PDF version
for printing

© 2005 Plant Management Network.
Accepted for publication 23 November 2004. Published 19 January 2005.

Intercropping Legumes in Hard Red Spring Wheat under Semi-Arid Conditions

Jochum Wiersma, Northwest Research and Outreach Center, University of Minnesota, 2900 University Avenue, Crookston 56716; Craig Sheaffer, Department of Agronomy & Plant Genetics, University of Minnesota, St. Paul 55108; George Nelson, West Central Research and Outreach Center, University of Minnesota, State Hwy 329, Morris 56267; Donald Wyse, Department of Agronomy & Plant Genetics, University of Minnesota, St. Paul 55108; and Kevin Betts, Department of Agronomy & Plant Genetics, University of Minnesota, St. Paul 55108

Corresponding author: Jochum Wiersma. wiers002@umn.edu

Wiersma, J., Sheaffer, C., Nelson, G., Wyse, D., and Betts, K. 2005. Intercropping legumes in hard red spring wheat under semi-arid conditions. Online. Crop Management doi:10.1094/CM-2005-0119-01-RS.

Abstract

Research has shown that intercropping legumes with grain crops can provide a green manure crop without the loss of a cropping year. The objective of this research was to determine whether legumes could be intercropped with hard red spring wheat (HRSW, Triticum aestivum L. emend Thell.) in a semi-arid cropping system. Alfalfa (Medicago sativa L. ‘Vernal’), hairy vetch (Vicia villosa Roth, local ecotype), and red clover (Trifolium pratense L., ‘Marathon’) were intercropped in the HRSW cultivar ‘Hamer’ at three locations in northwest and west central Minnesota in 1999 and 2000. Intercropping hairy vetch into HRSW reduced grain yield and test weight, but had no effect on grain protein. Hairy vetch was not suitable for intercropping with HRSW, as it grew too tall when the spring wheat crop matured, hindering grain harvest. Intercropping alfalfa or red clover did not affect wheat yields compared to wheat monoculture and neither of the two legume species impeded grain harvest. Thus alfalfa and red clover are more suitable to intercrop with HRSW than hairy vetch. All three legumes evaluated in this experiment grew after the HRSW was harvested and provided a green manure crop at the end of the season when soil moisture in the later part of the summer was not limiting.

Introduction

The value of legumes in crop rotations has long been recognized, but the use of legumes as green manure crops in cropping systems has declined due to the availability of low-cost synthetic N fertilizers (2). Currently, a typical rotation in northwest Minnesota consists of soybeans (Glycine max (L.) Merr.), spring wheat, and sugar beets (Beta vulgaris L.). Although it was a common practice until the late 1960s to grow sweet clover (Melilotus alba Medik.) the year prior to sugar beets, producers in the region can no longer justify the cost to grow a green manure crop to supply or supplement N to the principle cash crop during a fallow year.

The principal benefit attributed to legumes in crop rotations is their contribution of mineral N to the soil (1,3); however, the benefit of forage legumes in cropping systems is likely a combination of N contribution and yield-enhancing rotation effects not directly associated with N (4). These non-N rotation effects are attributed to increases in soil organic matter resulting in improved soil structure and increased water infiltration, disruption of pest cycles, and the addition of growth promoting substances (4). In addition, additional ground cover can reduce soil erosion due to water runoff and/or wind during the winter and following spring (9).

Small grains have been used to aid establishment of small-seeded perennial legumes (7). Intercropping HRSW and legumes in a crop production system where grain production is the primary objective is not common. The establishment of a small-seeded legume during the production of a HRSW crop may provide foliage for ground cover, or high protein biomass for harvest and/or incorporation. Providing ground cover can reduce soil erosion that occurs at high levels during the winter months in northwest Minnesota. The objectives of this research was to evaluate the effects of intercropping HRSW and selected legumes in a semi-arid cropping system on grain yield and grain quality of HRSW and biomass yield of selected small seeded legumes.

