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Critical periods of weed control in
Critical periods of weed control in naturally green colored cotton BRS Verde
Gossypium hirsutum; Weed community; Fiber; Textile
About 4500 years ago, naturally colored cotton was used by the Incas, Aztecs, and other old civilizations of America, Asia, Africa, and Australia (Beltrão and Carvalho, 2004). In Australia, among 50 wild cotton species found, 10 were naturally colored fibers. However, the textile industry historically opted to use white fibers because they would be easier to dye in order to obtain fabrics with any color (Beltrão and Carvalho, 2004). That option explains why naturally pigmented fiber cotton was neglected for some centuries (Hua et al., 2007). Cotton plants with colored fiber were considered a contaminant in several countries because they could cross and bring some color to white varieties (Beltrão, 1999).
However, cultivation of naturally colored cotton as a commercial crop is increasing due to its reduced environmental impact, as the dyeing process used for white fibers causes a significant negative environmental impact (Dutt et al., 2004 and Hua et al., 2007). Yields and fiber quality of naturally colored cotton varieties, however, are not as good as the white cotton ones, mostly because the traditional white cotton has been improved and studied for centuries, while studies about colored fibers are recent (Dutt et al., 2004 and Pan et al., 2010). Technology for cultivation of colored varieties needs to be developed, and information on weed management is one important piece for this agricultural system.
The cultivar BRS Verde, with naturally green colored fibers has an short cycle (120–140 days) and was originated from the cross of the green fiber Arkansas Green (introduced from the U.S.A.) and the white fiber cultivar CNPA 7H adapted to Brazil (Beltrão and Carvalho, 2004 and Embrapa, 2006).
The critical period of weed control (CPWC) is the period during the crop cycle in which weeds must be controlled in order to avoid reduction in crop yield. It is important for developing integrated weed management systems, which can minimize the use of herbicides without reduction in crop yields (Swanton et al., 2010). The CPWC starts in the critical timing of weed removal (CTWR), corresponding to the maximum amount of time that early-season weed competition can be tolerated by the crop before it suffers yield reduction, and it ends in the critical weed-free period (CWFP), corresponding to the minimum weed-free period required to prevent yield reductions (Knezevic et al., 2002 and Tingle et al., 2003). Theoretically, crop yield is only marginally influenced if the weed control occurs before or after the CPWC.
According to Melhorança and Beltrão (2001), the CPWC in cotton runs from 15 to 56 days after emergence (DAE); Salgado et al. (2002), studying the cultivar Delta Opal (late cycle) and considering yield reduction of 5%, found a CPWC of 8–66 DAE. Webster et al. (2009) studied cotton competing with one specific weed (Commelina benghalensis) and found that CPWC varied greatly depending on the planting date and yearly climatic variation: in the regular planting date (June), the CPWC was between 17 and 73 days after planting (DAP), but in early planting date (May), it was early and longer in a year (11–75 DAP) and later and shorter in another (39–57 DAP). Tingle et al. (2003), also studying the competition of cotton with smellmelon (Cucumis melo), found CPWC between 17 and 42 DAP. The critical period of competition for a naturally brown fiber cotton cv. BRS 200 organically managed in the Brazilian semi-arid climate was found to be as short as 9 days, starting at 38 days after sowing ( Silva, 2003).
This study was conducted in order to determine the critical period of weed control and to characterize the weed community in a field of green fiber cotton cv. BRS Verde in Brazil (State of Ceará). Weed community composition was analyzed through the phytosociological indexes of relative dominance and relative importance.
2.1. Field experiment
The experiment was conducted in the year 2007 in the experimental farm of Embrapa Algodão (Missão Velha, Ceará, Brazil), 7°42′S and 39°24′W, 360 m above sea level. The chemical analysis of the sandy-clay soil is presented in Table 1. The climate is hot tropical moderate semi-arid, with average annual rains of 987.3 mm. During the experiment, total rains were 322 mm, and average temperature was 26.4 °C (average of minimum: 25.2 °C, average of maximum: 28.9 °C).
The cultivar BRS Verde (green fibers) was planted with 1.0 m between rows and 0.2 m between plants in the row. Before sowing, the soil was submitted to plowing and harrowing. The experiment was planted in 8/March/2007. Management practices followed recommendations for cotton crop in that region (Beltrão, 1999). Integrated Pests Management was considered before any pest control action. The harvest was made by hand, starting at 120 DAE when 70% of cotton bolls were open and repeated later (as necessary) for the latest opened bolls. Yields are presented as lint + seed (before ginning).
2.2. Weed sampling
Weeds were sampled in the end of the weed control period of each treatment. Quadrats with internal area of 0.25 m2 were randomly placed four times in the plot, and every weed was cut close to the ground, separated by species, counted, oven dried (70 °C), and weighed. These data were used for calculation of relative importance and relative dominance, according to the methodology proposed by Mueller-Dombois and Ellemberg (1974). Relative importance consists of the frequency of each species compared to other species in the weed community; relative dominance consists of the dry mass of each species compared to the biomass of the whole weed community.
