1. The Special Role of Roots: The Ability to Seek Water and Nutrients (Tropism)
Since plants are stationary, roots must actively seek water and nutrients through tropic movement. Tropism is the plant’s response to stimuli in a specific direction:
• If roots grow towards the stimulus, it is called positive tropism.
• If roots grow away from the stimulus, it is called negative tropism.
For example, roots always grow towards water sources (positive hydrotropism) and essential minerals, while avoiding harmful substances in the soil. This demonstrates that roots are not passive but actively seek water and nutrients. However, improper fertilization methods, such as surface application only, can cause roots to grow horizontally near the soil surface, making them more vulnerable to damage from drought, heavy rains, or diseases.
Common Consequences: Damaged roots create conditions for diseases to invade and weaken the plant.
2. Root Distribution in Crops:
Most roots are concentrated in the cultivation layer, especially at a depth of 10–100 cm, with the highest density at 40–50 cm.
• Fruit and perennial crops: Seed-grown plants have deep and strong roots; cuttings or grafted plants have shallow and horizontal roots.
• Fertilization and irrigation: Fertilizer should be applied around the tree’s canopy and focused on moist root areas. During rainy months, avoid digging trenches for fertilization, as this can lead to disease infiltration.
3. Nutrient Absorption by Roots:
Roots absorb water and nutrients when:
• The soil has sufficient moisture (nutrients must be dissolved in the soil solution).
• Roots have enough energy from respiration (Oxygen is essential).
Oxygen-deficient soil forces roots into anaerobic respiration, reducing their ability to absorb water and nutrients. This also makes roots more susceptible to diseases like root rot and yellowing leaves.