Cover crops can also improve soil quality by increasing organic matter levels, through the contribution of cover crop biomass over time. Increased organic matter in soil improves soil structure as well as water content and nutrient capacity[8] It can also lead to increased soil carbon sequestration, which has been promoted as a strategy to help offset increased atmospheric levels of carbon dioxide[9]​.

Although cover crops can perform multiple functions in an agroecosystem at the same time, they are often grown for the sole purpose of preventing soil erosion. Soil erosion is a process that can irremediably reduce the productive capacity of agroecosystems. Dense cover cropping physically slows down the speed of rain before it makes contact with the surface, thus preventing splashing and soil erosion (surface runoff).[10]​ In addition, extensive coverage through networks of root crops helps to fix the soil in place and increase its porosity, as well as the possibility of generating suitable habitat for its macrofauna.[11]​.

In these circumstances the soil manages to produce optimal conditions so that crops can flourish. The main quality factors are soil salinization, pH, microorganisms, balance and prevention of soil contamination.

By decreasing soil erosion, cover crops often also reduce the rate and amount of water leaving the field, which typically pose environmental risks to downstream waterways and ecosystems (Dabney*et al.*2001). It includes crop biomass acting as a physical barrier between precipitation and the surface, allowing raindrops to arrive uniformly along the soil profile. Also, as we have said, cover crops add root growth that participates in the formation of soil pores, which in addition to improving the habitat of macrofauna, offer pathways for water to filter through the soil profile, instead of draining out of the field as a surface flow. With water infiltration, the potential for water storage in the soil increases and the recharge of aquifers can also be improved.[12]​.

Before cover crops, soils were affected by practices such as cutting, tilling, using disc plows, or by the application of herbicides. When cover crops are incorporated, soil moisture often increases, both at depth and above the surface. In agroecosystems where water for agricultural production is scarce, cover crops can be used as a cover to conserve water by shading and cooling the soil surface. This reduces evaporation of soil moisture. However, in other situations farmers try to dry the soil as quickly as possible before entering the planting season. Here prolonged soil moisture conservation can be problematic.

Indeed, while cover crops can help conserve water, in temperate regions (especially in years with below-average rainfall) it can decrease soil water supply in the spring, especially if growing weather conditions are good. In these cases, just before planting crops, farmers face a trade-off between the benefits of increased cover crop growth and the drawbacks of reduced soil moisture for that season's cash crop production.

Contenido

Se encuentra que el cultivo de cobertura espeso a menudo compite bien con las malezas durante el período de crecimiento de los cultivos y así pueden evitar que germinen la mayoría de las semillas de malezas y por lo tanto no puedan completar su ciclo de vida y reproducción. Si al cultivo de cobertura se lo deja en la superficie del suelo en lugar de incorporarlo al suelo como abono verde después de que su crecimiento se termina, puede formar una alfombra casi impenetrable. Esto reduce drásticamente la transmisión de luz a las semillas de malezas, por lo que en muchos casos reduce las tasas de germinación de las semillas de malas hierbas.[13]​ Además, incluso cuando las semillas de malezas germinan, a menudo se quedan sin energía almacenada para el crecimiento antes de construir la capacidad estructural necesaria para romper la capa de abono del cultivo de cobertura . A menudo se habla del cultivo de cobertura como "efecto sofocar".[14]​.

Algunos cultivos de cobertura suprimen las malezas, tanto durante el crecimiento como después de la muerte de los mismos[15]​ Durante el crecimiento los cultivos de cobertura compiten vigorosamente con las malezas por espacio, luz y nutrientes, y después que ellos mueren sofocan la recurrencia siguiente de las malas hierbas mediante la formación de una capa de mantillo en la superficie del suelo. Por ejemplo, encontraron que el uso de Melilotus officinalis (trébol de olor amarillo) como cultivo de cobertura en un sistema de barbecho (el período de barbecho es intencional para mejorar cualquier número de diferentes prácticas de manejo, incluyendo la siembra de cultivos de cobertura), la biomasa de las malezas sólo constituyó entre el 1-12% de la biomasa en pie total al final de la temporada del cultivo de cobertura. Además, después de la finalización de los cultivos de cobertura, los residuos del trébol de olor amarillo habían suprimido las malas hierbas a niveles de un 75-97% más bajos que en los sistemas en barbecho sin trébol de color amarillo.[15]​.

