In this project, we propose expanding soybean production and potentially increasing the economic returns to Iowa farmers and industry leaders by a sustainable intensification of the existing cropland.
Our strategy is to apply intercropping practices, which involve the harvest of our main cash crop- soybean- plus the harvest of a second crop in the same field, in the same year, reducing negative environmental costs. Moreover, planting soybean with winter crops, such as small grains, will be a way to take advantage of Iowa’s six-month fallow period. A winter crop can be planted immediately following the soybean harvest of, and it will have a double function as a cash crop and a cover crop, protecting the soil from erosion and nutrient runoff, which are the major causes of water pollution. Another key benefit of intercropping and crop biodiversification is the potential pest control and disease suppression by breaking disease cycles. In summary, there are multiple advantages of intercropping soybean with winter small grains: increased land use efficiency, soil fertility, better pest and weed control, and enhancement of overall crop productivity relative to conventional crop monocultures, which will allow Iowa farmers to implement an “eco continuous soybean system” instead of corn-soybean rotations.

Intercropping practices or relay intercropping consists of two or more crops grown in sequence with some overlap in the growth cycle. In this practice, a winter crop will be planted in the fall, soybean will be inter-seeded into a living winter crop, mature winter crop will be harvested in July, and mature soybean will be harvested in October. Brazil, which overtook the United States as the leading soybean-producing country since 2019, also is applying relay intercropping practices to take advantage of the yield benefits (https://www.embrapa.br/en/sistema-antecipe). These practices will be accomplished using innovative equipment solutions such as those being employed in Brazil and other projects in the US (Finley and Ryan, 2018, Wilson et al., 2019, Ott et al., 2019). Four reasons for this focus on intercropping are: 1- Iowa’s climate is changing. Today the average winter temperature in Iowa is 3 degrees higher than in the last 50 years and the time between the last freeze in the spring and the first one in the fall has increased by about 10 days since the beginning of the 20th century (USDA Midwest Climate Hub). This climate situation may provide an opportunity to establish a second crop. 2- The current global agricultural and food security situation. Due to Russia’s war against Ukraine, there is an imminent necessity for the US to produce more grains and oilseeds, especially wheat, barley, and sunflower. 3- The contribution of researchers (Sallam et al, 2021) and winter breeding programs in MN, MO, OH, and NE, among others (UMN Forever Green Initiative (FGI), Agricultural and Natural Resource Sciences (CFANS), MSU- Winter Breeding Program, etc.) have focused on developing winter-hardy seeds for Midwest farmers. New cultivars allow for greater timing flexibility and decreased inputs resulting in improved profitability of multi-cropping options. 4- The opportunity for growers to diversify their market. Small grains such as barley, oats, triticale and wheat can be excellent forage crops in the form of pasture, hay and silage. The market for barley, in addition to forage and feed grains, includes food grains, malting barley and ethanol.

General Objective: Increase soybean productivity through the adoption of intercropping practices with winter small grains with the purpose of implementing a sustainable continuous soybean system in Iowa.

Specific Objectives:
1-Optimize the “agronomics” of growing soybeans with winter crops :
a) Determine the winter crops/ varieties that can be better paired with soybean.
b) Address cultural management considerations: planting dates, seeding density, time to maturity, fertility management, ability to inter-seed, germinate, and establishment.
2-Evaluate the effect of winter crops on soybean seedling diseases (damping-off, SDS, white mold, stem diseases, foliar, and root diseases) and soybean cyst nematode. In addition, the small grains’ performance and any significant disease or pest occurrence will be evaluated.
3- Evaluate soil health impacts, including soil organic matter, C food source and bioavailable N.

