Progress report for OS22-155
Project Information
Cover crops have the potential to build-up soil organic matter (SOM), and enhance soil physical, chemical and biological properties (Jagadamma et al., 2019). They also reduce soil bulk density (Blanco-Canqui et al., 2011), increase soil macro-porosity and improve the saturated hydraulic conductivity (Villamil et al., 2006). Cover crops within no-till systems are gaining attention for their positive roles on sustainable agriculture and providing many benefits to soil (Mitchell et al., 2015). For example, on a silt loam soil, Villamil et al. (2006) reported that rye and hairy vetch cover crops in no-till corn–soybean rotations increased SOM, nutrient retention, enhanced soil aggregate stability, total porosity, and plant-available water, while bulk density and penetration resistance reduced as compared with no cover crops. Non-legume cover crops, including cereals, forage grasses and broadleaf species help in producing large residues and adding SOC to the soil. Continuous cropping systems without winter cover crops and soil amendments are perceived as unsustainable for both crop production and soil health (Ashworth et al., 2017). Furthermore, effective land-based solutions to climate change mitigation require sustainable actions that maximize soil carbon storage without generating surplus nitrogen (Cotrufo et al., 2019). Cover crops play a key role in providing such environmentally friendly solutions.
A large knowledge gap exists regarding the benefits of cover crop on soil health especially in the Southeastern US, and this research will focus on generating data that would be used to bridge some of this gap. The data generated through this project will be used to leverage a larger grant. Soil organic carbon and biomass will be measured and used as indicators for evaluating soil health and yield. Monitoring the buildup of SOC in soil will provide valuable information on the soil quality and how it changes between cover crop and the cash crop growing seasons. Correlating the association of SOC with crop yield will help in elucidating the beneficial effects of the types of cover crop being planted. Soil microbial communities are responsible for a wide range of soil functions including organic matter turnover and nutrient cycling (Lienhard et al., 2013). Measuring the soil microbial biomass, the organic matter and the flux rate of carbon dioxide from the soil will help in estimating the net carbon accumulation or sequestration in the soil.
Efficiently communicating the results of scientific studies to farmers through outreach activities is an essential component in agriculture research. Such communication will help create awareness, enhance adoption of sustainable practices, establish a strong collaboration between farmers and the scientific community, and advise scientists on questions that need to be addressed. For example, Mallory et al. (1998) found that for farmers participating in on-farm trials using cover crops, the primary motivation for adoption was the need to provide ground cover. The two main objectives of this proposal are: (i) to monitor the buildup rate of soil organic carbon between two cover crops and two cash crops growing seasons and use it as a tool to determine net carbon accumulation rates, and (ii) to effectively communicate the results through outreach activities targeting farmers and producers.
The scope of the current proposal has been revised and expanded based on reviewer comments from our previous two On Farm submissions (rated as ‘High Priority’ both times, 2020 and 2021). Previous reviewers recommended that we clarify the type of cover crops and sampling time, as well as expanding on the role of outreach. Special efforts have been made to clearly lay out the cover crops to be used, sampling plans, and have different focus groups for outreach.
The proposed research will address On Farm focus area #6 Soil Organic Matter Building/Protection/ Management – Projects that increase the sustainability of farming systems by developing soil organic matter and soil biota.
The research will be conducted in agricultural farmlands of the Mississippi Delta. Two farmers have each provided access to two of their plots located in Panola and Bolivar Counties, Mississippi, with soil types, Collins Silt Loam and Porter Bayou Sandy Loam, respectively. Mr. Skelton in the Bolivar county has only been planting cover crops in the past year, whereas Mr. Taylor in Panola has been using cover crops for the past eight years. Both farmers have been using Austrian winter peas (Pisum sativum), cereal rye (Secale cereale) or radish (Raphanus raphanistrum) as cover crops. These plots are therefore ideal to conduct cover crop related research and compare their effects on soil health.
During both years of the project, the type of cover crops (one of the three mentioned above) and cash crops, irrigation method, and fertilizer addition will be left to the decision of the farmer, but monitored in the project. A total of six field expeditions will be conducted each year, three each for the cover crops and cash crops seasons. Each sample cycle will include three time points over the respective growing season: (i) before seeding, (ii) mid-growth, and (iii) after harvesting (or burndown in the case of cover crops). Three soil samples will be collected and analyzed from three different locations in every study plot. One of these three sites will be an 8ft x 8ft section cordoned off in the corner of each plot, positioned at the topographical high section on each plot to prevent mass flow/diffusion of fertilizers. This section will be kept free from the addition of fertilizers to compare how cover crops can improve soil health and cash crop yield with and without fertilizers. This section would be purposefully kept small, so that the participating farmers can use majority of their land according to their preferred treatment method. A neighboring 'control' plot with no cover crops will also be tested and the soil will be sampled at the same time points as other plots. The total number of samples per sampling trip will be 15 (three from each plot for a total of four plots [3 x 4 =12], and three from control plots).
