Why does the united states purchase oil from other countries and the problem this sometimes causes

The oil produced in United States is light and low sulfur content and they do not have proper processing facilities, hence purchase it from other countries.

Explanation:

About 9.93 million barrels per day U.S purchase oil from 86 countries. Because the crude oil present is not homogeneous in nature. It is very light in nature with low sulfur content or may be high,this particular factor depends upon the method of the refining. Most of the oil are being exported by the Saudi Arabia and then comes Russia followed  by Iraq. Despite the collapse in price, U.S. dependence on foreign oil should continue to decrease.

1: most common garden plants prefer loam — soils with a balance of different-sized mineral particles (approximately 40% sand, 40% silt, and 20% clay) with ample organic matter and pore space. however, some plants grow better in sandy soils, while others are well-adapted to clay soils.

2: available water capacity is the maximum amount of plant available water a soil can provide. it is an indicator of a soil's ability to retain water and make it sufficiently available for plant use. available water capacity is the water held in soil between its field capacity and permanent wilting point.

3: it is the same for all living things (plants and animals). it also includes very tiny organisms that our eyes cannot see. they are known as microorganisms, and include viruses, bacteria and fungi.