Field Studies in Three Minnesota Locations Over Two Years

In 1999, a two-year study was initiated at Research and Outreach Centers of the Minnesota Agriculture Experiment Station located at Morris, Crookston, and Roseau, MN. These three locations represent the west central and northwest part of Minnesota. Morris, Crookston, and Roseau are just slightly to the west of the transition zone between humid climates to the east and arid climates to the west. All three locations have a humid, warm continental summer in which the majority of the annual precipitation is generally received in late spring and early summer. This was the case at all three locations in 1999, as well as 2000 (Table 1). Long-term, the potential evapotranspiration tends to exceed the potential precipitation and therefore the area is classified as semi-arid.

Table 1. Monthly, annual, and 30-year average precipitation totals (inches) in Crookston, Morris and Roseau, MN in 1999 and 2000.

 * Annual precipitation averaged over the previous 30 years.

The soil at Morris was a Nutley Flom clay loam (fine, smectitic, frigid chromic Hapluclerts and fine-loamy, mixed, superactive, frigid Typic Encloaquolls). In Crookston, the soil at the experimental site was a Hegne Fargo clay (fine, smectitic, frigid Typic Epiaquerts and fine, smectitic, frigid Typic Calciaquets), while in Roseau the soil was a Bearden-Colvin-Fargo complex (fine-silty, mixed, superactive, frigid Aeric Calciaquolls; fine-silty, mixed, superactive, frigid Typic Calciaquolls; fine, smectitic, frigid Typic Calciaquets).

Fertilizer was applied to all treatments in the spring based on soil test recommendations for a 60-bu/acre wheat crop. The HRSW cultivar ‘Hamer’, a short semi-dwarf cultivar, was either intercropped with alfalfa (Medicago sativa L. ‘Vernal’), hairy vetch (Vicia villosa Roth, local ecotype) or red clover (Trifolium pratense L., ‘Marathon’) or planted in monoculture. Legumes were inoculated with appropriate strains of Rhizobium. The three legumes cultivars were selected based on their adaptation to the region as well as their potential to allow for chemical weed control.

At all three locations the wheat was planted at 75 lbs/acre using a double-disk grain drill. In Morris, the legumes were planted with the grain drill when planting the wheat using a grass seed attachment. At the other two locations, the legumes seed was broadcast by hand and incorporated by raking prior to planting the wheat. Alfalfa was seeded at 6 lb/acre, red clover at 5 lb/acre, and the hairy vetch at 10 lb/acre. The legume seeding rates were half of recommendations for pure stands. Plots at all locations were 24 ft by 48 ft. The experimental design was a randomized complete block design with four replications in all three locations each of the two years.

In 1999, the experiment was planted on April 29 in Morris, May 15 in Roseau, and May 28 in Crookston. Grain harvest was completed on August 5 in Morris and September 11 in Roseau. In Crookston, the experiment was completely lost due to heavy rains that flooded the trial after the initial stand counts were taken. Similarly, the fourth replication was lost in Roseau that year. The legume biomass that accumulated following HRSW harvest was measured on August 5 in Morris and again on September 29 at Morris. In Roseau, the legume biomass was measured on September 11 and again on October 28.

In 2000, the experiment was planted on May 5 in Crookston, May 15 in Morris, and May 19 in Roseau. Grain harvest was completed on August 11 in Crookston, August 15 in Morris, and August 26 in Roseau. The legume biomass re-growth following HRSW harvest was measured on August 11 and again on September 30 in Crookston. In Morris, the legume biomass was measured on August 15. Because of very dry conditions very little, if any, re-growth occurred and no useful data could be collected in Morris that year. In Roseau, the legume biomass was measured on August 26 and again on October 27.

Grassy weeds were controlled with either one application of fenoxaprop with safener (Puma) at 0.062 lb a.i./acre or diclofop (Hoelon) at 1.0 lb a.i/acre. Broadleaf weed control was provided with one application of bromoxynil (Buctril) at 0.25 lb a.i./acre once the legumes had reached the second trifoliolate stage.

