Soil Science

Climate

Temperature & P/E

At the global scale, there is a strong correlation between soil properties and climate zone. Two aspects of climate are particularly influential on soil properties.

Temperature

 

Soil microbial activity increases from close to zero at 0°C to a maximum around 35-40°C. Many soil processes are affected by microbial activity, including nutrient cycling and soil organic matter turnover.

Precipitation / Evaporation

Examples:

Mt Kosciusko = High P, Low E
= High P/E
Alice Springs = Low P, High E
= Low P/E

The average water content of a soil profile and the amount of leaching it experiences are related to the ratio of water inputs as precipitation (P) to potential outputs as evapotranspiration (E).

High P/E ratio climates tend to produce moist, strongly leached soils.

A low P/E climate is associated with soils that are dry much of the time and are only weakly leached.


Soils and Climate zones

 

Low temperatures in the high latitudes (arctic and tundra) and in high alpine areas slow down soil chemical reactions. Growth of vegetation, soil biological activity, and soil-forming processes are all inhibited.

Cool climates of the mid-latitudes

The climate is moist and warm enough to allow vegetation to grow, including trees. It is also cool enough that annual evaporation is low. Soils tend to accumulate organic matter and be strongly leached. In the northern hemisphere, this includes the boreal zone dominated by conifer forests and podzols, and to the south, the deciduous forests associated with humus-rich soils and higher soil biological activity.

  

Warm Mid-Latitude Climates

In the mid-latitudes, areas with warm sub-humid to semi-arid climates are found in the interiors of all continents (prairie, steppe) and are characterized by grassland and woodland. Warm temperatures, moderate to low rainfall, and moderate to high evaporation mean that soil profiles are only partially leached. Calcium carbonate, alkalinity, and possibly salinity occur at depth. Soil organic matter tends to be low in the drier areas. Loss of surface cover by drought, overgrazing or cultivation can result in high soil losses by water or wind erosion. Disturbance of catchment hydrology can induce salinity.

Tropics

Soils in the tropics tend to be old, and this in combination with high rainfall and hot temperatures has resulted in deep, highly weathered soils.

In the humid tropics, where rainfall is highest, rainforest is the natural vegetation. Other areas have a savanna climate with lower, more seasonal rainfall. Soils tend to be leached and acidic, and high in kaolinite and sesquioxide clay minerals.

Deserts

 

In deserts, the low rainfall and high evaporation mean that there is no leaching of the soil profile. Soils accumulate soluble salts and calcium carbonate, and are alkaline. Plant residue production, humus accumulation, and nutrient cycling are restricted by the low available soil water. Wind erosion is a major soil-forming process, and the finer particle size fractions may be removed to leave sandy soil.

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