Which factor does NOT contribute to tree growth regulator degradation?

Tree growth regulators (TGRs) are substances that influence the growth of trees, and their effectiveness can be diminished through a variety of environmental factors. When considering these factors, soil type does not directly contribute to the degradation of TGRs. This is because degradation primarily occurs through processes such as photodegradation from sunlight exposure, chemical breakdown influenced by climatic conditions, or physical disturbances like wind which can enhance evaporation or dispersion of the regulator.

Sunlight is a critical factor since many growth regulators can break down when exposed to UV radiation. Climatic temperature influences the stability and activity of these chemicals, with extremes possibly accelerating degradation. Wind can also play a role in the physical dissipation of TGRs from the application site.

Soil type primarily affects the absorption and retention of water and nutrients but does not directly influence the breakdown of tree growth regulators in the same way that environmental factors such as sunlight, temperature, or wind do.