2.3. Experimental design and statistical procedure
Each experimental plot was 6.0 m long with 4 rows. Data was collected in the two central lines, excluding 0.5 m in extremities. A randomized block design with four replications was adopted. Ten treatments were arranged in a factorial distribution of five periods of competition (0, 20, 40, 60, and 80 DAE) and two weed groups (weedy and weed-free). In the first group, plants were kept under weed interference up to the periods of 0, 20, 40, 60, and 80 DAE, and thereafter weeds were eliminated; in the second group, plants were kept free of weed competition up to the periods of 0, 20, 40, 60, and 80 DAE, and thereafter weeds were allowed to grow.
Data on cotton yields and weed interference periods were submitted to a regression analysis, fitting one curve for weed-free periods and another for weedy periods, using the sigmoid Boltzmann model, as follow:
where Y = seed cotton yield; A1 = maximum yield (from weed-free plots); A2 = minimum yield (from weedy plots during all of the cycle); x = period of time in the treatment kept the longest weedy or weed free; x0 = weedy period of time in which cotton yield had the average value between the highest and the lowest yield; dx = calculated value to fit the equation corresponding to the tangent of the curve in the point x0.
Gossypium hirsutum; Weed community; Fiber; Textile
About 4500 years ago, naturally colored cotton was used by the Incas, Aztecs, and other old civilizations of America, Asia, Africa, and Australia (Beltrão and Carvalho, 2004). In Australia, among 50 wild cotton species found, 10 were naturally colored fibers. However, the textile industry historically opted to use white fibers because they would be easier to dye in order to obtain fabrics with any color (Beltrão and Carvalho, 2004). That option explains why naturally pigmented fiber cotton was neglected for some centuries (Hua et al., 2007). Cotton plants with colored fiber were considered a contaminant in several countries because they could cross and bring some color to white varieties (Beltrão, 1999).
However, cultivation of naturally colored cotton as a commercial crop is increasing due to its reduced environmental impact, as the dyeing process used for white fibers causes a significant negative environmental impact (Dutt et al., 2004 and Hua et al., 2007). Yields and fiber quality of naturally colored cotton varieties, however, are not as good as the white cotton ones, mostly because the traditional white cotton has been improved and studied for centuries, while studies about colored fibers are recent (Dutt et al., 2004 and Pan et al., 2010). Technology for cultivation of colored varieties needs to be developed, and information on weed management is one important piece for this agricultural system.
The cultivar BRS Verde, with naturally green colored fibers has an short cycle (120–140 days) and was originated from the cross of the green fiber Arkansas Green (introduced from the U.S.A.) and the white fiber cultivar CNPA 7H adapted to Brazil (Beltrão and Carvalho, 2004 and Embrapa, 2006).
The critical period of weed control (CPWC) is the period during the crop cycle in which weeds must be controlled in order to avoid reduction in crop yield. It is important for developing integrated weed management systems, which can minimize the use of herbicides without reduction in crop yields (Swanton et al., 2010). The CPWC starts in the critical timing of weed removal (CTWR), corresponding to the maximum amount of time that early-season weed competition can be tolerated by the crop before it suffers yield reduction, and it ends in the critical weed-free period (CWFP), corresponding to the minimum weed-free period required to prevent yield reductions (Knezevic et al., 2002 and Tingle et al., 2003). Theoretically, crop yield is only marginally influenced if the weed control occurs before or after the CPWC.
According to Melhorança and Beltrão (2001), the CPWC in cotton runs from 15 to 56 days after emergence (DAE); Salgado et al. (2002), studying the cultivar Delta Opal (late cycle) and considering yield reduction of 5%, found a CPWC of 8–66 DAE. Webster et al. (2009) studied cotton competing with one specific weed (Commelina benghalensis) and found that CPWC varied greatly depending on the planting date and yearly climatic variation: in the regular planting date (June), the CPWC was between 17 and 73 days after planting (DAP), but in early planting date (May), it was early and longer in a year (11–75 DAP) and later and shorter in another (39–57 DAP). Tingle et al. (2003), also studying the competition of cotton with smellmelon (Cucumis melo), found CPWC between 17 and 42 DAP. The critical period of competition for a naturally brown fiber cotton cv. BRS 200 organically managed in the Brazilian semi-arid climate was found to be as short as 9 days, starting at 38 days after sowing ( Silva, 2003).
This study was conducted in order to determine the critical period of weed control and to characterize the weed community in a field of green fiber cotton cv. BRS Verde in Brazil (State of Ceará). Weed community composition was analyzed through the phytosociological indexes of relative dominance and relative importance.
2.1. Field experiment
The experiment was conducted in the year 2007 in the experimental farm of Embrapa Algodão (Missão Velha, Ceará, Brazil), 7°42′S and 39°24′W, 360 m above sea level. The chemical analysis of the sandy-clay soil is presented in Table 1. The climate is hot tropical moderate semi-arid, with average annual rains of 987.3 mm. During the experiment, total rains were 322 mm, and average temperature was 26.4 °C (average of minimum: 25.2 °C, average of maximum: 28.9 °C).
The cultivar BRS Verde (green fibers) was planted with 1.0 m between rows and 0.2 m between plants in the row. Before sowing, the soil was submitted to plowing and harrowing. The experiment was planted in 8/March/2007. Management practices followed recommendations for cotton crop in that region (Beltrão, 1999). Integrated Pests Management was considered before any pest control action. The harvest was made by hand, starting at 120 DAE when 70% of cotton bolls were open and repeated later (as necessary) for the latest opened bolls. Yields are presented as lint + seed (before ginning).
