Detailed Explanation of Key Technical Points for Scientific Cultivation and Management of Carrots
Carrot (Daucus carota), also known as ganxun, is a biennial herbaceous plant of the genus Daucus in the Apiaceae family. Its fleshy root is consumed as a vegetable. It originated in southwestern Asia, with Afghanistan being the earliest center of evolution, and a cultivation history of over 2000 years.
Morphological characteristics of carrot
It has a taproot system, with the main roots distributed within a 20-90 cm soil layer, reaching 180-250 cm deep. The upper part of the taproot, including a small portion of the hypocotyl, thickens to form a fleshy root that extends below the soil surface, bearing four rows of slender lateral roots. The fleshy root shapes include round, flat-round, conical, and cylindrical. Root colors include purple-red, orange-red, pink, yellow, white, and green. It is mainly composed of secondary phloem, with a small xylem called the core. The exterior of the taproot is smooth.
Leaves are clustered on a shortened stem and are tripinnately compound. The petioles are slender, the leaf color is dark green, the leaf area is small, and the leaf surface is densely covered with fine hairs. After the fleshy root overwinters in storage, it bolts and flowers. The main bolt emerges first, followed by lateral branches. Each flower branch consists of many small umbels forming a large compound umbel. A single plant often bears over a thousand small flowers, with a flowering period of about one month. The flowers are perfect, white or pale yellow, and insect-pollinated. The fruit is a schizocarp that splits into 2 at maturity, commonly mistaken for seeds; it is oval, leathery, with dense bristles on the longitudinal ridges. The embryo is very small, often poorly developed or absent, with weak emergence ability, and the germination rate is as low as about 70%.
Biennial herb, 15-120 cm tall. Stem solitary, covered with white coarse stiff hairs throughout. Basal leaves membranous, oblong, 2-3 times pinnately parted, ultimate segments linear or lanceolate, generally 5-15 mm long, 0.5-4 mm wide, apex acute with a small mucro, glabrous or with hispid hairs; petioles 3-12 cm long; cauline leaves nearly sessile, with leaf sheaths, ultimate segments small or slender.
Compound umbels, peduncles 10-55 cm long, with hispid hairs; involucre with numerous bracts, leaf-like, pinnately parted, rarely undivided, segments linear, 3-30 mm long; rays numerous, 2-7.5 cm long, outer rays curving inward at fruiting; involucel bracts 5-7, linear, undivided or 2-3 lobed, margin membranous, ciliate; flowers usually white, sometimes tinged with pale red; pedicels unequal in length, 3-10 mm long. Fruit ovoid, 3-4 mm long, 2 mm wide, with white bristles on the ridges. Flowering period early May to mid-July.
Scientific Cultivation and Management Techniques for Carrots
Selection of Seed Plants
Carrot seed production generally adopts the mature plant seed production method. During harvest around “Lidong” (Start of Winter), field plant selection is carried out. Several excellent individual plants should be selected that have few leaves, proper leaf color, relatively upright leaf clusters, small fleshy root heads, uniform shape, slender root tips, deep color, bright skin color, smooth epidermis, no splitting, no forking, no pest or disease infection, and conform to the typical traits of the variety. The leaf clusters are cut off leaving 1 cm long petioles as seed plants.
Storage of Seed Plants
Winter storage of seed plants generally adopts trench storage. A trench 1 m wide, 80 cm deep, and of unlimited length can be dug. In the trench, a layer of carrots is placed and a thin layer of fine moist soil is sprinkled over it. When the carrot layer reaches 40-50 cm deep, a 10 cm thick layer of moist soil is applied on top. Afterwards, as the weather turns colder, soil can be added in layers, with the thickness of the soil cover being such that the seed plants are not frozen.
Planting Time and Method
After planting, carrot seed plants have relatively weak root growth potential, and the roots produced are mostly fibrous roots, with poor drought resistance and absorption capacity. Therefore, the seed production field should be reasonably fertilized and finely prepared early, which is the foundation for improving seed production yield.
Isolation Between Varieties
In addition to maintaining a distance of 2000 m between seed production fields of different varieties, wild carrots around the seed production field should also be removed to ensure seed purity.
Planting Time
The following spring when the soil thaws and the soil temperature stabilizes at 8-10°C (generally mid-to-late March in Shandong Province), the seed plants are taken out of the trench and planted. Practice has proven that if seed plants are left outside the trench for a long time, the fleshy roots shrink, growth after planting is not vigorous, and yield drops significantly. Therefore, it is best to take seed plants from the trench and plant them immediately. Seed plants not planted temporarily after being taken out of the trench can be covered with moist soil to prevent shrinkage of the fleshy roots.
