Cultivation Timing and Management Key Points for Licorice
I. Seed Germination Habits
(I) Water Absorption and Germination of Licorice Seeds Licorice seeds have a low emergence rate, generally around 10%, so they must be treated before sowing. Untreated seeds absorb water very slowly, and most seeds do not imbibe; seeds treated with concentrated sulfuric acid absorb water very rapidly, reaching over 100% within 4 hours. Generally, once water absorption exceeds 100%, the seeds have a very uniform germination capacity. If water absorption differs, the germination rate differs accordingly. At 20°C, after absorbing water for more than 1.5 hours, the germination rate reaches over 80%, at which point the moisture content is about 95%; after 4 hours, the germination rate can reach about 90%, and the moisture content is also above 150%.
(II) Effect of Temperature on Germination Untreated seeds have very low germination rates under various temperature conditions; however, when treated with concentrated sulfuric acid, germination rates are greatly improved under different temperature conditions. For example, at 10°C the germination rate can reach 63.3%, but germination is fast and uniform at 25°C; if below 10°C, the germination rate drops to 59%. From the above, it can be seen that imbibition at low temperatures has a damaging effect on seed germination. Licorice, like the seeds of many leguminous plants, is sensitive to low temperatures and prone to cold damage. Therefore, in production, sowing at 15°C is preferable; below this temperature, low-temperature cold damage easily occurs, affecting production.
II. Growth and Development and Requirements for Environmental Conditions Licorice is a xerophytic plant, and Glycyrrhiza inflata has the strongest drought tolerance. In its growing areas, annual precipitation is mostly within 100 mm, and in some places only 15 mm. Even when the groundwater table is as deep as 1-8 m, it can still grow and develop, and in some cases can form communities. The aboveground part of licorice dies each year in late autumn, overwintering in the soil as roots and rhizomes, and in early spring of the following year, from March to April, new buds grow from the rhizomes. The buds grow upward very quickly, producing long branches and leaves; from May to June the branches and leaves are luxuriant, from June to July it flowers and fruits, and in September the pods mature and fall to the ground. Under wild conditions, because the land is arid and unfavorable for seed germination, seedlings grown from seed are rarely seen. Licorice rhizomes have strong sprouting ability and extend horizontally for tens of meters below the ground surface around the old plant. One licorice plant can produce dozens of new plants in several years; three years after planting, new plants can grow at distances of 3-4 m away from the mother plant. Both its vertical rhizomes and horizontal rhizomes can produce roots. The depth of the root system varies with soil texture and groundwater depth, generally within 1-2 m, and some can reach more than 10 m, using very deep roots to absorb groundwater to adapt to arid environmental conditions. The areas where licorice is distributed are continental climate zones, mainly characterized by drought, large temperature differences, severe cold in winter with temperatures of -40°C to (-30°C), and frozen soil layers reaching more than 1 m deep, while summers are extremely hot. In open desert and semi-desert areas, there is strong light, little rain, and relative air humidity of 30%-40%. Because licorice has the characteristics of cold resistance, drought resistance, light preference, and heat tolerance, it grows and develops well under the above ecological conditions. It is an indicator plant of calcareous soils and also a plant with strong salt resistance; the soil salt content should preferably not exceed 0.2%.
III. Propagation Methods
(I) This method is mostly used in new production areas.
1. Seed Collection and Seed Treatment Directly sown licorice flowers and sets seed in the 4th year, while rootstock and division propagation can advance flowering and fruiting. After the seeds mature in August and September, cut the plants and dry them in the sun, then thresh to obtain the seeds, and store them in a ventilated and dry place. In places with wild distribution, they can be collected in the field. Because licorice seeds contain sweeteners, the rate of insect damage is relatively high, so they should be soaked in water and the insect-damaged seeds floating on top should be skimmed off. In addition, licorice seed coats are hard, impermeable to water and air, with a high hard seed rate, and are not easy to germinate, so treatment is required before sowing.
The germination rate of untreated seeds is only 30%-40%, so seed coat breaking treatment should be used to increase the germination rate. The specific methods are:
(1) Scarification by milling: Use a Model 20 vertical centrifugal rice mill for seed collision. During the collision process, the central grinding wheel of the rice mill can break the seed coat during rapid rotation, making the seeds easy to absorb water and germinate. Where a rice mill cannot be found temporarily, a roller mill can be used instead. This method is fast and simple, has a large processing capacity, and results in a low seed rot rate after treatment, and can raise the germination rate to over 90%. It is currently the method commonly used in household cultivation areas.
(2) Friction method: Mix coarse river sand or glass shards in equal amount with the seeds and rub for 1 hour, then soak in water for 12 hours, then continue rubbing the hard seeds, repeating 2-3 times. This method can raise the germination rate to over 80%. However, the processing volume is small, efficiency is low, and the seed rot rate is high, so it is suitable for small-scale planting.
(3) Sulfuric acid method: Add 20 mL of 80% concentrated sulfuric acid per kilogram of seeds, stir evenly with a wooden stick so that all seeds are coated with sulfuric acid, and soak the seeds for 2-3 hours at 20°C. After the seed coats are burned and broken, repeatedly rinse off the concentrated sulfuric acid, which can increase the germination rate to over 85%. The advantage of this method is that a relatively large quantity can be treated at one time; the disadvantage is that due to changes in environmental temperature, the treatment time is difficult to control. Too long easily burns the seeds and causes them to lose germination ability, while too short removes too few hard seeds. Moreover, concentrated sulfuric acid can easily injure people and livestock if not handled carefully, so it is not widely used in household cultivation areas.
