Final Report for GS07-057
Buckwheat is a promising cover crop for weed management in sustainable and organic cropping systems. Since the humid, subtropical climate in Florida is different considerably from the temperate areas of the country where buckwheat is typically grown, recommendations were needed for growing buckwheat cover crop to maximize its benefits. Buckwheat cover crop was compared with weedy fallow and a harrowed control at six planting dates in spring and fall in 2007 and 2008. Generally, buckwheat resulted in fewer weeds than the weedy fallow and was as effective at suppressing weeds as the harrowed control. With the mild weather in spring and fall in north-central Florida, climatic conditions at the beginning of May and mid October may be the most suitable for buckwheat growth and weed suppression. When termination practices of rolling, flail mowing, light tillage, and the combination of flail mowing and light tillage were compared, light tillage may be a promising option for buckwheat planted in fall. Rolling and flail mowing may be more applicable for use in spring and for systems in which growers wish to retain buckwheat residue as an organic mulch.
Weed management in horticultural production can be a major challenge in conventional, transitional, and organic production systems. In conventional systems, herbicide options are often limited and can be harmful to rotational crops. In transitional and organic systems nonsynthetic herbicides may be used if nonchemical approaches are insufficient. However, nonsynthetic herbicides are costly and thus far are all nonselective and can injure the crop. Efficacy and persistence of control with nonsynthetic herbicides are often insufficient. Cover crops could be used as an alternative to herbicides and as a part of an integrated weed management program to control weeds in conventional production systems and decrease the need for hand-weeding and cultivation in organic systems. Both living cover crops and cover crop residues can interfere with weed seed germination and seedling emergence.
Buckwheat [Fagopyrum esculentum Moench] is an annual broadleaf grain crop belonging to the Polygonaceae family and is generally utilized as a summer cover crop in temperate areas. It can be used as a weed-suppressive cover crop based on mechanisms of competition with weeds for resources, alteration of the soil physical environment, and allelopathy. To obtain the optimal growth for best benefits, it should be planted in cool and moist environments without frost and drought.
Cover crops can be terminated with chemicals or mechanically. Cover crop residues can be incorporated into the soil or retained on the surface of the soil as mulches. The effectiveness of termination practices may differ depending on the growth stage and species of the cover crops. Moreover, termination practices can also affect weed emergence and growth.
Since the humid subtropical climate of Florida is considerably different from the rest of the country, recommendations for cover crop utilization developed in other parts of the US may not be applicable. Termination practices may influence weed emergence and growth through soil disturbance or mulches or by allelopathy, whereas they may also affect residue decomposition and the persistence of the surface mulch or allelopathic effect. Therefore, the goal of this study was to generate information on planting period and termination practices for buckwheat to determine whether it can be a useful cover crop to suppress weeds effectively for sustainable and organic cropping systems in north central Florida.
- To determine the optimal planting period for buckwheat as a weed suppressive cover crop in Florida.
To compare methods for termination of buckwheat when used as a cover crop for weed suppression in Florida.
Objective 1: To determine the optimal planting period for buckwheat as a weed suppressive cover crop in Florida.
Experiments were conducted in Citra, Florida in spring and fall of 2007 and repeated in 2008. A buckwheat cover crop was compared with a weedy fallow and a harrowed control at six planting dates. Planting dates were separated by 2-week intervals from Mar. 13 to May 22 in spring 2007, from Feb. 28 to May 8 in spring 2008, from Sep. 20 to Nov. 29 in fall 2007, and from Sep. 24 to Dec. 3 in fall 2008. At each planting date, buckwheat cv. Mancan was drilled at a rate of 56 kg/ha. The control plots were harrowed with a spring tooth harrow at 2-week intervals to disturb the soil to control weeds. A linear overhead irrigation system was used only before seeding and when adult buckwheat plants wilted by 2 pm.
During the cover cropping period, buckwheat height, photosynthetically active radiation (PAR), non-destructive leaf area index (LAI), ground cover (GC), and weed counts were determined weekly beginning at 3 weeks after planting (WAP) until 5 WAP. In 2008, buckwheat emergence density was also evaluated. Above ground buckwheat biomass and weed biomass were harvested at 5 WAP from each plot, and then dried at 70 °C for 7 days and weighed. Weed biomass samples were separated into monocot and dicot categories in spring 2007, and into sedge, grass, and broadleaf categories in the other three seasons.
Buckwheat was terminated by mowing with a rotary mower at 35-40 days after planting (DAP) depending on the season. Non-buckwheat treatments were disked to simulate standard field preparation for a subsequent transplanted vegetable crop. Weed emergence was monitored at 2, 4, and 6 weeks after buckwheat termination. At the final weed counts, weeds were cut at the soil surface, separated into monocot and dicot categories in spring 2007, and into sedge, grass, and broadleaf categories in the later three seasons, and dried and weighed. Data were analyzed using SAS to compare the treatments in order to predict the optimal period for buckwheat planting.
Objective 2: To compare methods for termination of buckwheat when used as a cover crop for weed suppression in Florida.
Experiments were conducted in Citra, Florida in spring and fall in 2008. Four buckwheat cover crop termination treatments were used: rolling (R), flail mowing alone (M), light tillage alone (LT), and the combination of flail mowing followed by light tillage (M+LT). Rolling was accomplished with a 4-ft steel roller, flail mowing with a New Holland 918H flail mower, and light tillage with a roto-tiller.
Buckwheat cv. Mancan was drilled on Apr. 15 and Nov. 6 at the seeding rate of 56 kg/ha. Prior to buckwheat planting, fertilizer was applied to the field at a rate of 6.8 kg N per acre. At 35 DAP in spring and 40 DAP in fall (due to different rates of growth), the buckwheat cover crop was terminated with the assigned practices.