Methodology:
1-To determine the winter crops best paired with soybean: Winter barley, wheat, and rye will be evaluated. In addition, trials involving oat will be performed.
The field experiments will be established over three years at 2 different locations in Iowa (ISU-Research Farms) under different environments. In addition, in collaboration with ISU researchers (USDA-NRCS Grant), trials will be performed in 6 farmer-partner (aka on-farm trials) and three research plots (USDA).
Data on plant populations will be collected over the growing season. UAV imagery will be used to estimate above-ground biomass. Yield and quality data will be collected for soybean and winter crops; records will be maintained for all input costs. A conventional single-crop soybean treatment will be included for comparison.
2-To evaluate the potential impact of winter small crops in reducing soybean diseases and SCN. Field and greenhouse trials will be conducted.
a) UAV imagery will be used to monitor field health.
b) Disease incidence and severity over the season will be evaluated.
c) The effect of wheat/rye/barley on SCN populations in relay-cropping soybean will be investigated according to Rocha et al. (2021) and Hershman et al. (1995).
d) Growth chamber experiments will be conducted to test rye, wheat, barley and oat for disease suppression in controlled-environment conditions.
e) Barley and wheat varieties will be tested for their resistance to Fusarium graminearum in the greenhouse. This fungus is a common pathogen on soybean as well as barley and wheat and our goal is to determine what barley varieties would be less likely to lead to inoculum increase for soybean infections.
3-To evaluate soil health impact: We will collect 0-15 cm soil samples from the field sites at project initiation (fall of Year 1), and again at the end of the project in Year 3. The analysis will include mineralizable carbon, potentially mineralizable nitrogen, and carbon dioxide burst.

Updated December 11, 2024:

Updated June 5, 2025:
A- Relay Cropping Field trials:
• Year 1: Fall 2023: winter small grains (rye, barley) and oilseeds (canola, camelina) planting.
Spring 2024: soybean planting.
Location 1: Agricultural Engineering & Agronomy (AEA) Research Farm near Boone, IA.
In a randomized complete block design, winter cereals [Organic rye, Hazlet (90 lb/ac), and Organic MN-Equinox barley (96 lb/ac)] and winter oilseeds [camelina (Albert Lea, 6-8 lb/ac) and canola (Sitro, 3.5-5 lb/ac)] were drilled (in a 7.5-inch row spacing) separately in a 900 sq. ft. plot (30 ft. wide × 30 ft. long) per replication on October 10, 2023.
On May 17, 2024, soybean variety P14A12E was planted at 140k seeds/ac in a 30-inch row spacing using a 6-row John Deere 640 R planter in cereal rye and barley at the boot leaf stage. There was no emergence of canola in spring. The camelina emerged but did not survive the very low temperatures registered in March 2024. Earlier planting days, hardy winter seeds, and new locations in Iowa will be evaluated in our next field trials. Soybeans were planted in these plots to minimize weed infestations.
On April 11, 2024, cereal rye and barley plots were evaluated for emergence and growth stages and seedling diseases. Recorded growth stages, plant heights, and stand counts in soybean on May 28, 2024. On June 10, 2024, we assessed weed infestation (across 18 weed species) and types of weed infestation. In winter barley-soybean relay crop (SRC) and cereal rye-SRC, was significantly low (P<0.05) compared with no-till fallow/soybean monoculture plots. In the no-till soybean monoculture plots, 90-95% of weeds represented were downy brome, little barley, yellow foxtail, woolly cup grass, giant foxtail, and barnyard grass. Whereas in barley-SRC and cereal rye-SRC plots, yellow foxtail, giant foxtail, and waterhemp were observed with very low to low infestations (Navi et al, 2024). Cereal rye, barley, and soybean were monitored for seedling, foliar, stem, and panicle diseases at regular intervals starting June 17, 2024, and cereal rye and barley were harvested on July 19, 2024, using a portable Bushel Plus Mini-Combine, and soybean plots were combined on September 26, 2024.

