PDF version
for printing

© 2006 Plant Management Network.
Accepted for publication 25 July 2006. Published 18 October 2006.

Impact of Tillage and Crop Rotation on Spring Wheat Yield: I. Tillage 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: I. Tillage effect. Online. Crop Management doi:10.1094/CM-2006-1018-01-RS.

Abstract

Conservation tillage and crop diversification are increasing in the northern Great Plains. Few regional studies have determined if tillage influences crop rotation effects. Our objective was to determine if reductions in tillage affect grain yield of spring wheat (Triticum aestivum L. emend. Thell.) similarly in a rotation with field pea (Pisum sativum L.) and in a continuous spring wheat monoculture. Wheat grain yield under no-till averaged 40% higher compared with clean-till and 30% higher compared with reduced-till, regardless of cropping strategy (wheat-pea rotation and continuous wheat monoculture). An additional inch of stored soil water occurred under no-till compared with clean-till and probably explains much of the yield enhancement that resulted when tillage was eliminated. Better crop stand establishment under no-till also contributed to superior wheat grain yield in some years. Results of this research demonstrate that the beneficial effects of eliminating tillage on wheat grain yield apply across contrasting cropping strategies and support the continued replacement of clean-till with no-till systems in the northern Great Plains.

Much of western North Dakota along with the eastern half of Montana and northwestern South Dakota occur within a region characterized by widely varying precipitation and shortgrass prairie native vegetation (12). Historically, wheat-fallow dominated cropping strategies in that region, but cropping system intensification can occur following the adoption of no-till because of improvements in precipitation use efficiency. Data maintained at the Conservation Tillage Information Center located at Purdue University in West Lafayette, IN, indicate that no-till production of spring wheat and other spring-seeded, small-grain crops in North Dakota increased over 800% between 1989 and 2004, from under 250,000 to almost 2 million acres, respectively. Over 17% of spring seeded, small-grain crops were grown under no-till in the state in 2004, with an additional 28% grown under other conservation tillage practices (greater than 30% residue cover after seeding). By comparison, 20% of these crops were grown under reduced-till (15 to 30% residue cover after seeding) and 35% under clean-till (less than 15% residue cover after seeding) management in the state in 2004.

Lyon and Peterson (8) cited previous research indicating that replacement of fallow with grass and broadleaf crops was essential for the economic and environmental sustainability of wheat production systems in the US Great Plains. Among other things, cropping system intensification can create synergies among the species being grown that cannot be duplicated in wheat-fallow monoculture (14). The benefits of incorporating a diverse group of crops in a well planned sequence probably occur in different tillage systems, but recent studies (9,14) have limited crop sequence comparisons to no-till environments.

Three tillage systems along with three, four-year crop sequences were studied from 1986 to 1990 at Indian Head, Saskatchewan in western Canada (6). Crops included in the sequences were spring and winter wheat, flax (Linum usitatissimum L.), and field pea. One crop sequence also included fallow, i.e., the idling of land for a 14- to 21-month period between successive crops for soil water conservation. The authors reported that wheat yield tended to increase as tillage was reduced, presumably because of soil moisture conservation. In contrast, wheat yield generally was unaffected by cropping sequence. The presence or absence of interactions between tillage system and cropping sequence for soil moisture conservation and wheat grain yield were not discussed in that study.

Research is lacking on the impact of tillage on wheat grain yield in different crop sequences in the northern US Great Plains. The objectives of our study were to determine if: (i) changes in tillage practices affected grain yield of wheat in different crop sequences, and (ii) an interaction between tillage system and crop sequencing exists for wheat yield.

The study was conducted from 2000 through 2005 at the Dickinson Research Extension Center in southwestern North Dakota (46.5°N, 102.5°W, 2500-ft elevation) on a Farnuf fine sandy loam soil (Fine-loamy, mixed, superactive, frigid Typic Argiustolls). A two-year rotation comprised of spring wheat and field pea along with a spring wheat monoculture were established and maintained within 90- by 40-ft clean-, reduced-, and no-till management whole plots. Both phases of the wheat-pea rotation along with the spring wheat monoculture occurred each year, beginning in 1999. As a result, field pea followed wheat and vice-versa for the first time in 2000.

Cropping strategy (wheat-pea rotation and spring wheat monoculture) subplots were allocated within each tillage system whole plot as a randomized complete block in a split-plot arrangement. Both tillage and cropping strategy treatments were replicated four times. Cropping strategy subplots were allocated randomly within each tillage system whole plot when the study began, but thereafter the initial randomization was maintained. Field pea was seeded following spring wheat and spring wheat after field pea in crop rotation subplots, so there were three iterations of the wheat-pea sequence from 2000 through 2005.

