FANR 3060 1st Edition Lecture 15 Outline of Last LectureI. Soil Colloids – Variable Charge (con’t)II. Ion ExchangeOutline of Current LectureI. Soil ChemistryII. CECs/AECsChapter 5I. Soil Chemistrya. Moles of chargei. 6*10^23 chargesii. Aka an “equivalent”b. Milliequivalent (meq)i. 1/1000 of an equivalentii. Meq/100g soil 1. Typical unit for CECc. Centiequivalenti. Cmol/kg 1. Typical unit tooII. CECs/AECsThese 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.a. CECsi. Cation exchange capacityii. of clay minerals1. see table 5.1iii. of humus1. 80-150 cmol(+)/kg2. Varies with pH3. Table 5.7b. AECsi. Anion Exchange Capacity1. Of Fe oxidesa. 20-50 cmol(-)/kg oxide at pH 4c. CECs of Soilsi. Sandy Ap, low humus, mostly kaolinite, acidic1. 2-4 cmol(+)/kga. Very low2. Pacolet A in GAii. Clayey Ap, high humus, 2:1 clays, neutral1. 30-40 cmol(+)/kg2. Mollisol A in Illinoisd. Kinds of Exchangeable Cationsi. Bases1. Ca, Mg, Na, Ka. Don’t hydrolize nutrientii. Acids1. H+, Ala. Toxic to plant rootse. % Base Saturation equationi. Relative proportion of acids vs bases on CEC sitesii. %BS = (Sum of the bases/CEC) * 1001. CEC = sum of the cationsiii. At pH 5, %BS = <50%1. Al becomes more soluble and more toxiciv. Liming neutralizes acids, adds Ca to soil, raises pH1. pH = 6.5 is as high as you want to gov. You want %BS to be big1. Aka a small CECf. Application of CEC/AECi. Plant – available nutrients (K, Ca, Mg)1. Nearly all in exchangeable form2. Added fertilizer held on CEC sitesii. Contaminant adsorption1. Occurs on CEC sites2. Ionic pesticides, heavy
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