• Year 1: Fall 2023: mix of winter small grain (rye) and oilseed (camelina) planting.
Spring 2024: soybean planting.
Location 2: Farmer-partner in Monticello, NE-IA.
Following a no-till 2023 corn field, a mixture of winter camelina (1-2 lb/ac) and cereal rye (35 lb/ac), both VNS seeds, was drilled. Interestingly, no soybeans were planted in the past 6 years. This field had a history of white mold, but after switching to winter cropping, no white mold was observed. Soybean variety (RR) P30A75E was planted on May 12, 2024, at 140K seed/ac in a 30-inch row spacing when cereal rye and winter camelina were in the vegetative growth stage. We flagged eight plots, 25 ft. wide and 375 ft. long, for our evaluations. Seedling, foliar, stem, and panicle diseases in cereal rye, camelina, and soybean were assessed. No major weed infestations were observed across eight replications. Cereal rye and camelina were harvested using R75, Gleaner on July 12, 2024, and soybeans on October 8, 2024.
Disease evaluation at farms in Boone and Monticello (Summer 2024):
Soybean: No major diseases of soybean were observed in soybean relay cropped with cereals (except soybean vein necrosis) compared with monocropping/solo soybean, wherein Phytophthora root rot, sudden death syndrome, and Cercospora leaf blight were observed at the Monticello location. Such diseases were not observed at the Boone location.
Winter rye and barley:
a) Seedling: Early in the season, symptomatic seedlings with root/basal stem rot sampled from barley and cereal rye plots revealed the occurrence of four species of Alternaria, including Ascochyta, Bipolaris, Epicoccum, and Pyrenophora, five species of Fusarium, and three species of Pythium at AEA farm (Navi et al, 2024). No seedling diseases were observed at the farm in Monticello.
b) Foliar: Cereal rye rust (Puccinia triticinia) was observed at both locations. The disease severity varied from 20 to 30%.
c) Panicles: Ergot (Claviceps purpurea) of cereal rye and smooth bromegrass, and Fusarium head blight in cereal rye were observed in both locations.

Inputs to income of the winter cereals–soybean relay cropping systems compared to the mono-cropped soybean systems, based on yields observed in Boone and Monticello, IA, in 2024, revealed some advantages.
Soybean yields in the inter-cropped plots were generally slightly higher than those of mono-cropped soybeans. At Boone farm, the yield of soybean relayed with winter barley was 37.36 bu/ac, soybean relayed with winter cereal rye yielded 36.49 bu/ac, compared with monocropped soybean with 34.27 bu/ac for 1.4 maturity group of soybeans. This indicated a yield advantage of 3.09 bu/ac and 2.22 bu/ac, respectively. At Monticello farm, soybean yields of 70 bu/ac was recorded in soybean relay cropped with cereal rye compared with 67 bu/ac in monocropping soybeans for the 3.0 maturity group of soybeans.
In addition to the soybeans, the advantage is the economic return of cover crops (winter barley or rye relay with soybeans). Yields of winter barley were 20.50 bu/ac, yields of winter cereal rye were 30.47 bu/ac at Boone farm and 40 bu/ac at Monticello farm.

The gross advantages (USD/Ac) of relay cropping soybeans with winter cereals at the two locations will be calculated.

Summary: Inputs to income of relay cropping soybeans with winter cereal crops in Iowa of the first-year trial showed:
a. A significant (P<0.05) reduction in weeds and types of weed infestation in soybean relay cropped with cereals compared with monocropping soybean or sole soybean plots.
b. No major diseases of soybean were observed in soybean relay cropped with cereals (except soybean vein necrosis) compared with monocropping soybean.
c. Yields and economic advantages of relay cropping soybeans with cereals were observed at both locations (Boone and Monticello farms).

Remarks: These results are based on our results of the first-year trials. We may have comparable results in the next couple of years of studies at multiple locations.
UAV imagery collected at multiple growth stages of soybean relay cropping with cereals at the Boone location is being processed shortly.

• Year 2: Fall 2024: winter small grains (rye, barley) and oilseeds (canola, camelina) planting.
Spring 2025: soybean planting.
Location 1: Sorensen Research Farm, near Boone, IA.
After the first-year experience and several discussions with CO-PIs, farmers, and field crew, we conducted trials in strip-trials (15 ft. wide ×270 ft. long × 2) per crop. Each strip has four replications. This was mainly to adjust the relay cropping specific management practice better than in the RCBD in 2023-24. Winter small crops and oilseeds were planted on October 4, 2024, in a 6-inch row spacing, each with 20 rows. Seed rates for cereals were 90lb/ac, oilseeds 8 lb/ac. Soybeans were planted on May 14, 2025.

• Year 2: Fall 2024: winter small grain (rye) planting.
Spring 2025: soybean planting.
Location 2: Farmer-partner in Monticello, IA.

• Year 2: Fall 2024: mix of winter small grain (rye) and oilseed (canola) planting.
Spring 2025: soybean or corn planting, depending on crop rotation pattern at the farm.
Location 3: Farmer-partner in Sidney, IA.