The tillage systems were established prior to the study in 1993 and a spring wheat-fallow system maintained through 1998. Clean-till plots during that period were cultivated three times from May through August during the fallow phase and lightly disced prior to seeding spring wheat, while reduced-till plots were lightly disced prior to seeding spring wheat but otherwise not cultivated. No cultivation was performed in no-till plots. Establishment and maintenance of the tillage and seeding practices for whole plots between 1993 and 1998 are described elsewhere (2).

Maintenance of clean-, reduced-, and no-till whole plots was adjusted slightly to account for the cropping system intensification between 1999 and 2005. Clean-till plots were cultivated with a tandem disc to a three-inch depth in September or October each year and again the following April prior to seeding spring wheat or field pea. Reduced-till plots were lightly disced each April prior to seeding but otherwise were not cultivated. No soil disturbance except by a low-disturbance planter at seeding occurred in no-till plots.

Adequate fertilizer was applied as ammonium nitrate (34-0-0), diammonium phosphate (18-46-0), and triple superphosphate (0-44-0) for a 50 bu/acre yield goal for spring wheat, based on soil test results. Details of soil sampling and analyses methods as well as fertilizer applications strategies are discussed in another Crop Management article (3).

A 10-ft wide John Deere (Moline, IL) 750 low-disturbance drill was used to seed field pea in mid to late April and spring wheat 7 to 21 days later in 7.5-inch rows each year. Three separate passes were required to seed each 30- by 40-ft subplot. 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). The semi leafless, yellow cultivar Carneval was seeded each year in pea subplots, while ‘Parshall’ was seeded from 1999 through 2004 in spring wheat subplots. The solid-stem cultivar Ernest rather than Parshall was seeded in 2005 because of damage to spring wheat plots caused by the wheat stem sawfly (Cephus cinctus Norton) in 2004.

Glyphosate plus ammonium sulfate were applied as a burn-down to kill winter annuals and early-emerging summer annual weeds prior to seeding field pea and spring wheat in no-till plots each year. Rates used for the pre-plant burn-down treatments were 1 qt of ammonium sulfate per acre and 0.75 to 1.3 pt (product) of glyphosate per acre, depending on the year and the weed species and populations present. Pre-plant tillage was used to control weeds prior to seeding field pea and spring wheat in clean- and reduced-till plots. Post-plant applications of herbicides were used to control grass and broadleaf weeds. The rates and herbicides used in spring wheat subplots varied by year (Table 1), depending on the weed species and population present. Grass and broadleaf weeds were controlled with an application of imazamox (Raptor; BASF Corp., Research Triangle Park, NC) at 4 oz/acre, alone and sometimes in combination with bentazon (Basagran) at 8 oz/acre, in field pea subplots once plants emerged. Excellent weed control was achieved in all six years of the study.

Table 1. Application rates and herbicides applied after crop emergence to spring wheat for grass and broadleaf weed control, and post-harvest to field pea (pea) under no-till and reduced-till from 1999 through 2005 at Dickinson, ND.

 ^x Brand names and manufacturers for selected herbicides include:
Thifensulfuron + tribenuron = Harmony extra (Dupont, Wilmington, DE);
Fenoxaprop-P = Puma (Bayer CropScience, Research Triangle Park, NC);
and Tribenuron methyl = Express (Dupont).

Soil water content was determined to a 36-inch depth with a soil moisture probe prior to seeding in April at three locations selected randomly within each cropping strategy subplot in 2000 and 2001, following the procedure described by Brown et al. (1). Soil water content was determined gravimetrically for three soil cores collected randomly within each subplot for 0- to 12-, 12- to 24-, and 24- to 36-inch depths in 2004 and 2005. Gravimetric values were converted to a volumetric basis using soil bulk densities, following the procedure described by Miller and Holmes (9). Daily weather data were recorded at a National Oceanographic and Atmospheric Administration weather service station within 0.25 mi of the study each year.

Emerged spring wheat seedlings were counted within an 8.6-ft length of four interior rows within each wheat subplot approximately 21 days after seeding in all years except 2002. Plant density was determined for a 21.5-ft² area by adding together the four individual counts and reported as plants per square foot.

