Effect of recurring flooding on greenhouse gas emissions, soil C and N contents and forage quality in grazing and hay fields.

Progress report for GNC20-309

Project Type: Graduate Student
Funds awarded in 2020: $13,488.00
Projected End Date: 11/30/2022
Grant Recipients: Ohio State University; Ohio State University
Region: North Central
State: Ohio
Graduate Student:
Faculty Advisor:
Marilia Chiavegato
Ohio State University
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Project Information


Effect of recurring flooding on greenhouse gas emissions, soil C and N contents and forage quality in grazing and hay fields.

In OH, forage in areas prone to flooding is planted for grazing and as a tool to mitigate nutrients loss in environmentally sensitive areas. At the same time, generating more information on the performance of pastures in these areas is important to achieve increased productivity for farmers. In grazed pastures, over 80% of phosphorus (P) and nitrogen (N) is returned to soils by grazing animal manure deposition, creating hot spots of nutrient concentration, and consequently nutrient losses to air and water. In OH, grazed pastures are usually located in hilly and flood prone areas that create critical source areas for nutrient loading to freshwater systems. On the other hand, in the Western Lake Erie Watershed region of the state, croplands are predominant on more level land. In that region, sediment, nutrients and animal manure are transported via surface and subsurface water movement from the field to the watershed and eventually, Lake Erie. The establishment of forage cover on cropland near the environmentally sensitive areas is encouraged through the Ohio Working Lands Buffer Program. The program allows forage harvest and removal, with limited grazing. Through the lens of increasing concern for water quality and climate change impacts, alternatives to reduce nutrient losses to air and water are clearly needed. Therefore, the impacts on air and water contamination must be examined and quantified to allow for solid science-based recommendations to the farming community. Our objective is to understand the effects of flooding on greenhouse gas emissions from soils, C and N contents and forage quality in flooded and non-flooded grazing pastures and hay fields, in southern and northwestern OH. The main outcomes are a baseline understanding of recurring flooding on grazing systems, to allow future identification of strategies to increase systems resilience and resistance to flooding, and identification of potential the net environmental impacts of the use of forage crops as a buffer for nutrient losses.

Project Objectives:

The overarching outcome is to provide lacking knowledge regarding effects of recurring flooding on greenhouse gas (GHG) emissions from soils, soil and forage characteristics, and productivity of grazed and hay pastures, when compared to non-flooded fields. This project will focus on grazing systems under flood and non-flood areas (Scenario 1), and the use of forage crops for hay, as a buffer for nutrient losses (Scenario 2). The outcome of Scenario 1 is the definition of baseline for the flood impact on air, soil, and pasture. Once we know these impacts, we will identify and suggest strategies to increase system resilience and productivity.  

 The outcome of Scenario 2 will be the net environmental impact (balance between environmental impacts, such as GHG emissions, and benefits such as soil C and N contents, forage quality and productivity) of the use of forage crops as buffers for nutrient losses. This information will be useful for a holistic evaluation of the Ohio Working Lands Buffer Program (OH Department of Agriculture), that supports the implementation of forage crops to reduce P losses to water in environmentally sensitive areas (i.e. under flooding). This will allow early adjustments of the Program in order to decrease environmental impacts and increase farmer adoption.

This project will provide deep understanding about management of flood prone areas, a common problem in OH and in the NCR. Farmers will then be able to make a well-informed decision on how/if to use flood-prone areas in their farms, reducing unnecessary costs and increasing profitability.



Materials and methods:

This is a two-scenario project being conducted at two different locations in OH; southern (Jackson, OH – Scenario 1) and northwestern (Jenera, OH – Scenario 2). In Scenario 1, pastures for grazing and hay have been monitored at the Jackson Agricultural Research Station (OARDC/OSU). The Jackson station is a 334-acre pasture farm, managed with strip grazing, low stocking rate (0.8 cows/ha), and density (18,900 kg BW/ha; i.e. lenient grazing). Pastures are cultivated mainly with tall fescue, with the random occurrence of red clover, and orchard grass. Weeds are visibly present throughout the area. Pastures are fertilized with N-P-K and liming for pH control, which is common across the region. In certain areas of the farm, there is recurring flooding since its establishment. Three treatments were identified for this scenario at the farm in 2019: flood and non-flood pastures for grazing and non-flood hayfield. In order to study the effects of flooding only (not associated with grazing), areas were fenced off and grazing excluded.

            In Scenario 2, crops, such as corn and soybeans, are predominant. Flooding occurrence has been increasing, resulting in great nutrient loss to Lake Erie and eutrophication. Conversion to forage crops as a buffer for nutrients losses is encouraged through the Ohio Working Lands Buffer Program (WLBP), and farmers can harvest and remove forage for hay. Our experiment was conducted at a commercial partnering farm in the Western Lake Erie Watershed region, Northwest OH. Forage areas were established in 2019 under the program.