Exploitation of allelopathic phenomena

In addition to weed suppression based on physical competition, some cover crops are known to suppress weeds through allelopathy[16]. This occurs when certain biochemical compounds in cover crops are degraded and become toxic or inhibit the germination of seeds of other plant species. There are some well-known examples of cover crops that are allelopathic such as Secale cereale (rye), Vicia villosa (downy vetch), Trifolium pratense (red clover), Sorghum bicolor (sorghum, Sudan grass), and species of the Brassicaceae family, particularly mustard[17]. In one study, residues from rye cover crops were considered to contribute 80% to 95% of weed control early in the broadleaf season, when it was used as fertilizer in the production of different commercial crops, such as soybeans, tobacco, corn and sunflower.[18]​.

A 2010 study published by the Agricultural Research Service (ARS) examined how rye (planting density and planting patterns) affected crop production. Results show that planting more pounds per hectare of rye increased the production of this cover crop, as well as decreased the number of weeds. The same thing happened when scientists tested seeding rates in legumes and oats; A greater density of seeds sown per hectare decreases the amount of weeds and increases both legume production and oat production. Planting patterns, which consisted of either traditional row or grid patterns, did not appear to have a significant impact on cover crop production or on weed emergence in cover crops. ARS scientists concluded that increasing seeding rates could be an effective method of weed control.[19]​.

In the same way that the allelopathic properties of cover crops can eliminate weeds, it can also break disease cycles and reduce populations of bacterial and fungal diseases[20]​ and parasitic nematodes[21]​ In species of the Brassicaceae family, such as mustards, it has been widely demonstrated that they can suppress fungal populations through the release of naturally occurring toxic chemicals, in the degradation processes of glucosinolade compounds in their tissues. plant cells.[22]​.

Some cover crops are used as so-called "trap crops", to attract pests away from the valuable crop and move the pest to what it sees as more favorable habitat. Trap crop areas can be established within crops, within farms, or within landscapes. In many cases the trap crop is grown in the same season as the food crop of commercial interest. The limited area occupied by these trap crops can be treated with a pest pesticide since they are attracted to the trap and are attracted in sufficient numbers to reduce the total pest populations. In some organic systems, farmers consider the trap crop unit as an instrument based on generating a "big vacuum" in order to physically drag plant pests out of the field (Kuepper and Thomas 2002). This system has been recommended for use as an aid to control lygus bugs in organic strawberry production.[24]​.

Other cover crops are used to attract natural predators of pests by providing elements of their habitat. This is a form of biological control known as habitat augmentation and was achieved with the use of cover crops[25]. Conclusions on the relationship between the presence of cover crops and predator/pest population dynamics have been mixed and point towards the need for more detailed information on specific types of cover crops and management practices to best complement a given strategy (Integrated Pest Management). For example, the predatory mite Euseius tularensis (Congdon) is known to help control pest citrus thrips in orchards in central California. Researchers found that planting several legume cover crops (such as bell bean, woollypod pea, New Zealand white clover, and Austrian winter pea) provided sufficient pollen as a food source and caused a seasonal increase in Congdon populations, which combined with appropriate timing could introduce sufficient predatory pressure to reduce citrus thrips pest populations.[26]​.

Although cover crops are typically used to serve one of the purposes discussed above, they often simultaneously improve habitat for farm wildlife. The use of cover crops adds at least one more dimension to plant diversity than a cash crop rotation. Since the cover crop is usually not a value crop, its management is usually less intense, providing a "soft" window of human influence on the farm. It is considered relatively "hands-free" management; along with the increase in on-farm heterogeneity created by the establishment of cover crops, increases the likelihood that a more complex trophic structure will develop to support an increased level of wildlife diversity[27].

In one study, researchers compared arthropod and songbird species composition in the field between conventional and cover cropping in cotton fields in the southern United States. Cover crops for cotton fields were made using clover, which was allowed to grow in the middle of cotton rows throughout the cotton season, early in the crop (stripcover crop). During the migration and breeding season, they found that songbird densities were 7.20 times higher in cotton fields covered by clover crops than in conventional cotton fields. Arthropod abundance and biomass was also higher in fields with cover clover during much of the songbird breeding season, which was attributed to greater nectar supply from clover flowers. The clover cover improved the habitat of songbirds by providing shelter and nesting sites and the food source increased due to increased arthropod populations.[28]​.

Creamer, *, NG, MA Bennett, BR Stinner, Cardina J., and Regnier EE. 1996. Weed suppression mechanisms in production-based cover cropping systems. HortScience 31:410-413.