2.2. Weed sampling
Weeds were sampled in the end of the weed control period of each treatment. Quadrats with internal area of 0.25 m2 were randomly placed four times in the plot, and every weed was cut close to the ground, separated by species, counted, oven dried (70 °C), and weighed. These data were used for calculation of relative importance and relative dominance, according to the methodology proposed by Mueller-Dombois and Ellemberg (1974). Relative importance consists of the frequency of each species compared to other species in the weed community; relative dominance consists of the dry mass of each species compared to the biomass of the whole weed community.
2.3. Experimental design and statistical procedure
Each experimental plot was 6.0 m long with 4 rows. Data was collected in the two central lines, excluding 0.5 m in extremities. A randomized block design with four replications was adopted. Ten treatments were arranged in a factorial distribution of five periods of competition (0, 20, 40, 60, and 80 DAE) and two weed groups (weedy and weed-free). In the first group, plants were kept under weed interference up to the periods of 0, 20, 40, 60, and 80 DAE, and thereafter weeds were eliminated; in the second group, plants were kept free of weed competition up to the periods of 0, 20, 40, 60, and 80 DAE, and thereafter weeds were allowed to grow.
Data on cotton yields and weed interference periods were submitted to a regression analysis, fitting one curve for weed-free periods and another for weedy periods, using the sigmoid Boltzmann model, as follow:
where Y = seed cotton yield; A1 = maximum yield (from weed-free plots); A2 = minimum yield (from weedy plots during all of the cycle); x = period of time in the treatment kept the longest weedy or weed free; x0 = weedy period of time in which cotton yield had the average value between the highest and the lowest yield; dx = calculated value to fit the equation corresponding to the tangent of the curve in the point x0.
0/5000
Critical periods of weed control in naturally green colored cotton BRS VerdeGossypium hirsutum; Weed community; Fiber; TextileAbout 4500 years ago, naturally colored cotton was used by the Incas, Aztecs, and other old civilizations of America, Asia, Africa, and Australia (Beltrão and Carvalho, 2004). In Australia, among 50 wild cotton species found, 10 were naturally colored fibers. However, the textile industry historically opted to use white fibers because they would be easier to dye in order to obtain fabrics with any color (Beltrão and Carvalho, 2004). That option explains why naturally pigmented fiber cotton was neglected for some centuries (Hua et al., 2007). Cotton plants with colored fiber were considered a contaminant in several countries because they could cross and bring some color to white varieties (Beltrão, 1999). However, cultivation of naturally colored cotton as a commercial crop is increasing due to its reduced environmental impact, as the dyeing process used for white fibers causes a significant negative environmental impact (Dutt et al., 2004 and Hua et al., 2007). Yields and fiber quality of naturally colored cotton varieties, however, are not as good as the white cotton ones, mostly because the traditional white cotton has been improved and studied for centuries, while studies about colored fibers are recent (Dutt et al., 2004 and Pan et al., 2010). Technology for cultivation of colored varieties needs to be developed, and information on weed management is one important piece for this agricultural system. The cultivar BRS Verde, with naturally green colored fibers has an short cycle (120–140 days) and was originated from the cross of the green fiber Arkansas Green (introduced from the U.S.A.) and the white fiber cultivar CNPA 7H adapted to Brazil (Beltrão and Carvalho, 2004 and Embrapa, 2006). The critical period of weed control (CPWC) is the period during the crop cycle in which weeds must be controlled in order to avoid reduction in crop yield. It is important for developing integrated weed management systems, which can minimize the use of herbicides without reduction in crop yields (Swanton et al., 2010). The CPWC starts in the critical timing of weed removal (CTWR), corresponding to the maximum amount of time that early-season weed competition can be tolerated by the crop before it suffers yield reduction, and it ends in the critical weed-free period (CWFP), corresponding to the minimum weed-free period required to prevent yield reductions (Knezevic et al., 2002 and Tingle et al., 2003). Theoretically, crop yield is only marginally influenced if the weed control occurs before or after the CPWC. According to Melhorança and Beltrão (2001), the CPWC in cotton runs from 15 to 56 days after emergence (DAE); Salgado et al. (2002), studying the cultivar Delta Opal (late cycle) and considering yield reduction of 5%, found a CPWC of 8–66 DAE. Webster et al. (2009) studied cotton competing with one specific weed (Commelina benghalensis) and found that CPWC varied greatly depending on the planting date and yearly climatic variation: in the regular planting date (June), the CPWC was between 17 and 73 days after planting (DAP), but in early planting date (May), it was early and longer in a year (11–75 DAP) and later and shorter in another (39–57 DAP). Tingle et al. (2003), also studying the competition of cotton with smellmelon (Cucumis melo), found CPWC between 17 and 42 DAP. The critical period of competition for a naturally brown fiber cotton cv. BRS 200 organically managed in the Brazilian semi-arid climate was found to be as short as 9 days, starting at 38 days after sowing ( Silva, 2003). This study was conducted in order to determine the critical period of weed control and to characterize the weed community in a field of green fiber cotton cv. BRS Verde in Brazil (State of Ceará). Weed community composition was analyzed through the phytosociological indexes of relative dominance and relative importance.
