Reducing weed pressure on crops without affecting soil health through intense and frequent tillage and cultivation practices is a major challenge in sustainable crop production. South Carolina SARE Program farmer stakeholders have identified “cover cropping for weed management” as the highest priority topic for research and training. With the increasing interest toward organic grain production in the southeastern US, fall cover crops could be explored as a sustainable practice that improve cropping system intensity and diversity as well as improving soil health and reducing weed pressure. Despite the potential benefits, few grain producers in the southeast have included cover crops as part of their cropping systems because of several challenges. One of the major concerns of producers is the possibility that cover crops may reduce the amount of water stored in the soil profile for the next grain crop, potentially reducing yields. Therefore, it is imperative to test the effect of cover crops on stored soil water before they are introduced to the cropping system for sustainably managing weeds and improving soil health.
The objective of this study was to evaluate the common cover crops in SC for soil moisture retention and biomass production. We evaluated seven cover crop treatments including grasses, legumes, and brassicas as single species or in mixtures, and compared them with two controls, a weed-free fallow and a weedy fallow, in an on-farm trial. Soil moisture content was measured at 10, 20, 30, 40, 60, and 100 cm depths at approximately biweekly intervals during cover crop season and at one month after termination. Biomass was measured at monthly intervals during the cover crop season. We found that all cover crop treatments retained more or equal amount of soil moisture compared to controls (weed-free or weedy fallow). Rye and a mixture of Austrian winter pea, crimson clove, hairy vetch, oat, and rye were good ground covers in terms of number of plants per meter square, and had highest amount of biomass and water use efficiency values. Though the mixture of turnip and crimson clover and crimson clover retained good amount of moisture in the soil, they were poor biomass producers and ground covers. Taken together, our results will provide information to develop grower recommendations on specific cover crops to optimize biomass and soil moisture for subsequent crops.
Evaluate the common fall cover crops in South Carolina for water use, biomass production, and water use efficiency to identify cover crops that improve available soil moisture for the following cash crop.
On-farm trials were conducted in 2016-2017 and 2017-2018 on the Millam farm in Anderson County, SC to evaluate nine cover crop treatments for water use, biomass production and water use efficiency. The cover crop treatments are listed below.
- Mixture of five (Austrian winter peas, rye, wheat, crimson clover, hairy vetch, and oats), legume-brassica-grass combination, source-Adams Brisco Seed Company
- Mixture of five (oats, wheat, crimson clover, radish, and turnip), legume-brassica-grass combination, NRCS recommendation
- Mixture of two (crimson clover and rye), legume-grass combination, source-Adams Brisco Seed Company
- Mixture of two (oat and radish), grass-brassica combination, source-Adams Brisco Seed Company
- Mixture of two (crimson clover and turnip), legume-brassica combination, SARE recommendation
- Single species of legume (crimson clover), source-Adams Brisco Seed Company
- Single species of grass (rye), source-Adams Brisco Seed Company
- Control 1 – Fallow with herbicide control
- Control 2 – Fallow without herbicide control
Treatment selection criteria
One of the criteria for choosing the multispecies cover crop treatments-1&2 was combination of three functional groups (grass, legume, and brassica). In addition, we wanted to compare an available cover crop mix (Treatment 1, Adams Brisco Seed Company) with an NRCS recommendation (Treatment 2). Treatments 3-5 represent the possible duplex combinations of grass, legume, and brassica. We chose the commonly available fall cover crop species in the region to design treatments 3-7. Treatments-8&9 are common fallow-practices adopted by producers in SC.
Cover crop treatments were planted in plots of 6 m (20 feet) by 6 m. Seeding rates were based on recommendations of the seed company (Adams Brisco), NRCS, and SARE. Cover crops were terminated through herbicide application prior to flowering or one month prior to planting (whichever happens first) in order to prevent seed production and the potential to become a future weed.
Soil water content was measured at approximately biweekly intervals using a soil moisture probe (Delta T Devices PR2 soil moisture profile probe). Soil water content was measured starting from 74 days after planting (DAP) of cover crops. Measurements were continued until one month after planting of next cash crop (soybean). Measurements were taken at 10, 20, 30, 40, 60, and 100 cm (39 inch) depths. A rain gauge was installed in the field to measure daily precipitation. Cover crop water use for a given plot between two sampling dates was calculated using the soil water balance equation. Cumulative water use was calculated as the sum of biweekly crop water use during the cover crop growth period. Soil water depletion by cover crop treatments were compared with that of control treatments to determine the loss of stored soil water due to cover cropping.
