Current World Environment

Introduction

The soil of Andaman and Nicobar islands is affected by the halogen salts of alkali metals. The major content of the salt adsorbed on the land surface is leached out by heavy rainwater. Even though few contents of the salt remain adsorbed on the soil resulting the soil to be acidic. Few inorganic hetercyclics like tetrasulphurtetranitride (S₄N₄), thiotrithiazyl chloride (S₄N₃)⁺Cl^- have been successfully tested in reclamation of alkaline (Sharma, 1986, 2000) as well as acidic (Sharma, 1994) and to reclame alkaline soil (Sharma et al, 1994) has already been investigated. To explore the further utility of (S₆N₄)²⁺Cl₂^- in agriculture, a study of effectiveness of (S₆N₄)²⁺Cl₂^- on varying pH of acidic soil of Andaman and Nicobar islands is being presented here.

Material and Methods

(S₆N₄)²⁺Cl₂^- was prepared (Goehring, 1957) by refluxing S₂Cl₂ and NH₄Cl in nitromethane. The sequence of reaction in the preparation are:



Black green coloured product formed was separated and washed with distilled water, nitromethane and CS₂ to remove unreachted NH₄Cl, S₂Cl₂ and S. The formed product being soluble in water, nitromethane supports its ionic nature (Goehring, 1970), was dried in vacuo. To study the effect of (S₆N₄)²⁺ Cl₂^- on varying pH 3 - 4.5 of acidic soil, the soil samples from different places of Andaman and Nicobar islands namely Mayanbunder, Bambooflat and Miletilak were collected upto desired depth 15 cm by means of sampling tools. Each soil sample (20 gm) was taken in 100 ml beaker to which 40 ml distilled water was added. The suspension was stirred at regular intervals for 30 minutes. To determine the pH, the each suspension was stirred well just before the electrodes were immersed and then the pH of each extract was noted before and after each addition of fixed quantity (10 mg) of (S₆N₄)²⁺ Cl₂^- at 10 minutes time interval. In each determination, the electrodes were washed with distilled water and water was removed from the surface with a piece of filter paper. Different ions present in the soil sample were analysed by spot tests (Feizi Fritz, 1957).
 

Table 1: Change in pH of soils on adding (S6N4)2+ Cl2- Click here to view table

Results and Discussion

Quantities analysis of soil samples indicates that soil samples contain Cl^-, Zn²⁺, Fe²⁺ and Na⁺ ions. The acidic characters of soil may be due to Cl- ions. Zn²⁺ and Fe²⁺ show amphoteric character in aqueous extract of soil sample. (S₆N₄)²⁺ Cl₂^- having three planer fused rings possesses cyclic structure (Banister 1974, 1975). The S – S bonds (303 pm) holding the two S- N (161 pm) rings together and forming the middle ring are very long. (S₆N₄)²⁺ Cl₂^- undergoes hydrolysis in acidic soil as: 



The hydrolysis products were analysed qualitatively and quantitatively by standard methods (Vogel, 1968). The nitrogen is completely converted into NH₃ confirming the physical structural deduction that there is no N – N bond in the molecule but there are S- N and S – S bonds. During the present study (S₆N₄)²⁺ Cl₂^- used against acidic soils of different pH 3 – 4.5 show a remarkable increase in pH of acidic soil (Table 1) and the pH has increased upto 7.4 in normal time. There is no further increase in pH of the soil indicating that after retaining pH 7.4, (S₆N₄)²⁺ Cl₂^- creates a buffer state due to formation of NH₄Cl and NH₄OH during the hydrolysis in acidic soil.

S₂O₃^2-, Cl- ions formed during hydrolysis of (S₆N₄)²⁺ Cl₂^- are exchanged by Zn²⁺, Fe²⁺ and Na⁺.



(S₆N₄)²⁺ Cl₂^- is a suitable chemical to reclame acidic soil because.

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