New grass can turn yellow when stepped on due to a phenomenon called "mechanical damage." When you step on new grass, you exert pressure on the delicate blades, which can cause physical injury to the plant cells. This damage disrupts the normal functioning of the grass, leading to a yellowing or browning appearance.
The yellowing occurs primarily because the plant cells are ruptured or crushed under pressure. The damaged cells are unable to carry out photosynthesis effectively, which is the process by which plants convert sunlight into energy. As a result, the grass blades cannot produce sufficient energy and nutrients to sustain their growth and vitality. Consequently, the grass may exhibit signs of stress, such as yellowing or discoloration.
Additionally, stepping on new grass can compact the soil, reducing air circulation and impeding water absorption. This compaction can further hinder the grass's ability to uptake nutrients and moisture, exacerbating its yellowing or browning.
However, it's worth noting that well-established and mature grass is generally more resilient to mechanical damage and can recover more quickly. Nonetheless, if the damage to new grass is extensive or repeated frequently, it may take some time for the grass to recover and regain its green color. Providing proper care, such as watering and avoiding excessive foot traffic, can help minimize the yellowing and promote the recovery of the grass.