Zinc The Miracle nutrient called Zinc

Zinc

The same zinc that protects galvanized steel from rusting and the same zinc that is inside our pennies is the same zinc that is needed in infinitesimal amounts for all living things. An acre of healthy oats contains only one ounce. Yet, without this essential ounce of zinc no crop would grow at all! A grown man needs only seven one-thousandths of an ounce (25gm) of zinc per day. Yet this small amount helps build body protein, generate energy, promotes growth, and enhances taste and smell.
Only two ounces of zinc per ton of feed will prevent parakeratosis, or elephant hide, in hogs, promote hair growth on cattle, and generate healthy egg and chick development. Zinc is really a miracle micronutrient for plant life …an acre of corn needs only two ounces! But, this two ounces can increase yields by over 60 bu. per acre. Zinc is involved in most plant growth functions. Zinc helps produce auxins. Zinc is a growth promoting substance that controls the development of the shoot. Zinc also forms enzyme systems, which regulate plant life. Yet zinc is the most common micronutrient deficiency in agriculture today! Zinc deficiency can limit yields of corn, beans, wheat, cotton, sorghum, fruits, and vegetables.
The use of high yielding cereal varieties along with the increasing use of fertilizers containing major nutrients (N, P, and K) but without micronutrients through inorganic or organic fertilizers dramatically increased food production under intensified systems in early seventies. However, as a result of depleted Micronutrient reserves in the soil, this practice resulted in a number of nutrient disorders and associated nutrient imbalances. A sharp decline in the available micronutrient status of soil is reported in irrigated agricultural production systems in India under continuos cropping with recommended rates of only major nutrients.
For Example field scale deficiencies of Zinc in rice and wheat on alluvial soils, Fe deficiency in sugarcane, upland rice, chickpea and groundnut on sandy calcareous soils. Mn deficiency in rice-wheat systems on sandy soils and B deficiency in chickpea and rice on high pH, calcareous soil have been reported, mostly in intensified production systems. The deficiencies of micronutrients have assumed critical importance of sustaining high productivity in some areas of country. Among these Zinc deficiency is most prevalent in intensely cropped light textured alkaline soils. Boron deficiency has become more critical on highly calcareous soils, limed acid soils and reclaimed soils.
As an example, the Micronutrient requirement and removal of a few major cropping systems in intensified production systems are given below in Table 2. It is clear that micronutrient removal by various cropping systems varies from crop to crop {Source: Takkar (1996)}

Cropping systems	Total Yield (T/Ha)	Zn	Fe	Mn	Cu	B	Mo
Rice - Rice	8.0	320	1224	2200	144	120	16
Rice - Wheat	8.0	384	3108	2980	168	252	16
Maize - Wheat	8.0	744	7296	1560	616	-	-
Soybean - Wheat	6.5	416	3362	488	710	-	-
Pigeonpea -Wheat	6.0	287	4356	493	148	-	-

Under dry land agriculture, especially in the semi arid tropics with subsistence agriculture, the situation differs from the under irrigated intensified systems. In the first place soil erosion in some case, yields levels are low. Secondly soil erosion is severe resulting in the removal of top surface layers. Compounded with low use of organic manure, which were the dominant source of nutrients, micronutrients especially have dwindled in recent past.
Hence, there is a wide spread deficiency of Zn and B in watersheds of most parts of country. The deficiency is especially severe in Andhra Pradesh, MP and as indicated in table no. 1 intensive cropping area of Punjab, Haryana, West Bengal, UP and other states differing in severity. Hence, there is need for developing site specific nutrient management strategies for increasing the productivity of rainfed systems sustainability.

• Affects several biochemical processes in the plant, such as
• Cytochrome and nucleotide synthesis, auxin metabolism, chlorophyll production, enzyme activation and membrane integrity
• Growth is severely affected

Fundacao Mt/PMA (1999) took up the study on effect of micronutrients on soybean yields. He took different treatments of fertilizers that included one which had all fertilizers including NPK and fortified with micronutrients B, Cu, Mn and Zn. One treatment was without NPK and rest without one particular micronutrient. The results were as under:

Treatments	Yield (Kg/Ha)	% Yield
Complete ( C )	3492	100
Complete - B	3336	95
Complete – Cu	3242	93
Complete - Mn	3072	88
Complete - Zn	2910	83
Complete -Micro	2310	66