2.1. Field experiment
The experiment was conducted in the year 2007 in the experimental farm of Embrapa Algodão (Missão Velha, Ceará, Brazil), 7°42′S and 39°24′W, 360 m above sea level. The chemical analysis of the sandy-clay soil is presented in Table 1. The climate is hot tropical moderate semi-arid, with average annual rains of 987.3 mm. During the experiment, total rains were 322 mm, and average temperature was 26.4 °C (average of minimum: 25.2 °C, average of maximum: 28.9 °C).
The cultivar BRS Verde (green fibers) was planted with 1.0 m between rows and 0.2 m between plants in the row. Before sowing, the soil was submitted to plowing and harrowing. The experiment was planted in 8/March/2007. Management practices followed recommendations for cotton crop in that region (Beltrão, 1999). Integrated Pests Management was considered before any pest control action. The harvest was made by hand, starting at 120 DAE when 70% of cotton bolls were open and repeated later (as necessary) for the latest opened bolls. Yields are presented as lint + seed (before ginning).
2.2. Weed sampling
Weeds were sampled in the end of the weed control period of each treatment. Quadrats with internal area of 0.25 m2 were randomly placed four times in the plot, and every weed was cut close to the ground, separated by species, counted, oven dried (70 °C), and weighed. These data were used for calculation of relative importance and relative dominance, according to the methodology proposed by Mueller-Dombois and Ellemberg (1974). Relative importance consists of the frequency of each species compared to other species in the weed community; relative dominance consists of the dry mass of each species compared to the biomass of the whole weed community.
2.3. Experimental design and statistical procedure
Each experimental plot was 6.0 m long with 4 rows. Data was collected in the two central lines, excluding 0.5 m in extremities. A randomized block design with four replications was adopted. Ten treatments were arranged in a factorial distribution of five periods of competition (0, 20, 40, 60, and 80 DAE) and two weed groups (weedy and weed-free). In the first group, plants were kept under weed interference up to the periods of 0, 20, 40, 60, and 80 DAE, and thereafter weeds were eliminated; in the second group, plants were kept free of weed competition up to the periods of 0, 20, 40, 60, and 80 DAE, and thereafter weeds were allowed to grow.
Data on cotton yields and weed interference periods were submitted to a regression analysis, fitting one curve for weed-free periods and another for weedy periods, using the sigmoid Boltzmann model, as follow:
where Y = seed cotton yield; A1 = maximum yield (from weed-free plots); A2 = minimum yield (from weedy plots during all of the cycle); x = period of time in the treatment kept the longest weedy or weed free; x0 = weedy period of time in which cotton yield had the average value between the highest and the lowest yield; dx = calculated value to fit the equation corresponding to the tangent of the curve in the point x0.
2.1. Field experiment
The experiment was conducted in the year 2007 in the experimental farm of Embrapa Algodão (Missão Velha, Ceará, Brazil), 7°42′S and 39°24′W, 360 m above sea level. The chemical analysis of the sandy-clay soil is presented in Table 1. The climate is hot tropical moderate semi-arid, with average annual rains of 987.3 mm. During the experiment, total rains were 322 mm, and average temperature was 26.4 °C (average of minimum: 25.2 °C, average of maximum: 28.9 °C).
The cultivar BRS Verde (green fibers) was planted with 1.0 m between rows and 0.2 m between plants in the row. Before sowing, the soil was submitted to plowing and harrowing. The experiment was planted in 8/March/2007. Management practices followed recommendations for cotton crop in that region (Beltrão, 1999). Integrated Pests Management was considered before any pest control action. The harvest was made by hand, starting at 120 DAE when 70% of cotton bolls were open and repeated later (as necessary) for the latest opened bolls. Yields are presented as lint + seed (before ginning).
2.2. Weed sampling
Weeds were sampled in the end of the weed control period of each treatment. Quadrats with internal area of 0.25 m2 were randomly placed four times in the plot, and every weed was cut close to the ground, separated by species, counted, oven dried (70 °C), and weighed. These data were used for calculation of relative importance and relative dominance, according to the methodology proposed by Mueller-Dombois and Ellemberg (1974). Relative importance consists of the frequency of each species compared to other species in the weed community; relative dominance consists of the dry mass of each species compared to the biomass of the whole weed community.
2.3. Experimental design and statistical procedure
Each experimental plot was 6.0 m long with 4 rows. Data was collected in the two central lines, excluding 0.5 m in extremities. A randomized block design with four replications was adopted. Ten treatments were arranged in a factorial distribution of five periods of competition (0, 20, 40, 60, and 80 DAE) and two weed groups (weedy and weed-free). In the first group, plants were kept under weed interference up to the periods of 0, 20, 40, 60, and 80 DAE, and thereafter weeds were eliminated; in the second group, plants were kept free of weed competition up to the periods of 0, 20, 40, 60, and 80 DAE, and thereafter weeds were allowed to grow.
Data on cotton yields and weed interference periods were submitted to a regression analysis, fitting one curve for weed-free periods and another for weedy periods, using the sigmoid Boltzmann model, as follow:
where Y = seed cotton yield; A1 = maximum yield (from weed-free plots); A2 = minimum yield (from weedy plots during all of the cycle); x = period of time in the treatment kept the longest weedy or weed free; x0 = weedy period of time in which cotton yield had the average value between the highest and the lowest yield; dx = calculated value to fit the equation corresponding to the tangent of the curve in the point x0.
