soils

Question 1

what is soil?

Answer 1

-makes up outermost layer of earth
-formed from rocks and decaying plants and animals
-has varying quantities of organic matter, minerals and nutrients
-natural processes can take more than 500 years to form 1 inch of topsoil
-decaying organic matter is called humus
-humus is dark, soft and rich in nutrients

Question 2

what are properties of soil?

Answer 2

-soil pH, soil structure, aeration, soil temp, soil texture
-control the way the soil is used by plants and for human activities

Question 3

how does water content affect fertility?

Answer 3

-colder soils occur when the soil is saturated in water
-waterlogged soil means that roots have no oxygen so die
-dry soils mean no moisture for plant uptake so will die
-wet soils can mean more leaching

Question 4

how does water content and soluble materials affect fertility?

Answer 4

-soil moisture (water) is essential as it supplies nutrients to plants e.g. nitrates, phosphates
-plants can only take up gravitational (or free) water- this water enters the soil during precipitation and infiltrates through the pore spaces
-hygroscopic water is held by adhesive forces to mineral particles

Question 5

how does air content affect soil fertility?

Answer 5

-the roots of plants and biota such as earthworms need oxygen to survive
-air is present within pore spaces that arent completely filled with water
-if no air is present & soil is waterlogged, roots won’t grow
-the crop yields will be reduced and eventually cease
-soil can be aerated by ploughing

Question 6

how does soil pH affect fertility?

Answer 6

-pH range from 5.5 to 7 is considered most fertile
-alkaline conditions increase leaching of materials from plants
-some plant types have a very small pH range for ideal growth, whilst others are more tolerant

Question 7

how does soil biota affect fertility?

Answer 7

-decomposers= fungi and bacteria help breakdown organic matter in the soil, lay important roles in biogeochemical cycles
-plant roots and lichens= break up rocks which become part of new soil. roots loosen the soil, allowing oxygen to penetrate. this benefits animals living in the soil
-detritivores= earthworms digest organic matter, recycle nutrients, and make the surface soil richer

Question 8

how does soil texture affect fertility?

Answer 8

-soil texture refers to how coarse the soil particles are
-soil texture is controlled by the parent rock & how easily it is weathered
-soil texture can be improved by adding organic matter

Question 9

how do human activities affect soil fertility?

Answer 9

-aeration by ploughing and drainage
-soil nutrient levels
-irrigation
-soil compaction
-pH control

Question 10

how can aeration by ploughing and drainage increase fertility?

Answer 10

-ploughing and drainage make soils more aerobic
-this increases the rate of nitrogen fixation, nitrification, and the decomposition of dead organic matter

Question 11

how does soil nutrient levels increase fertility?

Answer 11

-farmers increase soil nutrient levels by adding inorganic fertilisers, organic matter or by supporting natural processes that increase nutrient levels such as bacterial nitrogen
-farming can also deplete soil nutrient levels due to soil erosion, biomass removal, inhibiting natural processes that increase nutrient levels or by increased leaching of dissolved nutrients

Question 12

how can irrigation increase soil fertility?

Answer 12

-irrigation increases the fertility of soil where water is a limiting factor on growth
-having sufficient water allows plants to keep their stomata open and continue gaseous exchange when the soil would otherwise be dry
-water also dissolves nutrients which can then be absorbed by plants in ionic form

Question 13

how does soil compaction affect soil fertility?

Answer 13

-the excessive use of heavy machinery or high level stock densities can cause soil to become compacted
-this reduces aeration and makes water logging more likely, especially when the soil is wet

Question 14

what are the main types of soil erosion?

Answer 14

-rain splash
-wind blow
-surface run off

Question 15

what are the natural reduction methods of soil erosion?

Answer 15

-windbreak
-reduction of raindrop impact
-organic matter
-plant roots
-infiltration

Question 16

how is reduced agricultural productivity an impact of soil erosion?

Answer 16

-removes fertile topsoil
-reduces agricultural productivity and leads to malnutrition and poverty

Question 17

how is sedimentation in rivers and reservoirs an impact of soil erosion?

Answer 17

-detached particles generated by erosion are deposited elsewhere on the land or in our lakes, streams or wetlands
-deposition of sediment occurs when soil-laden water slows enough to allow the different sized particles to settle out

Question 18

how is downstream flooding an impact of soil erosion?

Answer 18

-flow capacity of rivers is reduced due to the build up of sediment
-developments also reduce infiltration rate of water into the soil due to impermeable surfaces

Question 19

how is coastal sedimentation an impact of soil erosion?

Answer 19

-soil and sediments carried by rivers produce turbid water
-mangrove swamps slow the speed of moving water so that sediments settle in them

Question 20

how is increase atmosphere particulates an impact of soil erosion?

Answer 20

-dust storms transport small soil particles causing erosion in one area and deposition in another

Question 21

how is desertification an impact of soil erosion?

