m of the three interior rows of each subplot. A harvest sample was collected from a 0.76-m2 area to determine pod number, seed number pod–1, and weight per 100 seed. In 2004, seed yield was calculated from this sample because of contamination from cover crop seed during soybean combine harvest. In 2005, seed yield was calculated from the combine harvest of the interior three rows of each subplot. Subsamples were collected to determine the mass fraction of cover crop seed and subtracted to obtain soybean seed weight. Seed yield data were corrected to 130 g kg–1 moisture. Cover crop self-seeding plant density was obtained by counting all of the plants in a 2.3-m2 area in each subplot on 11 and 2 Nov. 2004 and 2005.
Daily rainfall and air temperature were recorded at a weather station about 3 km from the experimental site and presented by month for each growing season (Table 2). Statistical analysis was conducted using analysis of variance with block and block by species as random effects and cereal species and management system as fixed effects. Weed density data were square root transformed. Mean separation was accomplished using Fisher's protected LSD at P = 0.05.
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RESULTS AND DISCUSSION |
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TOPNOTESABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSREFERENCES |
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Early Season Measurements
Cover crop DM before soybean planting was greater for rye (566 g m–2) compared with wheat and triticale (443 g m–2) in 2004 (Table 3). These differences in DM production were not reflected in soil water content differences among species. In 2005, rye (598 g m–2) had greater DM production than wheat (437 g m–2), but was similar DM to triticale (504 g m–2). Similarly, no differences in soil water content were detected among species. Using fall plant density as a covariate in the analysis of early season DM was not significant either year. Among cover crop management systems, DM production was greater for the 2RBNC and 2RB (550 and 640 g m–2) in 2004 and 2005 compared with the four-row treatments (439 and 429 g m–2). Westgate et al. (2005) reported rye DM of 604 and 564 g m–2, when mechanical control occurred at anthesis during two growing seasons. In 2004, the check and 4RLB treatments had higher row-zone soil water content compared with the 4REB and 4RNB treatments. In 2005, no soil water content differences were detected. In 2004, soil water measurement occurred on 17 May, and only 35 mm of the monthly 208 mm was recorded. April rainfall in 2004 was also 31% below the 30-yr mean. The expectation of the 4REB treatment was to preserve soil water in the row zone for soybean. In 2004, the 4REB had lower soil water content than the 4RLB treatment. These results indicate that soil surface cover by the cover crop was more important than soil water use by the cover crop for conserving soil water during early soybean growth.
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Tiller density of regrowth was higher in wheat than triticale and rye in both years (Table 3). Tiller density was greater in the 2RBNC compared with all treatments in 2004 except the 2RB and all treatments in 2005. Both two-row treatments probably had greater tiller density than the 4RNB treatment because of greater light transmittance to the plant basal region. Westgate et al. (2005) reported no difference in rye tiller density when mechanical control occurred at the second node, boot, and anthesis growth stages (126 tillers m–2) in 2002 and higher tiller density in 2003 between the second node and anthesis treatments (80 vs. 61 tillers m–2). A species x management system interaction for tiller density was observed in 2005. The interaction occurred because tiller density in the 2RB treatment in wheat and rye were similar (141 tillers m–2), and were both greater than the 2RB in triticale (41 tillers m–2).
Weed densities in early June in each year were similar for species and most management systems (Table 3). In 2005, both two-row treatments had greater weed density than the four-row treatments. Presumably, this difference occurred because of greater light transmittance to the soil surface. In 2004, weed density was dominated by lambsquarters (Chenopodium album L.) and smartweed (Polygonum pensylvanicum L.), while only lambsquarters was dominant in 2005.
Cover Crop Growth
Cover crop DM at maturity was similar across species and averaged 630 and 370 g m–2 in 2004 and 2005 (Table 4). The 2RBNC treatment had greater DM than all other treatments both years. The 2RB treatment had greater DM than the 4REB treatment both years. Among the four-row treatments, differences in DM were limited to the 4REB and 4RLB in 2004. The 2RB treatment probably had greater DM than the 4RNB treatment because of less competition for resources. Although shields were used when the herbicide bands were applied, glyphosate drift may have affected cover crop growth and DM in the 4REB treatment. This treatment may have been affected more because stem elongation had not occurred when the herbicide band was applied.
