Soil Science (Sains Tanah) LU1 (Concept and Origin of Soil) PDF

STT1022 SOIL SCIENCE (SAINS TANAH) Concept and origin of Soil 1  SOIL SCIENCE Soil science is sometimes divided into two: EDAPHOLOGY The science of soils as media for plant production PEDOLOGY The science of soils as biochemically synthesi...

STT1022 SOIL SCIENCE (SAINS TANAH) Concept and origin of Soil 1  SOIL SCIENCE Soil science is sometimes divided into two: EDAPHOLOGY The science of soils as media for plant production PEDOLOGY The science of soils as biochemically synthesized bodies in nature (Brady, 1990) 3  SOIL – other definitions/ perspectives Geologic definition: Loose surface of the earth as distinguished from solid bedrock (support of plant life not required). Soil Taxonomy definition: Collection of natural bodies of the earth’s surface, in places modified or even made by man or earthy materials, containing living matter and supporting or capable of supporting plants out of doors. (Its upper limit is air or shallow water and its lower limit is the depth to which soil weathering has been effective.) 4  SOIL DEFINED The unconsolidated mineral and organic material on the immediate surface of the earth that serves as a natural medium for the growth of plants OR The unconsolidated mineral and organic material on the surface of the earth that has been subjected to and influenced by genetic and environmental factors of parent material, climate, macro- and microorganisms, and topography, all acting over a period of time and producing a product – soil – that differs from the material from which it is derived in many physical, chemical, biological, and morphological properties and characteristics 5 SOIL Component definition: Mixture of mineral matter, organic matter, water, and air. Example: Air 25% Mineral Matter 45% Water 25% 6 Organic Matter 5% 7  SOIL FORMATION (Genesis) Soil formation comprises 2 different processes: Weathering – the changes from a consolidated rock mass to the development of unconsolidated (loose) layer of material Soil Development – the changes occurring within the loose material as time passes 8  SOIL FORMATION WEATHERING SOIL the changes from DEVELOPMENT consolidated rock mass the changes occurring to the development of within the loose material loose layer of as time passes material PROCESSES: ADDITIONS LOSSES TRANSFORMATIONS TRANSLOCATIONS 10 Soil Forming Processes 11  WEATHERING (luluhawa) Two forms of weathering (disintegration & change): Physical Chemical Physical weathering – breaking or grinding particles to smaller sizes by agents such as water and ice wind temperature pressure 12  WEATHERING (contd.) Chemical weathering – the dissolving or alteration of minerals through various chemical processes: - hydrolysis - hydration - carbonation - oxidation-reduction - complexation producing dissolved ions & leaving resistant product! 13  Biogeochemical Processes Hydrolysis KAlSi3O8 + H2O -------- HAlSi3O8 + K+ + OH- (feldspar (solid) – solid) Hydrolysis 2HAlSi3O8 + 11H2O -------- Al2O3 + 6H4SiO4 (silicic acid) Hydration 5Fe2O3 + 9H2O ----------> Fe10O13.9H20 (Hematite) (Ferrihydrite) CO2 + H2O -- HCO3- + H+ Carbonation CaCO3 + H+ ------------> Ca2+ + HCO3- 14  Biogeochemical Processes Hydrolysis 3MgFeSiO4+2H2O ------ H4Mg3Si2O9+2SiO2+3FeO (Olivine (serpentine (soln) - solid) – solid) Oxidation 4FeO + O2 + 2H2O -------- 4FeOOH (Goethite) Complexation K2[Si6Al2]Al4O20(OH)4 + 6C2O4H2 + 8H2O --------- (Muscovite – solid) (Oxalic acid) 2K+ + 8OH- + 6C2O4Al+ + 6Si(OH)4 (Complex - soln) (soln) 15  What happens to the products of weathering? 1. Dissolved ions – some retained in the soil (mainly cations) - some leached out of soil profile 2. Least soluble materials – resolidify and remain as part of the soil solids 16 Weathering Scheme for Clay-Sized Minerals in Soils Minerals Most Easily Weathered: present only in slightly weathered soil (Gypsum, Calcite, Feldspars, Quartz) Secondary (Reformed) Minerals Produced from Soluble Products of Weathering Primary Minerals (Illite, Montmorillonite, Kaolinite, Gibbsite, Hematite) Minerals Most Resistant to Weathering Insoluble (Anatase, Zircon, Corundum) 17  SOIL FORMING FACTORS 5 soil forming factors that influence the rate of soil formation and type of soil formed: S = f(cl, o, p, r, t) ….. Hans Jenny (1940) or Parent material Climate (mainly temp. & precipitation) Biota (living organisms & organic residues) Topography (slope, aspect, & elevation) Time Thus, even if all soils were formed from the same weathering processes, they could still differ because of the above influences 19  Interactions of Soil Forming Factors - some examples Good drainage, mild temperature, high rainfall  rich biota  more residues  carbonic acid  dissolves parent material  bases leached, clay & organic matter particles move deeper Same climate, poor drainage  water-logged soils  poor biota Wet, cool forests  accumln of decomposing O.M.  strongly acidic, extensive colloid translocation Grassland, drier climates  dark O.M. accumulation 20  Conditions