Fact 1: The looseness of soil has a positive impact on a plant 's roots' growth in that soil.

Fact 2: To improve soil, add several top-dressings of dirt or compost.

Given the two facts above, answer the question "What has a positive impact on a plant's roots' growth?" with the following options: 
- reducing acid rain
 - color of dirt
 - looseness of dirt or compost
 - basic building blocks of life
 - biological diversity
 - lead in the soil
 - Evaporation of water
 - a lack of soil


 

   looseness of dirt or compost      