Cover crops can also improve soil quality by increasing organic matter levels, through the contribution of cover crop biomass over time. Increased organic matter in soil improves soil structure as well as water content and nutrient capacity[8] It can also lead to increased soil carbon sequestration, which has been promoted as a strategy to help offset increased atmospheric levels of carbon dioxide[9]​.

Although cover crops can perform multiple functions in an agroecosystem at the same time, they are often grown for the sole purpose of preventing soil erosion. Soil erosion is a process that can irremediably reduce the productive capacity of agroecosystems. Dense cover cropping physically slows down the speed of rain before it makes contact with the surface, thus preventing splashing and soil erosion (surface runoff).[10]​ In addition, extensive coverage through networks of root crops helps to fix the soil in place and increase its porosity, as well as the possibility of generating suitable habitat for its macrofauna.[11]​.

In these circumstances the soil manages to produce optimal conditions so that crops can flourish. The main quality factors are soil salinization, pH, microorganisms, balance and prevention of soil contamination.

By decreasing soil erosion, cover crops often also reduce the rate and amount of water leaving the field, which typically pose environmental risks to downstream waterways and ecosystems (Dabney*et al.*2001). It includes crop biomass acting as a physical barrier between precipitation and the surface, allowing raindrops to arrive uniformly along the soil profile. Also, as we have said, cover crops add root growth that participates in the formation of soil pores, which in addition to improving the habitat of macrofauna, offer pathways for water to filter through the soil profile, instead of draining out of the field as a surface flow. With water infiltration, the potential for water storage in the soil increases and the recharge of aquifers can also be improved.[12]​.

Before cover crops, soils were affected by practices such as cutting, tilling, using disc plows, or by the application of herbicides. When cover crops are incorporated, soil moisture often increases, both at depth and above the surface. In agroecosystems where water for agricultural production is scarce, cover crops can be used as a cover to conserve water by shading and cooling the soil surface. This reduces evaporation of soil moisture. However, in other situations farmers try to dry the soil as quickly as possible before entering the planting season. Here prolonged soil moisture conservation can be problematic.

Indeed, while cover crops can help conserve water, in temperate regions (especially in years with below-average rainfall) it can decrease soil water supply in the spring, especially if growing weather conditions are good. In these cases, just before planting crops, farmers face a trade-off between the benefits of increased cover crop growth and the drawbacks of reduced soil moisture for that season's cash crop production.

Contenido

Se encuentra que el cultivo de cobertura espeso a menudo compite bien con las malezas durante el período de crecimiento de los cultivos y así pueden evitar que germinen la mayoría de las semillas de malezas y por lo tanto no puedan completar su ciclo de vida y reproducción. Si al cultivo de cobertura se lo deja en la superficie del suelo en lugar de incorporarlo al suelo como abono verde después de que su crecimiento se termina, puede formar una alfombra casi impenetrable. Esto reduce drásticamente la transmisión de luz a las semillas de malezas, por lo que en muchos casos reduce las tasas de germinación de las semillas de malas hierbas.[13]​ Además, incluso cuando las semillas de malezas germinan, a menudo se quedan sin energía almacenada para el crecimiento antes de construir la capacidad estructural necesaria para romper la capa de abono del cultivo de cobertura . A menudo se habla del cultivo de cobertura como "efecto sofocar".[14]​.

Algunos cultivos de cobertura suprimen las malezas, tanto durante el crecimiento como después de la muerte de los mismos[15]​ Durante el crecimiento los cultivos de cobertura compiten vigorosamente con las malezas por espacio, luz y nutrientes, y después que ellos mueren sofocan la recurrencia siguiente de las malas hierbas mediante la formación de una capa de mantillo en la superficie del suelo. Por ejemplo, encontraron que el uso de Melilotus officinalis (trébol de olor amarillo) como cultivo de cobertura en un sistema de barbecho (el período de barbecho es intencional para mejorar cualquier número de diferentes prácticas de manejo, incluyendo la siembra de cultivos de cobertura), la biomasa de las malezas sólo constituyó entre el 1-12% de la biomasa en pie total al final de la temporada del cultivo de cobertura. Además, después de la finalización de los cultivos de cobertura, los residuos del trébol de olor amarillo habían suprimido las malas hierbas a niveles de un 75-97% más bajos que en los sistemas en barbecho sin trébol de color amarillo.[15]​.

