The natural fertility of soil depends on the amount of humus it contains, which is the most important factor for the yield of most agricultural crops. In which of the listed regions of Russia do soils have the thickest humus layer under natural conditions? 1) Arkhangelsk region 2) Tver region 3) Irkutsk region 4) Rostov region Write the number of the selected region.

Solution:

• The thickness of the humus layer is primarily influenced by climate and vegetation. Regions with a colder climate and abundant vegetation, such as the forest-steppe and steppe zones, tend to have thicker humus layers.
• The Rostov region is located in the southern European part of Russia, in a zone of typical and dark chestnut soils, which are fertile but may not have the absolute thickest humus layer compared to more northern regions with specific soil types like chernozems or grey forest soils under specific climatic conditions.
• Arkhangelsk and Tver regions are located in the northern and central parts of European Russia, respectively. While they have forests and some agricultural potential, their soils are generally not known for the thickest humus layer nationwide.
• The Irkutsk region is in Siberia and has varied soil types, but certain areas, especially those with steppe or forest-steppe vegetation, can develop deep humus horizons. However, it is the southern regions of Russia, particularly those with chernozem soils, that are renowned for their deep, fertile humus layers.
• Among the options provided, the Rostov region, situated in a major chernozem belt, is known for its highly fertile soils with a substantial humus content, supporting high agricultural yields.

Answer: 4