During each field trip, the researchers will coordinate with farmers to time the sampling events. Each plot of land will be tested for soil carbon dioxide emissions using a Licor carbon dioxide flux analyzer (the PI has access to this equipment). The analyzer attaches to a soil collar, which will be driven into the soil at a depth of 10-15 cm. The soil collar will be left in place for the entire 2 years of the project period. The location of these soil collars will be marked by flags so that the farmers can avoid them. Having a fixed location of these collars helps to generate consistent data from the same locations during every sampling trip. The locations will also be GPS tagged. Topsoil layer (0-15 cm) will be collected using a sterile shovel at a distance of ~2 ft from the locations where the carbon dioxide measurements are made. The collected soil will be subjected to the following analysis: soil bulk density, pH, phosphorous, potassium, calcium, magnesium, zinc, sodium, organic matter, total N and total C. Intact cores will be collected from each site for soil bulk density analysis (Blanco-Canqui et al., 2011). The ultimate goal of measuring all of these parameters is to calculate net ecosystem productivity (NEP), which will be used to represent the carbon balance of the system (Hu et al., 2004). When NEP is positive, it means that the system serves as a sink for atmospheric carbon dioxide, and vice versa. The formula for calculating carbon balance is as follows: NEP=NPP-Rm. NPP is the sum of the above-ground carbon accumulation (plant biomass) and the below-ground carbon accumulation of crops (roots and microbial biomass), and Rm is the carbon dioxide emission (Licor data) from farmland. Plant and root biomass above and below ground, respectively, will be collected from 50 cm x 50 cm plot in each trial plot and measured according to USDA protocol. Microbial biomass will be evaluated using a microbiometer kit method. Soil microbial biomass (SMB), excluding plant roots and animals larger than 5 µm³, occupies 2 to 5% of SOM and is therefore an important component to be measured (Vance et al., 1987). The NEP will be calculated for the 14 sites during each visit across a 3 ft x 3 ft area and will be averaged for the entire area of the respective plots. Measuring all these parameters at the three different stages of crop growth over the two-year period will help explain the changes that could occur in soil carbon during and after cover crop plantation. Additionally, the collected data will be used to calculate soil health using standard scoring functions (SSF) and Cornell’s Comprehensive Assessment of Soil Health.
The two farmers will actively participate during each of the sampling trips and will be directly involved in soil sample collection, plant biomass and soil carbon dioxide measurements. The farmers will also provide their yield data at the end of each harvest. The outreach component of the project is explained under the respective section. A thorough cost analysis will be done every year to monitor if the practice has increased the profitability or remained unchanged. This analysis will include cost for fertilizers as well.
The expected outcome of this research is that directly involving farmers in the scientific data collection process and studying the net gain of soil carbon will help to better communicate the usefulness of cover crops to the overall soil health and provide an additional motivation for farmers to adopt such systems. Moreover, with improved soil health, it is expected that the yield of cash crops will also increase.
Cooperators
Research
The purpose of this project is to involve farmers in a 2-year field study to evaluate the role of cover crops in the buildup of soil organic carbon. We are currently at the end of year 1 of the study period. Two farmers have each provided access to two of their plots located in Panola and Bolivar Counties in Mississippi. Mr. Skelton in Bolivar County has only been planting cover crops in the past two years, whereas Mr. Taylor in Panola has been using cover crops on and off for the past eight years. Three field trips have been conducted so far, in April 2022 (before cash crop seeding), December 2022 (after cash crop harvest, but before cover crop cultivation), and March 2023 (before cash crop seeding). In each farm, a control section was designated, where no fertilizers were added. Soil samples collected were tested for soil organic carbon, soil respiration and microbial biomass. Once the soil samples were collected, they were securely stored in ziplock bags, transported to the laboratory at Mississippi State University (MSU) and stored in the refrigerator until analysis.
Three soil chemical parameters were analyzed in the samples collected so far. Soil organic carbon content was measured in the Soil Testing Laboratory at Mississippi State University using a combustion technique. Soil respiration and microbial biomass were measured using Solvita® CO2 respiration and Microbiometer kits, respectively.
Based on preliminary measurements, SOC values showed similar trends in the three sampling points. After harvest of the cash crops, the SOC decreased in all fields, indicating that carbon is actively utilized by the crops. After this drop, SOC increased during the next sampling period (after cover crop removal), indicating that cover crops do add additional carbon to the soil. However, the control sections and the plots without cover crops also showed a similar trend, thereby suggesting organic content could increase with time (~6-25%) with or without cover crops. Both farms in Panola and Bolivar counties showed similar trends between all treatments, except for the control section in Panola, which decreased in SOC (~10%) from the mid to final sampling point.
The CO2 respiration kit measures the CO2 released through soil respiration and indirectly provides information on the soil activity levelfoote. All soil samples, regardless of where they were collected from, showed similar trends to SOC at the three time points. The CO2 respiration decreased from before seeding to after harvest, followed by an increase at the time cover crop plants were removed. This trend was seen even in control reactors. Cover crops increased CO2 respiration on average from ~10 to 15 lbs/acre, whereas fields with no cover crops showed a much higher CO2 respiration (~5 to 14 lbs/acre).
The trend in microbial biomass, however, was slightly different from the SOC and CO2 respiration. In this case, the cover crop fields showed an increase in the total microbial biomass after cover crop growth. Control and no cover crop fields, on the other hand, showed an overall decrease in soil microbial biomass, suggesting that cover crops could help increase the soil microbial content.
Future Work: Additional soil samples are planned to be conducted in 2023-2024 cycle and subjected to the same series of analysis. Data generated will be evaluated to monitor changes in the three soil chemical parameters over a period of two years.
Educational & Outreach Activities
Participation Summary:
On September 29, 2022, as part of the Land Stewardship Field Day organized by DELTA F.A.R.M. and other organizations, the scope and importance of the current research was presented. The event was attended by farmers and stakeholders. Since only one soil sample was collected at that point, no data was presented at this event. Future field days will be organized to showcase results from the study and communicate the benefits of cover crops on soil organic carbon.
No feedback/survey was collected during the field day. Following the presentation, a few farmers asked questions about the project in detail, such as what equipment will be used to analyze soil organic carbon.
Learning Outcomes
NA
Project Outcomes
A full assessment of the outcomes will be available after the study period. We expect to generate sufficient data on soil organic carbon and other important soil parameters that will be developed into a form of peer-reviewed publication. The field day event planned will be used to disseminate the results obtained from this project.