FANR 3060 1st EditionLecture 18Outline of Last LectureI. Plant Growth FactorsII. Plant Uptake of NutrientsOutline of Current LectureI. MacronutrientsII. Secondary ElementsIII. Micronutrient CationsChapter 6I. Macronutrientsa. Nitrogeni. Fig 6.3b. Phosphorusi. Total amount in soils isn’t high1. Solubility very lowii. May be limiting, especially for legumes1. N fixationiii. Forms in the soil1. “mineral” Pa. Ca3(OH)3(PO4)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.i. Apatiteii. Weathers by hydrolysisiii. Occurs in rocksiv. Very insoluble2. Strongly absorbed PO4a. Bound to Fe oxidesi. Problem in highly weathered soilsb. Fig 6.43. Weakly absorbed PO4a. AEC sitesi. Not muchb. Have this problem in GAiv. In high Fe soils, P solubility goes down (deficient)1. Some plants have high solubility bya. Exuding organic compounds from rootsi. Exudatesb. Having a mycorrhiza association with fungii. Pinus: symbiotic association1. Obligatec. Potassiumi. Electrolyte/osmotic regulator in plant sap ii. 0.5-2% in plant tissueiii. Lots in most soils, but in mineral structure1. Mostly insoluble2. Becomes soluble by weatheringa. Takes a long timeiv. Forms1. Minerala. Feldspar, mica2. Strongly absorbeda. In 2:1 clay mineralsb. K fixationi. Trapped in hydrous mica (vermiculite) interlayer3. Weakly absorbed a. CEC sitesi. Readily available, depleted over timeII. Secondary Elementsa. Ca, Mgi. Divalent cations (have a +2 charge)ii. Major cations on CEC sites1. Ca: 50-80% of CEC cations2. Mg: 5-15% of CEC cationsiii. Deficient in low CEC/acidic soils1. Root elongation requires Ca at root tip2. Sands3. Btsa. Limit root growth/development4. Can add lime or gypsum to help this problemb. Sulfate anion (SO4-)i. Found in humus in large amountsii. Held on AEC sitesiii. Seldom deficient1. Except very sandy soilsiv. Acidic rain input1. Environmental regulations stop this, so now we have to add itIII. Micronutrient Cationsa. Used in plant enzyme/catalysis/energy systemsb. Narrow range between deficient and toxicc. pH very important in determining solubility d. Cu, Zn, Fe (2+, 3+), Mn (2+, 4+), Nii. Metal cationsii. Soluble at low pHiii. Insoluble at pH above 7.5-8iv. Toxic at pH less than 4.5v. Strong absorption by soil humusvi. Deficient in sands, peats, high pH soilsvii. Toxic in polluted soils, low pH