تولیدات کتان ارگانیک Organic Cotton Production
Cotton sold as "organic" must be grown according to the federal guidelines for organic crop production. Soil fertility practices that meet organic certification standards typically include crop rotation, cover cropping, animal manure additions, and use of naturally occurring rock powders. Weed management is accomplished by a combination of cultivation, flame weeding, and other cultural practices. A wide variety of insects attack cotton. Management options include trap cropping, strip cropping, and managing border vegetation to encourage high populations of native beneficials. Certain biopesticides using bacteria, viruses, and fungal insect pathogens are available as insect control tools. We discuss specific insect management strategies for cutworm, cotton bollworm, tobacco budworm, pink bollworm, armyworm, loopers, thrips, fleahoppers, lygus bugs, aphids, whitefly, spider mite, and boll weevil. Seedling disease, soil disease, and foliar disease management is also discussed. Pre-harvest defoliation methods that meet organic certification are mostly limited to citric acid, flamers and frost. The publication concludes with sections on marketing organic cotton and the economics and profitability of organic cotton production
Organic cotton has provided significant price premiums for growers willing to meet the many challenges inherent in its production without the aid of conventional pesticides and commercial fertilizers. Growing organic cotton is demanding, but with commitment, experience, and determination, it can be done. This publication covers the major steps in organic production of cotton. It covers soil fertility, weed control options, and alternative pest controls for the many insect problems that plague cotton. Finally, marketing of organic cotton is discussed as well.
Organic cotton acreage declined 18% from 2000 to 2001 in the seven states where most of it is grown. (Marquardt, 2002) Most of this decline came from one large organic cotton farmer in New Mexico who lost it all to drought and withdrew from organic cotton farming altogether. A total of 11,459 acres of either certified organic or transitional organic cotton was produced in 2001. Texas produced the most organic cotton – 8,338 acres – with Arizona and California being the next two highest producing states.
World production of organic cotton amounts to 6,000 tons of fiber annually, or about 0.03% of global cotton production. Turkey produces the most at 29%, with the U.S. being second at 27% and India third at 17%. (Ton, 2002) Demand for organic cotton is highest in Europe (about 3,500 tons or 58% of the total) and the U.S. (about 2000 tons or 33%) (Ton, 2002). Demand in the U.S. increased at an annual rate of 22% between 1996 and 2000. (Organic Trade Association, 2001; cited by Ton, 2002)
نگاهی بر تولیدات ارگانیکOverview of Organic Production
Growing cotton organically entails using cultural practices, natural fertilizers, and biological controls rather than synthetic fertilizers and pesticides. A systems approach to organic production involves the integration of many practices (cover crops, strip cropping, grazing, crop rotation, etc.) into a larger system. Through good soil and biodiversity management, farms can become increasingly self-sufficient in fertility, while pest problems are diminished, and some pests are even controlled outright. A diverse rotation, using legumes and other cover crops, is at the heart of good humus and biodiversity management in an organic cropping system. Cotton, for example, would be but one of several crops an organic farmer would grow. For more complete coverage of general organic crop production, we recommend the ATTRA publication Organic Crop Production Overview.
Throughout this publication, we use examples from conventional farming that illustrate principles relevant to organic cotton production.
In order to market a crop as "organic," a grower must be certified through a third party. This process involves several on-farm inspections and paying a certification fee. More on this subject can be found in the ATTRA publication Organic Farm Certification and The National Organic Program. Applicants for certification are encouraged to become familiar with provisions of the Final Rule posted on the USDA's National Organic Program Web site.
Organic production begins with organically grown seed. If certified organic seed cannot be located, untreated seed may be used as long as it is not derived from genetically modified plants. Most certifiers will accept proof that growers have tried unsuccessfully to buy organic material from at least three different suppliers as evidence of unavailability. Federal organic regulations also address composting and the use of raw manures. These may have implications for cotton production when used as fertilizer.