The crown and seminal roots of spring wheat plants were evaluated for evidence of disease by first carefully digging up 20 to 25 plants at the tillering to early jointing stages [Zadoks growth stages 20 to 31; Zadoks et al. (15)] and gently shaking soil from the roots. The samples then were stored in plastic bags and refrigerated until further processing (2 to 24 h). Intact roots of 15 plants selected randomly from the larger sample were soaked and washed for 15 to 25 min to remove any remaining soil. Subcrown internodes were evaluated for the presence of root lesions using the system described by Ledingham et al. (7). Briefly, the percentage of the subcrown internode discolored with lesions was expressed numerically from 1 (0 to 25% of the internode discolored by lesions) to 4 (75 to 100% of the internode discolored by coalesced lesions). Crown and seminal roots also were counted, plant length measured (from the soil line to the tip of the last fully extended leaf), and growth stage recorded as described by Cook et al. (4). Root counts, plant length, growth stage, and subcrown internode rating were reported as a mean for the 15 plants evaluated.

Spring wheat grain was harvested at maturity (Zadoks growth stage 92) from the center seven rows within a 175 ft² area of each spring wheat subplot using a small-plot combine. Approximately 5 inches of erect wheat stubble remained in plots following grain harvest. Grain N yield was computed by dividing the grain protein concentration which was determined by near-infrared spectroscopy (Infratec grain analyzer, UAS Service Corp., Hawley, MN) by 5.8, and multiplying the quotient by the grain yield expressed in pounds per acre. Grain yield and N yield were reported on a 12% moisture basis.

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 effects, while blocks and years were considered random. Mean comparisons using an F-protected LSD were made to separate tillage and cropping strategy treatments where F-tests indicated that significant differences existed (P < 0.05). The year × tillage interaction was used to test tillage treatments and the year × cropping strategy interaction was used to test cropping strategy. The year × tillage × cropping strategy interaction was used to test the interaction between tillage systems and cropping strategies, while error_a was used to test the year × tillage interaction. The residual error term was used to test both the year × cropping strategy interaction and the interaction between years, tillage, and cropping strategy. 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 increased by eliminating tillage across the six years of the study and both cropping strategies. An additional 12 and 10 bu/acre of grain were produced under no-till compared with clean- and reduced-till, respectively. Overall, grain yield averaged 42 bu/acre under no-till compared with 30 bu/acre under clean-till and 32 bu/acre under reduced-till. These results agree with previous research indicating the positive effect on grain yield that results when tillage is eliminated in the Great Plains (11). Much of this yield enhancement was attributed to increases in stored soil water under no-till. In the present study, an additional 1.1 inches of water was stored in the top 2-ft of soil in no-till compared with clean-till plots (Fig. 1). This additional stored soil water could account for much of the grain yield increase under no-till that was observed, based on recent yield models using plant available water data that were developed at the Williston Research Extension Center in northwestern North Dakota (J. A. Staricka, personal communication, 2006).

Fig. 1. Inches of stored water in the top 3 ft of soil under clean-till (Clean tillage), reduced-till (Reduced tillage), and no-till (No-tillage) management prior to seeding spring wheat following field pea and spring wheat in April during 2004 and 2005 at Dickinson, ND.

Root disease lesions were more prevalent on the subcrown internode of spring wheat plants in no-till compared with clean-till subplots in this study (P = 0.04). However, percentage of the subcrown internode discolored with root rot lesions averaged less than 25% across clean-, reduced- and no-till systems. Fewer crown roots grew on spring wheat plants in no-till than clean-till subplots in one of the four years that crown roots were counted (data not provided). Differences in crown root numbers were not detected across the three tillage systems in other years. Grain yield was greater under no-till than clean-till in the present study, suggesting that the positive effects of no-till can be of greater magnitude than the negative consequences of eliminating tillage on root disease incidence in environments where disease pressure is limited. Reducing tillage can increase root pathogen numbers of some species but reduce numbers of other species (5), thereby making the impact of tillage reductions on root disease difficult to predict.

Spring wheat plant numbers increased as tillage was reduced in three of the five years that plant density was determined (Fig. 2). The increase was greatest in 2004, when plant density was increased by over 100% in no-till compared with clean-till plots. The improvements in plant stand under no-till probably explain some of the grain yield increases those three years, since wheat plant density was below the threshold for maximum grain yield in clean-till plots but above the value in no-till plots. Previous research indicated that spring wheat plant establishment was enhanced as tillage is eliminated in the northern Great Plains (10), although this observation likely depends on the status of soil water content at seeding within various tillage systems along with the amount of crop residue on the soil surface. In the present study, more plants occurred in no-till plots when drying winds appeared to exacerbate evaporation in reduced- and particularly clean-till plots at seeding, as occurred in 2000, 2001, and 2004 even though precipitation patterns suggested that favorable soil moisture levels existed across tillage systems (Fig. 3). Plant density was unaffected by tillage system in 2003 and 2005 when relatively moist conditions existed at seeding.

