A Short Course on Soil McDaniel s Nut Grove Wednesday, October 12 th, Soil Characteristics

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1 A Short Course on Soil McDaniel s Nut Grove Wednesday, October 12 th, 2005 Soils are unconsolidated natural mineral and organic materials at the earth s surface, differentiated by weathering and decomposition processes from the parent material Soil is a collection of natural bodies on the earth s surface, in places modified or even made by man of earthy materials, containing living matter and supporting or capable of supporting plants out-of-doors Soil Volume Mineral Organic Air Water Soil Characteristics - 1 -

2 Soil Solids (Mineral) Course Fragments gravel, etc. Fines Sand, Silt and Clay - 2 -

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4 Soil Structure Spheroidal or Granular Plate-like Prism-like columnar prismatic Block-like angular blocky subangular blocky Massive - 4 -

5 Soil Solids (Mineral) NB Organic matter improves structure improves drainage improves nutrient availability decreases bulk density Suspect if more OM present Poor drainage Toxicity issues - 5 -

6 Soil Volume (Water) 3 Phases Solid Liquid Gas Bent Molecule Neutral, but POLAR Polarity controls movement and retention in soil - 6 -

7 2 Stages of Water Movement 1) Infiltration 2) Subsurface Water Flow Infiltration Rate ~ cm/hr in general Infiltration rate are due to 1) hydraulic conductivity ~ a measure of water movement unique to each soil 2) incipient conditions ~ a measure of a soil s wetness and is a a function of: 1) soil water content 2) size distribution and tortuosity of pores - 7 -

8 Pores Pores are the tortuous pathways through which water and air flow - Pores occupy approximately 50% of the soil volume Interaggregate Pores vs Intraaggregate Pores Macropores Micropores - larger - smaller - important in water flow - little contribution to water flow & gas exchange & gas exchange Origin of Pores - roots decay to leave channels - worms and other animals burrow - soil drying shrinking and cracking - 8 -

9 2 Stages of Water Movement 1) Infiltration 2) Subsurface Water Flow - Saturated - Unsaturated Saturated Flow - occurs when pores are water-filled - most rapid in larger pores (e.g. sands) - flow in response to potential gradients: Gravity & Pressure - water drains freely from large pores by gravity and pressure potential s Unsaturated Flow - more common that saturated flow - more important than saturated flow? - controlled by liquid (water) adhesion and cohesion properties and the surface area of the soil - movement from areas of less negative to more negative potential - 9 -

10 Water Movement vs. Water Storage The soil matrix retains water against the pull of gravity - this is controlled by the adhesion and surface area - and is a function of Capillarity important in wet soils Adsorption important when soil is below field capacity

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12 Soil Volume (Air)

13 2 Saturated soils become quickly deficit of oxygen

14 IT S ALL ABOUT ENERGY! And it s a REDOX reaction CH2O (s) + O2 (g) 4e- CO2 (g) + H2O (g) Biologically mediated reaction RESPIRATION Respiration is a redox process in which O 2 serves as an electron acceptor

15 Redox Eh is the redox potential (volts) Measures the tendency of a substance to donate or accept an electron Related to a reference state (half reaction) H+ = e- + 1/2 H2 (arbitrarily taken at zero) More positive the Eh the easier the substance can be used as an terminal electron acceptor E 0 (volts) -.50 CO 2 /CH 2 O (-.43) H + /H 2 (-.42) S 0 /H 2 S (-.22) NO 3- /NO 2- (+.42) NO 3- /N 2 (+.74) +.70 Fe 3+ /Fe + 2 (+.76) ½ O 2 /H 2 O (+.82) Electron Tower Oxidation / Reduction Pairs - where first in pair is oxidizer (accepts e - ) - and second in pair is reduced (donates e-) Due to energy required to build molecules, strong e - donors are found at the top of tower, while strong e - acceptors are found at the bottom of tower. Therefore the amount of potential energy released by coupled redox reactions, is greatest the farther the e - falls

16 Soil ph Pools of Soil Acidity This is what 1. active - soil solution you measure 2. exchangeable - assoc w/ exchange sites on soil solids 3. residual - assoc w/ non-exchange site of soil solids Total Acidity = active + exchangeable + residual

17 Soils as/in a landscape Soil Forming Processes A. Additions B. Losses C.Translocation D.Transformation

18 Geomorphology

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23 Slope Classes 0 2% or 0 3% sometimes 0 6% A 2 8% or 3 8% sometimes 2 6% B 8 15% C 15 25% sometimes 12 20% D 25 35% sometimes 20 45% E 35 60% F Designated by a A, B, C, D, E or F at the end of the Map Unit Symbol Drainage Classes Redox Features and Mottling in Relation to Drainage Classes 0 6 in. very poorly drained 6 12 in. poorly drained in. somewhat poorly drained in. moderately well drained in. well drained in. somewhat excessively well drained > 52 in. excessively well drained

24 Reduced (anaerobic) Soil Conditions Consequences Carbon Accumulation (addition) Fe and Mn Reduction and Mobilization (transformation and loss) Sulfur sulfate to sulfide (transformation) Redoximorphic (Redox) Features causes Fe and Mn reduction and re-oxidation pattern Oxidized Fe = red Oxidized Mn = black Reduced Fe = blue/green gleyed (grey) = colors lost from area These colors are indicator of long-term conditions AND are reversible And the patterns are important!!! Soils with drainage classes = very poorly and poorly drained soils ~ Hydric Soils are soils soils saturated during growing season (soil temp > 5oC) sufficient to produce a reduced matric and support hydrophilic plants