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 solid solution Nutrients must be in a specific form – specie - for use by organisms Nutrient Cycling: N, S, P, K Soil Organic Matter (CHONPS) Minerals Primary Productivity (P, S, K) O Leaves & Roots A Decomposition Heterotrophic respiration B Gas loss SOM/Minerals Microbes leaching of nutrients plant nutrient uptake Nutrients: natural & anthropogenic sources (IN) and outputs (OUT) N2 fertilizers (chemical, manure, sludge) gases and particulates to atmosphere pesticides (fossil fuel combustion (coal/oil); cycles; trees) wet and dry deposition (acid rain, aerosols) harvesting plant tissue/residues root uptake IN OUT SOIL Pools (sinks) (SOM/clays/oxides) Fluxes (transformations) OUT IN ions and molecules in solution (leaching) roots (exudates, biomass) colloidal transport bedrock (1ry/2ry minerals in parent material) erosion runoff The Nitrogen Cycle + The Nitrogen Cycle Denitrification: - - NO3 is the most stable N2 (g) is prevalent in reduction of NO3 chemical form of N in the air of soil pores to reduced forms aerated soil solutions of N (N2) (energy- consuming) Atmospheric N deposition Nitrogen evolution (gases) Fertilizer additions 700 (+5) +5 Oxic - denitrification NO3 (+3) zone - NO2 (+2) (mV) NO (+1) h E N2O Suboxic (0) nitrification N state oxidation N2 236 zone immobilization N-mineralization N-fixation -3 NH3 Organic-N (-3) (-3) immobilization + NH4 sorption (~90% of soil N) N-fixation: enzyme- Nitrification: NH to oxidized Oxidation of N2 does not 3 catalyzed reaction (occurs forms of N (NO -, NO -) occur except in a few 2 3 only in living organisms) (energy-releasing) organisms (N-N triple bond) 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 2- Oxic SO4 oxidized zone environments Suboxic degradation of zone A large variety of organic materials organic forms of S (plant/animal) oxidation/reduction reduced organic S Anoxic 2- (thiol) zone S 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) Ca phosphates (non acid soils) (variscite, AlPO4.2H2O ) (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.