5.3 Soil degradation & conservation Flashcards
(22 cards)
why can fertile soil be considered a non-renewable resource?
because once depleted, it can take a significant time to restore the fertility, or in some cases it never recovers
Outline role of succession in soil fertility.
Exam-style Question
During succession, especially primary succession, soil is gradually formed from bare surfaces (like rock) through the breakdown of material by pioneer species such as lichens and mosses.
As more organisms colonize, they die and decompose, adding organic matter (humus) to the developing soil.
This increases nutrient availability, water retention, and improves soil structure, enhancing fertility.
Over time, as succession progresses toward a climax community, the soil becomes deeper, richer in nutrients, and more capable of supporting diverse plant life.
In secondary succession, soil is already present, but its fertility is improved more rapidly due to faster regrowth and increased biomass turnover.
what kind of human activity has caused processes of soil degradation/ reduce soil fertility?
overgrazing, deforestation, urbanisation, unsustainable agriculture like monoculture, irrigation
how does deforestation reduce soil fertility?
greater amount of trees removed = less interception = more soil compaction through raindrop impact = more soil erosion
how does urbanisation reduce soil fertility?
requires removal of vegetation through construction-> heavy machinery compacts soil surface = impermeable and water is unable to infiltrate into the soil -> instead it flows over the soil removing fertile topsoil
case study: the US prairies
The US prairies are so valuable because they have an extremely large amount of organic matter in their soil, with a large layer of topsoil that is extremely fertile, letting roots grow deep and making the soil very productive.
With the onset of drought in 1930, the overfarmed and overgrazed land began to blow away. The wheat shrivelled and died, and became exposed to bare earth leading to soil erosion, because there was no moisture to hold the soil together.
Thousands of residents died from dust pneumonia (clogging of lungs with dirt), there were food shortages, people fled into the city.
soil conservation in commercial farming: reduced tillage (ploughing). what is it?
the soil is not ploughed and ‘turned over’ after every harvest. new seeds are planted into holes, not into lines of ‘upturned’ soil.
soil conservation in commercial farming: reduced tillage (ploughing). evaluation
advantage:
- cheap
- not difficult to implement logistically
disadvantage:
- gets rid of traditional habits for many farmers potentially making it difficult to implement as one has to change mindsets
- could increase labour
soil conservation in commercial farming: reduced tillage (ploughing). why is it effective?
tilling/ploughing damages soil structure and kills soil fauna (eg: worms), so not tilling maintains the soil health better
soil conservation in commercial farming: mulch. what is it?
tiny pieces of organic matter, usually wood chips, are spread over the ground surface
soil conservation in commercial farming: mulch why is it effective?
it provides a surface cover, so less topsoil is eroded by the wind. also, the wood slowly decomposes to release nutrients and increase the soil carbon store
soil conservation in commercial farming: mulch evaluation.
strengths:
- cheap
- not difficult to implement logistically
- low timescale -> quick effectiveness
weaknesses:
- possibly not able to carry out in a large scale
how does intensive grazing reduce soil fertility?
- greater intensity grazing = more vegetation cover removed
- large herds/larger grazers = trampling = compact soil = impermable = increased potential for soil erosion (extreme cases eg. around bore-holes in semi arid regions -> desertification)
how does irrigation reduce soil fertility?
- salinisation
-> water used for irrigation evaporates -> leaves behind salts in the soil
-> salts build up, harder for plants to absorb water + nutrients
how does monoculture reduce soil fertility?
- only one crop needs the same set of nutrients -> nutrient imbalance (certain nutrients get used up faster than they can be replenished)
= soil exhaustion - loss of nutrients can be replaced by chemical / organic fertiliser = expensive
soil conservation in commercial farming = windbreak (wind reduction technique). what is it?
rows of trees or shrubs planted around fields to reduce wind speed across the soil surface.
soil conservation in commercial farming = windbreak (wind reduction technique). why is it effective?
by slowing down wind, they prevent wind erosion and protect topsoil (especially in open, dry areas)
soil conservation in commercial farming = windbreak (wind reduction technique). evaluate
pros:
- supports biodiversity
- can be a source of increased natural capital
cons
- takes time (trees need to grow)
- initial costs (planting/ maintanence) may be high
soil conservation technique in commerical farming = avoiding the use of marginal lands. what is it?
marginal lands are areas less suitable for agriculture due to poor soil fertility, steep slopes, low rainfall, or vulnerability to erosion.
soil conservation technique in commerical farming = avoiding the use of marginal lands. why is it effective?
helps prevent further degradation and maintains ecosystem stability
avoiding cultivation of these lands helps prevent further degradation and maintains ecosystem stability. evaluate
pros
- helps preserve native vegetation
cons
- LEDCs: ppl may rely on marginal lands for survival (land scarcity, poverty, population pressure)
- weak land tenure systems -> marginal land may be occupied informally and cultivated with no long-term planning
Explain why deforestation increases the amount of runoff. (2)
Exam style question
- Deforestation leads to more erosion, washing away the top layers of soil that are usually the best at absorbing water.
- Lack of roots means that the top layers of soil, that usually absorb the most water, can more easily wash away.
