Location: Soil Dynamics Research2020 Annual Report
Objective 1. Determine weed suppression, soil coverage, and agronomic and economic benefits for monoculture and mixed species high-residue cover crops in conservation tillage for diverse crop production systems of the southeastern U.S. Sub-objective 1a. Evaluate monoculture and mixtures of cereal, legume, and selected Brassica cover crop species on weed dynamics in corn, cotton, peanut, and soybean. Sub-objective 1b. Evaluate and develop integrated weed control systems to diminish herbicide resistant and troublesome weed yield loss in cotton. Sub-objective 1c. Evaluate cover crop management across single species and mixtures to compare soil health benefits, while improving biomass production. Objective 2. Integrate new equipment, high residue cover crops, and conservation tillage into cropping systems that foster sustainability and resiliency, increase efficiency, and reduce risk by promoting soil health and yield stability. Sub-objective 2a. Evaluate effects of different planting factors in a no tillage cotton system with a rye cover crop. Sub-objective 2b. Develop a no tillage equipment system compatible with a modular tractor for vegetable production. Sub-objective 2c. Determine the effects of cereal rye seeding rates and timing of termination methods on soybean production in a no tillage conservation system. Sub-objective 2d. Determine cash crop performance across high residue conservation tillage systems and different agronomic management factors.
Research objectives are designed to develop conservation systems that will improve soil quality, conserve natural resources, and increase production efficiency, while reducing risk for producers. These objectives will be accomplished by examining cover crop benefits (agronomic and economic) for single species and mixtures across diverse cropping systems of the southeast. In addition, we will also examine how integrating cover crops with management strategies designed to maximize benefits for cropping systems will promote soil health and productivity. Major areas of focus include: (1) examining weed germination across single species cover crops and mixtures for popular row crops grown across the southeast; (2) integration of cover crop mixtures into herbicide resistant weed control strategies; (3) comparisons of cover crop management strategies across single species cover crops and mixtures to identify how to maximize benefits; (4) evaluation of cover crop seeding rates, termination timing, and cash crop planting speeds on cash crop productivity; (5) development of equipment for a modular tractor suitable for vegetable production; (6) evaluation of cash crop performance across high residue cover crop systems; and (7) identifying tillage and seeding rate guidelines for a carinata biofuel crop.
Experiments designed to examine how cover crop management affects cover crop benefits are continuing. Experiments are also on-going that include comparisons between single cover crop species and multi-species cover crop mixtures for soil Carbon (C) levels, microbial activity, and weed suppression across various cropping systems. Research continues for carinata, a potential biofuel crop for the Southeast, that involves investigating interactions between carinata seeding rates and conventional and conservation tillage systems. Other tillage comparisons include an examination among different forms of surface tillage across different Nitrogen (N) rates for winter wheat production. In addition, experiments evaluating cover crop termination machinery design continue. Technology transfer activities have continued, which are related to many facets of all the previously described research. Activities include grower meetings, field days, scientific meetings, and factsheets available as handouts or accessed through the ARS website.
1. Engine exhaust heat device for terminating cover crops in no-till vegetable systems. An exhaust heat-based apparatus alone or with supplemental power take-off (PTO) driven electric heat strips was developed by an ARS researcher in Auburn, Alabama, to terminate a cover crop without herbicide use. High temperature transfer efficiency from exhaust manifold to steel delivery tube was 23% with a tube temperature of 204 degrees C contacting the cover crop. In contrast, transfer efficiency of heat strips was much greater (83 to 91%) at 460 degrees C. Shortening the flexible piping between the exhaust manifold and heat delivery tube, and improving the insulating material encasing the flexible pipe could increase heat transfer. Termination rates for cereal rye and crimson clover by exhaust heat and combining exhaust heat with supplemental heat strips were similar to traditional mechanical termination using roller/crimpers. This heat-based apparatus can be a viable option for cover crop termination or weed control in organic systems where commercial herbicides are not allowed and where effective cover crop termination is essential for an optimum cash crop growth.
2. Tillage systems for southeastern coastal plain wheat production. Minimizing surface and deep tillage operations for wheat production may enhance soil health benefits, but productivity, Nitrogen (N) requirements, and profit need to be examined for these systems across degraded Alabama Coastal Plain soils. An ARS researcjer in Auburn, Alabama, conducted an experiment to: (i) compare non-inversion and no tillage wheat yields, and (ii) evaluate N requirements across both tillage systems at three Coastal Plain locations. Wheat yields were inconsistent between tillage systems and varied up to 12% at two of the three locations. The greatest N rates applied (134 kg N ha-1 and 34 kg N ha-1), which are greater than current recommendations, produced yield increases of 17% and 30% compared to the average of the recommended N rates (67 and 101 kg N ha-1) at two of the three locations. No tillage produced 11% greater net returns than noninversion tillage for one location, while non-inversion tillage produced net returns nearly six times greater than no tillage for the other location. Results indicate that although no tillage may enhance soil health benefits, yield increases and net returns were small compared to non-inversion tillage across the Coastal Plain of Alabama.
