STATEMENT OF PROBLEM
By 2050 the world is projected to gain an additional 2 billion people. Experts predict that food production will need to increase by 50% to 70% to feed and clothe the increased population. The project partners recognize that the Southeastern USA has a preponderance of low quality soils. National soil degradation is directly linked to conventional agricultural practices of excessive tillage and leaving fields bare between plantings of cash crops. Soil health improvements are vital to enhancing the ability to grow more food for the rapidly increasing world population while minimizing impacts to natural resources. North Carolina’s number one economic driver is agribusiness with an annual impact of $84 billion dollars. North Carolina is also experiencing a rapidly expanding population impacting land use while the face of agriculture is changing. From moratoriums on animal production agriculture to an expansion in organic farming and the tobacco buyout program, now is the time to evaluate and introduce improved agriculture management techniques that will positively impact soil health.
Project partners want to learn how multi-species cover crops can benefit soil health while positively impacting on-farm sustainability in Southeastern farming systems. Soil health is defined as the continued capacity of soil to function as a living ecosystem. According to Managing Cover Crops Profitably, 3rd Edition, SARE, June 2012, cover crops improve soil structure, increase infiltration and water holding capacity, increase cation exchange capacity (allowing for more nutrient storage), and improve long term nutrient storage (nutrient banking). In the national 2012-2013 Cover Crop Survey conducted by the Conservation Technology Information and North Central SARE, the top challenges of adopting cover crops relate to establishment, cost, species selection, and management. The use of monoculture cover crop in conservation tillage production systems has been widely adopted in the Southeast; but the use of multi-species cover crops is far less prevalent. Consequently, information on establishment guidelines and soil health benefits has been borrowed from Midwest farming systems. Cropping systems, soil types, and climatic environments in the Southeast are notably different from those in the Midwest, such that scientifically documented and practical knowledge is not readily transferable. NRCS held a national forum on the Soil Health Initiative in February 2014. Satellite discussions were held at various locations in North Carolina. At the Nash County event, over 50 attendees participated with producers representing 6 counties. Districts reported that the forum created excitement on the concept of soil health. Producers wanted to see demonstrations of multi-species cover crops before considering whole farm adoption. Project partners started this endeavor with some simple questions. What are the short-term soil health benefits of multi-species cover crops? How do we change traditional farming practices in the Southeast to start to incorporate the benefits of multi-species cover crops?
STATEMENT OF PROPOSED SOLUTION
North Carolina is well positioned to act as a pilot evaluation area for multi-species cover crop best management practices and elucidate short-term fluxes in soil chemical, physical, and biological properties due to a favorable winter climate. North Carolina has a variety of cropping systems, soil types, and climate variations across the physiographic regions stretching from the mountains, to the Piedmont, and the coastal plane. Moreover, the knowledge gained from these broad geographic areas would be transferable to similar landscapes throughout the Southeastern USA. North Carolina is uniquely situated to facilitate the project since agribusiness is the number one economic driver, three physiographic regions allow for testing in a variety of cropping and climate situations, and the strong conservation partnership has a proven track records of delivering positive results that can be replicated in neighboring states. New management techniques are more readily adopted regionally when a local farmer is successful at the county level and farmer-to-farmer training occurs with multi-species cover crops being the next pilot project fitting the mold. The longer-term benefits of multi-species cover crops include reductions in input costs and providing effective mitigation against droughts and pest infestations. Demonstration projects are needed to reinforce proper management of multi-species cover crops such as proper time of planting, allowing for a greater accumulation of biomass and nitrogen, and proper time of growth termination that can be done effectively without using tillage. Soil functions are improved by the following principles: minimize soil disturbance, increase plant diversity to positively impact microbial and nutrient diversity, keep a living root growing year round, and keep residual cover at the surface as long as possible.
The primate goal of this project is to demonstrate to producers that a diverse mixture of cover crops, properly managed, will increase soil functions and can lead to a more sustainable farming system.
APPROACH AND METHODS
Project partners received $15,000 in funds to build upon the NC Foundation for Soil and Water Conservation’s soil health initiative to determine the early signs of soil health benefits of multi-species cover crops and promote adoption of the conservation practice. Other project funding sources include Cotton Incorporated, the NC Agriculture Development and Farmland Preservation Trust Fund and the USDA Natural Resources Conservation Service’s Conservation Innovation Grant program. Southern SARE On-Farm Research Grant Program’s funds will be used to offset additional sampling analysis, establish additional in-field data collection systems and overall program management.
