Functionality & Importance of few Micro Elements 

ZINC -AN ESSENTIAL MICRO-ELEMENT
 

Why is Zinc Important?

Zinc (Zn) is one among the seven Micronutrient elements that is indispensable for plant growth. Its presence activates a series of enzymes responsible for maintaining the course and tempo of several vital growth events. Zinc asserts in protein synthesis and production of auxins (growth promoting chemicals). Therefore, a low zinc supply encourages protein deficiency and dwarfism in plants. 

The net results of a zinc deficiency in soils are stunted crop plants, prolonged duration and poor yields. A severe deficiency can kill the crop. 

What is Zinc Deficiency?

For optimum function of crop plants a certain minimum level of zinc supply is essential. If a soil, the principal resource from which plants draw their zinc needs, is unable to supply that minimum, a zinc deficiency situation arises. Such soils may contain large quantities of fixed zinc, but lack in a current supply that plants can readily encash to meet their ongoing needs. Soils Scientists often refer to this current supply as available zinc below which plant growth is impaired is called critical level. Soil that tests lower zinc than the critical-level grows zinc deficient plants. High pH saline alkali soils, calcareous soils, low organic. matter sandy soils are more frequently zinc deficient. Man's intervention leading to loss of fertile surface soil or indiscriminate use of certain chemical fertilisers (specifically phosphatic) can aggravate zinc deficiency condition. 

Can Zinc Deficiency be Recognised in Growing Plants?

YES, Zinc deficiency in growing plants can be recognised by visual symptoms and by making analysis of plant tissue for zinc concentration. 

Zinc deficiency provokes abnormal metabolic signals in plants leading to certain visible symptoms; In fact, development of visual symptoms can be a guide to diagnose zinc deficiency. Most often zinc deficiency symptoms are seen on leaves. Their occurrence on other plant organs (toots or stems) is not completely ruled out. Different crop plants produce different symptoms (as illustrated in later sections). Zinc deficiency symptoms common to many crop plants are described hereunder: 

a. Development of abnormal spots (light green, yellow, bleached or brown rusty spots) on the leaves.
b. Very small leaves at the shoot tip producing a bushy rosette appearance.
c. Dwarfism due to shortening of stalk internodes.
d. Stunted growth, unhealthy looks. 
e. Delayed maturity. 
f. Death of affected tissue, uneven crop stand. 

Plant issue test for zinc can establish a zinc deficiency or otherwise. Whenever, zinc content in plants is sub-optimum, plants fail to put up normal growth despite recommended application of nitrogen, phosphate and potash fertilisers. As a rule of thumb, plant zinc concentrations less than 20 g per ton of dry tissue suggest probability of deficiency, and concentrations of less than 15 g per ton of dry tissue indicate definite deficiency. 

Can Soil Tests Forecast Occurrence of a Zinc deficiency ?

Yes, it is possible to forewarn on the possible occurrence of zinc deficiency in crop plants by soil testing. Scientists have devised special tests to assess ability of soils to supply plant available zinc. Soil test on zinc can be performed in any laboratory conscientious of clean working environment and provision for specialized equipment (atomic absorption spectrophotometer). 

Can a Farmer Confirm Suspected Zinc Deficiency ?

Yes, a farmer can confirm suspected zinc deficiency by diagnostic sprays. All he needs to do is to spray a section of deficient plant Zinc Sulphate Solution (0.5% Zinc Sulphate+0.25% Lime or 1% Urea) and watch for crop recovery. Ifzinc is deficient, the sprayed plants should improved growth within 10 to 14 days, the new leaves should be green in colour and free from symptoms. The success of the spray test is more if crop are sprayed immediately on the appearance of deficiency symptoms. F ew of narrow leaf crops like onions, are and exception in that they do not respond to a spray test. 

How to Correct Zinc Deficiency ?

By soil application 

Zinc deficiency can be corrected by the application of Zinc Fertilisers to soils. Zinc Sulphate (ZnSO4.7H20- about 21% Zinc) is the most common among all Zinc Fertilizers. 

Application of 25 kg. to 50 kg. Zinc Sulphate per hectare is recommended depending upon the level of deficiency of zinc. Low zinc levels are recommended for light textured sandy soils, where else high level of zinc application are necessary for heavy textured paid clayey soils and for rice grown on sodic and permanently wet soils. 


Once applied, zinc does .not move for in soil. As a result of immobile the heavier of zinc in soil, the zinc fertiliser should be place in such in a way that maximum routes can easily contact it. The successful techniques of application are. 

1. to broadcast Zinc Sulphate on the soil surface followed by ploughing it in. 
2. to drill Zinc Sulphate in the soil below and on the side of the seed. 

To drive maximum benefit from Zinc treatment, it is essential to apply it prior to sowing or transplanting of crops. Soil application with zinc fertiliser is not necessary to be repeated every year at the level of zinc suggested above, one application should provide ample zinc for one to two years for cropping.