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Critical periods of weed control in naturally green colored cotton BRS Verde
Gossypium hirsutum; Weed community; Fiber; Textile
About 4500 years ago, naturally colored cotton was used by the Incas, Aztecs, and other old civilizations of America, Asia, Africa, and Australia (Beltrão and Carvalho, 2004). In Australia, among 50 wild cotton species found, 10 were naturally colored fibers. However, the textile industry historically opted to use white fibers because they would be easier to dye in order to obtain fabrics with any color (Beltrão and Carvalho, 2004). That option explains why naturally pigmented fiber cotton was neglected for some centuries (Hua et al., 2007). Cotton plants with colored fiber were considered a contaminant in several countries because they could cross and bring some color to white varieties (Beltrão, 1999).
However, cultivation of naturally colored cotton as a commercial crop is increasing due to its reduced environmental impact, as the dyeing process used for white fibers causes a significant negative environmental impact (Dutt et al., 2004 and Hua et al., 2007). Yields and fiber quality of naturally colored cotton varieties, however, are not as good as the white cotton ones, mostly because the traditional white cotton has been improved and studied for centuries, while studies about colored fibers are recent (Dutt et al., 2004 and Pan et al., 2010). Technology for cultivation of colored varieties needs to be developed, and information on weed management is one important piece for this agricultural system.
The cultivar BRS Verde, with naturally green colored fibers has an short cycle (120–140 days) and was originated from the cross of the green fiber Arkansas Green (introduced from the U.S.A.) and the white fiber cultivar CNPA 7H adapted to Brazil (Beltrão and Carvalho, 2004 and Embrapa, 2006).
The critical period of weed control (CPWC) is the period during the crop cycle in which weeds must be controlled in order to avoid reduction in crop yield. It is important for developing integrated weed management systems, which can minimize the use of herbicides without reduction in crop yields (Swanton et al., 2010). The CPWC starts in the critical timing of weed removal (CTWR), corresponding to the maximum amount of time that early-season weed competition can be tolerated by the crop before it suffers yield reduction, and it ends in the critical weed-free period (CWFP), corresponding to the minimum weed-free period required to prevent yield reductions (Knezevic et al., 2002 and Tingle et al., 2003). Theoretically, crop yield is only marginally influenced if the weed control occurs before or after the CPWC.
According to Melhorança and Beltrão (2001), the CPWC in cotton runs from 15 to 56 days after emergence (DAE); Salgado et al. (2002), studying the cultivar Delta Opal (late cycle) and considering yield reduction of 5%, found a CPWC of 8–66 DAE. Webster et al. (2009) studied cotton competing with one specific weed (Commelina benghalensis) and found that CPWC varied greatly depending on the planting date and yearly climatic variation: in the regular planting date (June), the CPWC was between 17 and 73 days after planting (DAP), but in early planting date (May), it was early and longer in a year (11–75 DAP) and later and shorter in another (39–57 DAP). Tingle et al. (2003), also studying the competition of cotton with smellmelon (Cucumis melo), found CPWC between 17 and 42 DAP. The critical period of competition for a naturally brown fiber cotton cv. BRS 200 organically managed in the Brazilian semi-arid climate was found to be as short as 9 days, starting at 38 days after sowing ( Silva, 2003).
This study was conducted in order to determine the critical period of weed control and to characterize the weed community in a field of green fiber cotton cv. BRS Verde in Brazil (State of Ceará). Weed community composition was analyzed through the phytosociological indexes of relative dominance and relative importance.
2.1. Field experiment
The experiment was conducted in the year 2007 in the experimental farm of Embrapa Algodão (Missão Velha, Ceará, Brazil), 7°42′S and 39°24′W, 360 m above sea level. The chemical analysis of the sandy-clay soil is presented in Table 1. The climate is hot tropical moderate semi-arid, with average annual rains of 987.3 mm. During the experiment, total rains were 322 mm, and average temperature was 26.4 °C (average of minimum: 25.2 °C, average of maximum: 28.9 °C).
The cultivar BRS Verde (green fibers) was planted with 1.0 m between rows and 0.2 m between plants in the row. Before sowing, the soil was submitted to plowing and harrowing. The experiment was planted in 8/March/2007. Management practices followed recommendations for cotton crop in that region (Beltrão, 1999). Integrated Pests Management was considered before any pest control action. The harvest was made by hand, starting at 120 DAE when 70% of cotton bolls were open and repeated later (as necessary) for the latest opened bolls. Yields are presented as lint + seed (before ginning).
2.2. Weed sampling
Weeds were sampled in the end of the weed control period of each treatment. Quadrats with internal area of 0.25 m2 were randomly placed four times in the plot, and every weed was cut close to the ground, separated by species, counted, oven dried (70 °C), and weighed. These data were used for calculation of relative importance and relative dominance, according to the methodology proposed by Mueller-Dombois and Ellemberg (1974). Relative importance consists of the frequency of each species compared to other species in the weed community; relative dominance consists of the dry mass of each species compared to the biomass of the whole weed community.