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A species x management system interaction was also detected in both years for spike density. In 2004, spike density was greater in the 2RB (1032 spikes m–2) compared to 2RBNC (900 spikes m–2) treatment in wheat. In triticale and rye, spike density was greater in the 2RBNC (499 and 675 spikes m–2) compared with 2RB treatment (409 and 423 spikes m–2). In 2005, spike density in wheat was similar in the 4REB, 4RLB, and 4RNB treatments (329, 398, and 319 spikes m–2), but less than the 2RBNC (922 spikes m–2). The 2RB (422 spikes m–2) and 4RLB had similar spike density, both lower than the 2RBNC. In triticale, all treatments were similar (221 spikes m–2) except the 2RBNC (458 spikes m–2). In rye, spike density was similar in the 4REB and 4RNB (112 spikes m–2), which was lower than the 4RLB and 2RB (226 spikes m–2), which was lower than the 2RBNC (532 spikes m–2).
Although an interaction was detected for spike density, seed density did not exhibit the interaction. Seed density was similar across species in 2004 and averaged 10 656 seeds m–2 (Table 4). In 2005, wheat seed density (5070 seeds m–2) was greater than triticale and rye (3542 seeds m–2). The greatest seed density occurred in the 2RBNC treatment both years. In 2004, similar seed production occurred in the 4RLB and 2RB treatments (9895 seeds m–2), which was greater than the 4REB and 4RNB treatments (6574 seeds m–2). In 2005, all of these treatments had similar seed production (1436 seeds m–2), which averaged 90% lower than the 2RBNC treatment. The below-average rainfall and air temperature in June of 2004 may have contributed to the greater seed yield in 2004.
At the time of mechanical control, cover crop development stages ranged from the flag leaf just visible in wheat (Feekes 8.0), to first spikelet of the inflorescence just visible in triticale (Feekes 10.1), to one-half of the inflorescence emerged in rye (Feekes 10.3). The timing of the mechanical control favored regrowth of wheat, although no differences were detected either year for final DM yield and there were no species x management system interactions for final DM. Mechanical control of wheat at the earlier growth stage affected tiller density and spike density, which increased seed density in 1 yr compared with triticale and rye. Using final cover crop DM as a covariate in the analysis for soybean yield and yield components was not significant either year for any variable.
Soybean Yield and Yield Components
Harvest plant population densities were similar across species in both years and generally lower in the more competitive 4RNB and 2RBNC treatments (Tables 5 and 6). In 2004, the 4RNB treatment had lower plant density (29 plants m–2) than all other treatments (36 plants m–2) except the 2RBNC (33 plants m–2). In 2005, the check and 2RB treatments had greater plant density (37 plants m–2) than the 2RBNC treatment, while the 4REB, 4RLB, 4RNB, and 2RB had similar plant density (33 plants m–2). Final DM was similar across species in 2004 (490 g m–2) and 2005 (592 g m–2). The 4REB and 4RLB had similar DM both years. The 2RBNC had lower DM than the 2RB both years and the check had greater DM than the 4RNB both years. The 2RB had greater DM than the 4RNB only in 2004.
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The yield loss observed in this study was greater than expected. Reinbott et al. (1987) reported a 12% soybean grain yield reduction in their relay-intercropped system in wheat compared with full-season soybean when soybean was planted when wheat was at Feekes growth stage 10.3, no N was added, and soybean was planted in 80-cm row widths. Singer and Kohler (2005) reported a 30 to 60% yield reduction in a 2-yr study in Iowa using rye, averaged across mechanical control at the second node-, boot-, and anthesis-growth stages compared with a no-cover crop check. In their study, a skip-row system was not used. One explanation for the magnitude of the yield loss we observed compared with Reinbott et al. (1987) may have been the competitiveness of the cereal cultivars we selected. Identifying less competitive cereal cultivars may lower the soybean yield loss in self-seeding systems. Additional work could also explore cultivar selection and breeding of soybean to improve its competitiveness in systems with interspecific competition.