Mineral nutrition of crops in organic systems comes from proper management of soil organisms that are responsible for releasing nutrients. Rather than feeding plants with fertilizer, organic farmers feed the soil and let the soil organisms feed the plants. The biological activity in the soil can be likened to a digestive process whereby organic food sources are applied to the soil and then digested by soil organisms to release nutrients for the crop. Soil mineral levels are built up through the application of animal manure, compost, soluble rock powders, and deep-rooted cover crops that bring up nutrients from deep within the soil. Plant nutrition is supplemented with foliar fertilization in some situations. Soil fertility, levels of organic matter, minerals, pH, and other measurements can be monitored with regular soil tests. The overall cropping sequence fosters a system in which a previous crop provides fertility benefits to a subsequent crop - such as a legume cover crop providing nitrogen to a following corn crop. Much more detailed soil-fertility information is available in these ATTRA publications: Sustainable Soil Management, Manures for Organic Crop Production, Sustainable Management of Soil-Borne Plant Diseases, and Sources of Organic Fertilizers and Amendments.
Crop rotation is a traditional agricultural practice involving the sequencing of different crops on farm fields; it is considered fundamental to successful organic farming. Rotations are a planned approach to diversifying the whole farm system both economically and biologically, bringing diversity to each field over time.
Rotations can benefit the farm in several ways. Planned rotations are one of the most effective means of breaking many insect pest and plant disease cycles in the soil. Likewise, many problem weeds are suppressed by the nature and timing of different cultural practices. Rotations also affect the fertility of the soil in significant ways. The inclusion of forage legumes, in particular, may serve as the primary source of nitrogen for subsequent crops.
Rotation is an important means of controlling a number of cotton pests, including nematodes. Even basic corn-cotton rotations have been found effective in reducing some species of nematodes. (Anon., 1993) A minimum of two years planted to non-host species is the standard recommendation.
A long-term cotton study at Auburn, Alabama, showed that using winter annual legumes produced cotton yields equivalent to those grown using fertilizer nitrogen. The study found an 11% yield increase for a 2-year cotton-legume-corn rotation compared to continuous cotton grown with legumes each year. Adding conventional nitrogen fertilizer boosted the two-year rotation cotton lint yields in this study another 79 pounds per acre. A three-year rotation of cotton-vetch, corn-rye (fertilized with 60 pounds of conventional N/acre), followed by soybeans, produced about the same cotton yields as the two-year rotation. (Mitchell, 1988)
Cover crops are crops grown to provide soil cover and erosion protection. At the same time, cover cropping may accomplish a number of other objectives, including providing nitrogen to the subsequent cotton crop when tilled into the soil, improving tilth by adding organic matter, and serving as a catch crop when planted to reduce nutrient leaching following a main crop.
Fast, dense-growing cover crops are sometimes used to suppress problem weeds as a "smother crop" or allelopathic cover. The mere presence of most cover crops reduces the competition from weeds. Sometimes crops are no-till planted into such covers. If the cover crop is not killed, it is referred to as a "living mulch." Some cover crops that have been used successfully for weed suppression include small grains (particularly grain rye), several brassica species, hairy vetch, and forage sorghums.
For the humid Cotton Belt, crimson clover, field peas, and hairy vetch are excellent winter cover crops for nitrogen production. Also, a mixture of hairy vetch and rye works well for overall biomass production. When flowering, these provide nectar and pollen as alternate food for beneficials. Hairy vetch is noted for its dense spring cover and weed suppression. Cereal rye provides an enormous amount of biomass to the soil and is known to attract and shelter beneficial insects. It also suppresses germination of small-seeded weeds when left as a mulch cover on the soil surface. Natural allelopathic chemicals leach from the rye residue and inhibit weed germination for about 30-60 days. (Daar, 1986) Weed suppression effectively ends once the rye residue is incorporated. Weed suppression has made rye attractive as a cover crop/mulch in no-till and ridgetill systems. Mowing or a burn-down herbicide is often used in conventional systems to kill the rye cover crop so that no-till plantings of field crops can be established. An effective organic no-till system for cotton has yet to be developed, but early indications are that it will be. For more information on the potential for organic no-till, see the ATTRA publication Pursuing Conservation Tillage Systems for Organic Crop Production, which discusses progress in this area. It is important to mow rye at the flowering stage when the anthers are extended, and pollen falls from the seed heads when shaken. If mowing is done earlier, the rye simply grows back. As allelopathic weed suppression subsides, a no-till cultivator may be used for weed control. This is not a proven system for organic cotton production but only presented here as food for thought about the development of future organic no-till systems.