Fig. 2. Plant density of spring wheat in clean-till (Clean tillage), reduced-till (Reduced tillage), and no-till (No tillage) systems across a wheat-pea rotation and a continuous wheat monoculture during a six-year period (2000 through 2005) at Dickinson, ND. Heights of bars separated by a distance greater than the LSD bar within a year are different at the P < 0.05 level.

Fig. 3 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.

An interaction between tillage system and cropping strategy for grain N yield was not detected in this study (P = 0.70). Grain N yield was 13 to 27 lb/acre greater under no-till compared with clean-till in four years of this six-year study (Fig. 4). Differences in grain N yield were not detected between tillage systems in 2001 and 2005. Soil N levels were comparable or lower when tillage was eliminated. For example, there was a trend (P = 0.05) for soil nitrate levels to decline in the 0- to 4-ft depth as tillage was eliminated. Soil nitrate content was 83 lb/acre in clean-till, 67 lb/acre in reduced-till, and 61 lb/acre in no-till plots. Previous research indicates a depression in soil N levels can occur following the elimination of tillage in the Great Plains because of increased production of crop residue and subsequently greater immobilization of N, although this reduction may be transient (13).

Fig. 4. Grain N yield of spring wheat in clean-till (Clean tillage), reduced-till (Reduced tillage), and no-till (No tillage) systems across a wheat-pea rotation and a continuous wheat monoculture during a six-year period (2000 through 2005) at Dickinson, ND. Heights of bars separated by a distance greater than the LSD bar within a year are different at the P < 0.05 level.

This study failed to detect an interaction between tillage system and cropping strategy for spring wheat grain and N yield. The equipment used to implement and maintain tillage and cropping strategy treatments was similar to equipment used commercially at the time the study was conducted. New harvesting technology including stripper headers are creating seedbeds where tall erect crop stubble is left following grain harvest. Additional research should be conducted to determine if results of this study can be duplicated when tall cereal stubble is maintained in no-till systems.

A common suggestion directed at farmers moving from clean- to reduced- and no-till systems is to increase the seeding rates of crops being grown to account for problems achieving good seed-to-soil contact in high residue environments. Results of this study do not support this recommendation. Growing spring wheat under no-till increased grain yield compared with clean-till and reduced-till. The positive effects that no-till have on soil water conservation and wheat plant density explained much of the grain yield benefit derived from adopting no-till methods. Results of this study support the continued conversion of clean- and reduced- to no-till systems in the northern Great Plains.

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. 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.

2. 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.

3. Carr, P. M., Martin, G. B., and Horsley, R. D. 2006. Impact of tillage and rotation on spring wheat yield: II. Rotation effect. Online. Crop Management doi:10.1094/CM-2006-1018-02-RS.

4. Cook, R. J., J. W. Sitton, and W. A. Hagland. 1987. Influence of soil treatments on growth and yield of wheat and implications for control of pythium root rot. Phytopathology 77:1192-1198.

5. Krupinsky, J. M., Bailey, K. L., McMullen, M. P., Gossen, B. D., and Turkington, T. K. 2002. Managing plant disease risk in diversified cropping systems. Agron. J. 94:198-209.

6. Lafond, G. P., Loeppky, H., and Derksen, D. A. 1992. The effects of tillage systems and crop rotations on soil water conservation, seedling establishment and crop yield. Can. J. Plant Sci. 72:103-115.

7. 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.

8. Lyon, D. J., and Peterson, G. A. 2005. Continuous dryland cropping in the Great Plains: What are the limits? Agron. J. 97:347-348.

9. 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.

10. 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.

11. Nielsen, D. C., Unger, P. W., and Miller, P. R. 2005. Efficient water use in dryland cropping systems in the Great Plains. Agron J. 97:364-372.

12. Padbury, G., Waltman, S., Caprio, J., Coen, G., McGinn, S., Mortensen, D., Nielsen, G., and Sinclair, R. 2002. Agroecosystems and land resources of the northern Great Plains. Agron. J. 94:251-261.

13. Schlegel, A. J., Grant, C. A., and Havlin, J. L. 2005. Challenging approaches to nitrogen fertilizer recommendations in continuous cropping systems in the Great Plains. Agron. J. 97:391-398.

14. Tanaka, D. L., Anderson, R. L., and Rao, S. C. 2005. Crop sequencing to improve use of precipitation and synergize crop growth. Agron. J. 385-390.

15. Zadoks, J. C., Cheng, T. T., and Konzak, C. F. 1974. A decimal code for the growth stage for cereals. Weed Res. 14:415-421.