5.3 Soil degradation and conservation

how do soil ecosystems change

through succession, fertile soil contains a community of organisms that work to maintain functioning nutrient cycles and that are resistant to soil erosion

what are some human activities that can reduce soil fertility

deforestation, intensive grazing, urbanization, irrigation, monoculture

what effect do commercial industrialized food production systems generally have on soil fertility

they reduce soil fertility more than small scale subsistence farming

what can reduced soil fertility result in

soil erosion, toxification, salination, desertification

what are some examples of soil conservation methods

soil conditioners, wind reduction techniques, cultivation techniques, avoiding the use of marginal lands

how much area is now classified as having impaired biotic function as a result of poor land management resulting in soil loss

an area equal to the size of china and india combined

what are the two types of processes that can give rise to soil degradation

processes that take away the soil, processes that make the soil less suitable for use

when do processes that take away the soil occur

when there is no vegetation on the soil, wind and water can then simply take the soil away

when do processes that make the soil less suitable for use occur

where chemicals end up in the soil and turn the soil useless in the long run

what are three examples of human activities that lead to soil degradation

overgrazing, deforestation, unsustainable agriculture

when does overgrazing occur

when too many animals graze in the same area

what does overgrazing of grasslands do

leaves bare patches where roots no longer hold the soil together, when this is combined with the action of wind and rain, the bare patches become bigger and soil is removed from the area

how is the wealth of a man measured in many African countries

the number of cattle he has

what happened in the 70s and 80s in the Sahel area

a long dry period strongly reduced the growth of vegetation which was subsequently eaten by cattle, the soil particles were no longer kept in place by roots and were blown away by the wind, this resulted in the death of most of the cattle and a terrible famine

what often takes soil particles away in wet regions

rain water, especially when the rain water flows down slopes

what does overcropping do to the soil

depletes the soil nutrients and makes the soil friable (dry and susceptible to wind erosion), this reduces soil fertility as no nutrients are being returned to the soil

what can crop failure lead to in dry regions

removal of topsoil by wind

how big was the area affected by the dust bowl

an area about twice the size of the united kingdom

what is deforestation

the removal of forest, ranging from careful removal of some trees to complete removal of all vegetation

what happens as more and more vegetation is removed in areas of deforestation

as more vegetation is removed, more soil is prone to erosion

how will most erosion occur in deforested areas

due to water

how does vegetation in forest areas help stop soil erosion

leaves of forest trees deflect and slow down the progress of rain, the root systems help bind the soil together and give it stability while absorbing large quantities of water from the soil directly

what are unsustainable agricultural techniques

techniques that cannot be applied over a long period of time without decrease in productivity or increased inputs of chemicals like fertilizers or energy

what are some examples of unsustainable agricultural techniques

total removal of crops after harvest leaves the soil open to erosion, growing crops in rows with uncovered soil in between, plowing in the direction of the slope, this leave ready made channels for rainwater to flow down, taking the soil with it, excessive use of pesticides known as toxification, inefficient irrigation systems causing salinization, monocultures deplete nutrients and the soil loses its fertility

how is the land in cities changed

it is paved and built upon so removing it as a source of agricultural land and increasing run off which may erode soil elsewhere

why are many cities built on prime agricultural land

because major cities often expanded from early settlements that were based on agriculture

what are the three major processes of soil erosion

sheet wash, gullying, wind erosion

what is sheet wash

large areas of surface soil are washed away during heavy storm periods and in mountainous areas moving as landslides

what is gullying

channels develop on hillsides following rainfall, over time, these channels become much deeper

what is wind erosion

on dry soils, high winds continually remove the surface layer

what are typical soil conditioners

lime and organic materials

what additional benefit does lime have as a soil conditioner

it helps clay particles stick together so they act more like sand particles, the larger particles created are more free draining and trap more air, helping to improve decomposition by soil microorganisms

how does soil become more acidic

acid precipitation, the breakdown of organic matter releases carbon dioxide through respiration, this then dissolves into the soil water, creating carbonic acid, nitrification of ammonium ions to nitrates increases acidity, the removal of basic ions through leaching adds to soil acidity

what are some examples of organic materials that improve soil texture

straw or green manure crops

why are green manure crops a good source of nutrients

slow decomposition of the organic material means slow release of the nutrients and better absorption by the plant

how can the effect of the wind be reduced

by planting trees or bushes between fields (shelter belts) or by alternating low and high crops in adjacent fields (strip cultivation)

what can growing cover crops help with

helps keep the soil particles in place

what does terracing help with

reduces the steepness of slopes by replacing the slope with a series of horizontal terraces, separated by walls

what is contour farming and how does it help

plowing and cultivating along the contour lines by plowing parallel to the slopes, the ridges act as small terraces trapping soil and water and the water flow downhill and thereby erosion can be strongly reduced

what are the technical problems with contour farming

modern heavy machinery has a tendency to tip over when used parallel to the slope

how can plowing help

it breaks up the soil structure and temporarily increases drainage, traditionally plowing is done in the autumn and frost further breaks up clods of soil to make a seed bed for sowing

how can plowing be bad

it is bad for soil structure and microbial activity

what are some examples of ways irrigation can be improved

covering irrigation canals reduces evaporation, trickle flow irrigation reduces water lost through evaporation

how can we more effectively use land at the boundaries of deserts

we should accept that most of this land is not suitable for growing crops and would be better suited to cattle grazing

how many tonnes of soil are eroded from the landscape anually

24 billion

what is the Danum Valley area of Sabah, East Malaysia

an area of lowland tropical rainforest

what is the annual rainfall in the Danum Valley

over 2500 mm per year

what forestry operations occur in the Danum Valley

large parts of the forest are selectively felled

what is the consequence of the selective felling in the Danum Valley

there is an increase in stream flow compared to the areas with full canopy cover, this is because of the loss of transpiration returning water back to the atmosphere, though this increase is much less than in clear felled areas

why are the soils in the Danum Valley more sensitive to disturbance

because of the impermeable geology, water tends to flow in the top surfaces of the soil rather than percolating down into the bedrock, this means that heavy rainfall can create large flash floods

why is it very difficult for forest vehicles to cross the terrain without damaging it

the Danum catchment is covered by network of channels

what has happened where forestry companies have tried to drain areas in the Danum Valley

drainage channels have developed into large gullies that carry eroded soil into the river systems

how have logging roads in the Danum Valley affected the soil erosion

many of them have been built at very steep angles up slopes, the result of this is often mass movements of soil in large landslides, these eroded soils end up in local streams and rivers and are lost from the forest.