2.3. Experimental design and statistical procedure
Each experimental plot was 6.0 m long with 4 rows. Data was collected in the two central lines, excluding 0.5 m in extremities. A randomized block design with four replications was adopted. Ten treatments were arranged in a factorial distribution of five periods of competition (0, 20, 40, 60, and 80 DAE) and two weed groups (weedy and weed-free). In the first group, plants were kept under weed interference up to the periods of 0, 20, 40, 60, and 80 DAE, and thereafter weeds were eliminated; in the second group, plants were kept free of weed competition up to the periods of 0, 20, 40, 60, and 80 DAE, and thereafter weeds were allowed to grow.
Data on cotton yields and weed interference periods were submitted to a regression analysis, fitting one curve for weed-free periods and another for weedy periods, using the sigmoid Boltzmann model, as follow:
where Y = seed cotton yield; A1 = maximum yield (from weed-free plots); A2 = minimum yield (from weedy plots during all of the cycle); x = period of time in the treatment kept the longest weedy or weed free; x0 = weedy period of time in which cotton yield had the average value between the highest and the lowest yield; dx = calculated value to fit the equation corresponding to the tangent of the curve in the point x0.
Gossypium hirsutum; Weed community; Fiber; Textile
About 4500 years ago, naturally colored cotton was used by the Incas, Aztecs, and other old civilizations of America, Asia, Africa, and Australia (Beltrão and Carvalho, 2004). In Australia, among 50 wild cotton species found, 10 were naturally colored fibers. However, the textile industry historically opted to use white fibers because they would be easier to dye in order to obtain fabrics with any color (Beltrão and Carvalho, 2004). That option explains why naturally pigmented fiber cotton was neglected for some centuries (Hua et al., 2007). Cotton plants with colored fiber were considered a contaminant in several countries because they could cross and bring some color to white varieties (Beltrão, 1999).
However, cultivation of naturally colored cotton as a commercial crop is increasing due to its reduced environmental impact, as the dyeing process used for white fibers causes a significant negative environmental impact (Dutt et al., 2004 and Hua et al., 2007). Yields and fiber quality of naturally colored cotton varieties, however, are not as good as the white cotton ones, mostly because the traditional white cotton has been improved and studied for centuries, while studies about colored fibers are recent (Dutt et al., 2004 and Pan et al., 2010). Technology for cultivation of colored varieties needs to be developed, and information on weed management is one important piece for this agricultural system.
The cultivar BRS Verde, with naturally green colored fibers has an short cycle (120–140 days) and was originated from the cross of the green fiber Arkansas Green (introduced from the U.S.A.) and the white fiber cultivar CNPA 7H adapted to Brazil (Beltrão and Carvalho, 2004 and Embrapa, 2006).
The critical period of weed control (CPWC) is the period during the crop cycle in which weeds must be controlled in order to avoid reduction in crop yield. It is important for developing integrated weed management systems, which can minimize the use of herbicides without reduction in crop yields (Swanton et al., 2010). The CPWC starts in the critical timing of weed removal (CTWR), corresponding to the maximum amount of time that early-season weed competition can be tolerated by the crop before it suffers yield reduction, and it ends in the critical weed-free period (CWFP), corresponding to the minimum weed-free period required to prevent yield reductions (Knezevic et al., 2002 and Tingle et al., 2003). Theoretically, crop yield is only marginally influenced if the weed control occurs before or after the CPWC.
According to Melhorança and Beltrão (2001), the CPWC in cotton runs from 15 to 56 days after emergence (DAE); Salgado et al. (2002), studying the cultivar Delta Opal (late cycle) and considering yield reduction of 5%, found a CPWC of 8–66 DAE. Webster et al. (2009) studied cotton competing with one specific weed (Commelina benghalensis) and found that CPWC varied greatly depending on the planting date and yearly climatic variation: in the regular planting date (June), the CPWC was between 17 and 73 days after planting (DAP), but in early planting date (May), it was early and longer in a year (11–75 DAP) and later and shorter in another (39–57 DAP). Tingle et al. (2003), also studying the competition of cotton with smellmelon (Cucumis melo), found CPWC between 17 and 42 DAP. The critical period of competition for a naturally brown fiber cotton cv. BRS 200 organically managed in the Brazilian semi-arid climate was found to be as short as 9 days, starting at 38 days after sowing ( Silva, 2003).
This study was conducted in order to determine the critical period of weed control and to characterize the weed community in a field of green fiber cotton cv. BRS Verde in Brazil (State of Ceará). Weed community composition was analyzed through the phytosociological indexes of relative dominance and relative importance.
2.1. Field experiment
The experiment was conducted in the year 2007 in the experimental farm of Embrapa Algodão (Missão Velha, Ceará, Brazil), 7°42′S and 39°24′W, 360 m above sea level. The chemical analysis of the sandy-clay soil is presented in Table 1. The climate is hot tropical moderate semi-arid, with average annual rains of 987.3 mm. During the experiment, total rains were 322 mm, and average temperature was 26.4 °C (average of minimum: 25.2 °C, average of maximum: 28.9 °C).
The cultivar BRS Verde (green fibers) was planted with 1.0 m between rows and 0.2 m between plants in the row. Before sowing, the soil was submitted to plowing and harrowing. The experiment was planted in 8/March/2007. Management practices followed recommendations for cotton crop in that region (Beltrão, 1999). Integrated Pests Management was considered before any pest control action. The harvest was made by hand, starting at 120 DAE when 70% of cotton bolls were open and repeated later (as necessary) for the latest opened bolls. Yields are presented as lint + seed (before ginning).