The Foundation secured demonstration plots with local producers, in conjunction with soil and water conservation districts (Districts) in Alamance, Ashe, Davidson, Edgecombe, Henderson, Madison, Nash, Rowan, Stanly, and Wake counties. The Foundation is collaborating with NC State University’s Department of Soil Science with Dr. Wagger then Dr. Broome, and the Department of Crop Science with Dr. Reberg-Horton. The Foundation is also partnering with Dr. Franzluebbers with USDA Agriculture Research Service. Technical guidance is provided by Mr. Woodruff and Mr. Lowder with the USDA Natural Resources Conservation Service’s East National Technology Support Center. Each District has formed a local workgroup composed of farmer cover crop advocates, North Carolina Cooperative Extension agents, Natural Resources Conservation Service, NC Department of Agriculture and Consumer Services’ regional agronomists, and other interested parties.
The Districts partnered with a local producer that is using conservation tillage practices and has an interest in the next level of soil health management. Each demonstration is 5 to 10 acres in size and was established in 2014 (3 sites) to 2016 (7 sites). The demonstrations are established with alternating rows of monoculture cover crop or no cover crop to allow for statistical comparisons per field. Project partners will use the farms themselves as multiple observations of common treatments across farms. Districts are hosting annual soil health field days with a focus on farmer-to-farmer interactions and sharing lessons learned.
To refine best management practices for multi-species cover crops in North Carolina, the following factors are being
evaluated: 1) Seed mixtures with a minimum of 4 cover crop species, 2 of which are legumes, taking into consideration crop nitrogen requirements and impact on cash crop yield potential. 2) Cover crop seeding method (drilling, overseeding prior to cash-crop harvest, or self-reseeding, and broadcasting with or without incorporation). 3) Cover crop seeding dates (e.g. early September, late September, October, and November). 4) Cover crop termination strategy (chemical desiccation, rollercrimper, or both).
To determine the short-term benefits of multi-species cover crops in no-till and reduced till production systems, project partners will document changes in soil properties, as well as yield improvements. Project partners are documenting nutrient cycling benefits by evaluating results of soil tests for realistic yield expectations and various forms of soil organic matter, including soil microbial activity with the Solvita Soil CO2 Burst test (http://solvita.com/soil). Nutrient availability to plants will be documented with nutrient uptake of cover and cash crops. Some notable short-term changes in soil properties and nutrient cycling are noted in the preliminary results of the 2015-2016 cover crop demonstrations.
Surface-soil samples are collected from crop production fields in winter/spring by compositing 8 cores (4-cm diam) to represent depths of 0-6, 6-12, and 12-20 cm following collection of surface residue mass from 0.04 m2 areas at each of the coring locations (Franzluebbers et al., 2001). Soil will be split into two fractions following initial screening and mixing through 8 mm openings: (1) dried at 50°C, sieved to pass a 4.75-mm screen to determine chemical and physical properties and (2) kept moist at 4°C, sieved to pass a 2-mm screen to determine soil microbial communities.
The following properties will be determined from this sampling scheme:
1) Soil C and N fractions; (i) total with a Leco Tru-Spec CN analyzer, (ii) particulate organic matter with dispersion and sieving (Cambardella and Elliott, 1992; Franzluebbers et al., 1999b), (iii) microbial biomass with chloroform fumigationincubation (Jenkinson and Powlson, 1976; Franzluebbers et. Al, 1999a), (iv) inorganic N from 1:2, soil:2 M KCl extraction and colorimetric determination of NH4 and NO3 with automated, segmented-flow analyzer.
2) Surface residue C and N: Leco Tru-Spec CN analysis of ground (<1mm) residue along with dry weight determination of total mass.
3) soil bulk density: dry-weigh and volume of cores.
4) Soil microbial community structure: substrate utilization for bacterial and fungi on BIOLOG plates (Buyer el al., 1999; Buyer et al., 2001).
Additionally soil moisture availability will be documented by deploying moisture sensors and support technology, specifically Acclima water sensors and particle electron processors with 3G Cellular data transmitters. Data will be collected to document increased infiltration and retention of water. Leaf roll scoring will be tracked to determine the time of day the cash crop denotes signs of heat stress. The data will be correlated to soil moisture and allow for recommendations regarding effective water conservation methods and practices to increase infiltration.
