Direct seeding cultivation techniques for licorice in the Hexi arid region
Licorice is the most commonly used bulk medicinal herb, hailed as the king of medicines. The currently cultivated species is Glycyrrhiza uralensis (Ural licorice), a plant of the genus Glycyrrhiza in the Fabaceae family. It is highly water-saving, drought-tolerant and cold-tolerant, and is an excellent windbreak and sand-fixing vegetation for arid and semi-arid desert areas. The medicinal part is the dried root, which not only has effects such as tonifying the spleen and boosting qi, relieving cough and expelling phlegm, clearing heat and detoxifying, and harmonizing the properties of medicines, but is also widely used in daily necessities, light industry, animal husbandry and the food industry.
Minqin County, located on the edge of the Badain Jaran Desert and the Tengger Desert, is one of the major production areas for cultivated licorice in Gansu Province. In recent years, excessive digging has caused a sharp decline in wild licorice resources, and it has become one of the endangered species. The county has few people and much land, with large areas of wasteland, abandoned farmland and saline land available for artificial licorice cultivation. In addition, it benefits from the irrigation of the Shiyang River, abundant light, long sunshine hours, fertile soil and large diurnal temperature differences, making it the most suitable area for licorice planting in Gansu and also the largest artificial licorice cultivation base. The local artificial licorice cultivation techniques mainly include direct seeding and transplanting. The direct seeding cultivation techniques are summarized below.
1 Site selection and land preparation
1.1 Site selection. Licorice is a perennial herbaceous plant with a well-developed root system and deep soil penetration. It prefers light, is drought-tolerant, salt-alkali tolerant and afraid of waterlogging, and is suitable for growing in sandy land, grassland, riverbanks and desert and semi-desert environments. Therefore, for licorice cultivation, sandy loam with a relatively low groundwater table, good drainage, slightly alkaline soil, deep soil layers and convenient irrigation should be selected.
1.2 Fine land preparation. The land for planting licorice is best deep-plowed once in the autumn of the previous year, with a plowing depth of no less than 35cm. Before sowing in spring, deep-plow and prepare the land once more, and form it into small beds of 200-300 sq m.
2 Seed treatment
2.1 Seed selection. Select Glycyrrhiza uralensis seeds that are plump, uniform, free of insect damage, with a purity above 90% and a 1000-grain weight of about 10-12g.
2.2 Treatment. Licorice seeds have a hard-seed rate of 92%-98%, with a smooth and dense seed coat that water can hardly penetrate, resulting in a very low germination rate, so treatment before sowing is essential. The most effective method is treatment with concentrated sulfuric acid: place the cleaned seeds in an acid-resistant container, add 2500-3000ml of 80% concentrated sulfuric acid per 100kg of seeds, stir quickly and leave for about 1h. When acid-etched black spots appear on the seed coat, the treatment can be stopped. Remove all the seeds and rinse them with clean water several times, then sow immediately or dry them for storage. The germination rate can reach about 90%.
3 Sowing
3.1 Sowing time. The suitable germination temperature for licorice seeds is 20-25°C, and sowing in mid-to-late April is generally most suitable.
3.2 Sowing method. Licorice is generally sown in drills, in holes or by dibbling. The method to use should be determined according to the site type of the planting land. For flat terrain, large plots and easy mechanical operation, use a seeder for drilling, which gives uniform emergence and facilitates intertillage and weeding, with a row spacing of 25cm and a depth of 2.0-2.5cm. Irrigate the "seating water" 3-4d before sowing, and after sowing cover with soil and harrow in time to preserve moisture. For plots with complex terrain and large undulations, hole sowing or dibbling is suitable.
3.3 Sowing rate. To maintain 300,000-375,000 plants/hectare, the sowing rate for drilled licorice is 30-45kg/hectare.
4 Fertilizer and water management
4.1 Fertilizer selection. Licorice is relatively sensitive to phosphorus and potassium in the soil, so more phosphorus and potassium fertilizers should be applied.
4.2 Apply sufficient base fertilizer. Generally, before sowing, combine with deep plowing and apply 375-450kg/hectare of diammonium phosphate, plus 600kg/hectare of zinc compound fertilizer and 150kg/hectare of potassium fertilizer as base fertilizer. Where conditions permit, applying 45000g/hectare of decomposed farmyard manure gives even better results.
4.3 Reasonable topdressing. Licorice seedlings are generally not topdressed, but at the branching stage, 120-150kg/hectare of urea should be applied with irrigation to promote stem and leaf growth. Second-year licorice enters a rapid growth period; to avoid fertilizer deficiency affecting yield, 300kg/hectare of diammonium phosphate should be topdressed. Topdressing is best done by opening a furrow on both sides of the root system and burying it, in combination with intertillage and weeding.
4.4 Timely irrigation. Before sowing, licorice should be given sufficient bottom water. In the current year's growth period, irrigate 2-3 times: irrigate the first time when the seedlings are 7-10cm tall, and the second time at the branching stage. After that, the third irrigation should be timed according to drought conditions. For direct-seeded licorice in the second and third growth years, irrigate 2-3 times. For licorice that has already been given winter water, generally irrigate the first time at the branching stage; if during the high-temperature summer period the licorice stems and leaves show obvious leaf drop, a second irrigation may be given; from mid-August to early September, irrigation should be carried out in good time, because this is the best time for licorice to accumulate active ingredients and also the key time for licorice to gain weight.
4.5 Irrigate winter water well. It is best to arrange winter irrigation from early December to January of the following year.
4.6 Skillful application of plant growth regulators. During the licorice growth period, spraying plant growth regulators such as Aiduoshuo and Plant Power 2003 has a certain effect on increasing licorice yield.
5 Thinning and final singling of seedlings
When the licorice seedlings grow to 15cm tall, thinning can be carried out, with a plant spacing of 10-15cm, maintaining about 330,000 plants/hectare.
6 Intertillage and weeding
6.1 Chemical weeding. If grass-family weeds appear after licorice emergence, herbicides such as Pujing can be used; if weeds such as wheatgrass and reed grass appear, glyphosate can be used to remove them promptly. The effect is best when the weeds have 3-6 true leaves.
6.2 Intertillage and weeding. Intertillage is a major management step for increasing licorice yield, and intertillage should be carried out after each irrigation. Weeding in licorice fields requires hoeing early, hoeing small and hoeing completely.
7 Pest and disease control
The main insect pest of licorice is the licorice leaf beetle. The best time to control this insect is during the damage period of overwintering-generation adults and first-generation larvae. When a small number of feeding notches appear on licorice leaves, 40% omethoate emulsifiable concentrate at 1500 times dilution or 2.5% deltamethrin emulsifiable concentrate at 6000 times dilution can be used for control.
The main diseases of licorice include licorice brown spot and rust, among others. At sowing time, it is best to dress the seeds with chemicals. Generally, wettable carbendazim, thiophanate-methyl and similar chemicals are used to treat the seeds, dressing at an effective concentration of 0.5%-1% of the seed amount; after dressing, pile and cover for 1-2h before sowing. Soil can also be treated with 50% carbendazim; if rust or brown spot occurs in licorice, some diseased licorice plants can be pulled out and buried deep outside the licorice field; 20% tridemorph emulsifiable concentrate or 95% dinocap solution can also be sprayed twice in succession to control rust, and 70% thiophanate-methyl can be sprayed to control brown spot.