2.2. Weed sampling
Weeds were sampled in the end of the weed control period of each treatment. Quadrats with internal area of 0.25 m2 were randomly placed four times in the plot, and every weed was cut close to the ground, separated by species, counted, oven dried (70 °C), and weighed. These data were used for calculation of relative importance and relative dominance, according to the methodology proposed by Mueller-Dombois and Ellemberg (1974). Relative importance consists of the frequency of each species compared to other species in the weed community; relative dominance consists of the dry mass of each species compared to the biomass of the whole weed community.
2.3. Experimental design and statistical procedure
Each experimental plot was 6.0 m long with 4 rows. Data was collected in the two central lines, excluding 0.5 m in extremities. A randomized block design with four replications was adopted. Ten treatments were arranged in a factorial distribution of five periods of competition (0, 20, 40, 60, and 80 DAE) and two weed groups (weedy and weed-free). In the first group, plants were kept under weed interference up to the periods of 0, 20, 40, 60, and 80 DAE, and thereafter weeds were eliminated; in the second group, plants were kept free of weed competition up to the periods of 0, 20, 40, 60, and 80 DAE, and thereafter weeds were allowed to grow.
Data on cotton yields and weed interference periods were submitted to a regression analysis, fitting one curve for weed-free periods and another for weedy periods, using the sigmoid Boltzmann model, as follow:
where Y = seed cotton yield; A1 = maximum yield (from weed-free plots); A2 = minimum yield (from weedy plots during all of the cycle); x = period of time in the treatment kept the longest weedy or weed free; x0 = weedy period of time in which cotton yield had the average value between the highest and the lowest yield; dx = calculated value to fit the equation corresponding to the tangent of the curve in the point x0.
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วิกฤตช่วงการควบคุมวัชพืชในธรรมชาติสีเขียว Brs ผ้าฝ้ายสีเขียว
ฝ้าย ; ชุมชนวัชพืช ; เส้นใย ; สิ่งทอ
ประมาณ 4 , 500 ปีมาแล้ว ธรรมชาติ สีผ้าที่ถูกใช้โดย Incas Aztecs และอารยธรรมเก่าของอเมริกา , เอเชีย , แอฟริกาและออสเตรเลีย ( beltr ฮัล O และ คาร์วัลโญ่ , 2004 ) ในออสเตรเลีย ระหว่าง 50 ชนิดฝ้ายป่าพบ 10 เส้นใยสีธรรมชาติ อย่างไรก็ตามอุตสาหกรรมสิ่งทอในอดีตที่เลือกที่จะใช้เส้นใยสีขาวเพราะพวกเขาจะง่ายต่อการย้อมเพื่อให้ได้ผ้าที่มีสีใด ๆ ( beltr ฮัล O และ คาร์วัลโญ่ , 2004 ) เลือกที่อธิบายว่าทำไมสีธรรมชาติใยฝ้ายถูกทอดทิ้งสำหรับศตวรรษ ( หัว et al . , 2007 )ฝ้ายเป็นพืชที่มีเส้นใยสี ถือว่าเป็นสิ่งปนเปื้อนในหลายประเทศ เพราะพวกเขาสามารถข้ามและนำสีบางพันธุ์ขาว ( beltr ฮัล O , 1999 ) .
แต่การปลูกฝ้ายสีธรรมชาติเป็นพืชพาณิชย์ที่เพิ่มขึ้นเนื่องจากการลดผลกระทบสิ่งแวดล้อมขณะที่กระบวนการย้อมสีที่ใช้เส้นใยสีขาวให้เกิดความสัมพันธ์ทางลบผลกระทบต่อสิ่งแวดล้อม ( ดัต et al . , 2004 และหัว et al . , 2007 ) ผลผลิตและคุณภาพของเส้นใยฝ้ายสีธรรมชาตินานาพันธุ์ แต่จะไม่ดีเท่าที่ผ้าฝ้ายสีขาวเป็นส่วนใหญ่ เพราะผ้าฝ้ายสีขาวแบบดั้งเดิมได้รับการปรับปรุง และศึกษามาหลายศตวรรษในขณะที่การศึกษาเกี่ยวกับเส้นใยสีล่าสุด ( ดัต et al . , 2004 และแพน et al . , 2010 ) เทคโนโลยีการผลิตสีพันธุ์จะต้องมีการพัฒนา และการจัดการสารสนเทศบนวัชพืชเป็นหนึ่งที่สำคัญสำหรับระบบการเกษตรนี้
