Cover crop
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Soil erosion
Although cover crops can perform multiple functions in an agroecosystem simultaneously, they are often grown for the sole purpose of preventing
Soil fertility management
One of the primary uses of cover crops is to increase soil fertility. These types of cover crops are referred to as "
Often, green manure crops are grown for a specific period, and then plowed under before reaching full maturity to improve soil fertility and quality. The stalks left block the soil from being eroded.
Green manure crops are commonly
Another quality unique to leguminous cover crops is that they form
2) to biologically available ammonium (NH+
4) through the process of biological nitrogen fixation. In general, cover crops increase soil microbial activity, which has a positive effect on nitrogen availability in the soil, nitrogen uptake in target crops, and crop yields.[7]
Prior to the advent of the
An example of this is in the Mississippi Valley Basin, where years of fertilizer nitrogen loading into the watershed from agricultural production have resulted in an annual summer hypoxic "dead zone" off the Gulf of Mexico that reached an area of over 22,000 square kilometers in 2017.[13][14] The ecological complexity of marine life in this zone has been diminishing as a consequence.[15]
As well as bringing nitrogen into agroecosystems through biological nitrogen fixation, types of cover crops known as "
Catch crops are typically fast-growing annual cereal species adapted to scavenge available nitrogen efficiently from the soil.[18] The nitrogen fixed in catch crop biomass is released back into the soil once the cash crop is incorporated as a green manure or otherwise begins to decompose.
An example of green manure use comes from Nigeria, where the cover crop Mucuna pruriens (velvet bean) has been found to increase the availability of phosphorus in soil after a farmer applies rock phosphate.[19]
Soil quality management
Cover crops can also improve soil quality by increasing soil organic matter levels through the input of cover crop biomass over time. Increased soil organic matter enhances soil structure as well as the water and nutrient holding and buffering capacities of the soil.[20] It can also lead to increased soil carbon sequestration, which has been promoted as a strategy to help offset the rise in atmospheric carbon dioxide levels.[21][22][23]
Soil quality is managed to produce optimum conditions for crops to flourish. The principal factors affecting soil quality are
Water management
By reducing soil erosion, cover crops often also reduce both the rate and quantity of water that drains off the field, which would normally pose environmental risks to waterways and ecosystems downstream.[25] Cover crop biomass acts as a physical barrier between rainfall and the soil surface, allowing raindrops to steadily trickle down through the soil profile. Also, as stated above, cover crop root growth results in the formation of soil pores, which, in addition to enhancing soil macrofauna habitat provides pathways for water to filter through the soil profile rather than draining off the field as surface flow. With increased water infiltration, the potential for soil water storage and the recharge of aquifers can be improved.[26]
Just before cover crops are killed (by such practices including mowing, tilling, discing, rolling, or herbicide application) they contain a large amount of moisture. When the cover crop is incorporated into the soil, or left on the soil surface, it often increases soil moisture. In agroecosystems where water for crop production is in short supply, cover crops can be used as a mulch to conserve water by shading and cooling the soil surface. This reduces the evaporation of soil moisture and helps preserve soil nutrients.[27]
Weed management
Thick cover crop stands often compete well with weeds during the cover crop growth period, and can prevent most germinated weed seeds from completing their life cycle and reproducing. If the cover crop is flattened down on the soil surface rather than incorporated into the soil as a green manure after its growth is terminated, it can form a nearly impenetrable mat. This drastically reduces light transmittance to weed seeds, which in many cases reduces weed seed germination rates.[28] Furthermore, even when weed seeds germinate, they often run out of stored energy for growth before building the necessary structural capacity to break through the cover crop mulch layer. This is often termed the cover crop smother effect.[29]
Some cover crops suppress weeds both during growth and after death.[30] During growth these cover crops compete vigorously with weeds for available space, light, and nutrients, and after death they smother the next flush of weeds by forming a mulch layer on the soil surface.[31] For example, researchers found that when using Melilotus officinalis (yellow sweetclover) as a cover crop in an improved fallow system (where a fallow period is intentionally improved by any number of different management practices, including the planting of cover crops), weed biomass only constituted between 1–12% of total standing biomass at the end of the cover crop growing season.[30] Furthermore, after cover crop termination, the yellow sweetclover residues suppressed weeds to levels 75–97% lower than in fallow (no yellow sweetclover) systems.