Plant samples are collected from the cover crop for determination of biomass, botanical composition, and nutrient content. Three areas (0.5 x 0.5 m square) will be cut in each cover-crop treatment observation and sorted for discernible plant components and each component weighed separately after drying for at 50°C for 3 days. Dried samples are analyzed for C and N concentrations using dry combustion. Crop yield is determined either from strip-level determinations from the producer or from 3 randomly collected 1 m2 areas for easy treatment observation by project partners.
The general linear model procedure of SAS will be used to analyze variances for each of the soil (by depth), plant, and animal responses separately during each year. Soil depth, year of sampling, and within season plant biomass will be considered repeated measures and errors associate with them separated accordingly.
PROJECT RELEVANCE TO SUSTAINABLE AGRICULTURE
The overall goal of the program is to demonstrate to producers in North Carolina and throughout the Southeast that multi-species cover crops, when properly managed, will increase soil ecosystem functions and lead to improved on-farm sustainability. The project will quantify short-term changes in soil chemical, physical, and biological properties by measuring increased soil aggregation and organic matter, microbial activity, and water infiltration rates. The project will relate the short-term changes in soil properties to broader concerns for nutrient cycling within and from agro-ecosystems, overcoming soil water limitations, and improved crop yield and growth. Project partners will make recommendations to refine best management practices for multi-species cover crops in production systems common to North Carolina and neighboring states in the region. All of these lessons learned will be used to promote the increased soil health improvements from the use of multi-species cover crops regionally to increase agriculture sustainability.
Part of the program is to encourage Districts to work with producers to determine what seed mixes work best on their farms based on their specific soil types and proposed crop rotations. Each farmer is interested in testing out specific benefits such as alleviating compaction, nematode population reductions, building organic matter, and increasing N in the system. Due to the unique nature of issues being explored per farm, project partners are not recommending a specific set of seed mixes beyond the requirement to include a minimum of 4 species, 2 of which are legumes. The producers and the Districts work together to source the seed mix they want to test. Project partners are not privy to which seed mixes may contain genetically engineering varieties. The Districts indicated is it very uncommon for cover crop seed mixes to contain genetically engineered varieties. Please note Southern Region SARE funds will not be used to purchase seed for any of the demonstrations. By including Southern Region SARE funding, project partners will commit to collect data regarding the use of genetically engineering seed varieties and report back to the funder any concerns raised by their inclusion.
Demonstration Plot Requirements
Conservation Districts selected a field that was easily accessible for field days and had a minimal range of soil types. Demonstration plots in the Coastal Plain and Piedmont were required to be a minimum of 10 acres. Mountain demonstrations were allowed a smaller size of 2 to 5-acre plots. The reason for the acreage difference was that in many mountain counties the best farmland is on the floodplain of creeks in a narrow valley, and therefore many fields might not be as large as 10 acres. Starting in 2015, fields were required to accommodate the establishment of 4 test strips with a minimum width of 40 feet, allowing for comparison of test and control strips side-by-side. In the control strips, producers could plant either a single-species cover crop (to compare with more typical conservation practice) or no cover crop (to compare most typical conventional practice and address soil erosion concerns).
Cover Crop Requirements
Each Conservation District and producer were allowed to select their own seed mixes, based on the producer’s management goals and to highlight mixes that would work well in their county. Each seed mix was required to include 4 species at a minimum, including 2 legumes. Producers were allowed to broadcast or no-till drill the seed mix. If broadcasting, it was recommended to consider 25% more seed than if no-till drilling. All producers had access to a no-till drill through Conservation Districts. Chosen establishment methods were based on preference and cash crop harvesting needs. For termination, producers were permitted to roll down the cover crop and/or apply a chemical treatment. Termination method chosen was influenced by equipment available to the producer, as not many producers had access to a roller crimper. The following planting and termination dates were selected as target dates. In some cases, deviation from the established date was approved due to issues beyond the producers’ control such as weather events.
Plant and soil analyses
To determine short-term benefits of multi-species cover crops in no-till and reduced till production systems, Project Partners documented cover crop production and nutrient characteristics, surface soil residue accumulation and nitrogen content, and a variety of soil properties. Sampling sites in field demonstrations were typically from three locations within a field-length strip of cover crop treatment. Field strips were either (a) multi-species cover crop, (2) single-species cover crop, or (3) no cover crop. In a typical design of two strips of multi-species cover crop and two strips of no cover crop control, a total of 12 locations would have been sampled (i.e. 3 locations in each of 4 strips). Sampling locations within a strip were typically separated by 100’. Average values for the two treatments would have been derived from six replicate locations in each field.
