Key Technical Points for Standardized High-Yield Cultivation and Management of Chinese Milk Vetch

Chinese milk vetch, also known as qiaoyao, honghuacao, or caozi, originated in China. It prefers warm and humid conditions and has a certain degree of cold tolerance. It requires sufficient water throughout its entire growth period. Chinese milk vetch is not demanding regarding soil, with sandy and clay loam being more suitable. It has poor salt tolerance and belongs to the Fabaceae (legume) family, genus Astragalus. It is a biennial herbaceous plant. The main root is relatively thick and fleshy, while lateral roots penetrate the soil relatively shallowly. The stem is cylindrical, hollow, tender and juicy, with sparse fine hairs. The leaves are mostly odd-pinnately compound. The flowers are borne in umbellate inflorescences, generally axillary, rarely terminal. The pods are in two rows, united into a triangular shape. The seeds are kidney-shaped with a smooth seed coat. The roots, whole plant, and seeds can be used as medicine, having effects of dispelling wind and improving eyesight, strengthening the spleen and supplementing qi, and detoxifying and relieving pain. It is one of China's main nectar source plants.

Growth Habits of Chinese Milk Vetch

Chinese milk vetch prefers a warm climate and grows better in moist, well-drained soil. It has strong shade tolerance during the seedling stage and is suitable for intercropping during the late stage of rice cultivation. Chinese milk vetch prefers a warm climate and generally has a distinct overwintering period. During the seedling stage, growth is slow when temperatures are below 8°C; after the beginning of spring, when the daily average temperature reaches above 6°C-8°C, the growth rate increases markedly. The optimal temperature for flowering and pod setting is 13°C-20°C. Chinese milk vetch grows well in moist and well-drained soil; it is afraid of both drought and waterlogging. The most suitable soil moisture content for growth is 20%-25%, and soils with a relatively light texture, mainly loam, are preferred.

The optimal temperature for Chinese milk vetch seed germination is 15°C-25°C, and germination requires absorbing a relatively large amount of water and a large amount of oxygen. During the seedling stage, root system growth is faster than aboveground growth. During the overwintering period, both root and aboveground growth are relatively slow. After the beginning of spring, aboveground growth accelerates, but root growth remains relatively steady. After the bud stage, aboveground growth rate suddenly accelerates, and dry weight can increase by about 1.3 times within approximately half a month. Therefore, by the early flowering stage, the aboveground dry matter weight greatly exceeds that of the root system. At full bloom, the ratio of root system to aboveground dry matter is approximately 1:4-6. The rhizobia of Chinese milk vetch belong to the Chinese milk vetch rhizobium group. They are not part of the resident soil microbial flora, and in areas where Chinese milk vetch has never been planted, rhizobium inoculation is generally required. Rhizobium activity is very weak at the regreening stage, rises sharply after regreening, peaks at the early flowering stage, and then declines rapidly thereafter.

During the seedling stage, plant height of Chinese milk vetch increases slowly. After the beginning of spring, growth rate gradually accelerates as temperature rises, and increases rapidly after the bud stage. Growth rate is fastest from the beginning of flowering to full bloom. The increase in plant height from the bud stage to full bloom accounts for approximately two-thirds of the total increase by the end of flowering. The flowering period of Chinese milk vetch is generally 30-40 days. The flowers on the main stem and the first pair of large basal branches open first, and thereafter flowers open sequentially according to the order in which branches appear. On both the main stem and branches, inflorescences open one by one from bottom to top. The natural crossing rate of Chinese milk vetch is very high, generally above 60%. The pods generally require about 20-30 days from flowering to turning black. Fresh Chinese milk vetch forage can be ensiled in cement silos, earthen pits, polyethylene bags, as well as jars and barrels, and can be promoted and applied locally according to conditions. Because polyethylene bags are easily damaged, the storage time generally should not exceed 3 months. After harvesting fresh Chinese milk vetch forage, it should first be sun-dried for 2-3 days to reduce the moisture content to about 70%, then chopped and ensiled, so as to avoid nutrient loss caused by excessive moisture during ensiling. Chinese milk vetch has relatively high protein content but relatively low carbohydrate content, making it a forage that is relatively difficult to ensile. Adding distillers' grains, rice bran, gramineous forage, and other feeds with higher carbohydrate content can effectively solve the problem of dry matter and crude protein loss. When ensiling for a longer time, it is generally better not to add salt.

