SS_Soil Fertility Evaluation

• Soil fertility evaluation


  Process of estimating the amount of native and residual elements which could be available for use by growing crops in particular soil and the amount of fertilizer to be supplemented for a profitable crop production
• Soil fertility evaluation

  1. Determining the fertilizer needs of specific crops and soils

  2. Achieving reliable and economic fertilizer combinations

  3. Checking wastage of fertilizers

  4. Minimizing soil and water pollution
• Methods used in soil fertility evaluation

  • Nutrient Deficiency symptoms
  • Plant Analysis
  • Biological Tests (pot test, experimental fields, microbiological)
  • Soil analysis or Soil Testing
• Nutrient deficiency symptoms


  When the nutrients needed by crop are not adequately supplied or are not utilized by the crop, specific biological or enzyme activities are adversely affected
• Manifestation of nutrient deficiency symptoms

  • Complete crop failure
  • Stunting
  • Poor yield and quality
  • Leaf discoloration
  • Root stunting
• Nutrient deficiency symptoms

  • Nitrogen - appearance of light green to pale yellow starting from the older leaves
  • Phosphorus - Mature leaves (dark green to blue green coloration). Acute case (red, purple or brown leaf coloration)
  • Potassium - chlorosis along the leaf margins followed by scorching and browning of tips of older leaves
  • Sulfur - chlorosis starts from young leaves
• Important considerations for nutrient deficiency symptoms

  • Difficulty in distinguishing deficiency symptoms from disease or insect damage
  • Many of the classic deficiency symptoms are associated with more than one mineral deficiency and with other stresses
  • Symptoms appear only after the supply of one nutrient is low that the plant can no longer function properly
  • Emphasis is given on wise use of deficiency symptoms in conjunction with other diagnostic methods
  • Hidden hunger - situation where crops is deficiency of a given element but does not show any symptoms
  • Seasonal effects - nutrient shortages caused or intensified by abnormal weather conditions
• Plant analysis


  Determination of the nutrient content of a plant part or whole plant sampled at a specific plant growth
• Types of plant analysis

  • Tissue Test - done on fresh plant tissue, in the field
  • Total analysis - done in the laboratory using precise analytical techniques
• Principle of plant analysis

  • As more of a nutrient is applied or present in the medium, the nutrient concentration in the plant increases as the yield increases up to a given point
  • The total amount in the plant is a function of the available supply in the soil
• Advantages of plant analysis

  • Diagnosing or confirming the diagnosis of visible symptoms
  • Identifying hidden hunger
  • Locating areas of incipient (early stage) deficiencies
  • Indicating whether the applied nutrients have entered the plant
  • Indicating interactions or antagonisms among nutrient elements
• Tissue test


  Rapid test for determination of nutrient elements in plant sap of fresh tissue
• Plant parts to be tested for tissue test


  • Conductive tissue of the latest mature leaf
  • Immature leaves at top of a plant is avoided
• Timing of tissue testing

  • The most critical stage of growth for tissue testing is at the time of bloom or from bloom to early fruiting stage
  • Nitrates are usually higher in the morning than in the afternoon if the supply is short
• Total test


  Quantitative method performed on whole plant or on plant parts. The dried plant material is digested with acid mixtures and tested for different nutrients quantitatively by different methods.
• The total test determination gives both assimilated and unassimilated nutrients such as Nitrogen, Phosphorus, Potassium, Calcium, Magnesium, Sulphur, Iron, Manganese, Copper, Boron, Molybdenum, Cobalt, Chlorine, Silicon, Zinc, Aluminum etc., in plants.
• Recently matured plant material is preferable for accurate analysis.
• Total test


  • Laboratory determination of total elemental content of plants or of certain plant parts using precise analytical techniques
  • Used for monitoring nutrient status of crops and diagnose existing nutrient problems
  • Serves as basis for nutrient recommendation for perennial fruit crops
• Plant samples are dried, ground, ash
• Laboratory test


  • Many elements can be determined simultaneously
  • Use of ICP Optical Emission Spectrometry, Flame Atomic Absorption Spectrometry
• Plant parts to sample for laboratory test

  • Recently matured material (leaves)
• Biological tests

  • Field Experiment
  • Indicator plants
  • Microbiological methods
  • Laboratory test and of experiments
• Field experiment


  Comparison of several treatments of fertilizer, lime, etc., including a control to answer specific questions under field experiment
• Pot experiment


  • Comparison of several fertilizer treatments including a control in a small amount of soil in pots to have a better control of environmental factors
  • Preliminary in nature
• Advantages of field experiments

  • Shows the integrated effects of the treatments with plants, soil, and other environmental factors
  • Provides a basis for calibration of other methods of soil fertility evaluation
  • Ultimate basis for determining economic fertilizer recommendation
• Disadvantages of field experiments

  • Expensive
  • Time consuming
  • Difficult to conduct numerous experiments for every soil fertility variation
• Advantages of pot experiments

  • Less labor intensive, simple and more rapid, less expensive
  • Suitable for large number of soils
  • Gives preliminary answers to specific questions or suspected problems
  • More sensitive method to determine or detect effects of secondary and micronutrients
• Disadvantages of pot experiments

  • Under artificial conditions
  • Not a good basis for determining yield per hectare or economic representations
  • Does not represent field condition; yield is overestimated
• Soil analysis or soil test

  Determination of the available amount of nutrients in the soil or its chemical properties, followed by evaluation, or interpretation and formulation of fertilizer recommendations
• Principle of soil testing


  Soil testing attempts to simulate the extraction capacity of the plant under a given soil condition using chemical extractants of suitable concentration
• Objectives of soil testing

  • To accurately determine the status of available nutrients in the soil
  • To provide a basis for recommendations on the amount of fertilizer and lime to apply
  • To build and/or maintain fertility status of a given field
  • To predict the probability of obtaining a profitable response to lime and fertilizer
  • To obtain a value that will help to predict the amount of nutrients needed to supplement the supply in the soil
• Disadvantages of soil testing

  • Useful only when soil test values are calibrated with yield responses to fertilizer levels
  • Expensive equipment needed
• Laboratory analyses for soil testing

  • Soil pH - potentiometric method
  • Soil Organic Matter - Walkley and Black method
  • Total N (%) - Kjeldahl method
  • Available P (ppm) - Bray or Olsen method
  • Exchangeable K (cmolc kg-1)
  • CEC
  • Other macronutrients
  • Other micronutrients
• Interpretation of soil tests


  • Degree of accuracy depends on several factors: Knowledge of the soil, Expected yield level, Level of management, Climate
• Interpretative categories of soil test results

  • LOW - Nutrient concentration in the soil is inadequate for optimum growth of most crops and will likely limit growth and yield. High probability of favorable economic response to nutrient additions.
  • MEDIUM - Nutrient concentration in the soil may or may not be adequate for optimum growth of most crops. Plant growth and yield may be limited by the availability of this nutrient. Low to moderate probability of a favorable economic response to nutrient addition.
  • OPTIMUM - Nutrient concentration in the soil is adequate for optimum growth of most crops. Very low probability of favorable economic responses to nutrient additions.
  • EXCESSIVE - Nutrient concentration in the soil is more than adequate for optimum growth of most crops. Nutrient additions most likely unprofitable and my have undesirable effects on growth of most crops.
• Soil testing methods

  Soil test kits - To preserve and improve soil health, which is essential to achieved food security; To make immediate soil management decisions on the field; To reduce workload of national extension services and soil laboratories
• Soil testing (rapid vs. laboratory) is a key to sustainable soil management and judicious application of fertilizers.