In addition to producing nitrogen, cover crops often provide excellent habitat for predatory and parasitic insects and spiders. Some good insectary plants often used as cover crops include alfalfa, buckwheat, sweet clover, vetch, red clover, white clover, mustards, and cowpeas. Migration of beneficials from the cover crop to the main crop is sometimes associated with the post-bloom period of the cover crop. In these instances, mowing the cover crops in alternate strips may facilitate their movement, while the remaining strips continue to provide refuge for other beneficial species. Sickle-bar mowers are less disruptive to beneficials than flail mowers, rotary mowers, and mower conditioners with crimpers.
Long-term cotton cover-crop studies have also been done in Louisiana (Millhollon and Melville, 1991) and Arkansas. (Scott, 1990) The Arkansas study spanned 17 years, from 1973 to 1988. Cotton grown after winter cover crops of rye + hairy vetch produced an average of 234 pounds more seed cotton per acre than a control treatment of winter fallow. Cotton following pure vetch showed a 129-pound increase, while yields after rye + crimson clover had a 72-pound yield improvement.
In the long-term Louisiana study, cotton yields declined for the first nine years when cover crops were used, but increased steadily thereafter. In the final four years of the study, cotton yields were 360 pounds-per-acre higher following vetch, compared to fallow + 60 pounds of fertilizer N per acre. Averaged over the 30-year study period, the highest cotton yields followed wheat + 60 pounds of fertilizer N, hairy vetch alone, common vetch alone, or vetch + 40 pounds of N. For additional information on cover crops, see the ATTRA publication Overview of Cover Crops and Green Manures.
Cotton germinates at a soil temperature of 61° F at a depth of about 2 inches. With planting delayed until the soil temperature reaches 66°, the crop emerges rapidly and uniformly and is more vigorous (Head and Williams, 1996), giving it a competitive edge on weeds. The delay in operations also allows additional growth of winter cover crops where used. The downside of this strategy may include risks of increased damage from certain insect pests such as boll weevil, tobacco budworm, and cotton bollworm.
Tillage and cultivation are the traditional means of weed management for organic crops. Some specific tillage guidelines and techniques for weed management include the following:
- Preplant tillage. Where weeds such as johnsongrass are a problem, spring-tooth harrows and similar tools can be effective in catching and pulling the rhizomes to the soil surface, where they desiccate and die. Disking, by contrast, trends to cut and distribute rhizomes and may make the stand even denser.
- Blind tillage. Blind cultivation employs finger weeders, tine harrows, or rotary hoes during the pre-emergent and early post-emergent phase. These implements are run at relatively high speeds (6 mph plus) across the entire field, including directly over, but in the same direction as, the rows. The large-seeded crops like corn, soybeans or sunflower survive with minimal damage, while small-seeded weeds are easily uprooted and killed. Post-emergent blind tillage should be done in the hottest part of the day when crop plants are less turgid, to avoid excessive damage. Rotary hoes, not harrows, should be used if the soil is crusted or too trashy. Seeding rates should be increased 5-10% to compensate for losses in blind cultivation. (Anon., 1991; Doll, 1988)
- Inter-row cultivation. When annual weeds are the concern, cultivation is best kept as shallow as possible to bring as few weed seeds as possible near the soil surface. Where perennial, rhizomaceous weeds are a problem, the shovels set furthest from the crop row may be set deeper on the first cultivation to bring rhizomes to the surface. Tines are more effective than sweeps or duck feet for extracting rhizomes. Later cultivations should have all shovels set shallow to avoid excessive pruning of crop roots. Earliest cultivations should avoid throwing soil toward the crop row. This places new weed seed into the crop row where it may germinate before the crop canopy can shade it out. As the crop canopy develops, soil should be thrown into the crop row to cover emerging weeds.
Inter-row cultivation is best timed to catch weeds as they are germinating - as soon as possible after rain or irrigation, once the soil has dried enough to avoid compaction or surface crusting.