Planting Method
Before planting, apply 60,000 kg/ha of decomposed barnyard manure as base fertilizer, deep plow, rake level, and make beds. At planting, open furrows at a row spacing of 50 cm and plant spacing of 30 cm, or open furrows and plant obliquely. When planting, first cover half the soil and then water; after the water infiltrates, cover the top, with the top of the root level with the bed surface or slightly 1 cm above it. After planting, firm the soil and timely cultivate to conserve moisture.
Field Management
Cultivation and Weeding: After seed plants are planted and before bolting, the external temperature is relatively low and plant growth is slow. The main work at this stage is cultivation and loosening of the soil to help increase soil temperature and promote root growth. As the temperature gradually rises and inflorescences emerge, cultivation and weeding are carried out together to ensure that the field is basically free of weeds before the seed plants close their rows, so that flowering and fruiting occur under good environmental conditions.
Fertilizer and Water Management: At each growth stage of the seed plants, watering and topdressing should be carried out in a timely manner according to need. Generally, when inflorescences have emerged to a height of 15-20 cm, apply 225-300 kg/ha of nitrogen-phosphorus-potassium compound fertilizer and water. Water shortage during the flowering period must be avoided, otherwise seed yield is severely reduced; the bed surface should be kept alternately dry and moist. During full bloom, one topdressing can be applied with 150-225 kg/ha of ammonium sulfate, which can be applied with irrigation water.
Pruning and Staking of Seed Plants
If carrot seed plants are not pruned, the main branch and the first, second, third, …… and subsequent branch orders of flower umbels bloom in sequence. As the number of flower whorls increases, the flower whorls also become smaller, and seeds mature slowly. To concentrate nutrients and make seeds plump and mature uniformly, pruning techniques must be used to adjust the plant architecture of seed plants. Production practice has proven that for propagating production seed, leaving the main stem and 3-4 vigorous lateral branches and removing all other lateral branches is the most suitable method. Pruning is generally carried out when seed plants reach 40-50 cm in height. At this time, the external temperature gradually rises, and lateral branches emerge abundantly, so pruning must be done in a timely manner. After seed plants flower, to prevent lodging, soil can be hilled at the base or supports can be tied. One method is to insert a wooden stick or small bamboo pole beside each seed plant, then use plastic rope to encircle the main and lateral branches of the whole plant and secure them to the stick or pole. Another method is to stretch two thin ropes or plastic ropes along both sides of each bed of seed plants, fastened and tightened at both ends and in the middle with wooden stakes, to support the outer branches of the seed plants and prevent the branches from swaying and lodging.
Pest and Disease Control
Common pests and diseases of seed plants include soft rot, sclerotinia rot, and aphids. Plants with soft rot first show leaf wilting and yellowing, then the fleshy root softens and rots, emitting a foul odor. This disease should be prevented mainly by preparation. Before winter, prepare the land, fully sun-expose the soil clods to eliminate pathogens, and avoid continuous cropping. In addition, underground pests should be controlled in a timely manner to prevent the fleshy roots of carrots from being injured and infected by pathogens. After seed plants are infected with sclerotinia rot, the roots rot and soften, and white mycelium appears on the surface. If it develops further, sclerotia form, the diseased plants cannot produce new shoots, the lower leaves turn pale yellow and droop, and the aboveground parts shrink and die. Optional agents include 50% procymidone wettable powder at 1500 times dilution, 50% thiophanate wettable powder at 500 times dilution, and 40% dimethachlon wettable powder at 500-600 times dilution, spraying 750-900 kg/ha of solution, once every 7-10 d. For aphids, optional agents include 50% pirimicarb wettable powder at 1500-2000 times dilution, 10% imidacloprid wettable powder at 1000-1500 times dilution, 40% fenvalerate-malathion emulsifiable concentrate at 2000-3000 times dilution, or 40% omethoate emulsifiable concentrate at 1000-1500 times dilution, sprayed on the leaves.
Timely Harvest
Carrot seeds mature only about 30 d after flowering. When the inflorescences turn from green to yellow after flowering, they can be harvested with the flower stalk, that is, the inflorescence is cut promptly with scissors 10 cm below the lower end of the inflorescence. Afterwards, every 10-20 plants are tied into 1 bundle and placed upright in a ventilated, dry place to dry, then after-ripened for 7-10 d and threshed. Clean to remove fruit stalks and impurities, then sun-dry for another 2-3 d. When the seed moisture content drops below 14%, it can be packaged and stored.