2. Sowing Divided into direct sowing and seedling transplanting.
(1) Direct sowing: Sowing can be done from April to July each year. In areas without irrigation conditions, it is best to sow during the rainy season. On land that has been prepared and supplied with sufficient base fertilizer, sow with a seeding machine or a seed drill. The row spacing is 50 cm, and the sowing depth is 3 cm. On land with irrigation conditions, the sowing rate is 1.5 kg per mu; on dry land or land with poor soil moisture, the sowing rate can be appropriately increased. After sowing, cover with grass to retain moisture, and seedlings emerge in about 1-2 weeks.
(2) Seedling transplanting, that is, first raise seedlings in a nursery for 1 year, and transplant the seedlings into the field the following year. The sowing method is the same as direct sowing, with a row spacing of 30 cm. Transplanting is generally carried out in late autumn and early spring. On land that has been prepared and supplied with sufficient base fertilizer, plant the well-grown one-year-old seedlings at a row spacing of 50 cm x 30 cm. About 6000-7000 plants can be planted per mu. After planting, the 1st and 2nd waterings must be thorough, and thereafter field management should be carried out well.
(II) This method is mostly used in old production areas. The expansion of licorice populations mainly occurs through new plants sprouting from horizontal underground rhizomes; 1 plant can produce dozens of new plants. Rhizome propagation is to dig out rhizomes in spring and autumn, cut them into 7-8 cm segments, each with 1-2 buds, and bury them about 13-16 cm underground according to soil moisture, where they can sprout new plants. The row and plant spacing are the same as for seedling transplanting. Division propagation is to dig out new plants growing beside old plants in spring and autumn and plant them separately, with the same row and plant spacing as for seedling transplanting.
IV. Field Management
(I) Thinning and final spacing For direct sowing, thin the seedlings when the seedlings are about 6 cm tall in the same year. In the planting year, the final spacing should be 10-15 cm between plants, and in the 2nd year maintain a plant spacing of 30 cm.
(II) Drainage and irrigation Whether licorice is directly sown or propagated by rhizomes, the soil must be kept moist before emergence. Licorice has strong drought resistance, and after emergence, natural rainfall generally meets its growth needs. However, in prolonged drought it should be watered. The frequency of watering should not be too high, but each watering should be thorough, which is beneficial for root growth downward. During the rainy season, attention should be paid to drainage.
(III) Cultivation and weeding In the 1st year, when the licorice seedlings are small, weeds should be removed frequently and the soil loosened at the right time, with loosening from shallow to deep. After the plants grow larger, there are fewer weeds; pay attention to pulling out large weeds. Do not hoe the soil, so as to avoid damaging the new plants sprouting from the rhizomes.
(IV) Topdressing In late autumn, after the aboveground part of licorice withers, 2000 kg of decomposed farmyard manure per mu can be used to cover the bed surface to increase soil temperature and soil fertility. Phosphorus fertilizer can be applied as topdressing in early spring each year. Because licorice roots have root nodules and have nitrogen fixation, generally nitrogen fertilizer does not need to be applied as topdressing, and nitrogen deficiency is also mostly not a problem.
V. Pests and Diseases and Their Control
(I) Rust disease On the back of infected leaves, yellow-brown scab-like lesions appear. After the epidermis ruptures, brown powder is released, which are the urediniospore piles of the pathogen. From August to September, dark brown teleutospore piles form, causing leaves to turn yellow, wither, and even fall off. Control methods: remove diseased and residual plants and burn them in a centralized manner; in the early stage of disease, spray with 15% triadimefon 1000-fold solution or 97% dithianon sodium 400-fold solution for control.
(II) Brown spot disease It damages leaves, and affected leaves produce round or irregular lesions. The lesion edges are brown, the centers are grayish brown, and gray-black mold-like substances appear on both the front and back of the lesions. Control methods: clean the garden in winter and dispose of diseased residues; spray 200-fold non-toxic high-ester film for protection; in the early stage of disease, spray with 65% zineb or 50% mancozeb 500-fold solution, and also spray with 70% thiophanate-methyl wettable powder 1500-fold solution.
(III) Powdery mildew It damages both the front and back of leaves and produces white powder. It can be controlled by spraying 15% triadimefon 800-1000-fold solution.
(IV) Leafhoppers Mainly including elm leafhoppers, small green leafhoppers, and others, they cause damage throughout the entire growth period of licorice, with the most severe damage from late June to mid-August. Nymphs and adults suck the leaves, young buds, and young branches of licorice, first showing silver-white dotted spots, then the leaves lose green and turn light yellow, and finally fall off.
Control methods: clear elm trees and other overwintering hosts of leafhoppers around licorice fields; during the peak damage period, spray with 2.5% deltamethrin 1000-1500-fold solution for control; use natural enemies such as green lacewings and ladybugs for biological control.
(V) Underground pests At present, whether licorice production can develop rapidly and obtain good economic benefits depends critically on the control of underground pests. In addition to Porphyrophora ningxiana, during the emergence stage the main pests are mole crickets and Oriental crab beetles; during the adult plant stage the main pests are black wrinkled chafer beetles, yellow-brown heterophyllous chafer beetles, wireworms, darkling beetles, and others. Control methods: before sowing, carefully select habitats and regions with few underground pests and unfavorable conditions for their occurrence; carefully prepare the land, deep plow and heavy harrow to destroy their habitat and kill the insects; apply decomposed manure to prevent pests from being artificially brought into licorice fields; attach importance to pre-sowing germination acceleration and seed dressing treatment, using 40% isofenphos-methyl 0.2% (of seed weight), 50% parathion emulsifiable concentrate 0.2%, 25% phoxim emulsifiable concentrate 0.1%, etc. for seed dressing; when underground pest populations are relatively large, pesticide powder and 1605 powder can also be used for pre-sowing soil treatment; 3-5 year old licorice should be harvested in time.