NRES 201 Lecture 38 Outline of Last Lecture I Terminology II Potassium in plants III Potassium in soils IV The Potassium cycle V Losses of soil Potassium VI Factors affecting Potassium availability VII Potassium fertilizer source Outline of Current Lecture VIII Basic aspects of micronutrients IX Micronutrients in plants X Micronutrients in soils XI Losses of soil micronutrients XII Factors affecting micronutrient availability XIII Micronutrient deficiencies XIV Micronutrient fertilization Current Lecture Essential for all plants B Fe Cu Mn Mo Zn Essential for some plants Cl Co Ni V Si Na Essential for animals Cr I Se Micronutrient demand in plants essential but only required in trace amounts by most plants Excessive amounts are harmful Micronutrient Differences Natural Abundance o Extreme Range From the 4th must abundant element in the Earth s crust Fe to the very scare metal Mo Chemical Properties o Six exist as cations Co Cu Fe Mn Ni Zn o Two are oxy anions Reasons for increased emphasis on micronutrients Higher crop yields due to o Improved crop varieties 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 o Higher plant populations o More effective plant pest control o Increased macronutrient fertilization Increased demand for macronutrients Common role in enzymes constituent and activator Macronutrient content in soils highly variable Depends on o Micronutrient content of parent material o Stage of soil development Climate Topography Time o Cultivation Drainage and Synthetic N fertilization Organically Bound Chelated by soil organic matter Chelation involves replacement of two or more water molecules by electron rich organic groups Chelation decreases in the order Fe Cu Zn Fe Mn Chelation increases metal solubility Forms of micronutrient anions Water soluble o B o Mo Specifically adsorbed o Some retention of Mo under acidic conditions o B reacts with exposed OH groups on clay minerals and oxides Organically bound o Important for B but not Mo o B reacts with exposed OH groups on soil organic matter o Believed to be a major source of B Losses of Micronutrients in Soils Crop removal generally small compared to total soil Leaching negligible except for sandy soils Erosion Losses could be significant Volatilization Does not occur Deficiencies more common with organic soils Histosols than with mineral soils Soil pH Availability of Six Elements decreased by increased pH due to o Change in oxidation o Precipitation o Increased Microbial Activity o Increase Uptake of Ca Mg and K Mo and soil pH availability increased by liming acidic soils due to o Reduced fixation o Dissolution of Fe and Al o Ca molybdates decreased Mo availability at high pH o Analogous to P Differences to N P and K Apply micronutrients only if deficient Foliar applications common
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