NRES 201 Lectures 41-43 (Fall 2014): Practical Nutrient Management1NRES 201Practical Nutrient Management12Today’s lecture topics- Some fundamentals- Nutrient deficiency symptoms- Plant analysis- Basic aspects of soil testingPractical Nutrient ManagementNRES 201 Lectures 41-43 (Fall 2014): Practical Nutrient Management2Natural versus managed ecosystemsNutrient removal is critical- Nutrients recycle ina natural ecosystem- But must be replaced ina managed ecosystem,such as:- A tree farm- A fairway- Or a farm field 3Adapted from Foth (1984)Farming and nutrient managementManageable growth factors- Moisture supply is often limiting in drylandfarming, but is not manageable- Soil nutrients are manageableBasic goal- To ensure that nutrient supply does not limitcrop yieldsInteraction with moisture supply- Soil moisture affects nutrient supply- Adequate nutrients promote root growth- And increase plant utilization of subsoil moisture4NRES 201 Lectures 41-43 (Fall 2014): Practical Nutrient Management3Plant nutrient uptake:Fertilizer versus soilFertilizer myths- Nutrient uptake is mainly from fertilizer- The soil is a minor source- Good soils need more fertilizer than poor soilsFertilizer facts- Nutrient uptake is mainly from the soil- Fertilizers are supplemental- Poor soils need more fertilizer than good soils5What is the main source for plant N uptake?0501001502000 60 120 180 240N Applied (lb/A)N Uptake (lb/A)Total NSoil NFertilizer NSource: Stevens, W. B., R. G. Hoeft, and R. L. Mulvaney. 2005. Fate of nitrogen-15in a long-term nitrogen rate study: II. Nitrogen uptake efficiency. Agron. J.97:1046-1053.6NRES 201 Lectures 41-43 (Fall 2014): Practical Nutrient Management4Nutrient Sources for Crop UptakeSoilFertilizerCrop UptakeTime after Fertilizer Application7Importance of evaluating soil nutrient supplyEconomic implications- Soils differ in nutrientsupplying power- So fertilizer requirementsmust vary- For maximizing efficiency- And profitabilityEnvironmental implications- An accurate evaluation of soil nutrient supply- Helps avoid overfertilization- Or mining of the soilSource: Tisdale et al. (1993)Soil BSoil AOptimum fertilizer rate8NRES 201 Lectures 41-43 (Fall 2014): Practical Nutrient Management5Methods for evaluating soil nutrient supply- Nutrient-deficiency symptoms- Plant analysis- Soil testing9Origin 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 10NRES 201 Lectures 41-43 (Fall 2014): Practical Nutrient Management6Common nutrient-deficiency symptomsNitrogen- Pale, yellowish green, stunted plants- V-shaped yellowing along midrib(older leaves first)- Premature senescencecorn wheat riceSource: Bennett, W. F. (ed.). 1993. Nutrient deficiencies & toxicities in crop plants.Am. Phytopathol. Soc., St. Paul, MN.11Phosphorus- Reddish-purple leaf tips and margins- Most common on young plantscorn wheat tomato12Sources: http://www.sdstate.edu, http://cusomers.hbci.com, http://people.umass.eduNRES 201 Lectures 41-43 (Fall 2014): Practical Nutrient Management7Potassium- Yellowing and necrosis of leaf margins,beginning on the lower leaves- Lodging- Seldom seen on Illinois soilscorn soybean wheatSource: Bennett (1993)13Limitations of deficiency symptomsMisinterpretations- Many symptoms not unique- Or not due to nutrient deficiency- Varieties may differSeasonal occurrence- Many symptoms are temporary- Often promoted by cool weather- Intensive scouting may not be feasible 14NRES 201 Lectures 41-43 (Fall 2014): Practical Nutrient Management8Lack of predictive value- When deficiency symptoms appear, the damagehas already been done- The goal in nutrient management- Is to prevent problems from occurring- Not to wait until they do and then minimize thedamage15Plant analysisFundamental premise- Plant nutrient concentration is directly related tosoil nutrient availabilityInherent limitation- Plant nutrient concentrations also depend onplant growth16NRES 201 Lectures 41-43 (Fall 2014): Practical Nutrient Management9Implications- Any factor that limits growth will tend to increasenutrient concentrations- A deficiency of one nutrient will increase theconcentrations of others- If the deficiency is eliminated, other nutrientsmay become deficient- Unfavorable weather may or may not affectnutrient concentrations- Nutrient uptake will be reduced- But so will plant growth17Options for plant analyses- Tissue tests- Chlorophyll meters- Total analysis18NRES 201 Lectures 41-43 (Fall 2014): Practical Nutrient Management10Tissue testsDefined as- Semiquantitative tests of the cell sap to predictdeficiencies of N, P, K, or SProcedure- Sample the latest mature leaf- Collect cell sap on filter paper- Add color-developing reagents- Refer to a color chart that rates nutrient content as:-Very low- Low-Medium-HighCommercial source:LaMotte Co. (Chestertown, MD)(http://www.lamotte.com)19Source: http://www.enasco.comChlorophyll metersOperating principle- Measures leaf greencolor intensity, as anindicator of N supplyAdvantages- More convenient andrapid than tissue tests- A reading can be madein < 1 minute- Non-destructiveSource: Spectrum Technologies20NRES 201 Lectures 41-43 (Fall 2014): Practical Nutrient Management11Disadvantages- 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 standard21Total analysisMore quantitative than quick tests- Measurements are done in the labSampling- All or part of the plant- Choice of plant part isimportant- Usually the mostrecently matured leafSample preparation- Plant material is dried, ground, and digestedAnalysis- Can be done for one or more nutrients22Source: http://www.umass.eduNRES 201 Lectures 41-43 (Fall 2014): Practical Nutrient Management12Interpretation- Usually by comparison to acritical nutrient range (CNR)- The CNR must be appropriate- Not only for the specificcrop and nutrient- But also for the samplingtime- Nutrient balance is a problem- The concentration of onenutrient may affect theconcentrations of othersSource: Tisdale et al. (1993)23Basic aspects of soil testingDefined as- Rapid chemical analyses to assess the