Nutrients: Nitrogen (N), Sulfur (S), Phosphorus (P), Potassium (K)

Nutrients: Nitrogen (N), Sulfur (S), Phosphorus (P), Potassium (K) Essential for all life, their availability (or lack thereof) controls the distribution of flora and fauna Look into their: Sources Pools (sinks) Fluxes root uptake +microbial uptake leaching <ul style="display: flex;"><li style="flex:1">solution </li><li style="flex:1">solid </li></ul>Nutrients must be in a specific form – specie - for use by organisms Soil Organic Matter Nutrient Cycling: N, S, P, K (CHONPS) Minerals (P, S, K) Primary Productivity OLeaves & Roots ADecomposition Heterotrophic respiration BGas loss SOM/Minerals Microbes leaching of nutrients plant nutrient uptake Nutrients: natural & anthropogenic sources (IN) and outputs (OUT) N2 fertilizers (chemical, manure, sludge) pesticides gases and particulates to atmosphere (fossil fuel combustion (coal/oil); cycles; trees) wet and dry deposition (acid rain, aerosols) plant tissue/residues harvesting root uptake SOIL Pools (sinks) (SOM/clays/oxides) Fluxes (transformations) <ul style="display: flex;"><li style="flex:1">ions and molecules in solution (leaching) </li><li style="flex:1">roots (exudates, biomass) </li></ul>colloidal transport erosion bedrock (1ry/2ry minerals in parent material) runoff The Nitrogen Cycle +The Nitrogen Cycle Denitrification: reduction of NO3 to reduced forms of N (N2) (energyconsuming) <ul style="display: flex;"><li style="flex:1">-</li><li style="flex:1">-</li></ul>NO3 is the most stable chemical form of N in aerated soil solutions N2 (g) is prevalent in the air of soil pores Atmospheric N deposition Fertilizer additions Nitrogen evolution (gases) 700 236 (+5) NO3 +5 -3 Oxic zone -(+3) NO2 -(+2) NO (+1) N2O (0) N2 N-fixation Suboxic zone N-mineralization immobilization NH3 (-3) Organic-N + sorption NH4 (-3) (~90% of soil N) N-fixation: enzyme- catalyzed reaction (occurs only in living organisms) Oxidation of N2 does not occur except in a few organisms (N-N triple bond) Nitrification: NH3 to oxidized <ul style="display: flex;"><li style="flex:1">-</li><li style="flex:1">-</li></ul>forms of N (NO2 , NO3 ) (energy-releasing) The Sulfur Cycle The Sulfur Cycle Sulfur undergoes dramatic changes in redox cycling Oxidation states range from +6 to -2 O2 sorption Sulfate found in oxidized environments 2- Oxic zone SO4 Suboxic zone degradation of organic materials (plant/animal) A large variety of organic forms of S reduced organic S Anoxic zone (thiol) S2- H2S M2+ + S2- = MS (pptation of metal sulfides) metal sulfides tend to be “insoluble” (Hg, Ag, Cd, Cu, Pb, Zn, Fe(II)) 2- In soil, SO4 originates from • Organic matter mineralization • Weathering of soil minerals • Sulfur inputs from atmosphere The Phosphorus Cycle 3- P primarily as phosphate (PO4 ), with an oxidation state of 5+ Mostly in organic P and inorganic P forms 3- PO4 is strongly retained by soils but can be transported in colloidal forms 3- PO4 sorption onto Al and Fe oxides is strong Phosphate minerals (low solubility): Al and Fe phosphates (acid mineral soils) (variscite, AlPO4.2H2O ) Ca phosphates (non acid soils) (hydroxyapatite, Ca5(PO4)3OH ) (strengite, FePO4.2H2O ) The Potassium Cycle Potassium as K+ with no changes in oxidation state K+ flux controlled by CEC & chemical weathering ~ no organisms Sources: Primary and Secondary Minerals

Nutrients: Nitrogen (N), Sulfur (S), Phosphorus (P), Potassium (K)

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