Thus, it is clear that treatment with all fertilizer minus micronutrients had least yields (66%). Similarly treatment with all nutrients minus Zn yielded only 83% of control with all fertilizers including micronutrients, indicating that deficiency of Zn is very crucial and it deficiency results in very large reduction in yield

• Dusty brown spots on upper leaves of stunted plants
• Uneven plant growth
• Decreased tillering in cearals
• Increased spikelet sterility in rice
• Chlorotic midribs particularly near the leaf base of younger leaves
• Leaves lose turgidity and turn brown as brown blotches and streaks appear on lower leaves, enlarge, and coalesce
• White line sometimes appears along the leaf midrib
• leaf blade size is reduced

• important throughout the growth cycle of the rice crop
• Occurs in neutral and calcareous soils, intensively cropped soils, paddy soils and very poorly drained soils, sodic and saline soils, peat soils, soils with high available P and Si status, sandy soils, highly weathered, acid, and coarse-textured soils, soils derived from serpentine and laterite, and leached, old acid sulfate soils with a small concentration of K, Mg, and Ca
• Associated with S deficiency

• Burning appearance of plants
• Reduction in growth
• Reduction in yields
• Symptoms appear between two to four weeks after transplanting in case of paddy
• Dusty brown spots on upper leaves of stunted plants
• Uneven plant growth and patches of poorly established hills in the field, but the crop may recover without intervention
• Tillering in paddy decreases and can stop completely and time to crop maturity increases under severe Zn deficiency
• Increase spikelet sterility in rice
• Chlorotic midribs, particularly near the leaf base of younger leaves
• Leaves lose turgidity and turn brown as brown blotches and streaks appear on lower leaves, enlarge, and coalesce
• White line sometimes appears along the leaf midrib
• Leaf blade size is reduced

There are plant or soil tests to show Zinc deficiency .
The optimal ranges and critical levels of Zn in plant tissue are mm/kg:

Growth stage	Plant part	Optimum	Critical level for deficiency
Tillering	Y leaf	25-50	<20
Tillering	Shoot	25-50	<10

On plant, the ranges of Zn deficiency in the whole shoot during vegetative growth (tillering) are as follows:

• <10 mg kg -1 definite Zn deficiency
• 10-15 mg kg -1 very likely
• 15-20 mg kg -1 likely
• >20 mg kg -1 unlikely (sufficient)

The symptoms of Zinc deficiency may resemble those of Fe deficiency, which also occurs on alkaline soils. On alkaline soils, Zn deficiency is often associated with S deficiency. They may also resemble Mn deficiency and Mg deficiency.
Leaf spots may resemble Fe toxicity in appearance but the latter occurs on high organic status soils with low pH.
One or more of the following factors can cause Zn deficiency particularly in paddy:

• Small amount of available Zn in the soil.
• Planted varieties are susceptible to Zn deficiency (i.e., Zn-inefficient cultivars).
• High pH (close to 7 or alkaline under anaerobic conditions). Solubility of Zn decreases by two orders of magnitude for each unit increase in pH. Zn is precipitated as sparingly soluble Zn(OH) 2 when pH increases in acid soil following flooding.
• High HCO 3- concentration because of reducing conditions in calcareous soils with high organic matter content or because of large concentrations of HCO 3- in irrigation water.
• Depressed Zn uptake because of an increase in Fe, Ca, Mg, Cu, Mn, and P after flooding.
• Formation of Zn-phosphates following large applications of P fertilizer. High P content in irrigation water (only in areas with polluted water).
• Formation of complexes between Zn and organic matter in soils with high pH and high organic matter content or because of large applications of organic manures and crop residues.
• Precipitation of Zn as ZnS when pH decreases in alkaline soil following flooding.