In addition to competition-based or physical weed suppression, certain cover crops are known to suppress weeds through
In a 2010 study released by the Agricultural Research Service (ARS),[36] scientists examined how rye seeding rates and planting patterns affected cover crop production. The results show that planting more pounds per acre of rye increased the cover crop's production as well as decreased the amount of weeds. The same was true when scientists tested seeding rates on legumes and oats; a higher density of seeds planted per acre decreased the amount of weeds and increased the yield of legume and oat production. The planting patterns, which consisted of either traditional rows or grid patterns, did not seem to have a significant impact on the cover crop's production or on the weed production in either cover crop. The ARS scientists concluded that increased seeding rates could be an effective method of weed control.[37]
Cornell University's Sustainable Cropping Systems Lab released a study in May 2023 investigating the effectiveness of time-sensitive planting and strategic coupling of cover crop variants with phylogenetically similar cash crops. The primary researcher, Uriel Menalled, discovered that if cover and cash crops are planted in accordance with his research findings, farmers can decrease weed growth by up to 99%. The study provides farmers with a comprehensive framework to identify cover crops that would best suit their existing cropping rotations. In sum, the results from this study support an understanding that phylogenetic relatedness can be harnessed to significantly suppress weed growth.[38]
Disease management
In the same way that allelopathic properties of cover crops can suppress weeds, they can also break disease cycles and reduce populations of bacterial and fungal diseases,[39] and parasitic nematodes.[40][41] Species in the family Brassicaceae, such as mustards, have been widely shown to suppress fungal disease populations through the release of naturally occurring toxic chemicals during the degradation of glucosinolate compounds in their plant cell tissues.[42]
Pest management
Some cover crops are used as so-called "trap crops", to attract pests away from the crop of value and toward what the pest sees as a more favorable habitat.[43] Trap crop areas can be established within crops, within farms, or within landscapes. In many cases, the trap crop is grown during the same season as the food crop being produced. The limited area occupied by these trap crops can be treated with a pesticide once pests are drawn to the trap in large enough numbers to reduce pest populations. In some organic systems, farmers drive over the trap crop with a large vacuum-based implement to physically pull the pests off the plants and out of the field.[44] This system has been recommended for use to help control the lygus bugs in organic strawberry production.[45] Another example of trap crops is nematode-resistant white mustard (Sinapis alba) and radish (Raphanus sativus). They can be grown after a main (cereal) crop and trap nematodes, for example, the beet cyst nematode[46][47] and the Columbian root knot nematode.[48] When grown, nematodes hatch and are attracted to the roots. After entering the roots they cannot reproduce in the root due to a hypersensitive resistance reaction of the plant. Hence the nematode population is greatly reduced, by 70–99%, depending on species and cultivation time.
Other cover crops are used to attract natural predators of pests by imitating elements of their habitat. This is a form of
Biodiversity and wildlife
Although cover crops are normally used to serve one of the above discussed purposes, they often serve as habitat for wildlife. The use of cover crops adds at least one more dimension of plant diversity to a cash crop rotation. Since the cover crop is typically not a crop of value, its management is usually less intensive, providing a window of "soft" human influence on the farm. This relatively "hands-off" management, combined with the increased on-farm heterogeneity produced by the establishment of cover crops, increases the likelihood that a more complex
In one study, researchers compared
See also
- Agroecology
- Allelopathy
- Biological control
- Green manure
- Ground cover
- Nitrogen cycle
- Nitrogen fixation
- Organic matter
- Soil contamination
References
- ^ Carlson, Sarah (Summer 2013). "Research Priorities for Advancing Adoption of Cover Crops in Agriculture-intensive Regions". Journal of Agriculture, Food Systems, and Community Development. 3: 125–129.
- ^ "Cover Crops, a Farming Revolution With Deep Roots in the Past". The New York Times. 2016.
- ^ Weise, Elizabeth (28 December 2022). "Ancient farming practice makes a comeback as climate change puts pressure on crops". USA Today. Retrieved 28 December 2022.
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- ^ Tomlin, A. D.; Shipitalo, M. J.; Edwards, W. M.; Protz, R. (1995). "Earthworms and their influence on soil structure and infiltration". In Hendrix, P. F. (ed.). Earthworm Ecology and Biogeography in North America. Boca Raton, Florida: Lewis Publishers. pp. 159–183.
