Concept:Poorly drained soil retains excess water, causing oxygen deficiency that affects soil life.
Explanation:In a poorly drained soil, water fills the pore spaces and displaces air.
This reduces the oxygen available to soil organisms.
As a result, the activity of beneficial microorganisms like bacteria and fungi decreases.
Conditions such as termite presence, high humus, or high fertility are not promoted by waterlogging.
Thus, the key characteristic is reduced microbial activity.
Answer:C. Decrease in the activities of micro organisms