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© 2006 Plant Management Network. Impact of Tillage and Crop Rotation on Spring Wheat Yield: II. Rotation Effect Patrick M. Carr, Agronomist, and Glenn B. Martin, Research Specialist, 1041 State Avenue, Dickinson Research Extension Center, North Dakota State University, Dickinson 58601; and Richard D. Horsley, Professor, P.O. Box 5051, Department of Plant Sciences, North Dakota State University, Fargo 58105 Corresponding author: Patrick M. Carr. Patrick.Carr@ndsu.edu Carr, P. M., Martin, G. B., and Horsley, R. D. 2006. Impact of tillage and crop rotation on spring wheat yield: II. Rotation effect. Online. Crop Management doi:10.1094/CM-2006-1018-02-RS. Abstract North Dakota is the leading domestic producer of field pea (Pisum sativum L.) with almost 600,000 acres seeded in 2006. This level of production partially results from the belief that grain yield of spring wheat (Triticum aestivum L. emend. Thell.) is greater following field pea compared with a spring wheat monoculture. The reduction in tillage occurring in the Great Plains has generated interest among farmers in determining if crop rotation benefits of field pea extend to spring wheat across contrasting tillage systems. A six-year field study was conducted to determine the impact of field pea on grain and N yield of a subsequent spring wheat crop in clean-, reduced-, and no-till systems. A beneficial rotation effect occurred for spring wheat grain and N yield in four of the six years and ranged from 9 to 11 bu/acre and 13 to 28 lb/acre, respectively (P < 0.05). An interaction between cropping strategy (rotation and monoculture) and tillage system was not observed for either trait. These results suggest that the beneficial rotation effect of field pea is similar for spring wheat across different tillage systems and occurs in most but not all years, depending on environmental factors. North Dakota leads the USA in seeded area and production of spring wheat. Over 40% of the domestic spring wheat crop was grown in North Dakota on over 6 million acres in 2004 (17). In comparison, spring wheat was grown on less than 2 million acres that year in Minnesota, the second leading domestic producer of spring wheat (18). North Dakota also is the leading domestic producer of field pea, with over 300,000 acres harvested in the state in 2004 (17). North Dakota produced over 60% of the domestic field pea crop that year. Field pea was seeded on 580,000 acres in North Dakota during 2006 (E. Bartsch, personal communication, 2006). This level of production occurred even though projected economic returns to labor and management from growing field pea in 2006 are negative. For example, field pea production is expected to generate -$11/acre in the north-central region of North Dakota (16), where much of the field pea production is located. The popularity of this pulse crop among farmers in the state and across the field pea production area in the northern USA and Canada partially is explained by the perceived benefits provided by field pea to subsequent crops in a rotation. A positive rotation effect to spring wheat following field pea has been documented in several studies in the northern Great Plains, primarily in Canada (1,12,14,15). The benefits provided by field pea are believed to derive from the N-fixing effects of the legume species on subsequent crops, as well as non-N-fixing factors (e.g., pest suppression). Beckie and Brandt (1) concluded from two, two-year field experiments across four landscape positions in Saskatchewan that the N credit of field pea to the following spring wheat crop was 14 lb/acre. Other experiments discussed by the same two researchers suggested an N credit closer to 10 lb/acre in dry conditions. Similar research also conducted in Saskatchewan by Miller et al. (12) supported the rotational N credit values for field pea suggested by Beckie and Brandt (1). These values are notably lower than the 40 lb/acre rotational N credit currently used in North Dakota following field pea (7). Most of the rotation benefit associated with field pea was attributed to the N-fixing ability of this legume species in a study where comparisons of spring wheat following field pea and other broadleaf but non-N-fixing crops were made (1). Results of that study presently have limited relevance in western North Dakota since most spring wheat is grown following wheat in cropping sequences. For example, over 65% of spring wheat grown in 368 wheat fields surveyed in this region in 2004 followed wheat according to the IPM coordinator at North Dakota State University (M. P. McMullen, personal communication, 2006). Non-N-fixing factors explained a majority of the rotation effect for field pea when a wheat-pea sequence was compared with a continuous wheat monoculture in some previous research. For example, over 90% of the rotation effect for field pea was attributed to reduced root disease and grassy weed suppression in