Modified Relay Intercropping

Wheat is a flexible, adaptable plant (H. Lafever, 1990) with a growing season that starts with planting in the fall and ends with harvest in the early summer. This adaptability allows farmers to capture some 66 percent of the traditional growing season—May 1 to September 30—to produce a second crop through the inter-planting of soybeans into wheat in June. This practice is known as Modified Relay Intercropping (MRI).

Harvesting Two Crops in the Same Year

An MRI system involves the production of two different crops, with different growth and development requirements, in one growing season. In an MRI system, soybeans are planted into standing wheat between 20 and 60 days prior to wheat harvest.

In addition to allowing the harvesting of two crops in the same year, the MRI cropping system has the potential to increase farm income while hedging production risk and protecting the environment at the same time.

MRI recommends the planting of regular soybeans from around May 15 to June 20. Soybeans have been successfully planted as early as May 1. The goal of this planting date is to have a well-established soybean plant of 6 to 8 inches in height (V2 to V4 growth stage) at wheat harvest.

In the MRI system, two crops—wheat and soybeans—are harvested in the same year. However, because of the difference in crop growth requirements and grain markets, farmers can effectively hedge production and price risk in an MRI system in most years. Producers considering using an MRI system should plan to grow wheat in such a manner (wheat rows less than 15 inches in width do not differ in yield from narrow rows) that yield is not significantly reduced from wheat grown in a conventional system.

Long-term research at The Ohio State University's Ohio Agricultural Research and Development Center (OARDC)(D. Jeffers, 1995), in Crawford County (Prochaska, 2003), and other locations in Indiana (A. Kline et al., 2001) has shown that MRI or RI wheat will yield about 90 percent of conventional wheat.

Because of the high probability of growing wheat in an MRI system at about 90 percent of conventional wheat, farmers may hedge their crop production risk in an MRI system through the opportunity (option) to grow and harvest a crop of soybeans. Soybean production in an MRI system is more speculative than wheat production due to the need for adequate rainfall in July and August.

In 18 years of replicated field trials, soybeans averaged 34 bushels per acre, with a range from 0 to 56 bushels per acre. Wheat yields have averaged 74 bushels per acre, with a range of 65 to 91 bushels per acre(through 2017). Conventional monocrop wheat and soybeans averaged 73 and 56 bushels respectively from 2007 to 2018 in Crawford County. MRI has been implemented successfully by farmers in many areas of northern Ohio and various states across the country.

Finally, in the MRI system, a crop is growing in the field for 12 consecutive months of the year. Thus, soil protection and concomitantly water quality is preserved. The herbicide system for MRI wheat and soybeans has a similar cost to monocrop soybeans. A fall application of Sharpen with a spring treatment of 2,4-D is a good management strategy. After wheat harvest, a post-herbicide application may be needed to control weeds in wide-row wheat and soybeans.

Advantages of Intercropping

1. Potential for increased farm profitability.
2. Lower fixed costs for land and machinery as a result of the production of a second crop in the same field.
3. Better utilization of farm management labor, time, and equipment.
4. Low cost of production for MRI soybeans (as a result of a lower weed-control cost: two crops weed control for the price of one).
5. Hedge production risk (two crops in one growing season).
6. Hedge commodity price risk by being able to market both wheat and soybeans.
7. May be used for conservation compliance planning after planting. (Allows for 12 months of cover much like the goal of many cover crop programs.)
8. May be adapted to most available farm equipment.
9. Perhaps more consistent yield results for both wheat and soybeans than in other double-crop systems. (McCoy, 2001.)

Disadvantages of Intercropping

1. Not adaptable to droughty, poorly drained, or very heavy clay soils.
2. Potential increase in soybean pests such as Soybean Cyst Nematode.
3. Success of soybean crop is highly dependent on timely and adequate July and August rainfall.
4. Soybeans are susceptible to early fall frost damage (less than double cropping system.)
5. Wheat susceptibility to Fusarium head scab (not worse in wheat to be interplanted). In the event of severe infection, may greatly reduce the potential profitability of the system.
6. Possible additional machinery cost. (May require a special planter for interseeding depending on what you already have.)
7. Requires very timely field operations.

Modified Relay Intercropping—Row Spacing

Different wheat row spacings have been used successfully in MRI. Wheat is a very adaptable plant and will compensate for different row spacings by tillering. It should be remembered that sunlight is the energy source responsible for wheat and soybean production. Thus, a primary goal of MRI is to capture and utilize as much sunlight as possible. Light, or the lack of it, has a profound effect on the growth of intercropped soybeans. Different MRI systems have used row spacings from 10 to 15 inches. Wider spacings are possible; however, other production factors such as soybean planting date and the soybean weed control program will need to be considered.