B-Greenhouse Trials:
Experiment 1:
Fusarium graminearum (Fg) is a common pathogen on soybeans as well as cereal such as barley, wheat, and rye. We have conducted greenhouse experiments to assess (i) the susceptibility of cereals and oilseeds and soybeans to Fg and (ii) characterize the virulence of Fg in the varieties of soybean, winter cereal crops, and oilseeds that we are using in the field trials and to test whether rye, barley, canola, and/or cameline help to control Fusarium disease in soybean.
A total of 30 pots were filled with a potting mixture (2.83 L/pot), and Fg-inoculum (67 cc/pot) increased on white milo, while 30 other pots were filled with only potting mixture as uninoculated controls. Both the inoculated and uninoculated pots were planted with seeds of winter cereal rye, winter barley, winter camelina, winter canola, and soybeans. Also, 18 pots with cereal rye and 18 pots with barley were planted as borders around the experiment, laid out on greenhouse benches. Pots were irrigated twice daily and incubated on greenhouse benches with 12-h light from December 7, 2024, to May 6, 2025. Depending on the maturity dates of the cereals, oilseeds, and soybeans planted, the plants were harvested starting from March 28 to April 16, 2025, and assessed for stand counts (healthy and infected), fresh and dry weights of roots and shoots, number of pods and panicles, and nodules. After the harvests, pots were refilled with the potting mixture that was used at the planting, irrigated once daily until all the pots were planted with only soybeans on May 6, 2025. All these pots were evaluated for Fg-infections (if any), stand counts, and plant heights.
The results from this study will be presented at the APS-Plant Health Conference 2025 in Hawaii.

Experiment 2: A second experiment has been conducted since 4/22/2025 in order to characterize particularly the effect of F. graminearum (Fg) on root systems of soybeans and winter and spring variety of small crops and oilseeds using Rhizotrons.
Root health and biomass but also shoot health and biomass is been evaluated. As of now, the results are clearly distinguishable in the inoculated vs uninoculated on agronomic features (stand counts, plant height, root and shoot biomass) and disease incidence (%) of the crops studied so far.
The detailed methodology and results from this study will be presented at the APS-Plant Health Conference 2025 in Hawaii.