Biomass from cover crops was collected during a target period of two weeks prior to two weeks following growth termination. Dry matter and C and N concentrations were determined using two approaches. In fields that had relatively low biomass, plant material was cut with a bagging lawn mower (20” width x 20’ long strip) at 2” height. In fields that had high cover crop biomass, plant material was cut at 2” height from two squares (20” x 20”) separated by ~10’. In both cases, all plant material was placed into a cloth bag to be dried for several days in an oven (130 °F). Dried samples were ground and a subsample analyzed for C and N concentrations using dry combustion (Leco TruMac, St. Joseph MI).
In Spring 2016 only, surface residue samples were collected at the time of soil sampling to obtain a refined estimate of residue cover following termination of the cover crop. Surface residue was a combination of current and previous years’ residues in most cases. In Spring 2017, surface residue was not collected since cover crops were typically not yet rolled or laid flat by planting equipment. Surface residues were obtained by collecting all visible plant materials at ground level within either (a) eight, 12” diameter rings within a replicate location or (b) eight, 8” squares within a replicate location. Surface residues were placed into a paper bag, dried at 130 °F for at least 3 days, ground, and subsamples analyzed for C and N concentrations using dry combustion (Leco TruMac, St. Joseph MI) and ash content to adjust mass for soil contamination. Surface-soil samples were collected in spring in a target period of two weeks prior to two weeks following planting of summer crop by compositing 8-16 cores (1.6” diameter) from within each of the replicate locations within a field strip. Soil was collected at depths of 0-2” (16 cores) and 2-6” (8 cores); equal volume sampled from each depth. Soil was dried at 130 °F for at least 3 days, sieved to pass 0.2” openings (4.75-mm), and subsampled for various chemical and biological analyses. Soil bulk density was determined from the dry weight and volume of cores. The following chemical and biological analyses were performed:
North Carolina Department of Agriculture and Consumer Services Agronomic Services Division (http://www.ncagr.gov/agronomi/pdffiles/ustr.pdf)
- Humic matter (g / 100 cc)
- Density (g / cc)
- Cation exchange capacity (meq / 100 cc)
- Base saturation (meq / 100 cc)
- Phosphorus (mg / dm3)
- Potassium (mg / dm3)
- Calcium (mg / dm3)
- Magnesium (mg / dm3)
- Sulfur (mg / dm3)
- Manganese (mg / dm3)
- Zince (mg / dm3)
- Copper (mg / dm3)
- Sodium (mg / dm3)
Soil Ecology and Management Laboratory at NC State (according to Franzluebbers and Brock, 2007)
- Total soil C and N (g / kg); dry combustion with Leco TruMac following ball milling
- Particulate organic C and N (g / kg); dry combustion with Leco TruMac following ball milling of oven-dried sand fraction of soil obtained from dispersion of soil in Na4P2O7 solution
- Soil microbial biomass C (mg / kg); chloroform fumigation-incubation
- Mineralizable C and N (mg / kg / 24 days); aerobic incubation at 50% water-filled pore space and 77 °F
- Flush of CO2 following rewetting of dried soil (mg / kg / 3 days); aerobic incubation at 50% water-filled pore space and 77 °F
- Residual soil nitrate and total inorganic N (mg / kg); colorimetric determination with Bran-Luebbe segmented flow analyzer following KCl extraction
2017 Project Results
Overall, participating producers were pleased with the project and the process. Phillip Whitaker, Henderson County Producer, said “One positive I have noticed is that even without a pre-emergent pesticide, the no-till planting has very few weeds.” Frank Lee, Stanly County Producer, said “Cover crops are beneficial if they are properly managed.” A technical report is available at http://ncsoilwater.org as well as regional promotional fliers. Plant and soil properties were characterized, and included the following:
Biomass – Sufficient cover crop biomass is critical for controlling erosion, preserving soil water during the summer growing season, and improving surface-soil properties. Relatively low biomass was recorded for many of the 2015/16 demonstrations. In the 2016/17 demonstrations, three of eight sites achieved a biomass rate greater than a minimum target of 3000 lb/A. In only one of seven demonstrations did multi-species cover crop biomass produce less than a single-species cover crop, but in two cases multi-species cover crop produced more than a single-species cover crop. In all cases, biomass production was greater in demonstration sites with either cover crop type compared to no cover crop (i.e. winter weeds).
