Answer:
Desert soils are poor in organic matter because there are very less plant remains in the soil.
Explanation:
A desert has extreme conditions which support less life. Organic matter in soil called humus is formed by the deposition of dead plants and animals in the soil. Soil contains decomposing microbes which act upon the dead plant and animal remains converting them to organic matter.
In deserts the availability of water is very low which limits the growth of plants there. Animal population is also very less in desert areas. Above all that the extreme heat of the desert destroys the less amount of organic matter formed.