Slide 1 Cation Exchange CapacityCEC Slide 2 Cation Exchange Capacity https://www.spectrumanalytic.com/support/library/ff/CEC_BpH_and_percent_sat.htm Slide 3 Cations Cations are positively charged ions such as Calcium Ca++ Magnesium Mg++ Potassium K+ Sodium Na+ Ammonium NH4+ Slide 4 Cation Exchange Capacity The capacity of the soil to hold on to these cations the negatively-charged clay and organic matter particles attract the positive cations Slide 5 Cation Exchange Capacity These cations are easily exchangeable with other cations This makes them PLANT AVAILABLE Plants pick up nutrients in solution. Slide 6 Cation Exchange Capacity The CEC of a soil represents the TOTAL amount of exchangeable cations that a soil can adsorb this is mainly Calcium, Magnesium and Potassium also Sodium in drier climates Slide 7 CEC Units The CEC of a soil is expressed in meq/100g (milli-equivalents per 100 grams of soil) or cmol/kg Slide 8 What contributes to the CEC? Clay and organic matter particles are negatively charged the negatively-charged clay and organic matter particles attract the positive cations Slide 9 Clay particles & CEC Clay surfaces are negatively charged the negative charges on clay particles are permanent the charges do not change Slide 10 CEC & Organic matter OM 4-100X higher CEC than clay (per volume) depends on organic matter breakdown(surface area) the amount of charges (CEC) are pH-dependent https://www.pthorticulture.com/en/training-center/what-are-the-grades-of-peat-moss/ https://chathamtreeservices.com/chatham-kent-tree-services/wood-chips/ http://www.mryardoh.com/leaf_humus.html https://chathamtreeservices.com/chatham-kent-tree-services/wood-chips/ Low CEC High CEC Slide 11 CEC and pH as pH increases, CEC increases Visual Slide 12 Root Surfaces & CEC Cations are attracted to charged surface of cells within the root, called cortex cells. The plant root releases a hydrogen ion. The pH of the immediately surrounding soil decreases. Slide 13 Cation Aggressiveness as Valence increases aggression increases Na+ < K+ = NH4+ < Mg++ = Ca++ < Al+++(OH)2 < H+ Slide 14 Mass action all of you against me - pack mentality aggression is important one-on-one if you over apply NH4+ it WILL bump off Ca off the exchange sites Slide 15 Implications The higher the CEC the more clay or organic matter present in the soil This usually means that high CEC soils (clay) have a greater water-holding capacity than low CEC (sandy) soils Slide 16 Implications High CEC soils are less susceptible to leaching losses of these cations Slide 17 Implications For low CEC soils (sandy) a large one time addition of cations (fertilizers) can lead to large leaching losses the soil isn’t able to hold the excess cations more frequent additions of smaller amounts is better Slide 18 CEC Slide 19 Base Saturation a measurement that indicates the relative amounts of base cations in the soil it is the percentage of calcium, magnesium, potassium and sodium cations that make up the total cation exchange capacity Slide 20 Base Saturation For example, a base saturation of 75 % means that 75 % of the cation exchange capacity is occupied by the base cations Ca++, Mg++, Na+ and K+ Generally, the base saturation is relatively high in prairie soils (100%) The pH of soil increases as base saturation increases Slide 21 Soil base saturation at a neutral pH of 7 Slide 22 Slide 23 Slide 24 Slide 25 Slide 26 Slide 27 Determine how much specific nutrient is held on the Cation Exchange Complex STEP 1 Equation: base saturation % of specific nutrient X CEC (meq/100g) Calcium 84.9/100 X 26.7 meq/100gsoil = 22.67 meq Ca++/100g soil Slide 28 STEP 2 Determine ppm of specific nutrient (given meq/100g) Equation: meq/100g* X 10 X atomic mass/+charge * answer from step 1 Calcium 22.67 meq X10 X 40g/mol/2 = 4534 ppm Ca++/100g soil