Iowa’s climate, and precipitation patterns more specifically, are becoming more variable between and within years. This variability is likely to strongly impact soybean growth and productivity. We hypothesize that managing soybean production systems for enhanced soil health will add resilience and boost soybean yield under a changing climate.

We propose to test this hypothesis using a split-plot randomized complete block design (RCBD) experiment in Boone County, IA. Split-plot units will comprise two precipitation treatments: ambient precipitation and “future precipitation”. The future precipitation is based on trends and forecasted change in Iowa’s climate. Springs are getting wetter and summers are more variable, so +20% of monthly precipitation in spring and -50% precipitation in summer (mimicking a drought year). These treatments will be created with rain-out shelters and passive rain application apparatus. The site of the proposed work will be the Marsden Farm Experiment with long-term (>18 years) comparison between a conventional 2-year corn-soybean rotation (100% UAN fertilizer) and a diversified 4-year rotation of corn-soybean-oat/alfalfa-alfalfa (+ composted cattle manure and biological N fixation making up >80% N inputs). Preliminary data collected from the McDaniel Lab in 2018 show that the 4-year rotation increase soil microbial biomass by +62%, earthworms by +71%, and plant available water by 10% compared to the 2-year rotation. We also found that the 4-year rotation reduces root penetration resistance by 8% and increases maximum corn root length by 14%. We predict these changes will translate to more productive soybeans under years that are both too wet and too dry (as manipulated with split-plot treatments). We will measure soil moisture and soybean yield, grain quality, root architecture/morphology, root/nodule mass, and N2 fixation capacity approximated by leghemoglobin in the nodule in response to treatments.

1) Mimic future precipitation predicted for Iowa in next 50 years
2) Measure soybean response to stressful scenario under this future precipitation (+20% precipitation in spring, - 50% precipitation in summer).

1) 1 peer-review publication on findings
2) 1 extension publication
3) 2 or more extension presentations
2) 1 or more field day with ISA, ISU and other organizations

Update:
Rainout shelters are currently under construction and will be deployed, with soil moisture probes, after soybean 2023 planting. Some delay in acquiring materials and supply due to supply chain issues (likely residual to COVID issues).

Update:
Rainout shelters and moisture probes were installed in the field after soybean planting and removed before harvest.
We changed the water application scheme during this soybean season to test the effectiveness of the rainout shelters. The ambient precipitation shelter (AP) received water equivalent to 1 inch of rain weekly, whereas the future precipitation (FP) shelter did not receive any water. This scheme created the extreme drought we needed to monitor during the season.
Data collected on the following parameters during the season
Soybean yield, Soil moisture (Continuos with soil probes), Soil moisture data with a manual moisture meter(one-time) to measure the water distribution within the shelter, and Soybean Stomatal conductance data.
All the data collected will be soon analyzed to create a meaningful output.

View uploaded report

View uploaded report 2

The Precipitation Application and Exclusion Systems (PEAS) using rainout shelters were successfully constructed and used to create a severe drought in an already dry 2023 growing season. Photos of yellow versus green soybeans clearly demonstrate the difference between drought and sufficient water applied this year (See Photo #1). We also confirmed these clear visual differences with measurements of soil water content by both using continuous soil moisture measurements and a one-time measurement of variability of soil moisture under the PEAS. We have measured the soybean stomatal conductance and grain yield. Final visualization and data analyses are pending

While improvements in soil health can be documented by measuring several soil properties, there are some more tangible benefits of soil health that are more difficult to quantify. Here, for the first time, we will intentionally drought a long-term cropping experiment (Marsden Agricultural Diversity Experiment) to demonstrate the ability of 20-years of diversified crop rotations to maintain soybean yields in overly wet springs and dry summers through improved infiltration and water availability, ease of root penetration, and many other soil health benefits already documented from this long-term experiment.

This 'climate resilience', or ability of healthy soils, to maintain high yields in the face of extreme climate will become increasingly important to Iowa farmers. The response of farmers' soils to excess and deficient water is one of the most frequently reported anecdotal observations (typically with use of cover crops). This research will help not only to confirm some of these anecdotes but also systematically test the resilience of healthy soils to maintain profitable soybean yields.