Product Code Database
In agriculture, cover crops are plants that are planted to ground cover the soil rather than for the purpose of being . Cover crops manage soil erosion, soil fertility, soil quality, water, , pests, diseases, biodiversity and wildlife in an agroecology ecological system managed and shaped by humans. Cover crops can increase microbial activity in the soil, which has a positive effect on nitrogen availability, Plant nutrition in Cash crop, and Crop yield. Cover crops reduce water pollution risks and remove CO2 from the atmosphere. Cover crops may be an off-season crop planted after harvesting the cash crop. Cover crops are in that they increase the survival of the main crop being harvested, and are often grown over the winter. In the United States, cover cropping may cost as much as $35 per acre.
Often, green manure crops are grown for a specific period, and then tillage before reaching full maturity to improve soil fertility and quality. The stalks left block the soil from being eroded.
Green manure crops are commonly leguminous, meaning they are part of the pea family, Fabaceae. This family is unique in that all of the species in it set pods, such as bean, lentil, and alfalfa. Leguminous cover crops are typically high in nitrogen and can often provide the required quantity of nitrogen for crop production. In conventional farming, this nitrogen is typically applied in chemical fertilizer form. In organic farming, nitrogen inputs may take the form of organic fertilizers, compost, cover crop seed, and fixation by legume cover crops. This quality of cover crops is called fertilizer replacement value.
Another quality unique to leguminous cover crops is that they form symbiotic relationships with the rhizobacteria bacteria that reside in legume root nodules. Lupins is nodulated by the soil microorganism Bradyrhizobium sp. (Lupinus). Bradyrhizobia are encountered as microsymbionts in other leguminous crops ( Argyrolobium, Lotus, Ornithopus, Acacia, Lupinus) of Mediterranean origin. These bacteria convert biologically unavailable atmospheric nitrogen gas () to biologically available ammonium () 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.
Prior to the advent of the Haber–Bosch process, an energy-intensive method developed to carry out industrial nitrogen fixation and create chemical nitrogen fertilizer, most nitrogen introduced to ecosystems arose through biological nitrogen fixation. Some scientists believe that widespread biological nitrogen fixation, achieved mainly through the use of cover crops, is the only alternative to industrial nitrogen fixation in the effort to maintain or increase future food production levels. Industrial nitrogen fixation has been criticized as an unsustainable source of nitrogen for food production due to its reliance on fossil fuel energy and the environmental impacts associated with chemical nitrogen fertilizer use in agriculture. Such widespread environmental impacts include nitrogen fertilizer losses into waterways, which can lead to eutrophication (nutrient loading) and ensuing hypoxia (oxygen depletion) of large bodies of water.
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. The ecological complexity of marine life in this zone has been diminishing as a consequence.
As well as bringing nitrogen into agroecosystems through biological nitrogen fixation, types of cover crops known as "" are used to retain and recycle soil nitrogen already present. The catch crops take up surplus nitrogen remaining from fertilization of the previous crop, preventing it from being lost through leaching, or gaseous denitrification or volatilization. (2025). 9780120007974, Academic Press Inc.. ISBN 9780120007974
Catch crops are typically fast-growing annual cereal species adapted to scavenge available nitrogen efficiently from the soil. 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.
Soil quality is managed to produce optimum conditions for crops to flourish. The principal factors affecting soil quality are soil salination, pH, microorganism balance, and the prevention of soil contamination. It is noted that if soil quality is properly managed and maintained, it forms the foundation for a healthy and productive environment. One can design and manage a crop that will produce a healthy environment for quite some time.
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.
Some cover crops suppress weeds both during growth and after death. 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. 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. 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 allelopathy. This occurs when certain biochemical cover crop compounds are degraded that happen to be toxic to, or inhibit seed germination of, other plant species. Some well known examples of allelopathic cover crops are Secale cereale (rye), Vicia villosa (hairy vetch), Trifolium pratense (red clover), Sorghum bicolor (sorghum-sudangrass), and species in the family Brassicaceae, particularly mustard plant. In one study, rye cover crop residues were found to have provided between 80% and 95% control of early season broadleaf weeds when used as a mulch during the production of different cash crops such as soybean, tobacco, maize, and sunflower. In general, cover crops need not compete with cash crops, as they can be grown and terminated early on the season before other crops are established.
In a 2010 study released by the Agricultural Research Service (ARS), 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.
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.
Other cover crops are used to attract natural predators of pests by imitating elements of their habitat. This is a form of biological control known as habitat augmentation, but achieved with the use of cover crops. Findings on the relationship between cover crop presence and predator–pest population dynamics have been mixed, suggesting the need for detailed information on specific cover crop types and management practices to best complement a given integrated pest management strategy. For example, the predator mite Euseius tularensis (Congdon) is known to help control the pest citrus thrips in Central California citrus orchards. Researchers found that the planting of several different leguminous cover crops (such as bell bean, woollypod vetch, New Zealand white clover, and Austrian winter pea) provided sufficient pollen as a feeding source to cause a seasonal increase in E. tularensis populations, which with good could potentially introduce enough predatory pressure to reduce pest populations of citrus thrips.
In one study, researchers compared arthropod and songbird species composition and field use between conventionally and cover cropped cotton fields in the Southern United States. The cover cropped cotton fields were planted to clover, which was left to grow in between cotton rows throughout the early cotton growing season (stripcover cropping). During the migration and breeding season, they found that songbird densities were 7–20 times higher in the cotton fields with an integrated clover cover crop than in the conventional cotton fields. Arthropod abundance and biomass was also higher in the clover c-cover fields throughout much of the songbird breeding season, which was attributed to an increased supply of flower nectar from the clover. The clover cover crop enhanced songbird habitat by providing covering sites, and an increased food source from higher arthropod populations.
|
|