The original project proposed monitoring of flooded hayfields, non-flooded cropland, and flooded croplands. However, during a farm visit, we observed three different levels of flooded hayfields: non-flood, light flood, and heavy flood. Considering the lack of information regarding the effects of flooding on perennial areas, and the interest of the WLBP in converting croplands to forage lands, we decided to focus sample collection on the different levels of flooding on forage areas.

In both scenarios, three similar size plots were identified per treatment. Plots are considered pseudo-replicates (Hurlbert 1984). This study follows a systems approach field research (Amini 2001; Drinkwater 2002; Azapagic 2003; Ploeg et al. 2006; Fiksel 2006), where the management practices monitored are not simulated. True replication is not possible, because treatment allocation cannot be randomized. However, the advantage of this approach is the ability to capture the effects of the long-term history of recurring floods on soil and plant characteristics, that ultimately dictate GHG emissions, C and N contents, and forage quality. The alternative option (i.e. to simulate practices and flooding on a completely randomized area) would not generate the same relationships between soil microbial community × soil physical and chemical conditions × GHG emissions × C and N contents × forage characteristics, neither provide satisfactory results to address the research questions posed in this study. In order to build a more detailed and specific conceptual model and be able to understand the underlying relationships between flooding, and soil, forage and pasture characteristics, pseudo-replicates are the most appropriate option.

Soil texture (Bouyoucos 1951), density (Blake and Hartge 1986), total C and N (Brown 1998), and pH (Mulvaney 1996) were evaluated in 2021 and used to support the identification of plots (consistency among these characteristics were sought). The occurrence and intensity of the floods were monitored in both scenarios during 2021.  In both scenarios, flood frequency was measured after rain events during the experimental period using a 20-m-long nylon string with readings taken at every meter. The string was placed on the plot in a zigzag format. In every reading, the soil was classified as (1) not saturate at the surface, totally dry; (2) saturated at the surface and without the presence of surface pounding (Squelchy noise can be heard when stepping on the ground but no water is visible); or (3) saturated at the surface and with surface pounding (water can be seen on the soil surface). When classified (3), the height of the surface pounding was recorded. 20 points per plot were recorded (Rinderer et al. 2012). Besides that, in scenario 1, water table depth is constantly monitored using an observation well in the flood and non-flood pasture plots. The observation well was installed to a depth of approximately 1.4 m. In scenario 2, we are constantly estimating the water table depth using water pressure sensors installed in strategic locations. These same evaluations will be monitored in the 2022 growing season.

Soil and pasture variables and GHG emissions were monitored in four sampling periods (spring, early summer, late summer, and fall) of 2021, in both Scenarios. All evaluations will be monitored in the second sampling year, 2022. Initially, samples would be collected during two periods (early summer and late summer), but in conversation with farmers, we were made aware that flooding occurrence in late spring and early fall is increasing. Therefore, we decided to add two additional periods. In fall of 2021, we collected soil samples to determine permanganate oxidizable carbon, which represents the available pool of organic C (Weil et al. 2003; Culman et al. 2010) and soil protein (Hurisso, Culman, and Zhao 2018) that represents the available pool of organic N in the soil. Soil fertility and organic matter were determined by random soil collections during the experimental period. Soil bulk density was also evaluated in spring and fall of 2021.

Pasture was monitored for weed abundance and botanical composition, assessed using the dry-weight-rank method with quadrats randomly placed in each plot (Mannetje and Haydock† 1963). Bare ground frequency was monitored with a nylon string transect and readings were taken every 2 m. Forage was cut at stubble height for determination of total dry matter (DM), species participation on total forage DM, and forage quality parameters (crude protein, acid detergent fiber, neutral detergent fiber, lignin, and digestibility). In addition, rainfall and meteorological data were gathered from the weather station located at the Jackson farm and historical data from Jenera, OH.