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- ^ "NOAA: Gulf of Mexico 'dead zone' is the largest ever measured". National Oceanic and Atmospheric Administration (NOAA). August 3, 2017. Archived from the original on August 2, 2017. Retrieved August 3, 2017.
- ^ National Science and Technology Council Committee on Environment and Natural Resources (2000). Integrated Assessment of Hypoxia in the Northern Gulf of Mexico (PDF) (Report). Washington, DC.
- ^ Morgan, M. F.; Jacobson, H. G. M.; LeCompte, S. B. Jr. (1942). Drainage water losses from a sandy soil as affected by cropping and cover crops (Technical report). Windsor Lysimeter Series C. New Haven: Connecticut Agricultural Experiment Station. pp. 731–759.
- ISBN 9780120007974.
- ^ Ditsch, D. C.; Alley, M. M. (1991). "Nonleguminous Cover Crop Management for Residual N Recovery and Subsequent Crop Yields". Journal of Fertilizer Issues. 8: 6–13.
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- ^ "Managing Soil Health: Concepts and Practices". extension.psu.edu. Retrieved 2023-07-14.
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- ^ Nagabhushana, G. G.; Worsham, A. D.; Yenish, J. P. (2001). "Allelopathic cover crops to reduce herbicide use in sustainable agricultural systems". Allelopathy Journal. 8: 133–146.
- ^ "In Organic Cover Crops, More Seeds Means Fewer Weeds : USDA ARS". www.ars.usda.gov. Retrieved 2024-01-15.
- ^ "In Organic Cover Crops, More Seeds Means Fewer Weeds". USDA Agricultural Research Service. January 25, 2010.
- ^ Menalled, Uriel (2023). "Ecological Weed Management for Field Crop Production". ProQuest: 102–126.
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- ^ Kuepper, George; Thomas, Raeven (February 2002). "Bug vacuums" for organic crop protection (Technical report). Fayetteville, Arkansas: Appropriate Technology Transfer for Rural Areas.
- ^ Zalom, F. G.; Phillips, P. A.; Toscano, N. C.; Udayagiri, S. (2001). UC Pest Management Guidelines: Strawberry: Lygus Bug (Report). Berkeley, CA: University of California Department of Agriculture and Natural Resources.
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Further reading
- SARE National. Topic: Cover Crops. [1]
- Midwest Cover Crops Council. [2] Resources for growers, researchers, and educators.
- Clark, Andy, ed. (2007). Managing Cover Crops Profitably (PDF) (3rd ed.). Beltsville, Maryland: Sustainable Agriculture Network.
- Giller, K. E.; Cadisch, G. (1995). "Future benefits from biological nitrogen fixation: An ecological approach to agriculture". Plant and Soil. 174 (1–2): 255–277. S2CID 24604997.
- Hartwig, N. L.; Ammon, H. U. (2002). "50th Anniversary - Invited article - Cover crops and living mulches". Weed Science. 50 (6): 688–699. S2CID 86045745.
- Hill, E. C.; Ngouajio, M.; Nair, M. G. (2006). "Differential responses of weeds and vegetable crops to aqueous extracts of hairy vetch and cowpea". HortScience. 31 (3): 695–700. .
- Lu, Y. C.; Watkins, K. B.; Teasdale, J. R.; Abdul-Baki, A. A. (2000). "Cover crops in sustainable food production". Food Reviews International. 16 (2): 121–157. S2CID 28356685.
- Snapp, S. S.; Swinton, S. M.; Labarta, R.; Mutch, D.; Black, J. R.; Leep, R.; Nyiraneza, J.; O'Neil, K. (2005). "Evaluating cover crops for benefits, costs and performance within cropping system niches". Agron. J. 97 (1): 1–11. .
- Thomsen, I. K.; Christensen, B. T. (1999). "Nitrogen conserving potential of successive ryegrass catch crops in continuous spring barley". Soil Use and Management. 15 (3): 195–200. S2CID 96397423.
External links
- "Cover Crops", Cyclopedia of American Agriculture, vol. 2, ed. by L. H. Bailey (1911). A short encyclopedia article, early primary source on varieties and uses of cover crops.