Before termination, buckwheat height was measured and shoot biomass samples were harvested. Ground cover (GC) percentages were determined and grab samples of buckwheat residues were collected weekly until 5 weeks after termination (WAT) Grab samples were dried at 70 °C for 7 days and weighed to determine residue biomass.
At 3 and 5 WAT, weed densities were counted by species, and weed counts were also taken at 0 WAT right after termination in fall. Weed biomass samples were harvested at 5 WAT, dried at 70 °C for 7 days, and then separated into sedge, grass, and broadleaf categories and weighed. Data were analyzed using SAS to compare the termination practices and the persistence of weed suppression with each termination practice during the post-termination residue decomposition period.
Planting Period: In the study to determine the optimal planting period, we found that cool temperatures in early spring suppressed weed emergence and growth and late frost during February and March may cause adverse effects on buckwheat growth. However, in May warmer temperatures favored weed growth rather than buckwheat growth. Temperatures in early fall appear to be too hot for buckwheat, whereas early frost in late fall may stunt or even kill buckwheat. Although buckwheat suppressed total, monocot, and dicot weed biomass in spring, buckwheat was less effective at suppressing weeds in fall. In late fall low temperatures not only suppressed weed growth but also slowed down buckwheat growth. Therefore, our results suggest that optimal planting period in spring may be on or around May 1, and in fall it may be on or around Oct. 16.
Termination Practices: In the study of termination practices, all of the practices were able to kill buckwheat successfully at the rates of more than 90%. Rolling produces an organic mulch with retention of cover crop residues on the soil surface; however, rolled buckwheat residue was not sufficient to suppress established weeds. Flail mowing resulted in chopped and shredded buckwheat residue, which decomposed more rapidly than rolled plants. Light tillage and the combination of flail mowing and light tillage disturbed the top layer of soil and disrupted established weeds. However, they may also stimulate weed seed germination within this layer of soil. Incorporation distributes residues into the upper layer of the soil and reduces the amount of residue on the soil surface. Although the remaining surface residues may be insufficient for a mulch, incorporation may improve suppression of weed growth caused by allelopathic interaction. Depending on the cropping system, flail mowing and rolling may have utility for no-till and reduced tillage production systems. Although there was no significant difference in weed suppression with the two, the persistence of surface coverage with rolling may be better than with flail mowing. Depending on the season, light tillage alone may be more suitable for use in fall when cooler temperatures can inhibit weed germination and emergence and reduce the adverse effects caused by disturbing the soil. Since light tillage alone was as effective as a combination of flail mowing and light tillage, it is also a promising method to save energy and limit fuel cost.
Educational & Outreach Activities
Huang, P. 2009. Optimal conditions for buckwheat [Fagopyrum esculentum Moench] production as a cover crop for weed suppression in Florida. Master’s Thesis. Horticultural Sciences Department. University of Florida. http://purl.fcla.edu.lp.hscl.ufl.edu/fcla/etd/UFE0025074.
Hallberg, R. 2009. UF Researchers Explore the Use of Buckwheat as a Cover Crop in the South. Southern Exposure. Southern IPM Center Newsletter. Vol. 6 Iss. 3, pp 9-10.
Huang, P., C.A. Chase, B.M. Santos, and X. Zhao. 2009. Planting dates to optimize weed suppression with buckwheat in Florida. WSSA Abstracts, #311.
Huang, P., C.A. Chase, B.M. Santos, and X. Zhao. 2009. Spring planting dates to maximize weed suppression with buckwheat. Proc. Florida Weed Science Society. Page 9.
Huang, P., C.A. Chase, B.M. Santos, and X. Zhao. 2008. Buckwheat for weed suppression in Florida. Proceedings Southern Weed Science Society 61:150.
Huang, P., C.A. Chase, B.M. Santos, and X. Zhao. 2008. Optimal Planting Period for Buckwheat Cover Crop for Weed Suppression in Florida. HortScience 43(4):1183.
Treadwell, D. and P. Huang. 2008. Buckwheat: A cool season cover crop for Florida vegetable producers. EDIS. http://edis.ifas.ufl.edu/HS386
This project partially funded the master’s project of Pei-wen Huang who successfully completed a thesis and graduated in August 2009. She has prepared two manuscripts based on her research that will be submitted to refereed journals after appropriate revision. Her work has shown that it is possible to successfully grow buckwheat in Florida in spring and fall; however, the best weed suppression was obtained with buckwheat planted mid April to May 1. The results indicate that buckwheat as a sole cover crop will not have broad utility in Florida for weed suppression since frost during the cool season and hot weather from late spring through early fall can result in poor growth, lower biomass, and afternoon wilting. Buckwheat was readily terminated mechanically, which is particularly useful for organic cropping systems. Using buckwheat in mixtures may improve its utility for weed suppression outside of optimal planting dates and would allow growers to obtain the additional ecosystem services and benefits such as providing food and habitat for beneficial insects and pollinators, short-term cover for neighboring or preceding crops, rapid decomposition to allow planting of a cash crop, and excellent scavenging of phosphorus.
Treadwell and Huang (2008) have produced a factsheet that will provide information to growers interested in incorporating buckwheat into their cropping systems.
Areas needing additional study
In the future we propose to evaluate buckwheat as a nurse crop in spring to aid in the establishment of slow growing perennial living mulches for use in orchard crops. Additionally, buckwheat may have applicability as a flowering companion plant to provide habitat for beneficial arthropods. It is reported that buckwheat is used in a biculture with legumes in summer in the Tallahassee area. Utilizing it in mixtures during less optimal growing periods may allow growers to benefit from its other ecosystem services while the other species in the mixture contribute to weed suppression.