Soil emissions of the three main GHG were monitored (CO2, CH4, and N2O) using the static chamber methodology (De Klein and Harvey 2013). Five chambers were placed per plot between forage cuts. Emissions were monitored once daily, for 4-days during each sampling period (spring, early summer, late summer, and fall). Sample collection started at least 24 h after chamber placement to allow soil microbial populations to stabilize and avoid over-estimation of emissions. Static chambers are composed of a base and a cap and sealed with a rubber strap. Samples were collected for 20- min (at 0, 5, 10, and 20 min). Gas was collected from the chamber headspace with plastic syringes. Syringe contents were transferred to pressurized 20 mL vials. Sample vials were analyzed by gas chromatography. Flux was calculated based on gas concentration determined by chromatography, atmospheric pressure, and chamber volume. Chamber volume was measured once the chamber ring was placed in the ground to account for field variability. Environmental conditions were recorded daily during the data collection period: atmospheric pressure, soil water content, soil temperature, and ambient temperature (Chiavegato et al. 2015). Soil moisture was measured using a portable hand-held probe. Statistical analyses were conducted using SAS software and each scenario has been analyzed individually. Sampling periods were considered repeated measures. We found high variability in-between and within experimental plots, and variances were allowed to vary. The most appropriate variance-covariance matrix structure was chosen based on BIC criteria.

Jenera field

Jackson field

Jenera samplings

Jackson samplings


Research results and discussion:

So far, we have analyzed all data for 2021 of Jenera, OH. No significant differences between treatments were observed for forage dry matter and botanical composition in spring and early summer (Table 1). Forage dry matter production was higher during spring than in early and late summer for all treatments (Table 1). High forage production during spring was expected for cool-season grasses. After peak production in the spring, we usually have a forage slump for these grasses in Ohio during late summer. However, the slump was not observed for F1 plots. Instead, we observed higher forage dry matter in comparison to F0 and F2 (Table 1). During late summer, F1 treatment had lower forage digestibility than F0 and F2 (Table 2,), indicating a trade-off between high forage production and low forage digestibility.

CO2 emissions from soil are not of concern to climate change and it could be considered an indirect indicator of soil health (soil respiration and organic matter decomposition). During spring and late summer, F2 had the lowest CO2 emissions from soil among treatments, indicating decreased soil activity (Table 3,). Importantly, during these sampling periods (spring and late summer), there was water accumulation on the soil surface during the collection days of GHG emissions. Therefore, the lower CO2 emissions from soil may be related to the presence of flooding in the soil. During the following sampling period, lower CO2 emissions were not observed, suggesting a short-term effect. (Table 3, CO2 flux during Early summer). In both early and late summer, F2 had positive values showing CH4 emissions and F0 and F1 showed CH4 sinks (Table 3,). However, N2O emissions were higher in F0 when compared to F1 and F2 (Table 3). Increased soil moisture content favors a complete denitrification process resulting in N2 rather than N2O. Therefore, flood areas had lower N2O flux. The CO2 equivalent emissions showed a similar pattern to the N2O fluxes indicating this gas as the main driver of CO2eq flux (Table 3).

Table 1

Table 2

Table 3Preliminary conclusions

Participation Summary
1 Farmers participating in research

Educational & Outreach Activities

3 Webinars / talks / presentations

Participation Summary:

50 Farmers participated
50 Ag professionals participated
Education/outreach description:

In December of 2020, I submitted an abstract with my research proposal in the Horticulture and Crop Science Graduate Research Symposium at Ohio State University, titled “Effect of recurring, short-term flooding on soil, pasture and environmental characteristics of grazing and hay pasture”, and presented online by me.

In November of 2021, I presented my preliminary results from Jenera at the 2021 ASA, CSSA, SSSA International Annual Meeting (Salt Lake City, UT). An abstract with preliminary results from Jenera was written by Marina Miquilini, Ricardo Ribeiro, and Marilia Chiavegato titled “Forage Quality and Greenhouse Gas Emissions from Flood-Prone Hay Fields” and presented at the conference as a voluntary oral presentation in the C06 Forage and Grazinglands session by me (https://scisoc.confex.com/scisoc/2021am/meetingapp.cgi/Paper/134411). 

In February of 2022, Ricardo Ribeiro and I, presented our preliminary results in the 2022 Ohio Forage and Grasslands Council Conference, as part of the Ohio State University Forage Research Update, for about 50 farmers and ranchers, and we received very positive feedback from them.

In 2022, I will send abstracts, posters, and oral presentations with my preliminary results in the 2022 HCS Graduate Research Symposium at Ohio State University; 2022 ASA, CSSA, SSSA International Annual Meeting at Baltimore, MD; 2022 ASAS-CSAS Annual Meeting at Oklahoma City, OK. Plus, we are going to present my preliminary results on a Field Day in the Fall of 2022 at Ohio State University. After I finish all the data collection and have the final results by the end of 2022, I am also going to publish 3 peer-reviewed papers, extension publications, and a final report for the OH Department of Agriculture.

Talk at the 2022 Ohio Forage and Grasslands Council Conference, London, OH.

ASA, CSSA, SSSA International Annual Meeting, Salt Lake City, UT.

Next steps

Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture or SARE.