Prior to the 1950s, before modern herbicides became available, flame weeders were used in the U.S. to control weeds in cotton, sugar cane, grain sorghum, corn, and orchards. Interest in flame weeding has resurfaced in recent years with rising herbicide costs. Weeds are most susceptible to flame heat when they are young seedlings 1-2 inches tall or in the 3-5 leaf stage. Risk of damaging the cotton plants diminishes as the cotton grows and forms a bark on the stem. Broadleaf weeds are more susceptible to flaming than grasses. Grass seedlings develop a protective sheath around the growing tip when they are about 1 inch tall. (Drlik, 1994) Consequently, repeated flamings may be necessary on grassy weeds for effective control. Searing the plant is much more successful than charring. Excessive burning of the weeds often stimulates the roots and encourages regrowth, in addition to using more fuel.
Preplant flaming has commonly been referred to as the stale seedbed technique. Prepared seedbeds are flamed after the first flush of weeds has sprouted. Cotton planting follows the flaming without any further disturbance to the seedbed. Assuming adequate moisture and soil temperature, germination should occur within two weeks. Note that a fine-to-slightly-compacted seedbed will germinate a much larger number of weeds.
Costs associated with flame weeding can vary. Flamers have been built for $1,200 for an 8-row unit (Anon., 1993a) and for as much as $1,520 for a 12-row unit. (Houtsma, 1991) Commercial kits cost around $1900 for an eight-row from Thermal Weed Control Systems. These kits do not include hoses, a tank, or a tool bar. It is more cost-effective to pick these items up locally from a gas dealer or salvage operation. An Arkansas cotton grower uses a "water shield" to help protect the cotton plants, but still feels flaming should be delayed until the crop has developed a woody bark on the stem. (Vestal, 1992) Adapting flame technology requires careful implementation. Thermal Weed Control Systems (TWCS), Inc. of Neillsville, Wisconsin, and Flame Engineering, Inc. (FEI), of Lacrosse, Kansas, are two flame-weeding companies that can provide technical assistance and equipment. LP gas usage depends on ground speed but generally runs from 8-10 gallons per acre, according to sources at Thermal Weed Control. For an overview of weed management strategies and options for agronomic crops, please see the ATTRA publication Principles of Sustainable Weed Management for Croplands.
Insect Management Practices
Biological and cultural insect control involves understanding the ecology of the surrounding agricultural systems and the cotton field and making adjustments to production methods that complement the natural system to our benefit. To realize the full benefits of a biological approach we need to move beyond asking how to kill bugs and ask the larger question: Why do we have bugs in our cotton fields in the first place?
In a nutshell, we invite pest problems by planting large expanses of a single susceptible crop. When cotton is the only food available, bugs are going to eat cotton. When we have a more diverse farmscape involving many types of plants and animals, the likelihood of severe pest outbreaks diminishes. For more information on farmscaping, see the ATTRA publication Farmscaping to Enhance Biological Control.
Many types of insects feed on cotton plants and threaten yields. Proper identification of these pests as well as their natural enemies is the first step in successful management of pests. State Extension services typically have Internet-based information that can help with pest and beneficial insect identification. Once the pest is properly identified, a scouting program with regular monitoring can help determine the pest pressures and the densities of beneficial insects. When pest pressures reach the economically-damaging threshold, control actions become necessary. If biological controls are to be used, they must be started before the pests reach critical levels. That is why monitoring is so important.
The use of beneficial insect habitats along crop field borders has shown to increase the presence of beneficial insects. These habitats provide shelter, pollen and nectar sources, and refuge if the fields are treated with a pesticide. In the event you are releasing purchased beneficial insects, these field-edge habitats will encourage the beneficials to remain and continue their lifecycle in that location, helping reduce the pest population. Some pests may also inhabit the field-edge habitats; therefore, these habitats should be monitored along with the crop field. For additional information, see ATTRA publications Biointensive Integrated Pest Management and Farmscaping to Enhance Biological Control.
Though not completely organic, the Sustainable Cotton Project's BASIC program (Biological Agriculture Systems in Cotton) offers California growers strategies designed to save money and reduce the need for pesticides, chemical fertilizers, and water. The BASIC program utilized the following strategies in their 2002 program that showed a 73% reduction in pesticide use over the Fresno County average. (Figure 1) In Figure 1, the "enrolled acreage" had the free monitoring, habitat plantings, and insect releases provided to them. "Basic growers" had implemented the principles on their own fields but without the direct involvement of the basic program staff. Regular IPM, intensive monitoring, beneficials, and beneficial habitat can reduce pesticide use whether you are organic or conventional. For pesticide use questions or analysis questions, contact Max Stevenson at: email@example.com.
