Temperate soils exist under all types of conditions, including within forests, rain forests and in grasslands, but all have several key things in common. Temperate soils have a rich upper level that is high in minerals and nutrients, and in all cases micro-organisms work to break down decaying matter within the soil. The soil itself is considered to be temperate due to its layering, and these layers are referred to as horizons. In temperate soils there is a large Ohorizon and a rich Ahorizon, which is the upper layer and most defining.
In all temperate soils there is an army of microorganisms that work to break down both plant and animal matter as it dies and decays. The nutrients released from this breakdown are kept within the top two feet of the soil and provide a wealth of materials for new life to spring from. The ahorizon of temperate soils, the upper layer, is very dark and loaded with both minerals and nutrients. There is a sufficient amount of water present but not so much as to wash away the life-giving materials or to erode the soil.
In temperate forests, trees help trap water within the soil, and this slows the rate of decay so that more of the nutrients may be utilized by emerging plants and trees. These forests have a thick organic layer at the upper horizon, and at elevated temperatures they have been known to generate higher levels of Carbon Dioxide.
Temperate rain forests have many of the same characteristics, but there is a higher level of nutrient turnover and it is more rapidly used by plants. Another feature of temperate soils that comes into play here is the clay layer that they contain, which in a temperate rain forest helps to trap moisture within the soil. In this case the clay layer traps moisture that might otherwise have simply run off and caused the soil to erode and give up its nutrients.
Temperate grasslands have the same characteristics as temperate forests and rain forests except in this case it's the grasses that work to preserve nutrients within the soil. The upper level is indeed fertile, but the reason is slightly different, in this case being that the nutrients are created by the decomposition of shallow grass roots.
In all cases with temperate soils, there is a rich upper level of soil, microorganisms do the majority of the work during decomposition and there is enough water to slow the rate of turnover so that plants can better absorb the broken-down organic material. All of these environments are considered temperate regions of climate, regardless of whether it is forest, rain forest or grassland.