NRES 201 Lecture 22 Outline of Last Lecture I. Why is this topic important?II. Soil aeration: Basic ConceptsIII. Composition of soil airIV. Oxidation - reduction (redox) potential V. What happens when a soil is waterloggedVI. Factors affecting soil aeration and EbOutline of Current Lecture VII. Ecological effects of soil aerationVIII. Managing soil aerationIX. Wetlands and their soilsCurrent LectureEcological effects of soil aeration- Residue decompositiono Microbial activities depend on soil aerationo More rapid decomposition under aerobic conditions Because most soil microbes are active And there is a high level of metabolic efficiencyo Much slower decomposition in poorly drained soils Because of fewer anaerobic microbes And much lower metabolic efficiency So organic matter accumulates- Nutrient availability o Soil aeration controls the oxidation status of several elementso Water logging promotes reduction of Fe and Mn With higher plant availability in neutral or alkaline soils But toxicities can develop in acidic soilso Fe reduction can increase P availability Because Fe phosphates become more soluble- Toxicitieso Redox potential determines the solubility and mobility of - Arsenic (As) Chromium (Cr) Selenium (Se)These notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.o Soil drainage will reduce toxicity by As or Se By promoting oxidationo Organic matter additions will reduce Cr toxicity By promoting reduction (and chelation)- Soil Coloro Affected by the oxidation status of Fe and Mno Well - drained, oxidized soils are red, yellow, and reddish - browno Poorly drained, reduced soils are gray or grayish - blue- Greenhouse gas emissiono Poor soil aeration promotes microbial production of - Methane (CH4) And Nitrous Oxide (N2O)o Like CO2, these gases absorb infrared radiationo Their atmospheric concentrations have increased markedly within the past centuryo Wetland soils are a major source- Plant growtho Lack of O2 is the main problem for plant growth in flooded or saturated soilso Plants respond by closing leaf stomata, which reduces: Photosynthesis Sugar translocation Water and nutrient uptake Hormone activityo Symptoms include: Wilting, Nutrient deficiencies DeathManaging Soil Aeration - - Container grown plants - o Potting mixes formulated to minimize water logging and poor aeration As well as for nutrient supplyo Soil-based potting mixes ⅓ mineral soil by volume Inert, coarse-grained materials promote drainage:- Perlite (expanded volcanic glass)- Vermiculite (expanded mica)- Pumice (porous volcanic rock)- Coarse sandWetlands and their soils- What is a wetland?o An ecosystem in transition between land and watero Distinguished by soils that are water - saturated near the surface and become O2 depleted from plant and microbial growth. - No wetland:o If the water is too deep for rooted vegetation to emerge or if the soil does not become O2 depleted. - Wetland hydrologyo Water balance - Inflow from:- Surface runoff- Subsurface seepage- Precipitation Outflow from- Evaporation- Transpiration o Hydro-period Refers to the temporal pattern of water table changes Daily hydro-period for coastal marshes Seasonal hydro-period for inland swamps, bogs, or
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