Answer:
1. Trimming the roots could cause dwarfing because nutrients are obtained through the roots, which aid in growing the plant.
2. Yes! You wouldn't want roots going upwards towards the stem, or in whatever direction they pleased. That they go downward assists the stability of the plant (like it not falling over).
3. So that they don't break off from the soil. They wouldn't anchor the plant if they were at the surface only.
4. Yams and sweet potatoes contain starch, which is a carbohydrate derivative of glucose.
5. They need to moderate the amount of heat they apply. The plants won't grow well in the heated soil because the organic matter in soil that helps plant growth isn't present. Although sterilization can kill bacteria and small animals like nematode worms, it should be done in moderation.
