Final 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
- - Technical Advisor (Educator and Researcher)
Research
The purpose of this project was to involve farmers in a 2-year field study to evaluate the role of cover crops in the buildup of soil organic carbon. Two farmers had each provided access to two of their plots located in Panola and Bolivar Counties in Mississippi (Figures 1 and 2). 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. Austrian winter peas (Pisum sativum), cereal rye (Secale cereale) or radish (Raphanus raphanistrum) were used as cover crops in both fields. In the Panola Co plots, corn and cotton were planted in the two years, whereas soybeans were planted both years in the Bolivar Co. farms. Five field trips were conducted, in April 2022, March 2023 and April 2024 (before cash crop seeding; after cover crop killing), October 2022 and October 2023 (after cash crop harvest, but before cover crop seeding). The reason for sampling soils during this time was to evaluate whether cover crops planted during winter can increase the soil health before seeding of cash crop. In each farm, a control section was designated, where no fertilizers or cover crops were added. Once the soil samples were collected from the top 15 cm, they were securely placed in ziplock bags, transported to the laboratory at Mississippi State University (MSU) and stored in the refrigerator until analysis. Soil samples collected were primarily tested for soil organic carbon, soil respiration and microbial biomass. Organic carbon and soil pH were measured at MSU Extension soil testing laboratory. Soil respiration was tested using Solvita® CO2 Burst Tests, and microbial biomass using microBIOMETER test kits®.
Soil organic carbon (SOC) values showed somewhat contrasting trends between the sampling points. In Panola Co. farms, where the cover crops have been planted for a long time, after harvest of the cash crops, the SOC decreased in all fields (sampling points 1-2), indicating that carbon was actively utilized during the crop growth season (Figure 3). After this drop, SOC increased during the next sampling period (after cash crop removal, sampling point 3), indicating that cash crops added additional carbon to the soil. The plot with cash crops (D) only showed a large increase in OM at the end. However, the control plot section (CA) and the plots without cover crops also showed a similar trend, thereby suggesting organic content could increase with time (~6-25%) with (AS) or without cover crops (D). In Bolivar county, the first three sampling points, showed similar trends as that of Panola. However, the SOC in all the plots began to decrease steadily from sampling points 3 to 5. This could be because the organic matter was actively consumed likely due to changes in crop, soil and water management. Overall, the SOC results indicate that cover crops do not appear to produce any increases in SOC compared to plots that have only cash crops. While some previous studies have shown positive effects of cover crops on SOC (McClelland et al., 2021), few others reported no gains (Jagadamma et al., 2019). Similarly, the pH in the soil were not drastically altered in plots with or without cover crops, showing increases after winter/cover crop growth (Figure 4). The control plot (CB) in Bolivar Co showed opposite trends following winter with one season showing an increase, and the next showing a decrease.
The soil respiration kit measures the CO2 released through soil respiration and indirectly provides information on the soil activity level. In Panola Co., addition of cover crops (AS) seems to show a marginally larger CO2 respiration in the soil, compared to plots with only cash crops (D) (Figure 5). Interestingly, the control (CA) also showed an increase in the CO2 production between the 4th and 5th sampling points. The control plot in Bolivar Co showed a reverse trend between the 4th and 5th sampling points. An increase in CO2 respiration was noted before cash crop seeding, regardless of the presence of cover crops or not. Plots with cover crop (AS and BS) showed a higher jump in CO2 respiration in the final sampling point, compared to those without cover crops.
The trend in microbial biomass was slightly different from the SOC and CO2 respiration. Control sections in both fields showed an overall decrease in soil microbial biomass following winter season. The cover crop fields showed an increase in the total microbial biomass in the Bolivar Co farms, but did not show much change in the Panola Co farms with either management. An error occurred in the 4th and 5th analysis of microbial biomass and therefore did not produce any meaningful results.
References:
Jagadamma, S., et al., (2019). Total and Active Soil Organic Carbon from Long-term Agricultural Management Practices in West Tennessee. Ag. Environ. Letters, 4(1).
McClelland, S. C., Paustian, K., & Schipanski, M. E. (2021). Management of cover crops in temperate climates influences soil organic carbon stocks: a meta‐analysis. Ecological Applications, 31(3), e02278.
Educational & Outreach Activities
Participation Summary:
The project and the results were presented to the farmers at two separate events, organized by project cooperator Dr. Drew Gholson. Firstly, 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. The second event had a more focused theme. On February 21 and 22, the results from the research were presented in front of an audience of ~60 including extension agents, farmers, and other stakeholders as part of the Master Irrigator Program. A survey was handed out to the farmers and land managers about cover crops. The survey asked the participants about benefits and challenges to cover crop adoption, and general demographic data.
Learning Outcomes
yield
water management
cost savings
soil erosion
environmental benefits
Soil health
Project Outcomes
Research:
Overall, the 2-year study showed that cover crops provide only a marginally improved soil chemical health in the form of SOC, microbial biomass and CO2 respiration. The plot in Panola Co., which had been growing cover crops for a longer period before this experiment was started, showed slightly better gains in microbial biomass and CO2 respiration than Bolivar Co. plots, which adopted cover crops more recently. In contrast, overall organic carbon in the soil was marginally higher in the Bolivar plots compared to Panola. Previous studies also seem to indicate that long term adoption is necessary to show positive changes in SOC (Derpsch, 2008; Lu et al., 2000). The complex trends shown by the control plots, especially in Bolivar Co. farms, further reveal that additional factors, such as type of cover crops and cash crops, other soil physical parameters, etc., could also play an important role in influencing overall soil health.The farmer cooperators who provided their lands for the project and few of the participants in the outreach event were very interested in the measurement of soil organic carbon and its role in soil health. The investigators answered any queries regarding these topics and also addressed potential limitations, and external factors (irrigation, type of soil, crops planted, etc.) that can affect soil health.
Outreach:
During the second event, the investigators received feedback from 15 participants, including farmers and land managers. All of the participants were male, with majority white, and two black. Two-thirds of the participants were between 26-55 years. 87% had used crop crops on their plots for an average of 5.3 years. More than 70% of the participants agreed that they would adopt cover crops if they saw benefits in soil health, yield, cost savings, water management and environmental benefits. Climate resilience and pest management benefits due to cover crops received far less agreement. Participants listed that winter erosion control, water infiltration and preservation, soil health, water holding capacity, and better yields as reasons they adopted cover crops in their plots. They identified extended spring moisture, difficulties in planting and killing cover crops, seed cost, and species mix were challenges during cover crop management. One participant listed that they were not familiar with the benefits of cover crops.
Both outreach events were successfully used to disseminate the results obtained from this project. The survey results showed that farmers were more open to adopting cover crops on their plots, if not already practicing. Soil health, which was a key component in this research, was listed as an important criterion for farmers to consider cover crops. The results generated through this research, especially on soil organic carbon and microbial biomass, did not necessarily yield favorable results that could be directly attributed to cover crop implementation.
One farmer mentioned in the survey that they had observed their relatives using cover crops and that was the reason for them to potentially adopt cover crops on their field. This was an interesting note because observing neighbors or other farmers who use cover crops can influence one’s decision to pursue similar land management practices, thereby having a social effect.
We expect to develop the data on soil organic carbon and other important soil parameters due to cover crops into a form of peer-reviewed publication.
References:
Derpsch, R. (2008). No-tillage and conservation agriculture: a progress report. No-till farming systems. Special publication, 3, 7-39
Lu, Y. C., Watkins, K. B., Teasdale, J. R., & Abdul-Baki, A. A. (2000). Cover crops in sustainable food production. Food Reviews International, 16(2), 121-157.