Biomass was hand harvested from 1 m2 area within each plot at 83, 111, and 137 days after planting (DAP) to determine dry weight. Cover crop water use efficiency was estimated as the amount of dry biomass produced per unit of water used during the growing period. Identification of high water use efficient cover crops (single species/mixes) helps identify cover crops that produce large amount of biomass, use less amount of water or a combination of both.
Experimental design was a randomized complete block with five replications. Analysis of variance was performed using the MIXED procedure in Statistical Analysis Software to determine effect of cover crop treatments on soil water depletion and biomass production. Cover crop treatment was considered as a fixed effect and replication as a random effect.
All cover crop treatments retained more or equal amount of soil moisture compared to controls (weed-free or weedy fallow). This does not support the perception that cover crops will deplete soil moisture which will lead to water stress for the following cash crop.
Rye and a mixture of Austrian winter pea, crimson clove, hairy vetch, oat, and rye were good ground covers in terms of number of plants per meter square, and had the highest amount of biomass and water use efficiency values. These cover crops would be advantageous in terms of stored soil water, weed control, organic matter addition, and soil health that improve the cash crop performance. Though the mixture of turnip and crimson clover and crimson clover retained good amount of moisture in the soil, they were poor biomass producers and ground covers. Taken together, our results will provide information to develop grower recommendations on specific cover crops to optimize biomass and soil moisture for subsequent crops.
Educational & Outreach Activities
Ricardo St. Aime, the student working on this project presented the study in Organic Agriculture Research Symposium, 25-26 January 2017 at Lexington, Kentucky. This symposium was conducted in conjunction with Southern Sustainable Agriculture Working Group Conference. The events hosted >100 farmers/ranchers and agricultural professionals. Ricardo also presented the study in the Department of Plant and Environmental Sciences (Clemson University) seminar series and in American Society of Agronomy, Crop Science Society of America, and Soil Science Society of America annual meetings, 22-25 October 2017 at Tampa, Florida. His particular presentation attracted ~50 agricultural professionals. These meetings were great opportunities to reach out to a large group of producers, researchers, and students. In addition, these conferences brought researchers and students interested in sustainable crop production from the southern US. Therefore, these were great venues to disseminate the research results to researchers from the southern region, who were interested in region-specific research.
Anderson county extension agent, Chris Talley was involved in each step of the planning and implementation processes of the project. He has disseminated the research results to as many producers as possible through personal communication. Our farmer cooperator, Daniel Millam serves on the Anderson County Farm Bureau Board of directors and he also reached out to other producers through personal communication.
A workshop and on-farm demonstration are scheduled on 17 May 2018. We anticipate ~60 farmers/ranchers in these events.
A manuscript will be submitted to a peer reviewed journal by the end of this year. At least 2 more professional presentations will be conducted based on the results from this study by the end of the year. Ricardo will produce his Master’s thesis based on this study. We are happy that this study has trained a future leader for sustainable agriculture as Ricardo already committed to stay for his PhD on our newly funded Southern SARE research.
The conventional grain crop producers rely primarily on herbicides for weed control. On the other hand, organic grain crop producers rely primarily on cultural and mechanical practices to manage weeds, and consider weed control among their greatest production costs. Growing numbers of grain crop producers are adopting sustainable and organic practices in response to increased demands from both organic livestock producers and final consumers. This is evident from expansion of certified organic cropland by nearly 80%, to 3.1 million acres between 2005 and 2011 in the US. Thus, development of more effective non-chemical weed management strategies can have substantial positive economic and environmental impacts, as far as conventional (inorganic) and organic grain crop production are considered. The use of cover crops offers a more sustainable, systems-based approach to weed management than herbicides and tillage.
Cover crops reduce weed pressure and improve soil health and cropping system diversity, but they also use soil water, thus affecting soil water relations of the following cash crop. Therefore, if the cover crops are not water-use-efficient, it will cause additional irrigation cost for the producers, leading to poor economic viability of cover cropping practices. Our study has identified the ‘water-saver’ or water-use-efficient cover crops to improve the efficiency of utilization of an important on-farm resource, water. The study involved a farmer cooperator in each step of the planning and implementation processes, and has addressed some roadblocks to producer adoption through (1) Research to identify single species or mixtures of multi-species cover crops that produce large amount of biomass with the use of less amount water, (2) Generation of data on water use by cover crops compared with conventional fallow practices, (3) Dissemination of research results to producers, extension agents and other researchers. We anticipate that the project will result in greater adoption of cover cropping by grain crop producers, reduced use of herbicides, and development of soil organic matter leading to healthier soils. In addition, the use of water-use-efficient cover crops will improve the availability of soil water, which could reduce irrigation cost and thus improve the economic feasibility and sustainability of cover cropping practices.
We have submitted another proposal on cover crops based on the results from the current study. Another proposal is at the preparation stage.