Saskatchewan field studies (14,15). Others suggested that improved soil water content following field pea helped contribute to the non-N-fixing rotation effect (11,12). The impact of field pea and other crops on subsequent cereal crop performance was considered in Montana. Average grain yield of the cereal crops was less following field pea than spring wheat at two locations included in that study (10). Drought and a resulting depression in water use efficiency were suggested as explaining the lower yields following the low-residue crop (field pea) compared with the high-residue crop (spring wheat) in the no-till environments that were encountered. Results from an unpublished field study near Williston in northwestern North Dakota were reported in a review paper by Miller et al. (11), where wheat grain yield was unchanged following field pea compared with spring wheat monoculture. Annual precipitation averages less than 15 inches at Williston (11), suggesting that the positive rotation effect to a spring wheat crop following field pea may be marginalized in semiarid portions of the northern Great Plains. Limited published research on the effects of field pea on a subsequent spring wheat crop exists within a region encompassing most of western North Dakota and eastern Montana. Furthermore, no studies have compared the impact of a preceding field pea crop on grain yield of spring wheat across three tillage systems (clean-, reduced-, and no-till) presently used in the northern Great Plains. Thus, our objectives were to determine if: (i) a positive rotation effect following field pea occurs for spring wheat grain yield in western North Dakota, and (ii) tillage interacts with the rotation effect. The study was conducted from 2000 through 2005 in southwestern North Dakota on a Farnuf fine sandy loam soil (Fine-loamy, mixed, superactive, frigid Typic Argiustolls). Subplots consisting of a two-year rotation comprised of spring wheat and field pea along with a spring wheat monoculture were established and maintained across clean-, reduced-, and no-till management whole plots. Details regarding establishment and maintenance of the tillage whole plot treatments are described in a companion paper included in this issue of Crop Management (6). Cropping strategy (wheat-pea rotation and spring wheat monoculture) subplots and tillage system whole plots were arranged in a randomized complete block in a split plot arrangement. Tillage and cropping strategy treatments were replicated four times. The initial randomization of cropping strategy subplots within each tillage system whole plot was maintained during the study. Both phases of the wheat-pea rotation along with the spring wheat monoculture occurred each year. Soil cores (1.6-inch diameter) were collected randomly using a hydraulic soil probe from three locations within each field pea and spring wheat subplot to a 2-ft depth each year in October to determine soil N status, except during 2002. Soil cores from a 2- to 4-ft depth were collected in all years except 2000, 2002, and 2005. The cores were composited within each subplot from 0- to 6- and 6- to 24-inch depths, and from 24- to 48-inch depths when available. Soil nitrate content was determined for each depth using steam distillation (13) in the soil testing laboratory at North Dakota State University. Ammonium nitrate (34-0-0) and diammonium phosphate (18-46-0) granular fertilizers were broadcasted without incorporation prior to seeding spring wheat for a 50 bu/acre yield goal, based on soil test results of samples collected the previous fall and North Dakota State University fertilizer recommendations (7), ignoring the 40 lb of N per acre rotational credit for crops following field pea and lentil (Lens culinaris L.) in subplots where spring wheat followed field pea. Ammonium nitrate was applied at 200 lb/acre (68 lb of N per acre) uniformly to spring wheat subplots in 2003 since soil test results were not available from 2002. Triple super phosphate (0-44-0) granular fertilizer was broadcasted without incorporation to field pea subplots for a 50-bu/acre yield goal. Nitrogen was not applied as fertilizer to field pea plots, but seed was inoculated properly with Rhizobium leguminosarum just prior to seeding to stimulate biological N fixation. A low-disturbance drill was used to seed field pea in mid to late April and spring wheat one to three weeks later in 7.5 inch rows each year. Spring wheat was seeded at 28 live kernels/ft2 (1.2 million kernels/acre), and field pea at 7 live seed/ft2 (325,000 seed/acre). ‘Carneval’ was seeded each year in pea subplots. ‘Parshall’ was seeded in spring wheat subplots except in 2005, when the solid-stem cultivar Ernest was seeded because of damage to spring wheat plots caused by the wheat stem sawfly (Cephus cinctus Norton) in 2004. Excellent weed control was achieved in the study using a combination of tillage and herbicides in clean- and reduced-till whole plots, and herbicides