Why is there little humus in the soil in arctic climates?

Deserts have little humus, because sand normally carries a positive charge. The cation exchange capacity measures how well or how poorly soil attracts, holds onto, and exchanges positively charged particles called cations. Opposites attract. So similarly charged sand and cation particles can't hold onto each other. As a result, sand drains fast, and loses minerals. There can be no buildup of organic matter, or of fertility, in such a situation.