As zonal soils are formed by the cumulative effect of climate and vegetation, I will first evaluate the effect that climate has on vegetation, and subsequently the type of soil. Climate will define the vegetation of an area, for example a podsol soil can be found in cool and wet climates where precipitation exceeds evapotranspiration, infact for a podsol to occur rainfall usually has to be between 1000mm to 1500mm a year, for example a podsol in the arctic will gain enough snow melt during spring to allow significant leaching to occur. Furthermore, the coniferous vegetation which is essential in the formation of a podsol will only form effectively where average summer temperatures are around 10°C; this coniferous vegetation provides the mor humus podsols have which supports its acidic nature. Coniferous vegetation have thin waxy leaves, normally pine leaves, which have a high cellulose content allowing slow decomposition, which will lead to the formation of a podsol. In Britain, coniferous vegetation is often found in upland areas, where conditions are cooler and wetter. The hillsides also encourage the movement of water through the soil. The heather and coniferous vegetation release few bases, and instead release humic acids which allow iron and aluminium to be carried in solution down through the profile to be deposited in the B illuviated horizon. On the other hand, for a chernozem to occur precipitation (500mm) is more or less equal to evapotranspiration, and there are warm summers accompanied by cold winters, this allows for the formation of grasses and herbaceous plants which provide the soil with its rich organic matter together with a plentiful supply of mull humus; again here we can see how climate determines vegetation which determines the type of soil. The vegetation which needs to be present for a latosol is normally deciduous, which provides constant leaf fall, for such vegetation to develop effectively high annual temperatures are required varying between 27°C to 28°C, and rainfall up to 2000mm, these climatic characteristics allow the rapid growth of the abundant vegetation and the constant supply of leaf litter required to counterbalance the rapid efficiency of humification. As you can see climate is imperative in determining the vegetation medium for the formation of soils, here we see a clear relationship.
Parent rock and weathering also have an affect on soil formation and are somewhat affected by climate. For example, just because a soil is surrounded by coniferous vegetation and the correct climatic conditions for the development of that vegetation, does not necessarily mean it will be a podsol; infact a podsol also requires a well drained parent rock, for example a coarse textured soil such as sandstone or quartzite, allowing the process of leaching. The parent rock needs to be broken down sufficiently to allow this free drainage; this is achieved by the process of weathering i.e. breaking down of the parent rock in situ. Weathering is achieved by mechanical weathering which relies on the freezing of water which relies on climate (temperature); chemical weathering which relies on water and solution which relies on water and solutions (precipitation); and biological weathering which relies on vegetation, which as explained above relies on climate. For example, in a latosol, a clayish parent rock is found, and the subsequent weathering of this parent rock allows it to retain as many nutrients as possible to sustain the rapid uptake of nutrients and the constant supply of water required by the vegetation.
Biota or organisms within soils are actually quite sensitive to the conditions and environment they live in. They are actually both directly and indirectly affected by climate. A direct link is that climate may immobilise any biotic activity as it may be too hot or too dry which may lead to the desiccation of many soil organisms. For example in a podsol soil, the cold climate actually discourages organisms, whereas the opposite is true in a latosol soil. The indirect link is concerned with factors such as soil acidity, rate of decomposition, amount of food available which is all determined by climate. An ideal example of the indirect link is the podsol soil; its acidity lies around 4.0 due to the leaching of organic matter, bases and sesquioxides, which is as a result of leaching (precipitation-climate) and also the slow decomposition of vegetation (vegetation-climate), this will discourage the earthworm activity as it is too acidic for their survival, this is why podsols have distinct horizons. However, a chernozem is abundant in biota and earthworms as its acidity (mull humus-climate), around 7, is optimum for earthworms, and the grasses and herbaceous plants (vegetation-climate) will be broken down rapidly to give a plentiful supply of food resources for the biota to utilise, this, along with the thick grass cover provides an ideal environment for biota to thrive in, this is why chernozems have indistinct horizons. Organisms will aid in aeration of the soil and also the merging of horizons, which helps in incorporating intimate humus into the lower A and B horizons.
Time for soils to develop and the rate of decomposition are also determinants in soil formation, and have a degree of relevance to climatic affect. Decomposition is achieved by decomposers which may include detrivores such woodlice and other macro-organisms; these organisms can only tolerate certain conditions, where the climate is too cold, such as the climate in a podsol, then these bacteria are restricted in their activity and thus breakdown is slow giving the podsol a low nutrient content. However, where temperatures are high and there is a copious amount of organic matter, then these decomposers and macro-organisms will breakdown rapidly as their activity increases; this can be seen by the low species diversity found in podsol soil locations and the extremely high species diversity observed in latosol soil locations such as tropical rainforests, hence it has been studied that rapid breakdown or humification is found in hot climates.
In conclusion, it can be seen that climate is imperative in determining soil formation factors such as vegetation, humus and nutrient status, soil organisms, parent material and many more. However, we must remember that azonal soils are only formed under the assumption that there are no extremes of parent material, drainage and relief; if there were extremes climate would not have a maximum effect.
