soils Flashcards
(38 cards)
what is soil?
-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
what are properties of soil?
-soil pH, soil structure, aeration, soil temp, soil texture
-control the way the soil is used by plants and for human activities
how does water content affect fertility?
-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
how does water content and soluble materials affect fertility?
-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
how does air content affect soil fertility?
-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
how does soil pH affect fertility?
-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
how does soil biota affect fertility?
-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
how does soil texture affect fertility?
-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
how do human activities affect soil fertility?
-aeration by ploughing and drainage
-soil nutrient levels
-irrigation
-soil compaction
-pH control
how can aeration by ploughing and drainage increase fertility?
-ploughing and drainage make soils more aerobic
-this increases the rate of nitrogen fixation, nitrification, and the decomposition of dead organic matter
how does soil nutrient levels increase fertility?
-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
how can irrigation increase soil fertility?
-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
how does soil compaction affect soil fertility?
-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
what are the main types of soil erosion?
-rain splash
-wind blow
-surface run off
what are the natural reduction methods of soil erosion?
-windbreak
-reduction of raindrop impact
-organic matter
-plant roots
-infiltration
how is reduced agricultural productivity an impact of soil erosion?
-removes fertile topsoil
-reduces agricultural productivity and leads to malnutrition and poverty
how is sedimentation in rivers and reservoirs an impact of soil erosion?
-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
how is downstream flooding an impact of soil erosion?
-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
how is coastal sedimentation an impact of soil erosion?
-soil and sediments carried by rivers produce turbid water
-mangrove swamps slow the speed of moving water so that sediments settle in them
how is increase atmosphere particulates an impact of soil erosion?
-dust storms transport small soil particles causing erosion in one area and deposition in another
how is desertification an impact of soil erosion?
-gullies can form in a few weeks after heavy rain
-once if has formed, water naturally flows along it and increases erosion
how are landslides an impact of soil erosion?
-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
how does the human activity ploughing vulnerable soils lead to soil erosion?
-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
how does the human activity deformation and removal of hedgerows leads to soil erosion?
-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