Species response was similar for seed pod–1 (2.03 and 1.94), g 100 seed–1 (15.4 and 14.2), harvest index (HI) (0.59 and 0.50) in 2004 and 2005, and pod density in 2004 (946 pods m–2); but a species x management system interaction was detected for pod density in 2005 (Tables 5 and 6). The fewest seed pod–1 were found in the 2RBNC treatment in 2004 and 2005 (1.88 and 1.61). The 4REB, 4RLB, 4RNB, and 2RB had similar seed pod–1 in 2004 and 2005 (2.02 and 1.95), all lower than the check (2.22 and 2.21). In 2004, seed weight was similar among cover crop management treatments (15.3 g 100 seed–1), while the check and 2RB had similar seed weight (15.8). In 2005, generally, the more competitive treatments (4RNB and 2RBNC) had lower seed weight. Harvest index was generally not sensitive to cover crop management, which indicates soybean altered assimilate partitioning to compensate for assimilate supply and sink demand. The species x management system interaction for pod density in 2005 occurred primarily because the 2RBNC treatment responded differently among species. In wheat, all treatments had similar pod density except the check (1218 pods m–2) and 2RBNC (993 pods m–2). In triticale, pod density in the 2RBNC (648 pods m–2) was lower than all other treatments, but the 4RLB also had lower pod density (959 pods m–2) than the 4REB (1164 pods m–2). In rye, the 4REB (960 pods m–2) had lower pod density than the 4RLB and 4RNB (1231 pods m–2).
Fall Self-Seeding Densities
Self-seeding of all species and cover crop management systems occurred in the fall of 2004 and 2005. In 2004, wheat self-seeding exceeded triticale and rye (Table 7). Among management systems, the 2RBNC (53 plants m–2) had the greatest self-seeding compared with the other management treatments (15 plants m–2). These plant densities represent from 8 (4REB) to 38% (2RBNC) of the original fall densities, averaged across species. In 2005, a species x management system interaction was detected for self-seeding density. In wheat, the 4REB, 4RNB, and 2RBNC had similar densities (60 plants m–2), all higher than the 4RLB and 2RB (35 plants m–2). In triticale, the 2RBNC (58 plants m–2) had greater self-seeding plant density than the rest of the treatments, which had similar densities (13 plants m–2). In rye, the 2RBNC (49 plants m–2) had greater self-seeding plant density than the rest of the treatments, which had similar densities (4 plants m–2). Singer and Kohler (2005) reported similar fall self-seeding tiller densities for rye (23 tillers m–2) when mechanical control occurred at the second node-, boot-, and anthesis growth stages in 1 of 2 yr. In the second year, treatment differences were detected, but tiller densities ranged from 11 to 4 tillers m–2 for control at the second node-, boot- and anthesis growth stages. Because seed number was similar between rye and triticale both years, lower seed quality of rye or the physical process of self-seeding may have reduced the efficiency of self-seeding in rye in this study.
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CONCLUSIONS |
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TOPNOTESABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSREFERENCES |
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NOTES |
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TOPNOTESABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSREFERENCES |
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REFERENCES |
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TOPNOTESABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSREFERENCES |
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This article has been cited by other articles:
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  P. B. McDonald, J. W. Singer, and M. H. Wiedenhoeft Establishment and Growth of Self-Seeded Winter Cereal Cover Crops in a Soybean-Corn Rotation Agron. J., February 29, 2008; 100(2): 432 - 439. [Abstract] [Full Text] [PDF]
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P. B. McDonald, J. W. Singer, and M. H. Wiedenhoeft Self-Seeded Cereal Cover Crop Effects on Interspecific Competition with Corn Agron. J., February 29, 2008; 100(2): 440 - 446. [Abstract] [Full Text] [PDF]
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