Nutrient and physiological disorders – an overview:

This page provides an overview of nutrient and physiological disorders. The related tools listed at the end of the page provided detailed information about the identification and management of such disorders. It is important to have expert identification of nutrient and physiological disorders as symptoms may be confused with disease problems.

Nutrient disorders are caused by a lack of plant nutrients, or the presence of nutrients at levels toxic to the plant. They affect the functioning of the plant system. When suffering from nutrient or physiological disorders, the plant exhibits disease-like symptoms; therefore nutrient disorders are sometimes mistaken for a disease. Nutrient disorders may result in a reduction in yield.

Vegetable crops grow poorly when lacking a balanced and adequate supply of nutrients. It is vital that all of the essential nutrients needed by plants are present in adequate supply. A low supply of just one of them will limit growth until the nutrient is fully supplied.

The key to avoiding nutrient deficiencies is to ensure that the soil is healthy and contains plenty of well-rotted organic matter. The only way to confirm a nutrient deficiency (or toxicity) is to have soil or plant tissue tested. Soil tests also help to ensure that maintenance rates of fertiliser are not too high or too low.

Testing and correcting soil pH is important because it has an effect on the availability of plant nutrients. In slightly acidic to neutral soil the availability of plant nutrients is not restricted by pH. In moderately to strongly acidic soil, and as the soil becomes more alkaline, the availability of many plant nutrients decreases or increases to toxic levels.

Soil should be tested for pH and nutrient levels prior to planting, allowing for enough time to apply fertiliser. For example, P should be applied a few weeks before planting. Always discuss test results with a regionally based horticulturist as they will have experience on how plants respond to fertiliser applications on different soil types and in different production systems and regions. They will also be able to provide guidance regarding rates and timing of application, types of fertiliser, fertiliser placement and foliar applications.

Soil nutrients:

  • Macro-nutrients – Phosphorous (P), potassium (K), nitrogen (N), calcium (Ca), magnesium (Mg) and sulfur (S). Macro-nutrients constitute the main elements that a plant requires for its basic functioning.
  • Micro-nutrients or trace elements – Iron (Fe), zinc (Zn), manganese (Mn), boron (B), molybdenum (Mo), and copper (Cu). These elements are termed ‘minor’ because plants need them in only very small amounts; however, they are essential for normal growth.

Nutrient deficiencies – symptoms and remedies:

Symptoms are first seen in older leaves for some deficiencies, and in young leaves and/or tissues for others. This depends on the mobility of the nutrient. For mobile nutrients (N, P, K and Mg) deficiencies are first seen in older leaves; for immobile nutrients (Ca, B, Cu, Zn and Fe) deficiencies are first seen in youngest leaves and/or growing tissue. Typical nutrient deficiency symptoms and general information about corrective/preventative actions are provided in the table below.

Nutrient deficiency

Symptoms

Remedies
Phosphorous (P) – essential for cell division and plant growth; plays a key role in many physiological processes Poor germination, seedling establishment and plant growth; leaves may be dull bluish/greyish-green or have red pigment in leaf bases and dying leaves; oldest leaves may turn yellow and drop. Application of phosphorus fertilisers and manure, particularly from grain-fed animals.
Potassium (K) – vital component of plant functions such as nutrient absorption and water movement within the plant; increases vigour and disease resistance Older leaves have yellowing and scorching of edges and/or interveinal region; lettuce heads are loose; leaves may cup; fruit may be unevenly coloured or distorted. Increase K fertiliser rate; improve irrigation management.
Nitrogen (N) – needed for plant growth, fruit and seed production; a component of chlorophyll, the green pigment of plants that is responsible for photosynthesis Poor plant growth; older leaves are pale green to yellow and they eventually dry and drop; fruit and tubers are small. Add N fertiliser, for example as a side dressing before an irrigation; regular foliar sprays; improve irrigation management.
Calcium (Ca) – essential for new cell development; increases plant vigour Retarded growth; roots usually affected first, becoming brown; young leaves become yellow and distorted; blossom end rot in cucurbits and tomatoes; can be confused with the physiological disorder tipburn. Side dress with a Ca fertiliser; foliar spray susceptible crops at critical growth stages; apply lime or gypsum; existing damage is permanent.
Magnesium (Mg) – is vital for photosynthesis; regulates the uptake of other plant nutrients Growth retarded; chlorotic patches between the veins of older leaves; a triangle of green remains at base of leaf; leaf margins may burn. Application of fertiliser or weekly foliar sprays; main sources of Mg are dolomite and Epsom salts.
Sulfur (S) – required for protein formation and encourages vigorous plant growth and resistance to cold Yellowing of young leaves while older leaves remain dark green; growth stunted. Application of sulfate compounds.
 Boron (B) – essential for cell division, cell wall strength and development and transport of sugars; helps in the use of other nutrients Bushy stunted growth and dying growing tips; corky markings on plant parts; cankered patches on roots; internal brown rot; plant tissue can become brittle and split easily; hollow areas in stems. Application of boron-amended fertilisers or boron foliar fertiliser; existing damage is permanent.
 Iron (Fe) – essential for production of chlorophyll Leaves turn yellow/bleached between vein margins; stunting and abnormal growth; fruit may not mature. A weekly foliar spray of iron sulfate or chelate; reduce soil pH below 7.5.
 Manganese (Mn) – essential for the formation of chlorophyll and other plant processes Yellow patches between veins; reduced flower formation. Root drench or weekly foliar sprays with manganese sulfate; do not over-lime.
 Molybdenum (Mo) – required for chemical changes associated with nitrogen nutrition Symptoms depend on the function Mo has in N metabolism in the plant:
Legumes –unable to effectively fix N, plants may be stunted, pale green or yellow, similar to plants suffering from N deficiency; nodules on roots are green or colourless.Non-legumes – stunting and pale green or yellowish green colour between the veins and along the edges of leaves; leaf tissue of margins dies; older leaves more severely affected; cauliflower very susceptible (“whiptail” – drastic thinning of leaf blade, some leaf distortion, outer leaves yellow).		 Lime the soil to increase soil pH (to about 6.5, measured in water); soil or foliar applications of sodium or ammonium molybdate.
Zinc (Zn) – component of several plants enzymes; role in uptake of water  Plants appear stunted and pale with creamy yellow interveinal area; death of leaf margins; distorted young leaves. Application of a basal fertiliser containing Zn at sowing; application of a Zn foliar spray.
Copper (Cu) – important in processes that provide energy for growth and chlorophyll formation Chlorosis in young leaves; tips of leaves distorted; stunted growth. Apply a copper fertiliser

Nutrient toxicities: 

  • Chloride toxicity – Caused by saline water and soil conditions; plants wilt when soil moisture seems adequate; test and monitor irrigation water quality; plants vary in their tolerance to salinity.
  • Manganese toxicity – Yellowing of margins of older leaves; poor root development; favoured by acidic, waterlogged soil; lime soil to correct pH.
  • Ammonium toxicity “jelly butt” – Poor emergence followed by wilting and death of seedlings; browning of the central root tissue; favoured by excess ammonium from fertiliser or poultry manure in cold wet soil.

Physiological disorders of vegetable crops include:

  • Tipburn (physiological/nutritional) – a result of a calcium transport problem within the plant. 
  • Blossom end rot (physiological/nutritional) – caused by a deficiency of calcium or insufficient calcium uptake and translocation to growing points. 
  • Riciness of cauliflower.
  • Gomasho (grey speck) of cabbage and Chinese cabbage.
  • Measles on smooth skinned melons and cucumbers.

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