NRES 201 Lecture 39 Outline of Last Lecture I. Basic aspects of micronutrientsII. Micronutrients in plantsIII. Micronutrients in soilsIV. Losses of soil micronutrientsV. Factors affecting micronutrient availability VI. Micronutrient deficiencies VII. Micronutrient fertilization Outline of Current Lecture VIII. Some fundamentalsIX. Nutrient deficiency symptomsX. Plant analysisXI. Basic aspects of soil testingCurrent LectureNatural versus management ecosystems - - Nutrient removal is criticalo Nutrients recycle in a natural ecosystem but must be replaced in a managed ecosystem such as a tree farm, a fairway, or a farm field. Farming and Nutrient Management- Manageable growth factorso Moisture supply is often limited in dry-land farming but is not manageable. o Soil nutrients are manageable - Basic goal is to ensure that nutrient supply does not limit crop yields- Interaction with moisture supplyo Soil moisture affects nutrient supplyo Adequate nutrients promote root growth and increase plant utilization of subsoil moisturePlant nutrient uptake: Fertilizer versus Soil- Fertilizer mythso Nutrient uptake is mainly from fertilizero The soil is a minor sourceo Good soils need more fertilizer than poor soils- Fertilizer factso Nutrient uptake is mainly from the soilThese 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 Fertilizers are supplementalo Poor soils need more fertilizer than good soilsImportance of evaluating soil nutrient supply - - Economic implicationso Soils differ in nutrient supplying power so fertilizer requirements must vary in order to maximize efficiency and profitability - Environmental implicationso An accurate evaluation of soil nutrient supply helps avoid over fertilization or mining of the soilMethods for evaluating soil nutrient supply - - Nutrient - deficiency symptoms- Plant analysis- Soil testingOrigen of nutrient - deficiency symptoms: An indirect effect caused by nutrient imbalance- Certain organic metabolites accumulate while there may be a shortage of others, causing some type of abnormal condition that may produce diagnostic leaf symptomsCommon nutrient deficiency symptoms - - Nitrogen - yellowing of plants- Phosphorus - purpling of plants (most common on young plants)- Potassium - Necrosis of leaf marginsLack of predictive value - - When deficiency symptoms appear, the damage has already been done.- The goal is nutrient managemento To prevent problems from occurringo Not to wait until they do and then minimize the damagePlant analysis - - Fundamental premise: Plant nutrient concentration is directly related to soil nutrient availability - Inherent limitation:Implications - - Any factor that limits growth will tend to increase nutrient concentrations - A deficiency of one nutrient will increase the concentrations of others- If the deficiency is eliminated, other nutrients may become deficient - Unfavorable weather may or may not affect nutrient concentrations o Nutrient uptake will be reduced, but so will plant growthOptions for plant analysis - Tissue tests, chlorophyll meters, total analysisTissue Tests - - Defined as semi quantitative tests of the cell sap to predict deficiencies of N, P, K, or S- Procedure - Sample the MRMLChlorophyll meters - It measures leaf green color intensity, as an indicator of N supply- Advantages - o More convenient and rapid than tissue testso Non - destructive- Disadvantageso Expensiveo Variability of measurements due to the small sensoro Variability among hybrids in color intensity, leaf thickness o Environmental variability in soil moisture contents which affects leaf coloro Readings are relative, not absolute Interpretation is based on a comparison to a CNR (Critical Nutrient Range)- The CNR must be appropriate, not only for the specific crop and nutrient but also for thesampling time. - Nutrient balance is a problem - the concentration of one nutrient may affect the concentrations of others. Soil Tests - - Defined as rapid chemical analysis to assess the available nutrient status of a soil and theresulting interpretations and fertilizer recommendations. - Practical value - o The single most important guide to the profitable application of fertilizer and lime. o Inherently more useful than plant analysis because - Soil testing predicts what will be available Plant analysis measures what was available Requirements for a successful soil test - - Soil sampling should reflect the zone of active rooting- Extraction of the plant - available forms should be as complete as possible- The amount extracted should be measured with speed and accuracy- The amount extracted should be correlated with crop
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