Soil Around the World Answers

Soil fertility comes from a balance of the organic matter and mineral nutrients in a soil. The histosols of peat pogs are soils rich in organic material but poor in mineral nutrients, and are not fertile. Conversely, aridosols (desert soils) have an abundance of mineral nutrients but a dearth of organic matter and are also not fertile.

Fertile soils are generally those with well-developed horizons of both mineral and organic matter. In the case of the soils of flood plains, the soils lack such clearly defined, well-developed horizons and so they would not be expected to be fertile.

The over-irrigation of soil leads to water penetrating into deep soil layers and dissolving the salt present there. As the water evaporates out of the soil, the salt is drawn towards the surface with the water. This results in salt accumulating near the surface and reducing soil fertility.

Soil compaction results from human activities that press down on soil and eliminate much of the pore space between soil particles. This compaction and the loss of pore space reduces the soil’s ability to store water meaning that less water is absorbed by the soil when it rains. Instead the water flows as runoff, increasing the severity of flooding and erosion in the area.

Volcanic soil is rich in minerals from the volcanic deposits laid during eruptions and the lush plant life that adds necessary organic matter. The soil has not been leached of the minerals so it retains high fertility.

Over-irrigation adds excess water containing dissolved salts to the soil. As the water evaporates or drains away, the salts are left behind and build up, particularly when drainage is poor.

Heavy machinery can compact the soil and damage vegetation. Compacted soil absorbs less water, and with less vegetation to intercept and absorb rainfall, more water flows over the surface as runoff. This can make flooding more severe.

Flood-plain soils are generally fertile because floods deposit fresh sediment that replenishes soil nutrients. Although these soils are relatively young, the regular addition of sediment can support plant growth.

Organic matter can supply nutrients and improve soil structure, but plants also need essential mineral nutrients and suitable conditions such as the right pH, water availability, and drainage. If these are lacking, soil can remain infertile even when it contains a lot of organic matter.

Volcanic soil is fertile because it forms from ash and other volcanic materials that contain minerals. As these materials weather, they release nutrients that plants can use.