Expansion of agricultural production has irrevocably altered the earth’s landscape, impacting climate patterns, wildlife populations, soil health, water quality, and rural communities (USGS, 2007). Global meat and egg consumption are increasing: the USDA reports a 58% increase in global meat consumption over the past 20 years while egg production in the United States increased by 17% between 2008 and 2017. This demand is linked to a growing global population as well as changing human preferences and improved income levels. Coupled with meat and egg production is the production of manure, which can be managed as either a waste product or as a valuable resource to enhance crop production and build soil health. Here we propose an integrated study of novel management practices including manure management, tillage, and cover crops in corn-soybean cropping systems for long-term study of crop yield, soil health, and environmental resilience
We have conducted a long-term study on the impacts of poultry manure on crop yield, soil and water quality, and farm economics. The study was conducted over 20-years from 1998 – 2017, and considered spring manure application to corn-soybean rotation (phase 1, 1998-2008) and to continuous corn (phase 2, 2009-2017). The results of the phase 1 study show improved soybean yields when manure was applied to the plots during the previous corn year compared to UAN application. In addition, after 20 years of application the poultry manure amended fields had improved soil health as defined by particulate organic matter, showing potential for stabilized soil particles, increased infiltration, and water-holding capacity. Along with improved soil health, indicators of environmental and farm resilience were explored. Manure amended plots had lower or similar nitrate levels in drainage and compared to UAN treated plots (Hoover et al., 2019) and we identified the conditions (manure/fertilizer cost, transportation distance) over which manure application benefits farm economics.
While the findings from the study are encouraging, the scope was somewhat limited and did not consider a representative range of land management strategies. We will expand upon this study and initiate the next phase of a long-term study to evaluate the impacts on soybean and corn yields and the environmental benefits of a combination of manure application and cover crop implementation with chisel plow or strip tillage management. Previous studies have shown both increased and decreased soybean yields with cover crops, improved weed control, and soil health benefits from both cover crops and poultry manure soil amendments.

The goal of this project is to assess the benefits of manure application and cover crops on soybean yields, water quality, and soil health. A new field site has been designed for comparison of manure and land management practices, with immediate and ongoing goals of evaluating crop yield response to manure application timing and cover crops, and water quality impacts with different tillage practices. Our initial installation and experimental design will lead to multi-year study of environmental datasets. We will integrate our findings into educational materials and outreach activities led by Dr. Daniel Anderson and the Iowa Manure Management Action Group.

1) Active dissemination of information from this project through existing Extension programs and other scientific outlets. We will present information from these studies at ISU Research and Demonstration Farms Field Days, state and regional Extension meetings, and Iowa Learning Farms events as appropriate. Results from our current work on this topic have been presented at the Egg Industry Form (Kansas City, 2019), Iowa Poultry Association Winter Issues Conference (Des Moines, 2019), Soil Health Conference (Ames, IA, 2019), American Water Resources Association Annual Conference (Baltimore, MD, 2018), Iowa Water Center Conference (Ames, IA, 2018 and 2020),
2) Development of educational and outreach materials to be used by Iowa Manure Management Action Group
3) Semi-annual and annual reports will be submitted to ISA.
4) Peer reviewed journal articles will continue to be developed from our currently funded project and these new efforts.

Updated April 29, 2021:
Since initiation of our project, we have focused on finalizing treatment design and initial soil health analysis. The updated field design for this study has evolved into 27 quarter-acre plots installed in a grid pattern. This redesign reduces the size of the plots, and thus the variability within each plot, while increasing the number of plots by three to allow for a total of nine treatments.

Treatments:
Each of the nine system treatments will be replicated in triplicate and include strip tillage, with and without cover crops, and a variety of nutrient management strategies. The spring UAN treatments, with and without cover crops, will serve as the experimental control. Supplemental nutrients, such as phosphorus, will be applied as field conditions indicate. An additional UAN treatment has been added to the design, which will include a split UAN application with spring side dress to address concerns with yield loss due to potential low nitrogen availability following cover crops. The manure application treatments will allow for a side by side comparison of early winter and spring manure application with and without cover crops. We will also look at a balanced manure treatment with manure applied every 5 years (early winter application after soybeans in years 1 and 3). The plot installation is estimated to be completed toward the end of summer. Due to the later installation, the site will be planted to cover crops to start the experimental treatment and soybeans planted in 2022 to ensure the best conditions for crop yields.

Soil Sampling and Analysis:
Field level soil sampling and surveying was completed in the fall of 2020. Deep core (2” diameter x 48” depth) and Uhland cores (3” diameter x 6” depth) were collected and the sample locations flagged for elevation surveying to record the field profile.

Soil sample characterization and analysis is ongoing. Bulk density analysis has been completed through the Agricultural and Biosystems Engineering Water Quality Research Lab (ABE WQRL). The field site had an average bulk density of 1.34 g cm-3, with a range of values from 1.09 g cm-3 to 1.49 g cm-3. For this report, samples with results greatly different from nearby samples were omitted as outliers.

The Uhland cores have been dried and sieved to 2 mm and 8 mm fractions. A portion of the 2 mm samples have been ground with a mortar and pestle for total N and total C analysis to be conducted at Kansas State, and are weighed out for particulate organic matter analysis to be completed through ABE WQRL. Sample processing and POM analysis is being completed in the ISU WQRL lab.