Zinc is essential for several biochemical processes in the rice plant, such as:

• Cytochrome and nucleotide synthesis
• Auxin metabolism
• Chlorophyll production
• Enzyme activation
• Membrane integrity

Zn accumulates in roots and can be translocated from roots to developing plant parts. Because little retranslocation of Zn occurs within the leaf canopy, particularly in N-deficient plants, Zn deficiency symptoms are more common on young or middle-aged leaves.
Sources Of Zinc:
Some the sources of zinc are given as below:

Sl. No.	Name of Compounds	% age of Zn & other associated nutrients
1	Zinc Sulphate Heptahydrate ( ZnSO 4.7H 2O)	Zn - 21%, S - 15 %
2	Zinc Sulphate Monohydrate (ZnSO 4.H 2O)	Zn - 33%, S - 15%
3	Chelated Zinc as Zn-EDTA	Zn -12%
4	Chelated Zinc as Zn-EDTA	Zn - 9%
5	Zincated Urea	Zn - 2% N - 43%
6	Zincated Phosphate (suspension)	Zn - 19.4% P 2O 5-12.9%
7	Zinc Oxide	Zn - 60-80%
8	Zinc Carbonate (ZnCO3)	Zn – 52-56%
9	Zinc Chloride (ZnCl 2)	Zn – 48-50%

• Among various inorganic sources, zinc sulphate hepta hydrate (ZnSO 4.7H 2O) containing 21-22% Zn is found the most effective, commonly available, economically cheapest source of correcting Zn deficiency in most of crops and diverse soils as compared to sparingly soluble Zn sources, chelates, and mixtures. Mono hydrated and hepta Zinc sulphate containing (33% & 22%) were found equally efficient for correcting zinc deficiency either through soil or foliar application.
• Synthetic Zn-EDTA chelates were found better than zinc sulphate in combating Zn deficiency in crops in non-calcareous loamy sandy soils but at par in calcareous and aridisols soils. However, their high cost than zinc sulphate made chelated fertilizers most uneconomic and less effective for common use.
• Zinc chelated Zn-EDTA is at least three times more effective than Zinc Sulphate so far as uptake is concerned.
• Zinc chelate is easily is translocated within the plants, because unlike Zinc sulphate it is partly systemic.
• Zinc sulfate reduced phosphorus uptake and the phosphorus content of the shoots in plants, while Zn-EDTA increased it (Nammuang and Ingkapradit 1986).
• Micronutrient blended fertilizers sources such as zincated urea, zincated super and boronated super were found initially inferior to zinc sulphate or chelates in highly Zn or B deficient soils as they mismatched with nutritional requirement of crops. But long term effects of zincated urea, boronated super became as efficient as that of soluble sources in controlling hidden/emerging micronutrient deficiency in several crops.
• Zinc oxide is effective for roots dipping and seed coating before transplanted crops than zinc sulphate. Zinc phosphate has been found efficient source of for seed coating to control hidden hunger and cheaper than ZnO.

Based on extensive experiments by the scientist world over following inferences have been drawn on frequency of Zn application:

• Zinc leaves marked residual effect of 11 kg of Zn in soil, so it is not necessary to apply Zn to every crop. The residual effect of 11 kg per hac added to soil persists in four following crops in calcareous and on six crops in noncalcareous soils.
• In sandy loam alkaline alluvial soils 5.5 kg of Zn per hac for first four crops and 2.75 kg per hac for next 8 to 12 crops respectively gives the largest grain response and are found optimum.
• Under brackish water irrigation in a highly sodic soil (pH 10.4) amended with gypsum, @50% of the gypsum requirement (GR) the residual effect of 22 kg Zn per hac could last for four crops of rice -wheat sequence and fifth crop required repeat application of Zn.
• Alkali soil (pH10.4) when irrigated with normal quality water, the yield with fresh application of 2.25 kg Zn per ha continuously to each crop was not different from a single initial application of 18 kg Zinc per hac after seventh crop, suggesting that residual effectiveness of Zn applied once had not diminished.
• The beneficial effect of FYM alone or in combination with Zn is higher compared to Zn application. Integrated nutrient management proves better than Zinc alone.
• Organic manure 12 t per hac FYM, 5 t poultry manure and 2.5 tones of piggery manure were as efficient as 11.2 kg Zn per hac in meeting the Zn requirement of wheat – maize rotation. Also half or even less rates of these manures proved equally more efficient or better when amended with 5.6 kg Zn per hac for maize –wheat rotation.
• Application of 12 kg Zn per hac, 8-16 ton FYM and 4 T FYM + 3 kg Zn per hac were found equally efficient for enhancing soybean-wheat productivity in vertisols. Application of 12 kg of Zn per hac left residual effect for 2-3 cropping cycles in medium to deep vertisols.

Options on Zn application include