in no-till whole plots. Additional detail regarding weed control methods used in the study is provided elsewhere in this issue of Crop Management (6). Soil water content was determined to a 36-inch depth with a soil moisture probe prior to seeding within each cropping strategy subplot in 2000 and 2001 using a procedure described by Brown et al. (3), and gravimetrically in 2004 and 2005. Gravimetric values were converted to a volumetric basis using soil bulk densities, as described by Miller and Holmes (10). Daily weather data were recorded at a National Oceanographic and Atmospheric Administration weather service station within 0.25 miles of the study each year. A KCL frame estimator (Kriesel Certified Seed Enterprises, Gurley, NE) was used to determine the percentage of crop residue remaining on the soil surface after seeding in each cropping strategy subplot during both 2000 and 2001. The estimator consists of an 18-inch square frame with ten holes (0.4-inch diameter) in the frame through which the amount of soil surface covered with crop residue is observed. The frame was thrown randomly within each subplot 10 times with 10 observations made after each throw. The percentage of crop residue covering the soil surface was reported as the mean of the 100 observations that were made. Emerged spring wheat seedlings were counted within a 21.5-ft2 area in each cropping strategy subplot approximately 21 days after seeding in all years except 2002. The crown and seminal roots of spring wheat plants were evaluated for evidence of disease using the system described by Ledingham et al. (8) and discussed briefly elsewhere in this issue of Crop Management (6). Spring wheat grain was harvested from the center of each spring wheat subplot using a small-plot combine. Grain N yield was computed by multiplying the grain N concentration by grain yield and expressed in pounds per acre. Six soil cores (0.5-inch diameter) were collected randomly with an Oakfield soil probe within each cropping strategy subplot and composited from 0- to 6- and 6- to 24-inch depths in April prior to seeding in 2004 and 2005. Soil samples were collected using the same sampling procedure in early June and July both years. The samples were analyzed for nitrate as well as ammonium using the steam distillation method (13), and total N by a micro-Kjeldahl method (2). Data were analyzed across all years using the GLM procedure for balanced data available from SAS (SAS Institute Inc., Cary, NC). Tillage systems and cropping strategy were considered fixed while blocks and years were considered random effects. An F-protected LSD was used to separate tillage and cropping strategy treatment means where F-tests indicated that significant differences existed (P < 0.05). Years were evaluated individually for any interaction involving a year effect. An interaction between tillage system and cropping strategy for spring wheat grain yield was not detected in this study (P = 0.45). Grain yield for spring wheat was 9 to 11 bu/acre greater following field pea than wheat in four of the six years (Fig. 1). This amounted to a positive rotation effect for grain yield of 17 to 38%, depending on the year. A rotation effect was not detected in either 2004 or 2005. Damage to plants caused by the wheat stem sawfly may explain the inability to detect differences between cropping strategies in 2004. Likewise, widespread infection by the Fusarium head blight fungus, Fusarium graminearum Schwabe, was observed among plants in 2005 and may explain the lack of an observed rotation effect. Results of this study suggest that a positive rotation effect should be expected when spring wheat follows field pea compared with spring wheat monoculture in western North Dakota, except when pests reduce the yield potential of spring wheat following field pea.
Previous research indicated that spring wheat yields were not elevated and sometimes declined following field pea compared with wheat in eastern Montana and western North Dakota, particularly in no-till environments during drought (10). Results of that study indicated that high-residue cereal crops created a more favorable microclimate for growth by a following wheat crop compared with low-residue crops like field pea in dry environments. Presumably, some of the benefit provided to the wheat crop was greater amounts of stored soil water following high- rather than low-residue crops. There tended to be more crop residue on the soil surface following spring wheat than field pea in the present study (P = 0.07), but cropping strategy had no effect on stored soil water at any depth within any tillage system (data not provided). These results were expected, since Miller et al. (9) reported similar amounts of stored soil water following wheat and field pea when grown the previous year. Annual precipitation averaged only around 14 inches or roughly 80% of the 30-year average of almost 17 inches in both 2000 and 2003 (Table 1), yet a positive rotation effect following field pea was detected both years (Fig. 1). Our results suggest that grain yield for spring wheat can be elevated following field pea compared with wheat in the northern Great Plains, even during drought and regardless of tillage system. Table 1. Overwinter (1 September through 30 March) and growing-season precipitation (1 April through 31 August) for the years 2000 through 2005 along with the 30-year average at Dickinson, ND.