Exploitation of allelopathic phenomena

In addition to weed suppression based on physical competition, some cover crops are known to suppress weeds through allelopathy[16]. This occurs when certain biochemical compounds in cover crops are degraded and become toxic or inhibit the germination of seeds of other plant species. There are some well-known examples of cover crops that are allelopathic such as Secale cereale (rye), Vicia villosa (downy vetch), Trifolium pratense (red clover), Sorghum bicolor (sorghum, Sudan grass), and species of the Brassicaceae family, particularly mustard[17]. In one study, residues from rye cover crops were considered to contribute 80% to 95% of weed control early in the broadleaf season, when it was used as fertilizer in the production of different commercial crops, such as soybeans, tobacco, corn and sunflower.[18]​.

A 2010 study published by the Agricultural Research Service (ARS) examined how rye (planting density and planting patterns) affected crop production. Results show that planting more pounds per hectare of rye increased the production of this cover crop, as well as decreased the number of weeds. The same thing happened when scientists tested seeding rates in legumes and oats; A greater density of seeds sown per hectare decreases the amount of weeds and increases both legume production and oat production. Planting patterns, which consisted of either traditional row or grid patterns, did not appear to have a significant impact on cover crop production or on weed emergence in cover crops. ARS scientists concluded that increasing seeding rates could be an effective method of weed control.[19]​.

In the same way that the allelopathic properties of cover crops can eliminate weeds, it can also break disease cycles and reduce populations of bacterial and fungal diseases[20]​ and parasitic nematodes[21]​ In species of the Brassicaceae family, such as mustards, it has been widely demonstrated that they can suppress fungal populations through the release of naturally occurring toxic chemicals, in the degradation processes of glucosinolade compounds in their tissues. plant cells.[22]​.

Some cover crops are used as so-called "trap crops", to attract pests away from the valuable crop and move the pest to what it sees as more favorable habitat. Trap crop areas can be established within crops, within farms, or within landscapes. In many cases the trap crop is grown in the same season as the food crop of commercial interest. The limited area occupied by these trap crops can be treated with a pest pesticide since they are attracted to the trap and are attracted in sufficient numbers to reduce the total pest populations. In some organic systems, farmers consider the trap crop unit as an instrument based on generating a "big vacuum" in order to physically drag plant pests out of the field (Kuepper and Thomas 2002). This system has been recommended for use as an aid to control lygus bugs in organic strawberry production.[24]​.

Other cover crops are used to attract natural predators of pests by providing elements of their habitat. This is a form of biological control known as habitat augmentation and was achieved with the use of cover crops[25]. Conclusions on the relationship between the presence of cover crops and predator/pest population dynamics have been mixed and point towards the need for more detailed information on specific types of cover crops and management practices to best complement a given strategy (Integrated Pest Management). For example, the predatory mite Euseius tularensis (Congdon) is known to help control pest citrus thrips in orchards in central California. Researchers found that planting several legume cover crops (such as bell bean, woollypod pea, New Zealand white clover, and Austrian winter pea) provided sufficient pollen as a food source and caused a seasonal increase in Congdon populations, which combined with appropriate timing could introduce sufficient predatory pressure to reduce citrus thrips pest populations.[26]​.

Although cover crops are typically used to serve one of the purposes discussed above, they often simultaneously improve habitat for farm wildlife. The use of cover crops adds at least one more dimension to plant diversity than a cash crop rotation. Since the cover crop is usually not a value crop, its management is usually less intense, providing a "soft" window of human influence on the farm. It is considered relatively "hands-free" management; along with the increase in on-farm heterogeneity created by the establishment of cover crops, increases the likelihood that a more complex trophic structure will develop to support an increased level of wildlife diversity[27].

In one study, researchers compared arthropod and songbird species composition in the field between conventional and cover cropping in cotton fields in the southern United States. Cover crops for cotton fields were made using clover, which was allowed to grow in the middle of cotton rows throughout the cotton season, early in the crop (stripcover crop). During the migration and breeding season, they found that songbird densities were 7.20 times higher in cotton fields covered by clover crops than in conventional cotton fields. Arthropod abundance and biomass was also higher in fields with cover clover during much of the songbird breeding season, which was attributed to greater nectar supply from clover flowers. The clover cover improved the habitat of songbirds by providing shelter and nesting sites and the food source increased due to increased arthropod populations.[28]​.

Creamer, *, NG, MA Bennett, BR Stinner, Cardina J., and Regnier EE. 1996. Weed suppression mechanisms in production-based cover cropping systems. HortScience 31:410-413.