Standardized High-Yield Cultivation and Management Techniques for Chinese Milk Vetch

1. Select good varieties: Promoting good varieties is a key link in achieving high yields of Chinese milk vetch. For example, the average yield of Yujiang Large-Leaf Seed is 7.5 t/ha higher than that of other good Chinese milk vetch varieties. 2. Seed treatment: Before sowing Chinese milk vetch, seeds should first be selected with salt water and scarified, then soaked in 30-40% human urine for 10-12 hours, removed and air-dried, and finally mixed with rhizobia. Inoculating seeds with rhizobia is the most important step in Chinese milk vetch seed treatment and is very important for promoting early nodulation on the roots. Inoculation with rhizobia generally increases fresh forage yield by more than 10%, and can reach more than 40% at the highest. 3. Appropriate early sowing: Chinese milk vetch sown in early to mid-October has the highest fresh forage yield; yields gradually decline with later sowing, and yields are even lower when sown after November. This shows that timely early sowing is very beneficial for high yields of Chinese milk vetch. According to another experiment, within the range of sowing 60 kg/ha of seed, the seeding rate of Chinese milk vetch and fresh forage yield are basically proportional, that is, more sowing leads to higher yield, while the economic benefit is better at 22.5-37.5 kg/ha. 4. Scientific fertilization: Chinese milk vetch is a leguminous nitrogen-fixing crop with root nodules, so fertilization should focus mainly on phosphorus and potassium fertilizers, with appropriate application of nitrogen fertilizer, thereby achieving the goals of using phosphorus to increase nitrogen, using potassium to increase nitrogen, and using small fertilizer to nourish large fertilizer. Phosphorus fertilizer should generally be applied as base fertilizer or seed fertilizer to facilitate root development, enhance nitrogen fixation capacity, and improve stress resistance. Increasing potassium fertilizer can promote sturdy seedlings, early branching, and more nodulation in Chinese milk vetch, thereby increasing fresh forage yield. After spring warming, topdressing an appropriate amount of nitrogen fertilizer on Chinese milk vetch, especially on poor-growing second- and third-class seedlings, has a significant yield-increasing effect. In addition, applying trace element fertilizers such as molybdenum and boron also has a clear effect on increasing the fresh forage yield of Chinese milk vetch. 5. Strengthen field management (1) Open the "three ditches" well to prevent waterlogging and drought: Chinese milk vetch prefers moisture and avoids standing water. The three ditches should be opened well and connected so that there is no standing water after rain. When sowing into heavy clay soil, the field should be properly sun-dried so that the soil is soft and muddy, to avoid seed sinking and bud rot. For sandy soil, to avoid buds scorching because the soil is too dry after seed germination, shallow-water sowing should be adopted, and drainage should be carried out after the seeds germinate. In areas with good soil workability and convenient irrigation and drainage, the standard can be: at germination, the soil surface is soft with a water layer; at emergence, the soil surface is wet without a water layer. After Chinese milk vetch germinates, no water should accumulate during the intercropping period. After rice harvest, horse-race water should be irrigated in a timely manner to prevent drought, keeping the field surface from turning white. After spring warming, attention should be paid to clearing ditches to prevent waterlogging. (2) Cover with straw to prevent cold: The most suitable temperature for Chinese milk vetch growth is 15-25°C; when the temperature is below -3°C, it will suffer cold damage. After late rice harvest, covering with straw helps increase the yield of Chinese milk vetch. In addition, increasing the application of pig and cattle pen manure and plant ash also has a certain effect on preventing cold and resisting freezing in Chinese milk vetch. (3) Control pests and diseases: The main pests of Chinese milk vetch include aphids, leaf miners, thrips, and stem flies, all of which can be killed by spraying with a 1000-2000 times dilution of 20% dimethoate. Where water sources are convenient, if aphids or stem flies are found during the seedling stage, the field can be flooded above the leaf tips for 3 hours and then drained, which can drown a large number of insects and flies. Lime-sulfur mixture (0.3 degrees Baume) can be used to control the main diseases of Chinese milk vetch, powdery mildew and sclerotinia. 6. Turn under at the appropriate time: Turning under at the appropriate time is the last link in improving the yield and fertilizer efficiency of Chinese milk vetch, and it is often easily overlooked in production. Turning under too early results in low yield and low fertilizer efficiency. In addition, fresh forage turned under too tender has low nitrogen content and high moisture content. If turned under too late, although the yield is high, the cellulose and lignin in the fresh forage increase and the plants age, which is not conducive to decomposition and rotting, and fertilizer efficiency is also low. Moreover, the organic acids and large amounts of carbon dioxide and hydrogen sulfide produced by its decomposition can affect the survival and tillering of early rice seedlings. Therefore, Chinese milk vetch is generally most suitable for turning under at the full flowering stage.