Disease considerations failed to explain grain yield increases when spring wheat followed field pea compared with wheat in this study. Differences were not detected in numbers of crown root (P = 0.83) or seminal roots (P = 0.68), and in root rot lesions on the subcrown internode (P = 0.47) of spring wheat plants following field pea and wheat. These data suggest a lack of differential soil-borne disease pressure based on cropping strategy under the environmental conditions that occurred. In contrast, incidence of root rot lesions was three times higher in a continuous wheat monoculture compared with a wheat-pea rotation in one field experiment in Saskatchewan (14). However, differences in root rot lesions were not detected between spring wheat plants in a monoculture and a wheat-pea rotation in a separate field experiment included in the same Canadian study. Similarly, the Canadian researchers failed to observe differences in foliar disease symptoms between plants in the spring wheat monoculture and the wheat-pea sequence in either field experiment. Results of the Canadian and present studies suggest that differential disease pressure may not explain consistently the rotation effect of field pea on a subsequent spring wheat crop, except perhaps in those environments were disease pressure is severe. More spring wheat plants became established following field pea (19 plants/ft2) than wheat (18 plants/ft2) in the five years that plant stand was determined in this study. This increase in plant numbers was minimal but significant (P = 0.03), and could explain some of the positive rotation effect, since previous research indicated that more than 18 plants/ft2 is required for maximum spring wheat grain yield in clean-, reduced-, and no-till systems in southwestern North Dakota (4,5). The ability to detect plant density differences in the present study and the failure to do so in previous research by Miller and Holmes (10) may be due to differences in the seeding equipment used and possibly the amount of crop residue that was planted into, but this suggestion is speculative since detailed information on seeding equipment and crop residue production were not reported by those two researchers. These conflicting results suggest that more research is needed to clarify what factors determine when plant density is affected by the previous crop in a rotation. An interaction between tillage system and cropping strategy for grain N yield was not detected in this study (P = 0.70). Grain N yield for spring wheat was 12 to 18 lb/acre greater following field pea than wheat in four of the six years (Fig. 2), mirroring grain yield differences between cropping strategies (Fig. 1). A rotation effect was not detected for grain N yield in either 2004 or 2005 (Fig. 2). The elevation in grain yield for spring wheat following field pea did not reflect soil N levels, which were similar between both cropping strategies or lower for the wheat-pea rotation, depending on the form of N, soil depth, and year that were considered. For example, only 59 lb/acre of soil nitrate were detected in the top four feet of soil in the fall following field pea compared with 82 lb/acre following wheat across the four years (1999, 2001, 2003, and 2004) that these data were collected (Fig. 3). The differences in soil nitrate content in soils between the two cropping strategies disappeared by spring in the two years that spring soil nitrate content was determined, suggesting faster mineralization of N contained in field pea than wheat residue, immobilization of available N by decomposing wheat residue, possibly both or even other factors.
Fertilizer rates were based on fall soil samples so greater amounts of N were applied to spring wheat plots following field pea than wheat in four years (data not presented). The additional N applied to wheat following field pea was roughly 20 lb/acre more than following wheat during that period, while differences in grain N yield between spring wheat following field pea compared with wheat were 18 lb/acre or less (Fig. 2). Consideration of these along with soil N data fail to reveal a positive impact of field pea on the soil N pool or N uptake by a subsequent spring wheat crop, in contrast to previous studies conducted in the northern Great Plains (1,12). These seemingly contradictory results indicate that our understanding of the N-fixing contribution to the rotation effect of field pea is incomplete, but likely depends on soil moisture availability, unamended soil N