Modified Relay Intercropping (MRI) is the planting of soybeans into headed wheat that may occur up to 7 weeks prior to wheat harvest.   MRI is system where two crops, wheat and soybeans can be harvested in the same growing season.

In 2013 in the MRI system, soybeans averaged 54 bushels/acre and wheat 70 bushels per acre over 12 different small plot field trials (randomized complete block, 4 replications).  This year, soybeans were above the long term average MRI yield and wheat below the long term MRI average yield (soybeans 30 bushel/acre; wheat 76 bushel per acre).  

After 15 years of field trials, the following are observations of the MRI system:

1.            MRI (planting of soybeans into wheat) can be conducted with many different common farm implements (some fabricated on farm).  Equipment used includes drills, tool bar planters, corn planters and variations. The key concept with equipment is to plan for and if possible, practice in the fall prior to wheat planting with the tractor/soybean interseeding equipment into practice wheat rows.  Tram lines in the wheat are essential to allow not only for precision soybean planting but also wheat management (weed, disease and fertility treatments).  Most tram lines are set up to facilitate tractor and sprayer tires.

2.            Wheat row spacing may range from 10 to 20 inches.  Wheat rows greater than 10 inches may experience a small wheat yield drop. This drop in wheat yield is relatively small up to 15 inches (from 5 to 7%) over various studies conducted in Ohio, Kentucky and Ontario.

3.            Attempt to sow wheat at or soon after Hessian Fly Free Date; for example, by Oct 7 in North Central Ohio. Plan to use an appropriate soybean variety that is harvested early enough to permit timely fall wheat planting.  There is not any merit to planting wheat prior to the Hessian Fly free Data (for example: Sept. 26 in Crawford County, Ohio).  Plant wheat seed to achieve 1.6 to 2.2 million seeds/acre or if in 15 inch rows not more than 25 seeds per foot of row.

4.            Select wheat varieties that are:  high yielding; disease resistant; early maturing and short if possible.  Confirm that wheat seed is treated with appropriate fungicides.  Go to http://agcrops/osu.edu and check out the OSU Wheat variety performance trials and the 15 inch wheat row trial.

5.            Apply fall fertilizer per soil test and Tri- State Fertility recommendations for at least 76 bushel wheat and 30 bu/soybeans (our 15 year average). Spring wheat N should again follow Tri-State recommendations.     

6.            Control marestail and other weeds prior to planting wheat either with appropriate tillage (not vertical tillage) or use appropriate herbicides (glyphosate + Sharpen is an example of a treatment that can be used prior to wheat planting to control marestail and many other weeds).

7.            Grow the best wheat you can grow utilizing  best management practices( ie: soil testing, fall  fertility  with some nitrogen, an appropriate spring nitrogen rate applied prior Feekes GS 6, disease control as needed as needed, 2,4-D applied on wheat in the spring prior to  wheat jointing by  Feekes GS 6, etc.).  

8.              Interseed soybeans about 21 to 50 days prior to wheat harvest. The fall wheat planting date, variety, weather and wheat row spacing selected will influence the soybean interseeding date.  Interseeding can be done too early!  There must be adequate light onto the developing soybeans,

(and wheat).  If interseeding is conducted too early, there is the possibility that soybeans will decrease wheat yields via excessive competition and further the soybeans may be damaged as well at wheat harvest.   Wide wheat rows will facilitate earlier soybean planting, but a wheat yield reduction is possible.  This wheat yield loss is due to both increasing row width and the interseeding of the soybeans.  Use as late a maturity soybean as is appropriate for your locale and planting date.  In previous trials conducted a 3. 3 or later maturity soybean has been planted with not any freeze damage.  A later maturity soybean may allow for more leaf development, later flowering and pod development with late season rains.     In 15 inch rows, plant beans from 6 to 7 seeds per foot of row.  In 10 inch rows, plant 4 to 5 seeds per foot of row.    

9.            Available plant water for soybean growth and development is critical.  Stated in another way, timely rainfall in July and August are very important to soybean yields.  This year, MRI soybean yields were exceptional (54 bushels/acre) with about 25 inches of rain from the middle of May to Oct. 1.  Our data would suggest that rainfall amounts over the summer growing season and hence soybean yield in the MRI system follow a normal distribution.  What this means is: soybean yield 1 year out of 5 will be very poor and  soybean yield 1 year out of 5  will be very good;  with the remaining 3 years of  soybean yields being around  average. 

10.          Wheat may be in flower when interseeding.  This will not significantly harm wheat as long as it is not run down (there may be a small interseeding effect on wheat yield in some years).  Spreaders, fabricated iron into a V shape, attached to the tractor and/or the planter should be considered in some MRI systems that will spread the wheat at planting and allow the equipment to pass without running over the wheat.   

11.          The larger the soybeans are at wheat harvest; the more susceptible to injury or damage from the combine wheel traffic.  Significant soybean stand loss can occur and this is essentially in the area run over by the combine tires.

12.          Harvest wheat early as can be threshed,   if possible harvest wheat at 20% moisture and dry.

13.          Cut wheat at top of soybeans.

14.          Aggressively chop and evenly spread wheat residue behind combine as excessive residue on soybeans will limit yields.

15.          Control weeds.  With development of herbicide resistant weeds, glyphosate cannot be relied upon to control weeds such as marestail; however within the system, other herbicides effective on marestail can be applied.

16.          Scout for defoliators/pod feeders in late July and early August as they have the potential in some years to may damage interseeded or double crops beans and reduce yields.

As is the case every year, new information from our 2013 trials will be added to our previous experiences with this system and that new information will lead us to trial new MRI concepts in 2014.  Among the concepts up for test in 2014 are revised wheat/soybean row spacing’s, and interseeded corn and grain sorghum (the latter two concepts were conducted in 2013). 

Finally, there are many other cultural and risk management factors associated with MRI not discussed here and these factors may be associated with either the wheat or soybean production.  For more information on the Modified Relay Intercropping go to:  http://ohioline.osu.edu/agf-fact/0504.html