Figure 1: Pesticide reductions resulting from the BASIC program in California
1. Intensive Monitoring
Fields enrolled in the program were monitored weekly. Monitoring included an overall picture of the field and the local conditions, the levels of pests and beneficials, farmscape observations, the status of the adjacent beneficial habitat, and any unusual sightings or areas for concern. Farmers were given a copy of the monitoring form, and the overall results were published bi-weekly in a newsletter.
2. Strip Cutting of Alfalfa Intercropped with Cotton
One of the "best management practices" promoted by the BASIC program has been the strip cutting of alfalfa. This practice prevents the immigration of certain species at harvest time and keeps one of the main cotton pests, Lygus hesperus, from moving out of the alfalfa (its preferred host) into the adjacent cotton. BASIC field staff and mentor growers were also able to provide technical support for growers wanting to implement a system of strip cutting.
3. Bezzerides Weed Cultivator
A Bezzerides cultivator was tried by a BASIC grower during the 2002 season. The cultivator works in the planted row where conventional cultivators can't reach. Traditionally, this is the area where chemical herbicides are used to eliminate competing weeds. The trial was not considered a success, since the cultivator also removes cotton plants along with the weeds, and the growers who tested the equipment felt that it was not significantly better than their existing cultivators.
4. Beneficial Habitat Planting
Seventy percent of the growers enrolled in the 2002 BASIC program planted beneficial habitat adjacent to their enrolled fields. The habitat was intended to attract and hold naturally occurring beneficials. The remaining thirty percent of the enrolled fields were adjacent to alfalfa fields where strip cutting was practiced.
5. Beneficial Insect Releases
Releases of beneficial insects were also utilized during the growing season. Thousands of lace- wings and predatory mites were released to augment the naturally occurring insects. When growers see a pest problem starting to develop in their fields they want fast action and so will often turn to a chemical spray. Releasing insects helped them feel like something was being done, while the natural enemies took over the pest control.
A trap crop is planted specifically to attract pest insects. It is then sprayed with some type of insecticide, in conventional management, or left to detain the pests from the cotton crop, or the entire trap crop is tilled under to kill the pest insects. Early-sown cotton has been used as a boll-weevil trap crop. Using fall-planted-cotton trap crops to reduce the number of over-wintering boll weevils was first proposed as early as the late 1800s. (Javaid and Joshi, 1995) Both early and fall cotton trap crops are effective at attracting boll weevil adults and can be enhanced by adding pheromones such as GrandlureTM to the trap crop. The concentrated weevils can then be killed with organically accepted insecticides, which are limited to a few botanicals and biologicals. Crop consultants James and Larry Chiles were able to reduce the cost of boll weevil control by 30% using trap crops of early and late-planted cotton. Even with the cost reduction, they were able to maintain good yields of 1000 to 1200 pounds per acre. They planted a trap crop of cotton in early April, 30 days before the normal cotton planting time, and a late-planted trap crop on August 10. A weevil attractant pheromone was used to lure boll weevils to the cotton trap crops. The trap crops were sprayed for weevils whenever populations were high. This technique reduced the number of early emergent weevils infesting the main crop and reduced the number of weevils overwintering to attack the next year's crop. In a Mississippi study, Laster and Furr (1972) showed sesame (Sesamum indicum) to be more attractive than cotton to the cotton bollworm. Robinson et al. (1972) reported more predators on sorghum than on cotton in his Oklahoma strip cropping study. Lygus bug may also be kept out of cotton by using nearby alfalfa as a trap crop. Unmowed or strip-mowed alfalfa is preferred by that pest over cotton. (Grossman, 1988)
Strip cropping takes place when harvest-width strips of two or three crops are planted in the same field. The most common strip crop grown with cotton is alfalfa. Increasing the diversity of crops increases stability in the field, resulting in fewer pest problems, due to natural biological controls. Crop rotation is one means of introducing diversity over time. Strip intercropping creates biodiversity in space.
Strip cropping cotton fields with alfalfa generally increases beneficial arthropod populations. Among the most notable are carabid beetles that prey on cutworms and armyworms. (Grossman, 1989) Alfalfa has been found to be one of the best crops for attracting an