status, fertilizer management, and other factors identified by Miller et al. (11). Rotating spring wheat with field pea increased wheat grain yield up to 40% compared with a wheat monoculture in this study. Considerations of soil N status, root disease symptoms, and soil water content failed to explain the positive rotation effect of field pea. Wheat plant density was increased following field pea compared with wheat, suggesting that a superior seedbed is created by the pulse crop that may help explain the rotation effect in some dry environments. These results contradict some of the findings from previous research and support additional research to identify the factors that determine the N-fixing and non-N-fixing contributions to the beneficial effect of field pea on spring wheat in a crop rotation. Seeding rate adjustments based on the previous crop grown in a rotation generally are not considered when seeding spring wheat, but results of this study demonstrate that plant density can be affected by the preceding crop. Greater emphasis should be placed on how previous crops can affect plant density of subsequent crops, and in developing general guidelines that specify how seeding rates should be adjusted depending on the previous crop type (e.g., low vs. high residue) that was grown. Greater diversity and flexibility are represented in crop rotations used by many farmers presently compared with the wheat-pea rotation included in this study. Future research should be conducted which reflects this reality. In particular, quantification of the impacts field pea has on subsequent non-pulse crops over a three to four-year period is needed. Acknowledgments and Disclaimer The authors gratefully acknowledge the assistance of Roger Ashley, Extension Cropping System Specialist, for his expertise in providing the training for evaluating root disease symptoms of wheat plants. Partial funding for this study was provided by the Cooperative State Research, Education and Extension Service, US Department of Agriculture, under Agreement No. 2003-34216-13566. All opinions, findings, conclusions or recommendations expressed in this manuscript are those of the authors and do not necessarily reflect the view of the US Department of Agriculture. Mention of a proprietary product name is for identification purposes only and does not imply endorsement or warranty to the exclusion of other products. Literature Cited 1. Beckie, H. J., and Brandt, S. A. 1997. Nitrogen contribution of field pea in annual cropping systems. 1. Nitrogen residual effect. Can. J. Plant Sci. 77:311-322. 2. Bremner, J. M., and Mulvaney, C. S. 1982. Nitrogen-total. Pages 595-624 in: Methods of Soil Analysis. Part 2. Chemical and Microbiological Properties. A. L. Page, R. H. Miller, and D. R. Keeney, eds. ASA Monogr. 9. ASA, Madison, WI. 3. Brown, P. L., Black, A. L., Smith, C. M., Entz, J. W., and Caprio, J. M. 1985. Soil water guidelines and precipitation probabilities in Montana and North Dakota. Montana Coop. Ext. Serv. Bull. 356. 4. Carr, P. M., Horsley, R. D., and Poland, W. W. 2003. Tillage and seeding rate effects on wheat cultivars: I. Grain production. Crop Sci. 43:202-209. 5. Carr, P. M., Horsley, R. D., and Poland, W. W. 2003. Tillage and seeding rate effects on wheat cultivars: II. Yield components. Crop Sci. 43:210-218. 8. Ledingham, R. J., Atkinson, T. G., Horricks. J. S., Mills, J. T., Piening, L. J., and Tinline, R. D. 1973. Wheat losses due to common root rot in prairie provinces of Canada, 1969-71. Can Plant Dis. Surv. 53:113-122. 9. Miller, P. R., Gan, Y., McConkey, B. G., and McDonald, C. L. 2003. Pulse crops for the northern Great Plains: I. Grain productivity and residual effects on soil water and nitrogen. Agron. J. 95:972-979. 10. Miller, P. R., and Holmes, J. R. 2005. Cropping sequence effects of four broadleaf crops on four cereal crops in the northern Great Plains. Agron. J. 97:189-200. 11. Miller, P. R., McConkey, B. G., Clayton, G. W., Brandt, S. A., Staricka, J. A., Johnston, A. M., LaFond, G. P., Schatz, B. G., Baltensperger, D. D., and Neill, K. E. 2002. Pulse crop adaptation in the northern Great Plains. Agron. J. 94:261-272. 12. Miller, P. R., Waddington, J., McDonald, C. L., and Derksen, D. A. 2002. Cropping sequence affects wheat productivity on the semiarid northern Great Plains. Can. J. Plant Sci. 82:307-318. 13. Mulvaney, R. L. 1996. Nitrogen-inorganic forms. Pages 1123-1194. in: Methods of Soil Analysis. Part 3. Chemical Methods. D. L. Sparks, A. L. Page, P. A. Helmke, R. H. Loeppert, P. N. Soltanpour, M. A. Tabatabai, C. T. Johnson, and M. E. Sumner. Soil Sci. Soc. Amer. Book Series 5. SSSA, Madison, WI. 14. Stevenson, F. C., and van Kessel, C. 1996. A landscape-scale assessment of the nitrogen and non-nitrogen rotation benefits of pea. Soil Sci. Soc. Am. J. 60:1797-1805. 15. Stevenson, F. C., and van Kessel, C. 1996. The nitrogen and non-nitrogen rotation benefits of pea to succeeding crops. Can. J. Plant Sci. 76:735-745. |
