By Silvina Arias, Adjunct Assistant Professor Plant Pathology, Entomology and Microbiology, ISU

Project Collaborator:

• Mark Licht, Agronomy

   

Project Summary

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. 

Adopting a new and innovative system has challenges that need to be evaluated, such as effective cultural and disease management. Soybean diseases have negatively impacted the profitability of soybean production. Seedling diseases have caused an estimated total economic loss of $17.6 billion in the U.S. between 1996 and 2016. In 2014, the estimated yield losses associated with seedling diseases (~58.7 million bu) were second in yield losses compared to soybean cyst nematode (SCN). Interestingly, Huss et al. (2022)- Cornell Univ.-reported clear benefits of intercropping in agricultural systems for insect pest control, pathogens, and weeds. Jason Bond and Col. (2021, 2022) from Southern Illinois Univ. observed that double cropping soybean-winter wheat has the potential to suppress SCN field populations. However, farmers need strong support to deal with site-specific disease management and the challenges of managing polycultures.

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.

Additional Information

U.S. farmers need to increase production to meet growing global demand. However, common agricultural intensification (i.e., cropland expansion/heavily managed crop monocultures) has a high environmental cost. Adopting a new and innovative system, like intercropping practices with a cash crop, has challenges and risks that need to be evaluated.

We expect to achieve the best agronomic and disease management practices through the adoption of intercropping. We will evaluate if it helps suppress pathogens and crop pests in soybeans and positively impacts soil health.

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.

(3-year project funded fall 2023)