The data collected included stand counts for both wheat and the legumes at the 2- to 3-leaf stage of the spring wheat and again just before grain harvest. In addition, plant height of the spring wheat and the legumes were measured just before grain harvest. Grain yield was measured by harvesting a 5-ft strip through the center of each plot with a plot combine. The total area harvested from each plot was 240 ft². The grain was cleaned, and yield and test weight were expressed as bushels per acre and pounds per bushel, respectively. Grain protein content was determined, using a 1-lb subsample, by near infrared transmission using a Tecator Infratec 1229 Grain Analyzer (Foss North America, Inc., Eden Prairie, MN).

Biomass production of the legumes was estimated just prior to grain harvest by hand cutting two, randomly selected, one-square yard areas to a 1-inch height within each plot. With the grain harvested, a second estimate of the biomass production of the legumes was made by hand cutting the previously sampled one-square-yard areas to a 1-inch height within each plot after the first killing frost in late fall. Dry matter content of the biomass samples was determined by drying a 2-lb subsample at 150°F for 24 hours. The biomass production for either sampling date and the sum of both sampling dates were reported.

Each combination of years and locations were considered a single environment. Analysis of variance was computed for all traits measured, assuming all effects except replications as fixed, using SAS 8.02 (SAS Institute Inc., Cary, NC) across environments. Treatments differences were tested with the appropriate F-test and means were separated using Fisher’s protected LSD (0.05). Significant interactions between environments and treatments were detected for stand and height of the legumes but no rank changes occurred when combined across environments (data not shown). Hence, only data across environments is presented.

Wheat Population, Height, and Grain Yield

Competition from the legumes did not affect wheat populations compared to the monoculture at establishment or at harvest (Table 2). The legume treatments had no effect on wheat height (Table 2). Hairy vetch was taller than either alfalfa or clover and approached the top of the wheat canopy at harvest (Table 2). The ability of the hairy vetch to reach the top of the canopy resulted in a problem with the mechanical harvest as too much green material entered the combine and reduced harvest capacity. Furthermore, hairy vetch reduced grain yield and test weight compared to the wheat monoculture (Table 3). Intercropping alfalfa or red clover did not affect wheat yields compared to the wheat monoculture. Intercropping legumes in wheat had no effect on grain protein content (Table 3).

Table 2. Stand counts and plant height of wheat and three legumes when intercropping selected legumes and hard red spring wheat at three locations in Minnesota in 1999 and 2000.

 * Data are averaged for two years and three locations.

Table 3. Grain yield and quality of hard red spring wheat when intercropped with three legumes and biomass of three legumes at grain harvest and after the first killing frost at three locations in Minnesota in 1999 and 2000.

 * Data are averaged for two years and three locations.

Legume Yield

At grain harvest, the above ground biomass of the three legumes was the lowest for alfalfa and the greatest for hairy vetch (Table 3). By late fall, hairy vetch averaged the most re-growth and alfalfa the least amount of re-growth (Table 3). The total biomass produced was 0.5, 0.67, and 1.0 ton/acre for alfalfa, red clover, and hairy vetch, respectively (Table 3). In comparison, in the North Dakota State University’s dryland alfalfa variety trials at Fargo, ND seeding-year forage yields averaged 3.2 and 4.4 ton/acre of hay in 1999 and 2000, respectively (5,6). Alfalfa producers may expect 0.75 ton/acre of hay in the seeding year when establishing alfalfa with a companion crop of oats in the more humid climates to the east (Dr. Paul Peterson, personal communications)

Adequate soil moisture or additional precipitation immediately following grain harvest was essential for re-growth of the legumes as the experiment in 2000 in Morris showed. A period of hot and dry weather immediately following harvest resulted in no re-growth after the initial sampling at grain harvest. The lack of precipitation in late summer and early fall in the semi-arid climate of the Northern Great Plains may hinder the potential for intercropping these three selected legumes in HRSW for the purpose of growing a green manure or hay crop.

