- Agronomic: peas (field, cowpeas), radish (oilseed, daikon, forage), rye
- Crop Production: cover crops
- Soil Management: soil quality/health
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.
Project objectives from proposal:
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.