Soybeans planted too early into well-tillered wheat often will become very tall and spindly (etiolated) due to lack of light. In general, weak plants do not grow well. In MRI, soybeans planted about 20 to 45 days prior to wheat harvest have provided the most consistent yields. Theoretically, earlier planted soybeans should yield better; however, as was mentioned earlier, competition with wheat may produce a weak soybean plant. Conversely, if soybean growth is vigorous, wheat growth and perhaps yield is diminished (D. Jeffers, 1995). Therefore, in MRI, soybeans are planted into wheat that will soon ripen and allow more light onto the developing soybean plant. Wider row spacings also allow for more light to reach the soybean plants. With earlier planting dates, some producers are using header guards to protect soybeans from the sickle on the header.  

Wheat yields in Ohio were found by Beuerlein (Profitable Wheat Management, 1990) to not be significantly different for 7- and 10-inch wheat row spacings. The yield difference between 7- and 14-inch wheat was only about 3 bushels per acre. This research attests to the ability of the wheat plant to change its growth habit and thus continue to yield at high levels at wider row spacings.  

It should be noted that the wheat plant is very competitive with most weeds. However, wide row spacing or thin wheat may promote greater weed pressure in the subsequent soybean crop. Finally, there is an interseeding effect on wheat yield. Three years of trials in Crawford County plots (S. Prochaska, 2003) resulted in wheat yield reduction data of 10 and 14 percent. This correlates well with earlier research done in Ohio by D. Jeffers (Profitable Wheat Management, 1990).

Wheat Production in Modified Relay Intercropping  

Here are some guidelines to help farmers who are considering a Modified Relay Intercropping system.

1. Select a well-drained field.
2. Adjust fertility. Wheat nitrogen needs will be about 1 pound N per bushel of expected yield based on this equation: N (lb/a) = 40 + [1.75 x (yield potential - 50)]. Wheat will use 0.49 pound P₂O₅ per bushel and 0.24 pound K₂O per bushel, but application should be based on a soil test. Soil pH should be between 6 and 7. Calculate the row spacing needed to allow equipment to run through the wheat to plant soybeans. Many grain drill and planter units have been used successfully. The key requirements are narrow enough to fit between wheat rows, good down pressure to penetrate dry ground, and the ability to fully close the seed slot.
3. Sow wheat into rows with a spacing of 10 to 15 inches, to allow soybean planting with tractor and planter (or drill). Twin row spacing (wheat rows 8 inches apart with a 22-inch gap) has also been used successfully in research plots and by farmers utilizing the MRI system.
4. Set up a tramline system in the wheat to facilitate soybean planting. Tramlines allow for straight driving and for equipment to move through wheat, thus protecting the wheat from being run down by the equipment.
5. Seed wheat on or soon after the Hessian fly-free date.
6. Sow wheat at 23 to 28 seeds per feet of 10-inch row (attempt to achieve a seeding rate of around 1 to 1.3 million seeds per acre).
7. Plant wheat 1 to 1.5 inches deep.
8. Select a thin-line type of wheat of relatively early maturity to allow more light onto MRI soybeans and to facilitate early wheat harvest. Many wheat varieties have been tested with most high-performing wheat able to be interseeded. Wheat variety selection is also thought to be important from the standpoint of possible autotoxic effects on the soybean. Try new varieties on only a portion of your acres to spread the risk of that variety not performing well in MRI.
9. Apply an appropriate broadleaf herbicide on wheat, such a 2,4-D LV ester prior to Feeke's growth stage 6, if broadleaf weeds are a problem. If application timing on broadleaf weed growth is good, this is often the only spring herbicide needed for both wheat and soybeans. In wide-row wheat/soybean production, a post-emergent herbicide is often needed after wheat harvest.
10. Harvest wheat as soon as it can be threshed (20 to 25 percent moisture). Cut wheat right at the top of the soybean plant. Be sure straw is chopped and spread evenly behind the combine. All of these actions allow more light to reach the soybean plants.  

Soybean Production in Modified Relay Intercropping

Here are some guidelines to help with soybeans in a Modified Relay Intercropping system.