Nitrogen (N) – Soil fertility can be enhanced with cycling of N from cover crop biomass to cash crops through slow decomposition of residues throughout the year. Cover crop biomass was enriched in N compared with no cover crop (i.e. winter annual weeds). There was no difference in N content between single and multi-species cover crops in the 2015/16 demonstrations. We set a minimum target of 50 lb N/A in cover crop biomass to enhance long-term soil fertility, but this was attained at only one site in 2015/16. Although data are not yet available, we project that at least three of the eight sites in 2016/17 will have achieved this minimum N content in cover crop biomass.
Carbon (C) – Storage of C in soil as organic matter is a key to enhancing soil fertility in the long-term. Transfer of C from cover crop biomass to soil organic matter is a slow process with only a small fraction of cover crop C eventually retained as soil organic C. Only one demonstration in 2015/16 had enough biomass C to potentially enhance soil organic C, provide a thick enough layer to benefit surface-soil moisture retention, and act as a biological source for microbial activity. No changes in total organic C were recorded; we didn’t expect it to, as changes require several years before differences are detectable.
Surface residue – Like cover crop biomass, surface residues (i.e. combination of cover crop biomass and previous crop residues) are critical for controlling erosion, preserving soil water during the summer growing season, and improving surface-soil properties. When measured in 2015/16 demonstrations, surface residue mass was greater with single or multi-species cover crops compared with no cover crop in two of three direct comparisons.
Soil bulk density – Compaction is a concern in some soil types when no-tillage management is utilized. Bulk density was not impacted by cover crop treatment at any of the demonstrations in 2015/16. When measured in spring of 2016/17 near cover crop termination, soil bulk density was significantly greater with multi-species cover crops at three sites as compared with single-species or no cover crops. We will want to monitor this assessment over a number of years and pair it with in-field observations of water runoff or infiltration.
Soil biological activity – Energy embedded in soil organic matter and cover crop inputs drives soil biological activity. Trillions of bacteria, fungi, and actinomycetes in soil perform a variety of functions vital to soil health, e.g. decomposing plant litter, cycling nutrients, creating stable aggregates in soil, enhancing and stabilizing rooting channels, and competing with pathogenic organisms. One measure of soil biological activity is the potential of soil to mineralize N, i.e. the conversion of organic N that is unavailable to plants to inorganic N that is available to plants. In 2015/16, one of eight demonstration sites with multi-species cover cropping had greater N mineralization potential than adjacent plots without cover crops. Another measure of soil biological activity is the flush of CO2 following rewetting of a dried soil. When averaged across eight demonstration sites in 2016/17, the flush of CO2 in soil from multi-species cover crops was significantly greater as compared to either no cover crop or single-species cover crops. Even though the cover crop demonstrations were short in duration, we observed an increase in soil biological activity – suggesting it was a sensitive measure of soil health.
Lessons Learned To Date
- A variety of multi-species cover crop mixes were developed and proven successful based on producer interests, district knowledge, and recommendations from other sources.
- Establishing multi-species cover crops was feasible at each location. Broadcasting seed was possible, but establishment success was dependent on timely rainfall. Drilling may be more successful in many instances.
- Matching cropping sequences with the right cover crop mixture can be a challenge. Adaptive management may be necessary.
- Producer concerns for late planting of cash crop after cover crops are substantial but could be overcome with continued demonstration of soil and economic attributes of a functioning system.
- Engaging producers fully into seed selection and planting of cover crops is essential to make demonstrations viable.
- Field days enhanced local interest in cover crops and structuring events with a focus on producers talking to producers was a key element.
- Successful demonstration activities are possible only with the broad teamwork and skills offered by project partners. We found that an effective network involved a nonprofit serving as project coordinator, conservation districts, resource specialists from USDA-NRCS, and scientists from NC State University and USDA-ARS.
- Funding is secured for further demonstrations in Fall 2018 with ten current Conservation Districts. Partners are mobilizing equipment to measure soil moisture and heat stress in three demonstrations. Project partners will seek ways to share lessons learned throughout 2018 and continue the Field Days.
Educational & Outreach Activities
Since 2013, over 1000 producers and technical assistance providers have attended a field day. Due to secondary funding requirements, not all events were held at the time of cover crop termination. Producer pamphlets have been prepared and are included as an upload. A graduate student assigned to this project presented scientific details of the project: (a) as poster at the Annual Meeting of the Soil Science Society of America, (b) as oral presentation at the Annual Meeting of the Soil Science Society of North Carolina (Pritchett, 2017), and (c) as graduate seminar to the Department of Crop and Soil Sciences at North Carolina State University. Project partners have been invited to speak at NC Cotton Growers Association Meeting as well as several soil and water conservation district events. As other opportunities arise, project partners will offer their services, pending funding and time availability.