What are the key techniques for green cultivation of Asarum in farmland?
Northeast Asarum is a perennial herbaceous plant of the genus Asarum in the family Aristolochiaceae. It was originally used as a whole herb in medicine, but the Pharmacopoeia of the People's Republic of China (2005 edition) changed it to use the root as medicine. It mainly contains volatile oil and has effects such as dispelling wind and dispersing cold, warming the lungs and resolving fluid retention, and opening the orifices and relieving pain. It is mostly grown artificially under forests or on mountain land, and in recent years many medicinal herb growers have used farmland to cultivate it. The key techniques for green cultivation of Asarum in farmland are briefly introduced below for the reference of medicinal herb growers.
1 Reasonable site selection
1.1 Surrounding environment
There must be no pollution sources such as construction sites or hospitals around the Asarum plot, and it must be more than 200 m away from main highways and far from polluted rivers and ponds.
1.2 Soil conditions
The Asarum planting site should be chosen at the foot of a mountain or in valley land between two mountains. These plots are affected by mountain forests, have humid air, and are suitable for Asarum growth. The soil quality is best as loose, fertile, moist but not water-accumulating loam or sandy loam, with pH 6-7. If herbicides were used on the previous crop, the land should be plowed and left fallow for 0.5-1 year before use. When choosing a large area of farmland to plant Asarum, soil samples should be taken from multiple points before planting to test for pesticide residues and heavy metal content, and planting should be carried out only after passing the test, so as to avoid major economic losses.
2 Reasonable close planting
Farmland receives long hours of light, has high soil moisture evaporation, low relative air humidity and soil water content, and relatively higher temperature, which is unfavorable for Asarum growth. Therefore, the planting density should be appropriately increased so that the aboveground plants of Asarum close the rows early, reducing water evaporation and lowering soil temperature. Generally, a row spacing of 20 cm and a hole spacing of 15-20 cm is suitable. For example, with a hole spacing of 15 cm, plant 4 two-year-old seedlings per hole; with a hole spacing of 20 cm, plant 5-6 seedlings per hole.
3 Reasonable light regulation
3.1 Light regulation with shade nets in seedling fields
When planting Asarum in farmland, shade nets with different light transmittance should be selected for Asarum of different ages. In farmland seedling fields, 1-2-year-old plants can be shaded with shade nets of 30% light transmittance, with a canopy density of 0.65-0.7; 5-6-year-old seedlings should be shaded with shade nets of 40% light transmittance, with a canopy density of 0.6.
3.2 Light regulation by planting corn plus shade nets in transplant fields
Transplant fields use shade nets with 40% light transmittance for shading. In 3-4-year-old Asarum plots, corn should also be planted beside the beds for light regulation. For beds made in a north-south direction, plant corn on the west side of the bed; for beds made in an east-west direction, plant corn on the south side of the bed, with a plant spacing of 20-30 cm, and the planting time is the same as field corn. When 5-6-year-old Asarum plants close the rows, corn may be omitted to facilitate field management.
4 Bed surface mulching
To lower the soil temperature on the bed surface, increase soil moisture, prevent weed overgrowth, and reduce the spread of diseases, transplant fields should be mulched between rows on the bed surface, with a thickness of about 2 cm. The mulching material is best as larch needles or rice straw. When mulching with fallen leaves, do it in autumn after the aboveground plants wither and before emergence in spring; when mulching with rice straw, do it after emergence and before leaf expansion.
5 Preventing frost damage and herbicide damage
5.1 Preventing frost damage
Asarum is an early-spring plant, and its emergence period coincides with the late frost period. One-year-old seedlings will suffer frost damage, while plants more than 2 years old are not afraid of frost. Preventive measures: 1) After the soil freezes in late autumn, cover the bed surface with leaves or rice straw more than 10 cm thick, and remove it later in the following spring. This can delay soil thawing, postpone the emergence period, and avoid emergence during the late frost period, thereby preventing frost damage. However, check the emergence situation frequently. When more than 50% have emerged, remove the covering material in time, so as to prevent Asarum seedlings from growing into "bean sprouts" under the covering material and developing sunscald after exposure to light. 2) After emergence and removal of the covering material, set up a small plastic arch tunnel. Pay attention to ventilation during the day and cover it tightly at night, and remove the tunnel after the final frost.
5.2 Preventing herbicide damage
When planting Asarum in a small area of farmland, the Asarum plot is mixed among other farmland plots. After Asarum emerges, it is exactly the time when pre-emergence herbicides are applied in corn fields; therefore, consult the neighboring landowner in advance, and when applying herbicides, lower the spray nozzle to prevent the spray liquid from drifting onto Asarum plants with the wind and causing herbicide damage.