Updated March 27, 2026:
Progress update:
1-To determine the winter/spring crops best paired with soybean, agronomics, and polyculture
management:
• In Fall 2024/Sp 2025, field experiments were established at the ISU Sorenson Research Farm,
Boone, Iowa, in strip trials:
o In Fall 2024, we evaluated, for a second time, four relay-cropping (RC) systems treatments
with winter crops to be interseeded with soybean in spring. We planted winter cereal crops
(rye and barley) and oilseeds (canola and camelina), each replicated 2 times. Plots were 20
rows in a 6” row spacing by 300 ft. Control (no-till fallow/soybean monoculture: MC) was
included.
o In early Spring 2025, additional five RC treatments were tested, this time with spring crops.
We planted spring cereal crops (wheat and oats) and spring oilseeds (canola, camelina,
sunflower), each replicated 2-3 times. Plots were also 20 rows in a 6” row spacing by 300
ft, except for sunflowers, which were planted in 6 row plots in a 30” row spacing. Control
(no-till fallow/soybean monoculture: MC) was included.
o Five rows of soybean (P23Z82E, MG: 2.3) by 300 ft were relay-cropped with cereals and
oilseeds.
o We evaluated the establishment of winter crops. Soybeans in RC and MC were assessed
for shoot and root biomass, pod number, and nodulation. Yield and inputs to income of
soybean relayed with winter/ spring crops were evaluated.
o Data analysis from UAV imagery (collaboration with Iowa State’s Remote Sensing and
Imaging Laboratory) has been processed to characterize the performance of our primary
crop, soybean, in RC (establishment, competition, biomass accumulation after cereal and
oilseeds harvested).
• 2 farmer partners (aka on-farm trials): Monticello (NE Iowa) and Sidney (SW Iowa).
Sidney:
o Sidney was the only location in Iowa where winter canola (CP1066 WC) survived the winter
and established. However, soybeans were not relay-cropped because canola presented an
indeterminate growth pattern. For our third-year project, a new canola variety will be
planted following the advice of a Kansas breeder collaborator. Stand counts, pod counts,
and plant height and yield were evaluated.
o For reference, we recorded stand counts for soybeans and corn planted adjacent to winter
canola plots.
Monticello:
o In spring 2025, sp. camelina (Suneson from Montana State University, 0.4 Ac), winter
canola (CP1066 WC, 0.795 Ac), and spring canola (P612L NY41, 1.27 Ac) were drilled in 8-
inch row spacing on March 14, 2025, and soybeans (variety P30A75E) were planted on
April 30, 2025, in 30” row spacing at 110k seed/ac. This field was planted to corn in 2024.
o Stand counts, plant heights, and biotic and abiotic stress data were collected on June 12,
2025. Panicle samples of ergot-infected winter cereal rye and Broome grass were collected
on June 27, 2025.
o Yields of spring canola, spring camelina, winter rye, and soybean have been processed.
2-To evaluate the potential impact of winter small crops/ oilseeds in reducing soybean diseases and SCN.
Field and greenhouse trials.
a) We collected data on plant populations, biotic, and abiotic stresses from all the plots. Biotic stress
data, primarily isolations from diseased cereals and oilseed plants, are to be confirmed using
molecular tools.
b) During the cropping season, we flew a drone on June 11, July 1, and August 28, 2025. UAV
imagery has been used to monitor field health.
c) The effect of cereal and oilseeds on SCN populations in RC- soybean has been evaluated. After the
harvest in Boone, IA, three soil samples, each with 15 cores, were collected from each of the 12.5
ft-wide × 300 ft-long strips on November 14, 2025, and the 66 samples were tested for SCN egg
counts (100 eggs/100cc). Additional SCN will be included in the third year project.
d) Growth chamber experiments were conducted to test winter cereal crops and winter oilseeds for
Fusarium root rot disease suppression in controlled-environment conditions (results presented at
the Plant Health 2025 conference).
e) Winter small grains and oilseeds were tested for their susceptibility to Fusarium graminearum in
the greenhouse. This fungus is a common pathogen on soybean and cover crops, and the goal was
to determine which crops would be less likely to lead to increased inoculum for soybean
infections (results presented at the Plant Health 2025 conference).
3-To evaluate soil health impact: We collected soil samples (3 reps, each with 15 cores) from the field sites
at Sorenson Farm, Boone, IA, in Nov 2025. The analysis included S-4 soil routine, total organic carbon, bulk
density, wet aggregate stability, and S-1794 available water holding capacity, rather than organic matter.
The samples were analyzed by WARD Lab in Nebraska on Jan 16, 2026. This soil analysis was critical for
comparison with a few additional soil analyses to be conducted in 2026 and 2027 to assess any change in
soil health resulting from relay cropping soybeans with cereals and oilseeds.
Conferences and Outreach activities
Our RC-research was shared in different research and outreach meetings during 2025:
? Practical Farmers of Iowa (PFI), Field Day in Monticello, IA, July 7, 2025. Hosted by our farmer-partner,
Jason and Sarah Russell. We were invited to explain the layout, the advantages of soybean relay cropping
with winter cereal rye, and the oilseeds to a group of ~50 farmers.
? Plant Health Conference 2025. We presented our research at the American Phytopathological Society
meeting in Honolulu, Hawaii, on August 2-5.
Navi, S., Leandro, L., Licht, M., Marco, F.M., Arias, S. 2025. Benefits of relay cropping soybeans
with winter cereals in Iowa. Plant Health 2025, Aug 2-5, Honolulu, Hawaii.
Navi, S., Arias, S. 2025. Evaluation of the impact of winter small crops and oilseeds on soybean
diseases caused by Fusarium graminearum in a relay cropping system. Plant Health 2025, Aug 2-
5, Honolulu, Hawaii.
Navi, S., Arias, S. 2025. Phenotypic characterization of winter/spring cereals and oilseeds, and
soybeans in response to Fusarium graminearum using Rhizotrons. Plant Health 2025, Aug 2-5,
Honolulu, Hawaii.
? ISU Research Day hosted by ISRC in 2025.
? ASTA (American Seed Trade Association)- Field Seed Crop Convention 2025. Relay Cropping with Rye:
Opportunities, Challenges, and Fusarium Management. Orlando, Florida. Dec 10th.

This research is important to soybean farmers and the soybean industry because it will open the door to an eco-continuous soybean system and diversify the market.