6 Parent Rock affects …DepthTextureDrainage / permeabilityQuality / nutrientsColourSome rock types are the dominant soil forming factor in the U.K. …Limestone soils –ThinstoneyAlkalineMuch calcium carbonate
7 CLIMATE – most important soil forming factor at the world scale CLIMATE – most important soil forming factor at the world scale. BIOTIC or ABIOTIC ?Wet climateMuch vegetationMore leaf litterMore humus
8 If Precipitation is heavy Main soil water movement will be downwardsLeaching nutrients downwards (K, Ca, Mg etc.)Eluviation of clay minerals
9 Where evapotranspiration Exceeds precipitationMain soil moisture movement is upwardsBy capilliary actionTaking nutrients up towards the surfaceGiving darker surface layers
10 RELIEF or TOPOGRAPHY BIOTIC or ABIOTIC? Higher land is wetterHigher land is cooler with shorter growing seasonAspect is important – south facing slopes are sunnier and drier in the northern hemisphere
11 Leaching on well drained slope Peaty gley – on flat summitPoor drainage on flat groundAt bottom of slope= waterlogging and gleying
12 The catena concept – nature of soil varies with position on a slope
13 ORGANISMS ( BIOTA) BIOTIC or ABIOTIC Plants, bacteria, fungi and animals all interact in the nutrient cycle.Plants take up nutrients from soil waterPlants return nutrients in leaf litterDecomposers rot the litter and make humus. Others mix it into the soil.
14 Mull HumusDeciduous leaves Not too acidic Encourage bacteria and worms Mix quickly into the soilCrumbly , black, nutrient rich soil e.g Brown EarthsMor HumusAcidic pine needles slow to decompose cold, wet upland areasFibrous, acidic and nutrient deficient surface horizon called mor e.g. in Podsols.
15 TIME BIOTIC or ABIOTIC?Soils form slowly400 years for 10 mms.Upland Northern Britain soils are under 10,000 years oldParent material and climate influence rate of developmentSand or clayWet and hot or cold and dry?
16 Originally the soil is like its parent material Over time the soil is less of a regolithWith more organic matter and organismsHorizons develop as the soil reaches a state of equilibrium with the environment.
17 A mature soil has four main components Biotic = …% Abiotic = …% 40%45% interchangeable10% + 5%