Our primary goal here is to answer the question (and title of the proposal): do soil health promoting practices make soybean production more climate resilient?

We will leverage the ISA-funded (FY 2022) precipitation exclusion, application systems (PEAS) to test specifically soybean physiological response to future climate scenarios. Climate models predict wetter springs (>15 %) and more variable summer precipitation that will include more droughty summers (NOAA National Climate Assessment, 2023). Our intent is to add 20% precipitation to ambient rainfall between months of April through June 21, and thereafter remove 50% precipitation until end of September. This will simulate a ’worse-case’ future precipitation (FP) scenario with wetter springs making it more difficult to get in the field, and drier summer mimicking soybean-limited soil moisture conditions that may occur more frequently in the future. We will have an ambient precipitation (AP) and FP sub-plots within a long-term (22 years), randomized, replicated trial crop rotation experiment – the Marsden Agricultural Diversity Experiment (MADE) – that has three rotations: corn-soybean plus synthetic N fertilizer (2-year), corn-soybeans-oat/redclover (3-year), and corns-soybean-oat/alfalfa-alfalfa plus composted cattle manure (4-year). Prior research from PI-McDaniel’s group, Soil Health Institute, and others have documented the many soil health benefits from the 4-year rotation compared to the 2-year. We will focus on comparing whether these increases in soil health translate to more climate resilience in 4-year rotation compared to the 2-year. In other words, does improving soil health buffer soybean yields against these changes in precipitation?

1. Determine if long-term adoption of soil health promoting practices (e.g., diversified crop rotations and manure) increase soybean resilience to drought.

2. Determine effects of future precipitation in Iowa - wetter springs drier summer - affects soils and crops more generally.

- Peer-reviewed publications
- Field days
- Extension/outreach presentations
- Contacts with farmers using similar practices

Updated March 28, 2024:
Precipitation Exclusion and Application Systems (PEAS) created a severe drought under the drought treatment compared to the irrigated treatment. In 2023, to measure the effectiveness of the PEAS as a tool to create drought conditions, we altered the treatments to irrigated (1-inch rainfall weekly) vs. 100% drought. We collected continuous moisture data from the middle of the PEAS and a one-time grid-scaled moisture and temperature measurement to see if the moisture distribution inside the PEAS is uniform. Figure 1 shows the implications of this process six weeks after the treatment implication. This further brought our attention to the possibility of water seeping into the drought plot due to the sprinkler overlay. In the next cropping season, we plan to address this issue with a movable tarp.
By the end of the season, we collected plant samples for yield analysis, which showed no significant differences between the treatments. However, a slightly lower soybean yield was observed in a 2-year drought rotation than in all other treatments. This indicates our hypothesis that diversified crop rotations can be more resilient to drought than business-as-usual rotations (Figure 2). We are working on a manuscript with the data collected last season.
During the winter (after February), we have been collecting N2O emission data to understand better the N dynamics in the cropping systems that are supposed to get the PEAS treatment in the summer. For the coming season, we have planned to use our original treatments of ambient precipitation vs. future precipitation (+20% high rain in spring and -75% lower rain in summer).
Next season, we plan to deploy the PEAS as soon as soybean planting occurs and get some additional measurements that we didn’t collect last season.

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Updated November 18, 2024:
The second year of Precipitation Exclusion and Application Systems (PEAS) research continued in the summer of 2024. This season, the soybeans (Pioneer P22A67E) were planted on May 30th, 2024, and the PEAS was deployed on June 6th, 2024. Water application for the season began on June 18th, 2024, and continued until September 24th. The irrigation protocol included two treatments: AP- Ambient Precipitation and FP-Future Precipitation. The AP shelters received the total amount of precipitation the previous week, and the FP shelters received 20% more water than last week's total precipitation until June 20th,2024, and 75% less water for the rest of the cropping season. Rotations were similar to the previous year: 2-year rotation and 4-year rotation. In addition to these rotations, we observed an imaginary outside plot to compare the shelter effect to our collected measurements.
Measurements collected this cropping season include soil moisture at 12 depths using Sentek drill and drop sensors, soil matric potential at 12-inch depth using Teros-21 sensors from the METER group, soybean stomatal conductance, N2O emission, PAR readings inside shelters, Soil samples, and continuous readings for soybean plant temperature, PAR readings, and net energy balance. Soybean harvesting was done on October 3rd for the yields.

The Precipitation Application and Exclusion Systems (PEAS) using rainout shelters were successfully constructed and used to create a severe drought in 2023. In 2024 cropping season we continued the same experiment with a different water application scheme than in 2023. This summer being less dry compared to last year we did not see any visual differences in plants. But we observed moisture changes in different depths (moisture distribution graph) and expect that to be different between two crop rotations. This year we measured continuous N2O emission data and periodical soil samples to analyze for N. Additionally we measured Stomatal Conductance and yield, which still needs to be analyzed. Final data analysis and graphs are pending

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Updated November 18, 2024:

Springs are getting wetter and summer precipitation is more variable making growing soybeans more difficult for farmers.
Wetter springs reduce the days of operation and drier summers can hinder crop yields.

We're testing whether long-term management - in this case including small grains and forages plus animal manure as source of nutrients - can help buffer some of these changes.