NRES 201 Lectures 41 43 Fall 2014 Practical Nutrient Management NRES 201 Practical Nutrient Management 1 Practical Nutrient Management Today s lecture topics Some fundamentals Nutrient deficiency symptoms Plant analysis Basic aspects of soil testing 2 1 NRES 201 Lectures 41 43 Fall 2014 Practical Nutrient Management Natural versus managed ecosystems Nutrient removal is critical 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 Adapted from Foth 1984 3 Farming and nutrient management Manageable growth factors Moisture supply is often limiting in dryland farming but is not manageable Soil nutrients are manageable Basic goal To ensure that nutrient supply does not limit crop yields Interaction with moisture supply Soil moisture affects nutrient supply Adequate nutrients promote root growth And increase plant utilization of subsoil moisture 4 2 NRES 201 Lectures 41 43 Fall 2014 Practical Nutrient Management Plant nutrient uptake Fertilizer versus soil Fertilizer myths Nutrient uptake is mainly from fertilizer The soil is a minor source Good soils need more fertilizer than poor soils Fertilizer facts Nutrient uptake is mainly from the soil Fertilizers are supplemental Poor soils need more fertilizer than good soils 5 N Uptake lb A What is the main source for plant N uptake 200 Total N 150 100 Soil N 50 Fertilizer N 0 0 60 120 180 240 N Applied lb A Source Stevens W B R G Hoeft and R L Mulvaney 2005 Fate of nitrogen 15 in a long term nitrogen rate study II Nitrogen uptake efficiency Agron J 97 1046 1053 6 3 NRES 201 Lectures 41 43 Fall 2014 Practical Nutrient Management Crop Uptake Nutrient Sources for Crop Uptake Soil Fertilizer Time after Fertilizer Application 7 Importance of evaluating soil nutrient supply Economic implications Soils differ in nutrient supplying power So fertilizer requirements must vary For maximizing efficiency And profitability Soil B Optimum fertilizer rate Soil A Source Tisdale et al 1993 Environmental implications An accurate evaluation of soil nutrient supply Helps avoid overfertilization Or mining of the soil 8 4 NRES 201 Lectures 41 43 Fall 2014 Practical Nutrient Management Methods for evaluating soil nutrient supply Nutrient deficiency symptoms Plant analysis Soil testing 9 Origin of nutrient deficiency symptoms An indirect effect Caused by a 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 10 5 NRES 201 Lectures 41 43 Fall 2014 Practical Nutrient Management Common nutrient deficiency symptoms Nitrogen Pale yellowish green stunted plants V shaped yellowing along midrib older leaves first Premature senescence corn wheat rice Source Bennett W F ed 1993 Nutrient deficiencies toxicities in crop plants Am Phytopathol Soc St Paul MN 11 Phosphorus Reddish purple leaf tips and margins Most common on young plants corn wheat tomato Sources http www sdstate edu http cusomers hbci com http people umass edu 12 6 NRES 201 Lectures 41 43 Fall 2014 Practical Nutrient Management Potassium Yellowing and necrosis of leaf margins beginning on the lower leaves Lodging Seldom seen on Illinois soils corn soybean wheat Source Bennett 1993 13 Limitations of deficiency symptoms Misinterpretations Many symptoms not unique Or not due to nutrient deficiency Varieties may differ Seasonal occurrence Many symptoms are temporary Often promoted by cool weather Intensive scouting may not be feasible 14 7 NRES 201 Lectures 41 43 Fall 2014 Practical Nutrient Management Lack of predictive value When deficiency symptoms appear the damage has already been done The goal in nutrient management Is to prevent problems from occurring Not to wait until they do and then minimize the damage 15 Plant analysis Fundamental premise Plant nutrient concentration is directly related to soil nutrient availability Inherent limitation Plant nutrient concentrations also depend on plant growth 16 8 NRES 201 Lectures 41 43 Fall 2014 Practical Nutrient Management 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 Nutrient uptake will be reduced But so will plant growth 17 Options for plant analyses Tissue tests Chlorophyll meters Total analysis 18 9 NRES 201 Lectures 41 43 Fall 2014 Practical Nutrient Management Tissue tests Defined as Semiquantitative tests of the cell sap to predict deficiencies of N P K or S Procedure Sample the latest mature leaf Collect cell sap on filter paper Add color developing reagents Refer to a color chart that rates Source nutrient content as http www enasco com Very low Commercial source Low LaMotte Co Chestertown MD Medium http www lamotte com High 19 Chlorophyll meters Operating principle Measures leaf green color intensity as an indicator of N supply Advantages More convenient and rapid than tissue tests A reading can be made in 1 minute Non destructive Source Spectrum Technologies 20 10 NRES 201 Lectures 41 43 Fall 2014 Practical Nutrient Management Disadvantages Expensive approx 1 500 Variability of measurements Due to the small sensor 2 mm2 Variability among hybrids In color intensity leaf thickness etc Environmental variability Soil moisture content affects leaf color Readings are relative not absolute In field comparisons to a high N standard 21 Total analysis More quantitative than quick tests Measurements are done in the lab Sampling All or part of the plant Choice of plant part is important Usually the most recently matured leaf Source http www umass edu Sample preparation Plant material is dried ground and digested Analysis Can be done for one or more nutrients 22 11 NRES 201 Lectures 41 43 Fall 2014 Practical Nutrient Management Interpretation Usually by comparison to a critical nutrient range CNR 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 Source Tisdale et al 1993 23 Basic aspects of soil testing Defined as Rapid chemical analyses to assess the available nutrient status of a soil And the resulting interpretations and fertilizer recommendations Practical value