It is unclear whether the legumes mined available N or provided additional N through N₂ fixation. The total amount of N available at planting was 150 lb of N per acre. The grain yield was approximately 75% of the yield goal for which it was fertilized. Thus, additional nitrogen likely was available for the legumes to utilize after the spring wheat was harvested. Neither the amount of nitrogen in the biomass nor the nitrogen credit the following year, using a nitrogen rate response experiment, were determined. However, based on previous research the amount N available the first year after the plow-down may be as high as 35 lb/acre for red clover, 60 lb/acre for hairy vetch, and 95 lb/acre for alfalfa (8,10). The cost of the legume seed varied between $7.50/acre to $10.00/acre. Assuming that producers can readily seed the wheat and the legume simultaneously and adequate weed control can be exercised with the limited options available when intercropping any of the three selected legumes, the intercropping of the legumes and wheat may be economically viable.

Conclusion

Although it produced the greatest amount of biomass following small grain harvest, hairy vetch is unsuitable for intercropping with spring wheat, as it grew tall enough to hinder grain harvest and reduced grain yield. Intercropping alfalfa or red clover did not affect wheat yields compared to the wheat monoculture and neither of the two legume species impeded grain harvest. All three legumes that were evaluated in this experiment grew after the HRSW was harvested and provided a green manure crop at the end of the season when soil moisture in the later part of the summer was not limiting.

Acknowledgments

Funding for this research provided by the Minnesota Agricultural Experiment Station and the Minnesota Environmental and Natural Resources Trust Fund as recommended by the Legislative Commission on Minnesota resources.

Literature Cited

1. Badaruddin, M., and Meyer, D. W. 1989. Forage legume effects on soil nitrogen and grain yield, and nitrogen nutrition of wheat. Agron. J. 81:419-424

2. Badaruddin, M., and Meyer, D. W. 1990. Green-manure legume effects on soil nitrogen, grain yield, and nitrogen nutrition of wheat. Crop Sci. 30:819-825.

3. Baldock, J. O., Higgs, R. L., Paulson, W. H., Jakobs, J. A., and Schrader, W. D. 1981. Legume and mineral N effects on crop yields in several crop sequences in the upper Mississippi Valley. Agron. J. 73:885-890

4. Liebman, M. 1988. Ecological suppression of weeds in intercropping systems: A review. Pages 197-212 in: Weed Management in Agroecosystems: Ecological Approaches. M. A. Altieri and M. Liebman, eds. CRC Press, Boca Raton, Fla.

5. Meyer, D. W., Norby, W. E., and Ashley, R. O. 1999. North Dakota Alfalfa Performance Tests in 1999. N. Dak. Agric. Exp. Station, N. Dak. State Univ., Fargo.

6. Meyer, D. W., Norby, W. E., and Berdahl, J. D. 2000. North Dakota Alfalfa Performance Tests in 2000. N. Dak. Agric. Exp. Station, N. Dak. State Univ., Fargo.

7. Moynihan, J. M., Simmons, T., and Sheaffer, C. C. 1996. Intercropping annual medic with conventional height and semidwarf barley grown for grain. Agron J. 88:823-828.

8. Rehm, G. W., Schmitt, M. A., Lamb, J. A., and Eliason, R. 2001. Fertilizer recommendations for agronomic crops in Minnesota. BU-06240. Univ. Minn. Ext. Serv., Univ. of Minn., St. Paul.

9. Sustainable Agriculture Network. 1998. Managing Cover Crops Profitably. 2nd ed. Sustain. Agric. Pub., Univ. of Ver., Burlington.

10. Undersander, D. J., Ehlke, N. J., Kaminski, A. R., Doll, J. D., Kelling, K. A. 1992. Alternative Field Crops Manual. Univ. of Wis. Coop. Ext. Serv., Madison.