Lesson 15. Nutrient Deficiency, Toxicity and Control Measures

15.1 INTRODUCTION

Whenever the supply of an essential element becomes limited, plant growth is retarded. The concentration of the essential element below which plant growth is retarded is termed as “The element is said to be deficient when present below the critical concentration”.

15.2 NUTRIENT DEFICIENCY

In the absence of any particular element, plants show certain morphological changes. These morphological changes are indicative of certain element deficiencies and are called deficiency symptoms. The deficiency symptoms vary from element to element and they disappear when the deficient mineral nutrient is provided to the plant. However, if deprivation continues, it may eventually lead to the death of the plant. The parts of the plants that show the deficiency symptoms also depend on the mobility of the element in the plant. For elements that are actively mobilised within the plants and exported to young developing tissues, the deficiency symptoms tend to appear first in the older tissues. For example, the deficiency symptoms of nitrogen, potassium and magnesium are visible first in the senescent leaves. In the older leaves, biomolecules containing these elements are broken down, making these elements available for mobilize younger leaves.

The deficiency symptoms tend to appear first in the young tissues whenever the elements are relatively immobile and are not transported out of the mature organs, for example, elements like sulphur and calcium are a part of the structural component of the cell and hence are not easily released. This aspect of mineral nutrition of plants is of a great significance and importance to agriculture and horticulture.

The kind of deficiency symptoms shown in plants include chlorosis, necrosis, stunted plant growth, premature fall of leaves and buds, and inhibition of cell division. Chlorosis is the loss of chlorophyll leading to yellowing in leaves. This symptom is caused by the deficiency of elements N, K, Mg, S, Fe, Mn, Zn and Mo. Likewise, necrosis, or death of tissue, particularly leaf tissue, is due to the deficiency of Ca, Mg, Cu, K. Lack or low level of N, K, S, Mo causes an inhibition of cell division. Some elements like N, S, Mo delay flowering if their concentration in plants is low.

15.3 Nutrient deficiency and management

Generalized symptoms of plant nutrient deficiency

Nutrients

  Visual deficiency symptoms

N

: Light green to yellow appearance of leaves, especially older leaves, stunted growth, poor fruit development

P

: Leaves may develop purple colouration,  stunted plant growth and delay in plant development

K

: Marginal burning of leaves, irregular fruit development

Ca

: Reduced growth or death of growing tips, poor fruit development and appearance

Mg

: Initial yellowing of older leaves between leaf veins spreading to younger leaves, poor fruit development and production

S

: Initial yellowing of young leaves spreading to whole plant, similar symptoms to N deficiency but occurs on new growth

Fe

: Initial distinct yellow or white areas between veins of young leaves leading to spots of dead leaf tissue

Mn

: Interveinal yellowing or mottling of young leaves

Zn

: Interveinal yellowing on young leaves, reduce leaf size, short internodes, brown leaf spot on paddy

Cu

: Stunted growth, terminal leaf buds die, leaf tips become white and leaves are narrowed and twisted.

B

: Terminal buds die, breakdown of internal tissues in root crops, internal cork of apple, impairment of flowering and fruit development

Mo

: Resemble N deficiency symptoms, whiptail diseases of qualiflower, leaves show scorching and whithering

Cl

: Chlorotic leaves, some leaf necrosis

    Nitrogen deficiency symptoms in maize

Phosphorus deficiency symptoms in maize

Potassium deficiency symptoms in maize

Sulphur deficiency symptoms in maize

 

   Zinc deficiency symptoms in maize

Nutrient deficiency may not be apparent as striking symptoms such as chlorosis on the plant, especially when mild deficiency is occurring. However, significant reduction in crop yields can occur with such deficiencies. This situation is termed hidden hunger and can only be detected with plant tissue analysis or yield decline.

15.4 MANAGEMENT (CORRECTIVE MEASURES)

Nutrient deficiency can be correct by (i) addition of nutrient through fertilizer in soil as well as foliar application and (ii) addition of organic manure as per fertilizer recommendation.

Deficiency of Nutrient

Corrective measures

N

(1) Use of nitrogen fertilizer in the soil.

(2) Foliar spray of urea.

P

Application of phosphatic fertilizer in the soil e.g., DAP, super phosphate

K

Use of potassic fertilizer in the soil e.g., muriate of potash.

Ca

Use of calcium carbonate or calcium hydroxide in the soil.

Mg

Soil or foliar application of magnesium sulphate.

S

Soil or foliar application of sulphur or sulphate.

Fe

Soil or foliar spray of ferrous sulphate.

Mn

Soil or foliar spray of manganese sulphate.

Zn

Soil or foliar application of zinc sulphate

B

Soil or foliar spray of boric acid or borax

Cu

Soil or foliar spray of copper sulphate

Mo

Soil or foliar application of sodium molybdate or ammonium molybdate.

 

15.5 NUTRIENT TOXICITY AND MANAGEMENT

The requirement of micronutrients is always in low amounts while their moderate decrease causes the deficiency symptoms and a moderate increase causes toxicity. In other words, there is a narrow range of concentration at which the elements are optimum. Any mineral ion concentration in tissues that reduces the dry weight of tissues by about 10 per cent is considered toxic. Such critical concentrations vary widely among different micronutrients. The toxicity symptoms are difficult to identify. Toxicity levels for any element also vary for different plants. Many a times, excess of an element may inhibit the uptake of another element.

Nutrient toxicities in crops are more frequent for manganese (Mn) and boron (B) than for other nutrients.

Boron toxicity symptoms

Manganese toxicity symptoms

Manganese toxicity is found on acid soils. It is important to know that manganese competes with iron and magnesium for uptake and with magnesium for binding with enzymes. Manganese also inhibits calcium translocation in shoot apex. Therefore, excess of manganese may, induce deficiencies of iron, magnesium and calcium. Thus, what appears as symptoms of manganese toxicity may actually be the deficiency symptoms of iron, magnesium and calcium.

Boron toxicities occur in irrigated regions where the well or irrigation waters are exceptionally high in B. Most other nutrient toxicities occur when large amounts of nutrients in question have been added in waste, e.g., sewage sludge. Crops grown near mines and smelters are prone to nutrient toxicities. Generally, the symptoms of toxicity in crops occur as burning, Chlorosis and yellowing of leaves. Toxicities can result in decreased yield and/or impaired crop quality.

15.6 Prevention of toxicity

(1)   With the exception of Mo, toxicity of other nutrients can be reduced by liming.

(2)   Following recommended rates of fertilizers and the safe and controlled use of waste materials, such as sewage sludge and coal fly ash, should reduce metal loading and nutrient toxicity in crops.

(3)   Use of crop species and genotypes less susceptible to toxicity are recommended where toxicity is suspected.

(4)   Provided   sufficient drainage because availability of nutrients like Fe and Mn is increases up to toxicity level under water logged condition.

(5)   Ground water must be monitored regularly, if content of B and Cl is too high stop to applied water or applied with dilution.

(6)   Addition of sufficient amount of organic matter binds some of the toxic elements.

(7)     Ploughing in dry soil so increase the infiltration rate and leach the toxic element with rain water.

 

Excess Fe (iron) causes Mn (manganese) deficiency
Excess Ca (calcium) causes Mg (magnesium) deficiency

Excess P (phosphorus) binds to Fe, making it unavailable
And the reverse.