Deep core soil samples have been divided into five depth increments (0-6”, 6-12”, 12-24”, 24-36”, and 36-48”) and processed for nutrient analysis to be completed by AgSource-VAS Laboratories (Ellsworth, IA). In addition, we are evaluating the unique horizon characteristics observed in these samples for site description and future discussion of potential variation in nutrient movement. Additional soil sampling has been planned once plot installation has been completed. Additional topsoil (0-12”) samples will be collected at the individual plot level after the tile installation has been completed this summer and before cover crops are planted.

Progress Toward Project Metrics:
Our group has made good progress toward KPI #1. Soil samples have been collected and detailed analysis is in progress. We will have a full set of soil nutrient and soil health data analysis for evaluation in the next semi-annual report. In addition, baseline water quality data will be collected and analyzed after the tile installation has been completed at the plots and will continue through the fall as drainage conditions allow. Due to the later installation, we plan to plant soybeans as our first crop in the corn-soybean rotation in 2022. The first year of crop data will reflect the impact of cover crops on soybean yields.

KPI #2- improved understanding of manure integrated cropping systems and their impact on crop yield and water quality will be achieved through continued progress on KPI #1 and additional years of monitoring and data collection. The first comparative water quality samples from spring and fall manure application will be collected in year three (2023), which will reflect water quality impacts from the early winter 2022 spring manure application and the spring 2023 poultry manure application (Table 3).

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Updated October 18, 2021:
See attached document for figures and results.

Tiling and sampling sump installation was completed in June of 2021. Each quarter-acre plot is 120’ wide, divided by existing border tiles (shown in white) and 90’ long. The individual plot drainage tiles (shown in blue) are a combination of perforated tile at each sampled plot and solid tile to route the sampled plot’s drainage into the sampling well. Twenty-four of the plots flow north and the three plots farthest to the east flow south. Each sampling well receives drainage from three plots.

The experimental treatments have been reassigned to the individual plots based on the site soil map and supported by various analyses (% organic matter, % sand, phosphorus, and particulate organic matter) results from the early field level sampling (Figure 2). Our results for soils within the L138B mapping units tended to have higher sand content, lower phosphorus, and/or lower organic matter. The plots were divided into three blocks of nine based on field location and soil information, then treatments were assigned within the blocks.

Deep core soil samples (2” diameter, 0-48” depth) and Uhland core samples (4” diameter, 0-6” depth) were collected at Field 40 in the fall of 2020 for a field level analysis of soil characteristics. The deep core samples were separated into five depth increments (0-6”, 6-12”, 12-24”, 24-36”, and 36-48”) and sent to VAS Laboratories (formerly AgSource) in Ellsworth, IA for nutrient, pH, and organic matter (OM) analysis. The Uhland cores (4” diameter, 0-6” depth) samples were processed for texture, bulk density, and POM analysis in the Agricultural and Biosystems Engineering Water Quality Research Lab (ABE WQRL), with further analysis completed through Kansas State University. The results indicate some variability in soil characteristics in the field that could potentially influence various treatment effects, such as soil P accumulation and organic matter changes, over time. Select analyses are presented in Table 1. The lowest organic matter, sand percentages, and P levels, and were typically measured in samples collected from the L123B soil map units. There was some variability in measure soil pH, ranging from 5.2-7.5. The particulate organic matter (POM) results are a measure of organic matter available for microorganisms to consume and is a valuable indicator of soil health because of associated improvements in water-holding capacity, infiltration, and soil particle stability.

Year 1- Soybean crops, treatment maps, and fall 2021 soil sampling
Soybeans were planted immediately after tile installation in June of 2021, following the original experimental design to start year 1 with soybeans. The soybeans are set to be harvested toward the end of October once they have had time to reach maturity.

Soil analysis in the fall of 2021 will provide a plot level assessment of the soil conditions after a season of soybean growth. Shallow core (2” diameter, 0-12” depth) and Uhland core (4” diameter, 0-6” depth) samples will be collected after harvest and before poultry manure application to assess soil conditions at the plot level before cover crop and manure treatments. The samples will be analyzed similarly to the fall 2020 field level samples. Cover crops will be planted each year (fig. 4). Figure 5 shows plots that will receive the 2021 early winter.

Progress Toward Project Metrics
Our group has made good progress toward KPI #1. Soil samples have been collected and detailed analysis is presented in this report. Because of extremely dry conditions this summer, no water quality data was able to be collected, but we will continue to monitor field conditions and collect samples if the weather pattern changes yet this fall. Soybeans were planted in spring 2021 and yield data will be available after harvest (anticipated harvest date is 10/19/2021).

KPI #2- improved understanding of manure integrated cropping systems and their impact on crop yield and water quality will be achieved through continued progress on KPI #1 and additional years of monitoring and data collection. The first comparative water quality samples from spring and fall manure application will be collected in year two (2022), which will reflect water quality impacts from the early winter 2021 spring manure application and the spring 2022 poultry manure application.

View uploaded report

The long-term outcome of this study would be to inform manure management and cover cropping management to optimize crop yield and environmental benefits. Our hope is that these efforts will lead to fewer impaired waters, protected public health, and more sustainable agricultural systems. This information will be important for producers who are making management decisions and for state agencies that have responsibility for water quality. Producers will have valuable information to help guide management options to minimize contaminants from tile drainage water. Policy makers will have new information on manure management as part of watershed management plans.