Explain the causes of soil degradation Explain the causes of soil degradation. Discuss the environmental and socio‑economic consequences of this process, together with management strategies.

What is soil composed of ?

Minerals = weathered fragments of rock (regolith) Organic matter = dead and living organic matter (bacteria, fungus, insects, rotting plant material (humus)) The decaying organic adds nutrient to the soil and these are absorbed again by plants growing in the soil. This is the nutrient cycle.

Soil is composed of three sizes of particles

The mix of the 3 types of particles in soil, gives soils different qualities. For instances, the ability to hold water.

Soil degradation……… A severe reduction in the quality of soils. The term includes soil erosion, salinization and soil exhaustion (loss of fertility). (this definition is in the syllabus so it could be on an exam!)

Soil degradation results from the following natural processes: Erosion by wind and water

Overgrazing as a cause of soil degradation Overgrazing removes vegetation cover and exposes the soil to wind and water erosion. Overgrazing can also remove nutrient matter from the cycle. The loss of decaying grass changes the amount of humus in the soil. Soils lacking in humus are nutrient poor and less able to hold moisture.

Many other agricultural practices (not just grazing)can damages soils in many ways: Overuse of pesticides may kill helpful organisms in soil. Bacteria, fungus and insects all assist in the decomposition and transfer of organic matter in soil Poor ploughing practices may expose soil to erosion and result in moisture loss. Ploughing turns the soil over and loosens it.

More on agriculture impacting soil… Monocultures may lead to depletions of certain nutrients from soil. Generally, over-cultivation may lead to nutrient depletion. Over-irrigation: Increased run-off resulting in soil erosion Leaching of nutrients (nutrients being washed out of the soil vertically) Salinization of soil

Salinization….

Deforestation as a cause of soil erosion Removal of trees and other vegetation results in the soil being exposed to water and wind erosion. Removal of vegetation removes nutrient from the nutrient cycle, less nutrient availble to the soil. Less decaying organic matter in the soil means less water retention by the soil.

The graph above represents the global pattern of soil degradation

Describe the regional variation for causes of soil degradation. Suggest reasons for the pattern you have described.

Impacts of soil erosion LOSS OF ARABLE LAND Arable land is any land that can be used to grow crops. Many of the practices used in growing those crops can lead to the loss of topsoil and destruction of soil characteristics that make agriculture possible. CLOGGED AND POLLUTED WATERWAYS Soil eroded from the land, along with pesticides and fertilizers applied to fields, washes into streams and waterways. This sedimentation and pollution can damage freshwater and marine habitats and the local communities that depend on them. INCREASED FLOODING Land is often transformed from a forest or other natural landscape, such as floodplains and wetlands, into a crop field or pasture. The converted land is less able to soak up water, making flooding more common. There are methods to improve soil water holding capacity as well as restoration and maintenance of wetlands.

Soil conservation methods: Shelter belts / wind breaks Terracing Reduced tillage methods Contour ploughing Drip irrigation Mulch Drought resistant crops Strip cultivation / intercropping Cover crops Green manure Soil conditioners Organic fertilisers

Shelter belts

Terracing

Terracing with vetiver grass

Reduced tillage

Contour ploughing

Drip irrigation

Mulch

Intercropping

Cover crops and Green manure

Soil conditioners add structure and nutrient to soil … Soil conditioners add structure and nutrient to soil …..lime, hay,bone meal,manure

Compost tea and giant veggies in Alaska.. https://www.youtube.com/watch?v=GaMNAfaebNc