Molecular Soil Biology 2025, Vol.16, No.4, 214-229 http://bioscipublisher.com/index.php/msb 216 will lack oxygen and the plants will not grow. Especially in plots with heavy soil or repeated planting, if deep plowing or drainage ditches are not dug, the problem of waterlogging will be more serious. Leonurus japonicus is very sensitive to root oxygen. Once the soil is compacted and waterlogged, the roots are prone to rot, the seedlings will turn yellow and thin, the emergence rate will be lower, and the early growth will be poor (Yu et al., 2022). 3.2 Low temperature and microbial activity reduction Off-season planting is mostly carried out in cold weather, such as early spring or late autumn. At this time, the soil temperature is often below 15 ℃, and the activity of microorganisms in the soil will be greatly reduced. The mineralization of nitrogen, the decomposition of organic matter, and the reproduction of beneficial bacteria will all slow down. As a result, the plants can absorb less nitrogen, phosphorus, and potassium. The micro-ecosystem in the soil that helps fight diseases is also disrupted, making it easier for harmful bacteria to invade (Ado et al., 2022). Once the root environment of the ‘copper’ deteriorates, the roots will not grow well and the disease resistance will weaken. The accumulation of flowers and medicinal ingredients in the later stage will also be affected. 3.3 Nutrient leaching and availability In off-season planting, if there is too much watering or heavy rainfall, the nutrients in the soil are easily washed away, especially nitrogen, boron, zinc and other elements. In addition, some farmers’ organic fertilizers are not yet fully decomposed, which will also increase nutrient loss. In cold weather and when the soil humidity is too high, some phosphorus and potassium will become insoluble, and the crops cannot absorb them, and the nutrition will not keep up. If there is an imbalance of nitrogen, phosphorus and potassium or a lack of certain elements during the critical growth stage of the ‘copper’, the plant may grow short, with small and thin leaves, less flowering, slow fruit growth, and ultimately reduced yield and quality (Nogales et al., 2023). 3.4 Empirical examples of yield reduction under poor soil conditions Many field studies have shown that if the soil is not improved, off-season planting of L. japonicus can easily reduce yield. Under continuous planting, low temperature and high humidity, the yield of L. japonicus will be 15%~40% less than normal. In 2022, a planting base in Guizhou directly planted L. japonicus off-season on unimproved heavy clay soil. As a result, the yield was only 60% of the control plot, and the total alkaloid content decreased by 32%. A test site in Yancheng, Jiangsu, planted in a greenhouse in winter. Due to severe soil waterlogging and compaction problems, 28% of the seedlings died in the seedling stage, and the final quality of the medicinal materials did not meet the standards (Zhang et al., 2025). 4 Classification of Soil Improvement Techniques 4.1 Physical methods There are many ways to do deep tillage, such as intermittent deep tillage, deep ridge planting, and deep loosening. Their main function is to break up the compacted parts of the soil layer, reduce the density of the soil, make the soil softer, and make it easier to retain water. In this way, the roots of plants can go deeper and absorb nutrients more smoothly, and the yield and disease resistance will be improved (Hussein et al., 2019; Li et al., 2020; Tian et al., 2020; Wei et al., 2021; De Campos et al., 2022; Gu et al., 2022; Li et al., 2022; Hu et al., 2024; Kong et al., 2024; Benevenute et al., 2025). Studies have found that deep tillage can increase yields by 6% to 54% and is also beneficial to soil microorganisms and the root environment (Gu et al., 2022; Li et al., 2022; Hu et al., 2024; Kong et al., 2024; Benevenute et al., 2025). Mulching, such as covering the ground with straw or plastic film, can reduce water evaporation, maintain ground temperature, and suppress weeds and prevent soil from being washed away by rain. This method can also increase organic matter in the soil, improve soil quality, and promote microbial activity (Lal, 2015; Tian et al., 2020; Khangura et al., 2023). Sand mixing is to add some sand to heavy clay soil. This makes the soil more permeable and breathable, reduces compaction, and is also helpful for root growth (Lal, 2015; Khangura et al., 2023). Raised bed cultivation is to raise the planting bed so that drainage is better and water is not easily accumulated. This method is suitable for plots that are prone to waterlogging, which is beneficial to root health and more stable yields (Wei et al., 2021; Khangura et al., 2023).
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