3. Corn response to irrigation and plant density in a conservation system. Corn production in the Southeast can be risky due to inconsistent summer rainfall and sandy soils with low moisture holding capacities. However, irrigation combined with conservation tillage and cover crops may support greater plant populations arranged in different row patterns to improve yield. An ARS researcher in Auburn, Alabama, and an Auburn University researcher, located in Auburn, Alabama, examined data from five site-years across sandy and clay soil types. They compared corn yields in a conservation system across three plant populations planted in single- and twin-row configurations in both dryland and irrigated moisture regimes. Different moisture environments (low and moderate) were also defined by observed growing season rainfall across site-years. Increased rainfall and irrigation clearly reduced soil moisture stress across drought prone soils, but no consistent yield response was observed for increased plant densities. No advantage was observed for either row configuration, indicating that single or twin rows can be successfully adopted for corn production across the region. However, increased plant densities required non-limiting soil moisture conditions to maintain yield levels. Growers across the region already plant peanuts in twin-rows; therefore, the same planter can be used to reduce costs. In addition, results indicate that the increased costs for additional seed is not warranted without the ability to supplement soil moisture, despite using a conservation system.
4. Nitrogen mineralization from different peanut residue components. Field observations have shown that a substantial portion of peanut leaves separate from stems during pod curing, leading to an uneven distribution of leaves and stems following peanut harvest. Possible differences in N mineralization rates between peanut leaf and stem residues may lead to variability of available N for subsequent crops. University of Florida and North Carolina State researchers in conjunction with an ARS researcher in Auburn, Alabama, conducted a 252-day microlysimeter incubation to quantify soil N mineralization. Soil amended with peanut leaves, stems, and a 1:1 mixture of leaves and stems of three peanut varieties was compared with a soil-only control. Conventional or conservation tillage was also simulated by placing the plant materials on the soil surface or incorporating into the soil. Over the duration of the incubation, peanut leaves supplied only 25 kg N ha-1 at the 0-15 cm depth, which would likely not produce a yield response for a subsequent crop. These results confirm previous reports that peanut residue N contributions to a subsequent crop are minimal across the southeastern US. Growers should exercise caution to ensure crops grown following peanut are not under fertilized based on an anticipated N contribution from a preceding peanut legume.
5. Impact of different cover crops and termination methods on collard yield. Cover crops are an essential component in most conservation production systems in the Southeastern US, but managing the termination of these cover crops are critical to the success of the systems. An ARS researcher in Auburn, Alabama, conducted field experiments to evaluate the effects of six summer cover crops and their management (rolling and flail mowing) on collard green yield in a no-till system. Cover crop termination rates were lower than recommended (>90%) for planting collard and were associated with regrowth of already rolled plants. In addition, uneven soil surface across the width of the roller inhibited termination rates, as plant stems in depressions (voids) were not crimped by crimping bars and were able to recover. Cover crops such as velvet bean and iron clay peas that are vines are generally more difficult to terminate because of their long stems that do not tend to crush like taller crops. With exception of iron clay pea, rolled residue was shown to hold more soil water than standing cover crops during three growing seasons. Higher collard yield was associated with the presence of legume cover crops compared to non-legumes. This was most likely due to release of nitrogen from the decomposition of the cover crops during the growing season. Overall, because of lower weed pressure, collard green yield was higher for flail mowed cover crops compared to rolled/crimped cover crops.
Jani, A.D., Mulvaney, M.J., Balkcom, K.S., Wood, C., Jordan, D.L., Wood, B.H., Devkota, P. 2019. Peanut residues supply minimal plant-available nitrogen on a major soil series in the USA peanut basin. Soil Use and Management. 36:274-284. https://doi.org/10.1111/sum.12563.
Kornecki, T.S., Price, A.J. 2019. Management of high-residue cover crops in a conservation tillage organic vegetable on-farm setting in Alabama. Agronomy Journal. 9(10):640. https://doi.org/10.3390/agronomy9100640.
Balkcom, K.S., Schomberg, H.H., Lee, R. 2020. Cover Crop Management. In: Bergtold, J., Sailus, M., editors. Conservation tillage systems in the Southeast: Production, profitability, and stewardship. SARE Handbook Series Book 15. Sustainable Agriculture Network. p. 56-76.
Kornecki, T.S., Balkcom, K.S. 2020. Cover Crop Management. In: Bergtold, J., Sailus, M., editors. Conservation tillage systems in the Southeast: Production, profitability, and stewardship. SARE Handbook Series Book 15. Sustainable Agriculture Network. p. 119-132.
Balkcom, K.S. 2019. No tillage and non-inversion tillage comparisons across wheat nitrogen rates in Alabama. Journal of Soil and Water Conservation. 74:560-570. https://doi.org/10.2489/jswc.74.6.560.
Balkcom, K.S., Bowem, K.L. 2020. Corn response across plant densities and row configurations for different moisture environments. International Journal of Agronomy. vol. 2020. Article ID 4518062, 10 pages, https://doi.org/10.1155/2020/4518062.
Kornecki, T.S., Prior, S.A. 2019. Engine exhaust heat device for terminating cover crops in no-till vegetable systems. Applied Engineering in Agriculture. 35(5):787-793. https://doi.org/10.13031/aea.13101.
Raper, R.L., Busscher, W.J., Meier, A.D., Balkcom, K.S. 2020. In-Row subsoiling to disrupt soil compaction. In J. Bergtold and M. Sailus (ed.) Conservation tillage systems in the Southeast: Production, profitability, and stewardship. SARE Handbook Series Book 15. Sustainable Agriculture Network. p.77-87.
Kornecki, T.S. 2020. Impact of different cover crops and termination methods on collard yield. European Agrophysical Journal. 6(4):50-66.