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Imbalanced nutrition causes a-biotic and increases biotic diseases in crops              
By M. Mithal Jiskani

Plant nutrients prevent crops from diseases, if are available in adequate quantity; otherwise, imbalanced use or deficiency of nutrients causes a-biotic (non infectious) diseases and also help to increase biotic (infectious) diseases, wherever crops are sown timely or in case of off time sowing in proper as well as improper way.

Therefore, growers must be aware about presence of all nutrients in their crop fields, or they must use balanced nutrients, otherwise, there is no way to overcome losses.

The soil, which is an important source of crop production, varies from place to place, depending upon the effect of different soil forming factors (Chart 1). If the soil supplies all the essential nutrients in reasonable amounts and on soluble balance to the crop plants.

It can be called fertile, otherwise, may cause non infectious and help to increase infectious diseases in crops, as low or high soil temperature, moisture, light, gasses, acidity and alkalinity (pH) causes not transmitting (un-spread-able) diseases in crops.

The plants need 21 essential nutrient elements (Fig. 1) including gasses and mineral elements, from the soil for growth and development. These all basically are obtained from air, water and soil.

About 95-99.5% of fresh plant tissue is made up of Carbon, Hydrogen and Oxygen, only about 0.5-5% remain as ash after fresh plant tissue is died and burned.

On a whole, all nutrients are important, but NPK are being used in greater quantities and play important role. Much more studies are carried out on status of NPK in Pakistan, but still needs more analyses, whereas, only little work has been carried out on other 13 nutritional elements, and there is dire need to extend work on all needful aspects.

Our common growers are totally unaware to the major soil fertility affecting factors like high temperature, leaching, soil erosion and improper fertilizer application, whereas, most of the growers are also not knowing that which factors may affect fertilizers efficiency up to how much extent (Table 1)?

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

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

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

However, the soil fertility can be managed with the application of fertilizers but farmer must aware of the nature and severity of the nutrient problems in his field in order to arrive at decision regarding the kind and dose of fertilizer to be applied.

It is therefore very important to classify the soil according to their fertility status as they tend to vary from place to place due to various soil forming processes. Only the soil analysis provides actual data for physico-chemical and biological properties at various soil depths.

According to reports, Pakistan soils are very seriously and severely deficient in different major and minor plant nutrients. 100% of analyzed Pakistan soils found deficient in Nitrogen due to very low organic matter, whereas, phosphorous and zinc deficiency also observed higher to that of potassium, boron and iron deficiency in the soils of Pakistan (Table 2).

Symptoms or a-biotic diseases of crops occurring due to imbalanced nutrition

The growers have no idea that which type of symptoms or a-biotic (non-infectious or un-spread-able) diseases are occurred in crop plants, in case of nutrient deficiencies or due to imbalanced use of plant nutrients. They become worry and mostly considering as virus problem to all the appeared symptoms. No doubt, most of the diseases show similar symptoms but this may also not be regretted that the signs which are considered as infectious diseases may also be due to deficiencies or non judicious use of fertilizers for fulfillment of plant nutrient requirements. Therefore, the most common and major symptoms are discussed here under which are most possibly occurred due to nutritional deficiencies also.

Nitrogen

In case of nitrogen deficiency, the leaves become small, turn in to yellow color. Deficiency inhibits the cell division hence vegetative growth retarded. It also causes lowering of respiratory rate. Some fruits shed leaves and causing heavy set back

Phosphorus

Leaves appeared dark green in color. Some times dead patches appear on leaf petioles. Retarded growth and purplish discoloration of foliage are most typical symptoms. The leaves of deciduous trees become narrower, fruit become soft prior to maturity. In apple, fruit drop is common, juice decrease in fruit. Fruits and leaves fall early.

Potassium

This deficiency causes die back of young shoots and leaves. Scorched appearance observed due to the tips of young leaves take up. The leaf margins become dull yellow in color. Appearance V- shaped chlorotic spots, rolling, cupping and curling is common in deciduous fruits, major quality of fruit and vegetables also affected.

Sulfur

The pale green color or chlorosis occurs due to lack of sulfur. Younger leaves affected more then older leaves because element is immobile. Leaf margin and tips ruled in words and rapid leaf fall, stunted chlorotic growth, thinner and woody stems are sulfur deficiency symptoms.

Calcium

Stunted growth, apical buds disintegrate and secrete gummy fluid, blossom end rot in tomatoes and pepper, bitter pit in apples, hindered seed formation, appearance of chlorotic patches on leaf margin occurs. While calcium also retards movements of carbohydrates.

Magnesium

Magnesium deficiency leads to inter-veinal chlorosis. In vegetables, Crimson Reddish or orange yellow color in cabbage, dead spots on turnips, yellowing in foliage structure and retardation in cell division occurs.

Boron

Young growing cells discolored, young leaves brittle, flowering suppress, slow pollen tube growth, reduces stigmatic secretion and corky core of apples, hard fruit of citrus, hollow stem of cabbage and cauliflower. The deficiency appears first as abnormal of apical growing points. The youngest leaves misshapen and wrinkled and are often thicker and of brackish blue green color. Deformed and curled leaves appear in rapeseed and mustard plants. Root development is also affected and found thickened with necrotic tips and appear slimy.

Chlorine

Due to lack of chlorine there is burning of leaf tips or margins, abscission of leaves and also result reduction in yield and quality.

Copper

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

Iron

Chlorosis in young leaves. Veins remain green but in new leaves yellowing of inter-veinal areas are observed. Iron deficiency seriously retarded growth and some time plant dies.

Manganese

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

Molybdenum

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

Zinc

Zinc deficiency show rosette formation and short internodes. Zinc deficient pea plants produce seedless pods.

Improving nutrient deficiencies

The nutrient deficiencies could be improved through integrated plant nutrition management system (IPNMS).

Conclusion