Answer 21

-gullies can form in a few weeks after heavy rain
-once if has formed, water naturally flows along it and increases erosion

Question 22

how are landslides an impact of soil erosion?

Answer 22

-occur on steep slopes
-volume of sediment increases because the transported particles scour and dislodge more particles
-as runoff water moves down a slope, it increases in velocity and increases the potential of erosion

Question 23

how does the human activity ploughing vulnerable soils lead to soil erosion?

Answer 23

-vulnerable soils include: soil structure is poor, soils are dry, soils have poor drainage, rainfall is heavy, the land is sloping
-loses valuable topsoil
-increases erosion
-increases infiltration, leading to depletion

Question 24

how does the human activity deformation and removal of hedgerows leads to soil erosion?

Answer 24

-loss of natural vegetation and leaf litter reduces interception of rainfall, increases raindrop impact and increases the amount of runoff
-plant roots can’t hold soil together
-wind velocity at ground level increases due to lack of wind breaks
-impermeable bare surface

Question 25

how does the human activity overgrazing lead to soil erosion?

Answer 25

-if livestock density is too high, the vegetation will be eaten faster then it can grow, increasing the exposure of soil and the risk of erosion
-soil left exposed
-disturbance and root damage by hooves increase the risk of erosion

Question 26

how does the human activity reduced organic matter and soil biota lead to soil erosion?

Answer 26

-ploughing, reducing soil organic matter and the use of agrochemicals and all reduce the number of living organisms in the soil
-organic matter isn’t decomposed quickly and so cannot be incorporated into the soil
-nutrients can’t bind into soil

Question 27

how does the human activity cultivating steep slopes lead to soil erosion?

Answer 27

-surface water runoff flows more rapidly down steep slopes so it has more kinetic energy to pick up and carry soil particles
-cultivating with techniques that disturb the soil such as ploughing add to erosion risk
-increased speed of runoff so erosion will be accelerated due to more transported and dissolved materials

Question 28

how does the human activity soil compaction lead to soil erosion?

Answer 28

-the use of heavy farm machinery, high livestock densities and a reduction in soil detritivores make it more likely that soil will be compacted
-compacted soil has smaller interstitial spaces which reduces the infiltration rate so it’s more likely that rainfall will produce surface runoff and cause erosion

Question 29

what are some effects of accelerated soil erosion?

Answer 29

-reduced productivity
-sedimentation in rivers
-increased atmospheric particulates
-desertification

Question 30

how does long term crops reduce soil erosion?

Answer 30

-growth of crops that don’t require frequent replanting and soil disturbance reduces the erosion rate
-harvested after minimum of 5 years
-also include crops where plants aren’t dug up, just parts of them removed

Question 31

how does zero tillage reduce soil erosion?

Answer 31

-cultivation of the soil, using specialised machines, seeds are planted over previous years crop residue so no ploughing occurs
-cultivation that minimises soil disturbance reduces risk of soil erosion

Question 32

how does contour ploughing reduce soil erosion?

Answer 32

-ploughing up and down a slope creates furrows which speed up runoff
-ploughing along the contours creates ridges which slow water down, increase infiltration and reduce runoff and erosion

Question 33

how does tied ridging reduce soil erosion?

Answer 33

-increase water available to plants by collecting rainfall from unplanted sloping basins and catching it in furrows and ridges
-planting takes place on either side of the furrows, where the water infiltrates
-used on land almost flat
-field divided with criss-cross in intersecting ridges

Question 34

how does terracing reduce soil erosion?

Answer 34

-steps cut into steep hillsides and held together in place by walls
-they lower the gradient and shorten the slope thus reducing the amount and speed of runoff
-the walls also hold back the soil
-terraces are mainly used in tropical areas where rainfall is often very heavy
-expensive to construct and large machinery can’t be used

Question 35

how does windbreaks reduce soil erosion?

Answer 35

-hedges reduce wind velocity for 20 times its height but only if the wind is blowing in the right direction e.g. sunflowers

Question 36

how does multi-cropping reduce soil erosion?

Answer 36

-several crops are grown in the field at the same time or one after the other
-planting and harvesting are therefore at different times of the year, so soil isn’t left exposed
-works most easily when farmers use human labour rather than machinery

Question 37

how does increasing organic matter reduce soil erosion?

Answer 37

-increases humus content and binds the soil together
-legumes which fix nitrogen can be grown and then ploughed back into the soil
-this adds organic matter and increases nitrate levels
-protect soil from wind and impact of rain drops

Question 38

how does controlling livestock reduce soil erosion?

Answer 38

-overgrazing and trampling vegetation increases erosion
-if cattle congregate near water the soil can become boggy and compacted
-this is known as ‘poaching’
-reducing access to riverbanks where trampling is more likely to cause erosion into the river