1. Adjust fertility for two crops. Pay attention to P and K needs of the soybeans. Soybeans will use 0.79 pounds of P₂O₅ and 1.14 pounds of K₂O per bushel of production.
2. Plant soybeans at a rate of 150,000 to 200,000 seeds per acre.
3. Plant at a 1-inch depth or perhaps deeper. Crusting should not be a problem in this system.
4. Select a soybean of the longest relative maturity for your area, 3.2 to 3.9 relative maturity has worked well in northern Ohio, and one that will produce strong vegetative growth and is tolerant of dry weather.
5. Plant soybeans into the wheat approximately 20 to 60 days prior to wheat harvest. Evaluate wheat vigor and soil moisture to determine the soybean planting date. If wheat is vigorous with little light reaching the row middles, delay soybean planting. We have successfully intercropped to June 22. The last date to intercrop is when wheat stems begin to break.
6. Avoid the use of cell-membrane disrupter mode-of-action herbicides (Blazer, Reflex, Flexstar, Cobra, Resource) on MRI soybeans. Soybeans in an MRI system are in a weakened state after wheat is combined and may be less able to recover from herbicide stress compared to conventional soybeans. Thus, for best results, control broadleaf weeds before soybean planting or two to three weeks after wheat harvest if non-Roundup Ready soybeans are planted so as to allow soybean plants to harden. GMO soybeans have performed satisfactorily in MRI systems and should be used where annual and/or perennial weeds are a problem.
7. When planting soybeans into wheat, place metal arrow-shaped spreaders in front of all tires to move wheat out of row middles to allow for passage of equipment. These spreaders may also be necessary ahead of planter units. Narrow tires on the tractor may also facilitate planting of soybeans into wheat and reduce plant damage.
8. Row guidance systems may also be used to facilitate interseeding.

MRI Returns per Acre

Returns for MRI systems have been favorable when compared to conventional wheat, soybeans, or corn. Gross dollars per acre for 170 bushel corn, 52 bushel soybeans, and 80 bushel wheat (no straw sold) are compared here for one set of prices.

More complete enterprise budgets for conventional soybeans, wheat, and MRI are shown after the references below.

Original author: Dr. Steven C. Prochaska, Professor Emeritus, Agriculture and Natural Resources, Ohio State University Extension (Originally published in 2004).

References 

James E. Beuerlein and Colleagues. Profitable Wheat Management. (1990). Bulletin 811. Agdex 112/10. Ohio State University Extension. Columbus, OH: The Ohio State University.

Beuerlein, James.(2001). Relay cropping wheat and soybeans. Fact Sheet AGF-106-01. Ohio State University Extension. Columbus, OH: The Ohio State University.

Kline, A., McCoy, S., Vyn, T., West, T., Christmas, E. (2001). Management considerations for relay intercropping: I. Wheat. Agronomy Guide. AY-315. Purdue University Cooperative Extension Service.

McCoy, S., Vyn, T., Kline, A., West, T., Christmas, E. (2001). Management considerations for relay intercropping: II. Soybean. Agronomy Guide. AY-316. Purdue University Cooperative Extension Service.

Ohio Agronomy Guide, 13th Edition(1995). Bulletin 472. Ohio State University Extension. Columbus, OH: The Ohio State University.

Prochaska, S. C. (2003). Three-year summary of effect of modified relay intercropping on wheat yield in 15-inch rows. Rzewnicki, P. (Ed.) Agronomic Crops Team On-Farm Research Projects, 2002. Special Circular 190. Wooster: Ohio Agricultural Research and Development Center. The Ohio State University.

Prochaska, S. C. (2001). Effect of row width on wheat yield in a modified relay intercropping system. Rzewnicki, P. (Ed.) Agronomic Crops Team On-Farm Research Projects, 2000. Special Circular 179. Ohio Agricultural Research and Development Center. Wooster, OH: The Ohio State University.

Prochaska, S. C. (2001). Evaluation of USDA soybean inoculate in a modified relay intercropping system. Rzewnicki, P. (Ed.) Agronomic Crops Team On-Farm Research Projects, 2000. Special Circular 179. Ohio Agricultural Research and Development Center. Wooster, OH: The Ohio State University.

Prochaska, S. C. (2001). Modified relay intercropping. 110th Annual Meeting of Ohio Academy of Sciences. Alliance, OH: Mount Union College.

Prochaska, S. C.(2000). Effects of intercropping and tramlines on wheat yield. Rzewnicki, P. (Ed.) Agronomic Crops Team On-Farm Research Projects, 1999. Special Circular 176. Ohio Agricultural Research and Development Center. Wooster, OH: The Ohio State University.

Prochaska, S.C. (1997). Profitability plus environmental sustainability equals modified relay intercropping. Journal of Extension, 35(1).

Hartschuh, J.M (2015) Soybean seeding Rates for Modified Relay Intercropping. Agronomic Crops Team On-Farm Research. The Ohio State University. Retrieved from agcrops.osu.edu/sites/agcrops/files/ofr_reports/Soybean%20seeding%20Rates%20for%20MRI.pdf

Hartschuh, J.M., Prochaska, S.C (2014) Effect of Soybean Maturity in an MRI System. Agronomic Crops Team On-Farm Research. The Ohio State University. Retrieved from agcrops.osu.edu/sites/agcrops/files/ofr_reports/2014%2520maturity%2520in%2520MRI%2520two%2520DOP.pdf