Recently, strong convective weather has been frequent in Guangxi, and excessive rainfall can easily cause waterlogging in Tea gardens, leading to wet damage to tea plants. Tea plants are Crops that prefer moisture but fear flooding. In tea gardens with poor drainage or high groundwater levels, tea plants often grow poorly in large areas and have low yields. After wet damage, even repeated renovation of the tree canopy and increased fertilization levels cannot change the low-yielding appearance of the tea garden, and the plants may even gradually die.
01 Symptoms of Wet Damage
The main symptoms of wet damage to tea plants include fewer branches, sparse buds and leaves, slow growth or cessation of growth, grayish-white twigs, yellowing leaves, stunted and diseased trees, gradual death, extremely low tea yield, fewer absorbing roots, limited lateral root extension, shallow root layers, some lateral roots growing horizontally or upward instead of downward. In severe cases, the outer skin of the conducting roots turns black, is less smooth, and develops many small, tumor-like protrusions.
When wet damage occurs, the fine roots at greater depths are affected first. Soon after, the shallower fine roots also begin to suffer. The surface of the thick roots appears slightly black, followed by the rotting of the fine roots and the darkening of the insides of the thick roots, ultimately leading to the complete blackening and death of the thick roots.
Due to the damage to the underground parts, the tea plant loses its absorption capacity, and the growth above ground is gradually affected. First, the tender leaves lose their luster and turn yellow; then the bud tips droop and shrink. The response of mature leaves is more delayed, manifested by a loss of luster and Wilting before shedding.
02 Causes of Wet Damage
The fundamental cause of wet damage in tea plants is an increase in the ratio of Soil moisture and a decrease in the ratio of air. Due to insufficient oxygen supply, the root system experiences breathing difficulties, and the absorption and metabolism of water and nutrients are impeded. Waterlogging promotes the activation of mineral elements, increasing the concentration of iron and manganese in the solution. Applying higher amounts of organic matter can further promote the leaching loss of iron. In waterlogged soils, the pH value tends to become neutral and, over time, the pH value of acidic soils increases.
Additionally, in waterlogged soils, the oxidation of organic matter is slow, and due to the lack of oxygen, aerobic microorganisms die while anaerobic microorganisms proliferate, accelerating the reduction processes in the soil and causing various reducing substances to be produced.
Under these conditions, the soil environment deteriorates, available nutrients decrease, toxic substances increase, and the disease resistance of the tea plant is lowered, resulting in the peeling, necrosis, and rotting of tea roots. This phenomenon is more common when there is immobile water accumulation in the soil.
03 Preventing Wet Damage
Wet damage often occurs in areas that were artificially leveled during land preparation, such as ponds or depressions, or where there is an impermeable layer below the cultivated layer, or in tea gardens on hill slopes or in valleys where water accumulates. Therefore, preventive measures should be taken based on the causes of wet damage, lowering the groundwater level or shortening the time that runoff remains in low-lying areas.
During the establishment of the tea garden, if there is an impermeable layer within 80 cm of the soil, it should be broken up during cultivation. For areas with hardpan or Clay layers, deep cultivation should be performed to break them up, ensuring there is no water accumulation within a 1 m soil layer. If the hardpan was not broken up initially in a tea garden, once planted, and an impermeable layer is discovered, timely deep cultivation between rows should be carried out to address the issue.
Improving the drainage ditch system is an important means of preventing water accumulation. For tea gardens located near reservoirs or dams, deep cross-drains should be constructed at the junction to intercept seepage. For tea gardens in low-lying areas, more cross-drain ditches should be opened, and the depth of the ditches around the tea garden should reach 60–80 cm. When there are hard rocks within an 80 cm soil layer (covering a small area of the tea garden) or where there was originally water collection, such as in ponds, blind drains should be installed. Specifically, a blind drain should be dug every 5–8 rows of tea plants, with a bottom width of 10–20 cm and a depth of 60–80 cm, connecting to the longitudinal drainage ditch. The bottom of the ditch should be filled with rubble, covered with gravel and sand.
To prevent clogging by mud and sand, a layer of polyethylene film should be laid on top, which is then covered with soil and compacted. The soil layer above the blind drain should be at least 60 cm deep. If the soil is heavy clay, it is best to mix it with sand to facilitate water penetration. Since the installation of blind drains requires significant labor, careful consideration should be given to the use of such plots during the planning of new tea gardens.
For tea gardens with poor foundations and severe wet damage, replanting and redesign should be considered.