พันธุ์ Brs เวอร์เดเส้นใยธรรมชาติสีเขียวมีวงจรสั้น ( 120 - 140 วัน ) และมีที่มาจากกางเขนสีเขียวไฟเบอร์อาร์คันซอสีเขียว ( แนะนำจากสหรัฐอเมริกา ) และเส้นใยสีขาว พันธุ์ cnpa 7H ดัดแปลงบราซิล ( beltr ฮัล O และ คาร์วัลโญ่ , 2004 และ embrapa
, 2006 )ช่วงเวลาที่สำคัญของการควบคุมวัชพืช ( cpwc ) คือในช่วงรอบพืชที่วัชพืชจะต้องควบคุมเพื่อหลีกเลี่ยงการลดผลผลิตของพืช มันเป็นสิ่งสำคัญสำหรับการพัฒนาแบบบูรณาการระบบการจัดการวัชพืช ซึ่งสามารถลดการใช้สารเคมีกำจัดวัชพืช โดยการลดผลผลิตพืช ( สวอนตัน et al . , 2010 ) การ cpwc เริ่มในเวลาวิกฤตของการกำจัดวัชพืช ( ctwr )ที่สอดคล้องกับจำนวนเงินสูงสุดของเวลาที่การแข่งขันของวัชพืชต้นฤดูสามารถยอมรับโดยพืชก่อนมันจะทำให้ผลผลิตลดลง และจบลงในช่วงวิกฤตวัชพืชฟรี ( cwfp ) สอดคล้องกับวัชพืชน้อย ฟรี ระยะเวลาป้องกันลดผลผลิต ( knezevic et al . , 2002 และซ่า et al . , 2003 ) . ในทางทฤษฎี
ฝ้าย ; ชุมชนวัชพืช ; เส้นใย ; สิ่งทอ
ประมาณ 4 , 500 ปีมาแล้ว ธรรมชาติ สีผ้าที่ถูกใช้โดย Incas Aztecs และอารยธรรมเก่าของอเมริกา , เอเชีย , แอฟริกาและออสเตรเลีย ( beltr ฮัล O และ คาร์วัลโญ่ , 2004 ) ในออสเตรเลีย ระหว่าง 50 ชนิดฝ้ายป่าพบ 10 เส้นใยสีธรรมชาติ อย่างไรก็ตามอุตสาหกรรมสิ่งทอในอดีตที่เลือกที่จะใช้เส้นใยสีขาวเพราะพวกเขาจะง่ายต่อการย้อมเพื่อให้ได้ผ้าที่มีสีใด ๆ ( beltr ฮัล O และ คาร์วัลโญ่ , 2004 ) เลือกที่อธิบายว่าทำไมสีธรรมชาติใยฝ้ายถูกทอดทิ้งสำหรับศตวรรษ ( หัว et al . , 2007 )ฝ้ายเป็นพืชที่มีเส้นใยสี ถือว่าเป็นสิ่งปนเปื้อนในหลายประเทศ เพราะพวกเขาสามารถข้ามและนำสีบางพันธุ์ขาว ( beltr ฮัล O , 1999 ) .
แต่การปลูกฝ้ายสีธรรมชาติเป็นพืชพาณิชย์ที่เพิ่มขึ้นเนื่องจากการลดผลกระทบสิ่งแวดล้อมขณะที่กระบวนการย้อมสีที่ใช้เส้นใยสีขาวให้เกิดความสัมพันธ์ทางลบผลกระทบต่อสิ่งแวดล้อม ( ดัต et al . , 2004 และหัว et al . , 2007 ) ผลผลิตและคุณภาพของเส้นใยฝ้ายสีธรรมชาตินานาพันธุ์ แต่จะไม่ดีเท่าที่ผ้าฝ้ายสีขาวเป็นส่วนใหญ่ เพราะผ้าฝ้ายสีขาวแบบดั้งเดิมได้รับการปรับปรุง และศึกษามาหลายศตวรรษในขณะที่การศึกษาเกี่ยวกับเส้นใยสีล่าสุด ( ดัต et al . , 2004 และแพน et al . , 2010 ) เทคโนโลยีการผลิตสีพันธุ์จะต้องมีการพัฒนา และการจัดการสารสนเทศบนวัชพืชเป็นหนึ่งที่สำคัญสำหรับระบบการเกษตรนี้
พันธุ์ Brs เวอร์เดเส้นใยธรรมชาติสีเขียวมีวงจรสั้น ( 120 - 140 วัน ) และมีที่มาจากกางเขนสีเขียวไฟเบอร์อาร์คันซอสีเขียว ( แนะนำจากสหรัฐอเมริกา ) และเส้นใยสีขาว พันธุ์ cnpa 7H ดัดแปลงบราซิล ( beltr ฮัล O และ คาร์วัลโญ่ , 2004 และ embrapa
, 2006 )ช่วงเวลาที่สำคัญของการควบคุมวัชพืช ( cpwc ) คือในช่วงรอบพืชที่วัชพืชจะต้องควบคุมเพื่อหลีกเลี่ยงการลดผลผลิตของพืช มันเป็นสิ่งสำคัญสำหรับการพัฒนาแบบบูรณาการระบบการจัดการวัชพืช ซึ่งสามารถลดการใช้สารเคมีกำจัดวัชพืช โดยการลดผลผลิตพืช ( สวอนตัน et al . , 2010 ) การ cpwc เริ่มในเวลาวิกฤตของการกำจัดวัชพืช ( ctwr )ที่สอดคล้องกับจำนวนเงินสูงสุดของเวลาที่การแข่งขันของวัชพืชต้นฤดูสามารถยอมรับโดยพืชก่อนมันจะทำให้ผลผลิตลดลง และจบลงในช่วงวิกฤตวัชพืชฟรี ( cwfp ) สอดคล้องกับวัชพืชน้อย ฟรี ระยะเวลาป้องกันลดผลผลิต ( knezevic et al . , 2002 และซ่า et al . , 2003 ) . ในทางทฤษฎี
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- ฉันกลัวคุณรำคาญ
- Chào con ! Con học cùng trường huỳn
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- Critical periods of weed control in natu
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