NRES 201 Lecture 39 Outline of Last Lecture I Basic aspects of micronutrients II Micronutrients in plants III Micronutrients in soils IV Losses of soil micronutrients V Factors affecting micronutrient availability VI Micronutrient deficiencies VII Micronutrient fertilization Outline of Current Lecture VIII Some fundamentals IX Nutrient deficiency symptoms X Plant analysis XI Basic aspects of soil testing Current Lecture Natural versus management ecosystems Nutrient removal is critical o 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 factors o 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 supply o Soil moisture affects nutrient supply o Adequate nutrients promote root growth and increase plant utilization of subsoil moisture Plant nutrient uptake Fertilizer versus Soil Fertilizer myths o Nutrient uptake is mainly from fertilizer o The soil is a minor source o Good soils need more fertilizer than poor soils Fertilizer facts o Nutrient uptake is mainly from the soil 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 Fertilizers are supplemental o Poor soils need more fertilizer than good soils Importance of evaluating soil nutrient supply Economic implications o Soils differ in nutrient supplying power so fertilizer requirements must vary in order to maximize efficiency and profitability Environmental implications o An accurate evaluation of soil nutrient supply helps avoid over fertilization or mining of the soil Methods for evaluating soil nutrient supply Nutrient deficiency symptoms Plant analysis Soil testing Origen 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 symptoms Common nutrient deficiency symptoms Nitrogen yellowing of plants Phosphorus purpling of plants most common on young plants Potassium Necrosis of leaf margins Lack of predictive value When deficiency symptoms appear the damage has already been done The goal is nutrient management o To prevent problems from occurring o Not to wait until they do and then minimize the damage Plant 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 growth Options for plant analysis Tissue tests chlorophyll meters total analysis Tissue Tests Defined as semi quantitative tests of the cell sap to predict deficiencies of N P K or S Procedure Sample the MRML Chlorophyll meters It measures leaf green color intensity as an indicator of N supply Advantages o More convenient and rapid than tissue tests o Non destructive Disadvantages o Expensive o Variability of measurements due to the small sensor o Variability among hybrids in color intensity leaf thickness o Environmental variability in soil moisture contents which affects leaf color o 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 the sampling 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 the resulting 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 response
View Full Document
Unlocking...