that Retard Soil Development 1. Low rainfall (slow weathering, little soluble material is washed from soil) 2. Low relative humidity (little growth of microorganisms) 3. High lime or Na carbonate content of parent material (PM) (keeps soil materials less mobile) 4. PM that are mostly quartz sands with few weatherable materials 5. High % of clay (poor aeration, slow water movement) 6. Resistant parent rock materials eg. Quartzite 21  Conditions that retard Soil Devlpmt (contd) 7. Very steep slopes (erosion, little leaching) 8. High water table (slight leaching, low weathering rate) 9. Cold temperatures (all chemical processes & microbial activity slowed) 10. Constant accumulation of soil materials by deposition 11. Severe wind or water erosion of soil material 12. Mixing by animals (burrowing) and humans minimizes net downward colloid movement 13. Presence of substances toxic to plants 22 SOIL HORIZONS Horizons = soil layers that are approximately parallel with the soil’s surface Horizon developed because of: differences in weathering with depth amounts of humus accumulated translocation of colloids by water other accumulations or losses Letter Horizons – labels on different soil layers – O, A, E, B, C, R Diagnostic Horizons – having specific characteristics that are indicative of certain classes of soils 23 A typical soil PROFILE (2-dimensions) & PEDON (3- dim) indicating the common layers or horizons: O; organic layer, and the 3 major horizons A; surface horizon B; subsoil C; substratum (unconsolidated or loose parent material) R; rock 25  What Soil Provides for Plants All soils provide the same growth factors to plants: 1. Physical support 2. Oxygen for roots need good porosity a few plants, eg. rice can transport air internally thro’ aerial part to roots 3. Water 300 – 800 mm/4-5 mths growing season for most crops 4. Temperature moderation 5. Nutrients 13 of 16 plant nutrients supplied by soil 6. Protection from toxins 26  Degradation and Destruction of Soils Degraded soil is one that becomes less productive as a result of: Intensive and over-utilization thereby exhausting the organic and mineral contents Soil erosion Salinization/salination Dumping of toxic wastes and chemicals Destruction of soils – due to: burning especially of organic soils heavy contamination by toxic heavy metals or large accumulation of salts that make reclamation impossible or impractical We will discuss more later towards the end of the semester!! 27  SOIL FORMATION PROCESSES FACTORS cl,o,r,p,t PARENT MATERIAL SOIL WEATHERING DEVELOPMENT ADDITION LOSSES SOIL TRANSFORMATION TRANSLOCATION 28  CONCLUSION Soil formation is stimulated by climate and living organisms acting on parent materials over a period of time and under the modifying influence of topography. Soil genesis starts when layers or horizons not present in the PM begin to appear in the soil profile - OM accumulation in upper horizons, downward movement of soluble ions, synthesis and downward movement of clays, and development of soil particle groupings in both upper and lower horizons. The 4 general processes of soil formation (gains, losses, transformations, and translocation) and the 5 major factors influencing these processes provide an invaluable logical framework in site selection and in predicting the nature of soil bodies likely to be found in a particular site. Conversely, analysis of horizon properties of a soil profile can tell us much about the nature of the climate, biological, and geological conditions, past and present, at the site. 29 MINERALS and ROCKS 30  What are MINERALS? Minerals are inorganic (non-living) substances that are homogenous, have a definite composition, and have characteristic physical properties such as shape, colour, melting temperature, and hardness – 2 classes Secondary Primary 31  Types (classes) of Minerals Primary Minerals (formed from cooling of molten rock) – eg Quartz (SiO2) Feldspars Orthoclase (K,Na)AlSi3O8 Plagioclase (Ca,Na)Al(Al,Si)Si2O8 Micas Muscovite KAl3Si3O10(OH)2 Biotite KAl(Mg,Fe)Si3O10(OH)2 Dark minerals (augite, hornblende, biotite, mica) Apatite 3Ca3(PO4)2.CaF2 Secondary Minerals (precipitated or recrystallized as solids from soluble substances) – eg Calcite (CaCO3), Dolomite ((Ca,Mg)(CO3)2) and Gypsum (CaSO4.2H2O) --- can also be primary! Iron oxides Fe2O3.xH2O Clays eg. Kaolinite, Illite, Montmorillonite, Vermiculite 32  What are ROCKS? Rocks are combinations of minerals into solid masses; classified into 3 major divisions: 1. Igneous (cooled molten rock, volcanic or extrusive if expelled from the earth, plutonic or intrusive if not expelled) eg. Granites, Diorites, Gabbros (intrusive) Rhyolites, Andesites, Basalts (extrusive) 2. Sedimentary (sediments deposited in water and consolidated – made into a hardened mass of rock) eg. Sandstones, Shales, Limestones, Quartzites 3. Metamorphic (igneous or sedimentary rocks changed by heat or pressure – hardened or changed mineral orientations) or chemical solution) eg. Gneiss, Schist, Slate, Quartzite, Marble 33