Nutritional Deficiencies In Crops!

November 27 2006: PLANT nutrients, if available in adequate quantity, prevent crops from diseases. If inadequate, these can cause abiotic (non-infectious) and biotic (infectious) diseases.

In this scenario, soil tests and plant tissues analysis are used to determine the status of various nutrients and to diagnose the deficiencies that may exist for sustained productivity of crops.

Soil fertility assessment may be defined as a chemical or physical measurement of soil, but in the customary sense, it refers to laboratory analysis to assess the available nutrient status and elemental toxicity.

A soil testing programme includes the analysis of electrical conductivity, soil pH, and organic matter, lime content and physico-chemical characteristics.

However, soil fertility can be managed with the application of fertilisers but a farmer must be aware of the nature and severity of the nutrient problem in his field for arriving at a decision regarding the kind and dose of fertiliser to be applied. It is important to classify soils according to their fertility status as they tend to vary from place to place due to various soil forming processes. Only a soil analysis provides actual data for physico-chemical and biological properties at various depths.

According to reports, Pakistani soils are seriously and severely deficient in major and minor plant nutrients. About 100 per cent of the analyzed soils found were deficient in nitrogen due to very low organic matter, whereas, phosphorous and zinc deficiency was also high to that of potassium, boron and iron.

Nutrient deficiencies could be improved through judicious and balanced use of fertilisers; introduction and use of micro-nutrients and potash; integrated use of bio-organic and mineral sources of nutrition; and improved techniques like fertigation, foliar fertilisation, composts, and mulching etc. All this needs integrated plant nutrition management system (IPNMS) which includes the following three objectives:

* To maintain or enhance soil productivity through the balanced use of mineral fertilisers combined with organic and biological sources of plant nutrients.

* To improve the stock of plant nutrients in soil.

* To improve the efficiency of plant nutrients, thus limiting losses to the environment.

Soil sources (13 essential nutrients); mineral fertilizers and organic fertilizer (such as the farm yard manure, animal droppings, green manures, crop residues (wheat straw, cotton sticks, sugarcane trash and rise husk), industrial wastes (filter cake and stillage), sewage sludge (waste water, fish pond effluent, city refuse and wastes of food processing industries), biofertilizers (nitrogen fixers, decomposers, nutrient solublizer, plant growth stimulator, plant growth promoting bacteria) and compost are main components of the IPNMS.

Symptoms of abiotic diseases in crops occur due to nutritional deficiency. Growers fail to identify the symptoms whether these are due to nutrient deficiencies or imbalanced use of plant nutrients. They mostly consider these as virus.

No doubt that most of the diseases show similar symptoms but these may also not be the signs of infectious diseases as it may be due to deficiencies or non-judicious use of fertilisers for nutrients. Therefore, the most common and major symptoms are discussed which mostly are due to nutritional deficiencies.

Nitrogen: In case of nitrogen deficiency, the leaves become small, turn to yellow in colour. Deficiency inhibits the cell division hence vegetative growth is retarded. It also causes lowering of respiratory rate. Some fruits shed leaves causing heavy setback.

Phosphorus: Leaves appear dark green in colour. Sometimes dead patches appear on leaf petioles. Retarded growth and purplish discoloration of foliage are most typical symptoms. The leaves of deciduous tree become narrow and fruit becomes soft prior to maturity. In apple, fruit drop is common, juice decrease and leaves fall early.

Potassium: This deficiency causes dieback of young shoots and leaves. Scorched appearance is observed. The leaf margins become dull yellow. Appearance of V-shaped chlorotic spots, rolling, cupping and curling is common in deciduous fruits, major quality of fruit and vegetables are also affected.

Sulfur: The pale green colour or chlorosis occur due to lack of sulfur. Younger leaves are affected more. Leaf fall is rapid with stunted chlorotic growth, and thinner and woody stems.

Calcium: Calcium deficiency stuns growth, apical buds disintegrate and secrete gummy fluid, causes blossom end rot in tomatoes and pepper, bitter pit in apples, hindered seed formation, and chlorotic patches on leaf margin appear. Calcium also retards movements of carbohydrates.

Magnesium: Magnesium deficiency leads to inter-veinal chlorosis. In vegetables, crimson reddish or orange and yellow colour in cabbage, dead spots on turnips, yellowing in foliage structure and retardation in cell division occur.

Boron: Young growing cells discolour, young leaves brittle, flowering suppress, slow pollen tube growth reduces stigmatic secretion with corky core in apples make citrus hard and hollow stems in cabbage and cauliflower appear. The deficiency appears first as abnormal of apical growing points. The youngest leaves lose shape and wrinkle and are often thicker and of brackish blue green colour. Deformed and curled leaves appear in rapeseed and mustard plants. Root development is also affected and found thickened with necrotic tips.

Chlorine: Due to lack of chlorine there is burning of leaf tips or margins with abscission of leaves and reduction in yield and quality.

Copper: In fruits, gum pockets develop under bark, twigs die back in citrus, fruit drops before maturity, cupping in tomatoes and rolling of leaves is common. The leaf tips later become white and leaves narrow and get twisted. Depressed internodes result in dwarf and bushy plant. The ears are jagged and mostly empty at grain filling stage.

Iron: Chlorosis in young leaves take place. Veins remain green but in new leaves yellowing of inter-veinal areas are observed. Iron deficiency seriously retards growth and at times plants die.

Manganese: Leaves become small and curled near shoots tips. Small yellow spots on leaves and inter-veinal chlorosis also occur.

Molybdenum: Old leaves become chlorotic first. Growth is disturbed. Yellow spot disease also appears on leaves. Whiptail in cauliflower and gum deposition in lower leaf surface occurs in citrus.

Zinc: Zinc deficiency shows rosette formation and short internodes. Zinc deficient pea plant produces seedless pods.

Recommendations: The symptoms developed due to imbalanced and improper use of fertilizers or because of nutritional deficiencies must not be considered as virus infections or other widely transmittable infectious diseases, as mostly publicised in media reports. In view of the continued increase in population, it is important to enhance crop productivity by adopting modern techniques as suited to different soils of the area.

A protocol assessment of soil fertility status is thus essential to identify nutrient deficiencies and other soil-related problems in advance. Meanwhile, we should check our soil in laboratory; apply chemical fertilizers according to suggestions and maintain soil fertility by applying organic matter. Courtesy DAWN

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