Deep tilling literally refers to the act of plowing the soil deeply. The benefits gained from deep tilling include loosening the soil, stirring the organic layer, and regenerating root systems.

Because tea bushes are a long-term crop cultivated over several decades, the tea field's soil accumulates various issues over time. One major factor is the weight of people and machinery. Machinery used to manage tea gardens can sometimes exceed 100 kilograms, and a farm worker carrying fertilizer reaches a similar weight. As this weight repeatedly tramples the rows dozens of times, the soil becomes compacted and hard. Compacted soil loses its breathability and drainage, which hinders healthy root growth. Performing deep tilling loosens this hardened soil, improving its physical properties and promoting a healthy soil environment.

A second issue is the accumulation of an organic layer. Tea bushes are constantly pruned. Except for what is harvested, all twigs and leaves cut during pruning are returned to the rows between the bushes. While small amounts of organic matter are eventually broken down by soil microorganisms, any undegraded matter accumulates on the soil surface. This layer acts as a buffer when fertilizer is applied, reducing its effectiveness.

Finally, there is root regeneration. New tea roots are white, but as they age, they become woody and brown. Nutrient absorption and the accumulation of theanine are primarily driven by these young, white roots. By deep tilling and severing the old roots, new roots are able to grow into the freed-up space.

As described above, deep tilling in tea fields is a crucial task for supporting healthy root growth and maintaining high productivity. However, cutting the roots undeniably weakens the plant's vigor temporarily. Sufficient root volume must be secured from autumn to spring, when the plant absorbs nutrients for the following year's first-flush tea (Ichibancha). Therefore, deep tilling must be completed by early September at the latest, making it an extremely physically demanding task during the severe heat of late summer.

Written by Hiroki A.