NRES 201 Lecture 40 Fall 2014 Micronutrients NRES 201 Micronutrients 1 Micronutrients Today s lecture topics Basic aspects of micronutrients Micronutrients in plants Micronutrients in soils Losses of soil micronutrients Factors affecting micronutrient availability Micronutrient deficiencies Micronutrient fertilization 2 1 NRES 201 Lecture 40 Fall 2014 Micronutrients Elements considered micronutrients Essential for all plants 3 Essential or beneficial for some plants 4 2 NRES 201 Lecture 40 Fall 2014 Micronutrients Essential for animals but not plants 5 Micronutrient similarities Plant demand Essential but Required in only trace amounts by most plants From mg kg parts per million To g kg parts per billion Potential for toxicity Excessive amounts are harmful For part per billion ppb multiply the right hand commodity times 1 000 Source http www thejuryexpert com 6 3 NRES 201 Lecture 40 Fall 2014 Micronutrients Micronutrient differences Natural abundance Extreme range From the fourth most abundant element in the earth s crust Fe To a very scarce metal Mo Chemical properties Six exist as cations Co Cu Fe Mn Ni Zn Two exist as oxyanions B Mo Source http www periodictable com 7 Reasons for increased emphasis on micronutrients Higher crop yields Due to Improved crop varieties Higher plant populations More effective pest control Increased macronutrient fertilization Increased demand for micronutrients Source http www montgomerycountymd gov 8 4 NRES 201 Lecture 40 Fall 2014 Micronutrients Use of high analysis fertilizers Lower content of micronutrients as impurities Escalating production pressure Any yield limitation cuts profits Increased awareness of deficiencies Micronutrient deficiencies more likely to be diagnosed due to Fewer macronutrient deficiencies More sensitive methods of analysis Source http www deere com 9 Micronutrient functions in plants Known functions Source Brady and Weil 2002 Common role in enzymes As a constituent As an activator 10 5 NRES 201 Lecture 40 Fall 2014 Micronutrients Micronutrient content of soils Highly variable Among micronutrients And sometimes for a single micronutrient 11 Depends on Micronutrient content of parent material Stage of soil development as affected by Climate Topography Vegetation Time Cultivation drainage and synthetic N fertilization Leads to a decrease in organic matter content Organic matter binds many micronutrients 12 6 NRES 201 Lecture 40 Fall 2014 Micronutrients Forms of micronutrient cations Water soluble and exchangeable 13 Organically bound Chelated by soil organic matter Metal ions in solution are surrounded by oriented water molecules Chelation involves Replacement of two or more water molecules By electron rich organic groups Chelation decreases in the order Fe3 Cu2 Zn2 Fe2 Mn2 Chelation usually increases metal solubility 14 7 NRES 201 Lecture 40 Fall 2014 Micronutrients Minerals The major soil form Secondary precipitates formed by weathering Such as carbonates in calcareous soils 15 Forms of micronutrient anions Water soluble 16 8 NRES 201 Lecture 40 Fall 2014 Micronutrients Specifically adsorbed Some retention of Mo under acidic conditions Similar to P B reacts with exposed OH groups on clay minerals and oxides And becomes bound through ligand exchange Believed to be a major mechanism for B retention in Oxisols 17 Organically bound Important for B but not Mo B reacts with exposed OH groups on soil organic matter Believed to be a major form of soil B 18 9 NRES 201 Lecture 40 Fall 2014 Micronutrients Minerals The major soil form Secondary precipitates formed by weathering B adsorbed on CaCO3 in calcareous soils Mo reacts like P to form Fe and Al molybdates in acidic soils Ca molybdates in calcareous soils 19 Losses of micronutrients from soil Crop removal Generally small compared to total soil content 20 10 NRES 201 Lecture 40 Fall 2014 Micronutrients Leaching Negligible except for sandy soils All eight micronutrients retained by the solid phase Source http www ctic org Erosion Losses could be significant Volatilization Does not occur Source http www nrcs gov 21 Plant availability of micronutrient forms Available Water soluble Exchangeable Slowly available Specifically adsorbed Organically bound Unavailable Minerals Precipitates Source https www behance net 22 11 NRES 201 Lecture 40 Fall 2014 Micronutrients Factors affecting micronutrient availability Total soil content Determined by Micronutrient content of parent material Stage of soil development Deficiencies may be due to low soil content Co in New Zealand Source http hurricanecattlecare ie Soil texture Deficiencies of micronutrient cations more likely with sandy soils due to Low CEC Greater leaching losses 23 Organic matter content A source of micronutrients because organic matter Contributes CEC Chelates micronutrient cations Especially Cu Binds B in a stable form May decrease the availability of micronutrient cations By forming insoluble metal chelates Micronutrient deficiencies more common with organic soils Histosols than with mineral soils Especially for Cu Zn and Mn 24 12 NRES 201 Lecture 40 Fall 2014 Micronutrients Soil pH Availability of Fe Mn Zn Cu Co Ni and B decreased by higher pH due to A change in oxidation state For Fe and Mn Fe OH 3 H e Fe OH 2 H2O MnO2 4H 2 e Mn2 2H2O The oxidized form is much less soluble Precipitation As insoluble carbonates Increased microbial activity Promotes Fe and Mn oxidation Produces CO2 and HCO3 Greater uptake of Ca Mg and K 25 Mo and soil pH Availability increased by liming acidic soils due to Reduced fixation Dissolution of Fe and Al molybdates Fe2 MoO4 3 6 OH 2 Fe OH 3 3 MoO42Al2 MoO4 3 6 OH 2 Al OH 3 3 MoO42 Ca molybdates decrease Mo availability at high pH Analogous to P 26 13 NRES 201 Lecture 40 Fall 2014 Micronutrients Soil aeration Fe and Mn much more soluble in flooded soils Present as Fe2 and Mn2 Fe and Mn toxicities can develop Promoted by acidity Nutrient interactions Most are antagonistic Source Brady and Weil 2002 27 Micronutrient deficiencies Source Brady and Weil 2008 28 14 NRES 201 Lecture 40 Fall 2014 Micronutrients Micronutrient fertilization Differences compared to N P and K Apply micronutrients only if deficient Foliar applications common To maximize availability esp for Fe and Mn Low rates avoid salt burn Source Brady and Weil 2008 29 Micronutrients Today s lecture topics Basic aspects of micronutrients Micronutrients in plants Micronutrients in soils Losses of soil micronutrients Factors affecting