Download Soil Science: Origins, Factors, and Formation and more Study notes Earth Sciences in PDF only on Docsity! SOILS Introduction • True soil science is relatively new – In the US • Less than 100 years • Most of the good information is less than 20-25 years old • Major impetus was the dust-bowl days of 1930-33 • Originally conservation oriented – Europeans • Began worrying about soils in the late 1800’s • They ran out of land sooner than we did Definitions • Geologist’s concept – Regolith or weathered surface of the Earth – The junk that hides the good stuff • Agronomist's view—stuff to grow plants in • Soil Scientist’s View (a la Mueller + additions) – Soils are natural bodies which support plant life, with characteristics resulting from the integrating and synthesizing effects of living matter and climate acting upon parent material, as conditioned by relief, over periods of time, and modified by man. Factors in Soil Formation • Climate – Most important single factor – Controls both temperature and rainfall • Those control both mechanical and chemical weathering • Influence both type and abundance of vegetation Factors in Soil Formation • Living Organisms – Plant and animal matter – Organic accumulation – Nutrient cycling • Plants maintain the type of soil they like – Plants take up the nutrients they need – Other stuff is removed – Needed nutrients are returned when plant dies • Locally, plants love acid soils – Acid-making nutrients are held in the biomass – Alkali elements are leached away – Soil remains acid Docsity.com Factors in Soil Formation • Living organisms (continued) – Profile mixing • Ants bring yellow subsoil to the surface • In Iowa, the upper meter of soil is completely overturned by earthworms every 75-100 years – Nitrogen fixation – Roots impart structural stability to soil Factors in Soil Formation • Parent Material – Material that breaks down to form soil • Often, but not always bedrock • Locally it is sand that was transported – Controls initial chemical and mineral composition • Carbonate valley soils are basic • Local soils are acidic • Soils formed on shales are clay-rich, never sandy – Influences rate and course of the weathering cycle – Floodplain soils are rich because new parent material and nutrients are added regularly Factors in Soil Formation • Topography – Controls rate of erosion—always greater on steeper slopes – Controls moisture accumulation which influences rate of chemical weathering and vegetation • Soils thickest in valley bottoms where it is wettest • Thinner on hilltops • Thinnest on slopes where there is erosion – Can produce microclimates—low areas are coolest – Slope aspect • North-facing slopes are wetter and cooler and have more vegetation • South-facing slopes experience faster weathering due to more sunlight Factors in Soil Formation • Time – Older soils have better developed profiles • At what developmental stage is this soil? • Has this soil been subjected to a complex history? – As soils age they become more similar—Parent material becomes less and less important • Man modifies soils – Cultural activity – Agriculture Docsity.com
