Effect of Organic manures and Inorganic Sulphur on Releasing pattern, Adsorption and Desorption of Sulphur on Typic Haplustalf

Laboratory experiments were carried out at the

Sulphur has been recognised as the fourth major plant nutrient after N,P and K. Crops in general require as much sulphur as they need phosphorus. and processed. From this two hundred grams of soil was taken in plastic containers and imposed the treatments. The treatment structure consist of 5 levels It is supplied to the soil from weathering of rocks of inorganic S (M -Control, M -20 kg S ha -1 ; M -40 0 1 2 and minerals, mineralized from the organic matter or kg S ha -1 ; M -60 kg S ha -1 ; M -80 kg S ha -1 ) and from added fertilizer. A part of the released sulphate remain in soil solution and a part gets adsorbed or fixed on the soil colloidal complexes and its availability in the labile pool get reduced (Parfitt, 1982;Bhogal et al. 1996). The lability of sulphur in soil depends upon soil properties. Among these pH, presence of complexing anions (Lande et al, 1977), clay content and sesquioxides (Johnson and Todd, 1983;Fuller et al, 1985), CaCO3 and native extractable sulphur are most important. Parfitt (1978) stated that due to ligand exchange mechanism, the organic anions make chelates with Fe and Al and reduces the adsorpti on of SO 42 -. Evans (1986) reported that the SO 42 -and the low molecular weight organic anions compete for the similar sorption sites. Based on the analysis of 1000 soil samples collected from the farmers holdings in Sivaganga district, more than 70 per cent of soil samples were found to be deficient in available S (< 10 mg kg-1). Therefore in order to know about the releasing pattern, adsorption and desorption behaviour of applied S alone and in conjoint with organic manures the present study was conducted

Materials and Methods
Bulk soil samples were collected from the experimental field from Sivagangai at 15 cm depth *Corresponding author's email: pandian1968@ rediffmail.com 4 sources of organics (N0-Control, N1-press mud 5 t ha -1 ; N -FYM 5 t ha -1 and N -vermicompost 5 t ha -1 ). The experiment was conducted in a Factorial Completely Randomised Design with two replications. Sulphur was added in the form of gypsum and respective organic manure was added and incubated for 70 days at field capacity moisture level. Soil samples were drawn once in 10 days and analysed for available S using 0.15% CaCl2 and the availability of S over a period of time was studied. Fifty grams of soil samples were taken in 250 ml polythene bottles to know the adsorption -desorption behaviour of S, Sulphur was added in the form of K 2 SO 4 @ 0, 100, 200, 300, 400, 500, 600, 700, 800, 900, 1000 mg kg -1 . The same concentration of S were added to the following treatments also • 50 g soil + Press mud @ 5 t ha-1 • 50 g soil + FYM @5 t ha-1 • 50 g soil + Vermicompost @5 t ha-1 The contents were shaken in a reciprocating mechanical shaker for 24 hours (Barrow, 1970). The contents were centrifuged and the supernatant solution was decanted and S was estimated in an aliquot of the solution by turbidimetrically as per the procedure described by Chesnin and Yien (1951). From the amount of S lost from solution, the amount 4 3 of S adsorbed by soil for each organic manure was x calculated. The sorption data was fitted into the = Amount of S sorbed (mg kg -1 ) Langmuir and Freundlich adsorption equations.

Langmuir equation
Freundlich equation x 1 log log k log c m n Where C = Equilibrium concentration of S in solution (mg l -1 ) m b = S sorption maxima (mg kg -1 ) k = Constant related to bonding energy n and k = empirical constants.
After removing the supernatants, the soil samples in the bottles were washed five times with 50 ml portion of 0.5 N NH 4 NO 3 and the washings were collected in 250 ml separate volumetric flasks. After the final washing, the volume was made upto 250 ml with 0.5 N NH4NO3 (Haque and Walmsley, 1972). The solution was analysed for SO 2--S by turbidimetrically (Chesnin and Yien, 1951) and the amount of available S was calculated.

Effect of organic manures and incubation time on S availability
The results revealed that various organic manures significantly influenced the availability of S over a period of time (Table 1). It ranged from 12.8 to 17.4 mg kg -1 and the highest availability of 17.4 mg kg -1 was registered with the application of vermicompost 5 t ha -1 (N ) closely followed by treatment receiving pressmud (N1) however, they were statistically onpar with each other. Increased availability of S

Organic
Incubation period ( in vermicompost and pressmud might be due to narrow C:S ratio and active carbon pool present in vermicompost and pressmud. The incubation period also had a significant influence on the availability of S. It varied from 12.9 to 16.3 mg kg -1 . Significant increase in the available S was observed upto 40 DAI there after it got declined with advancement of incubation period. This might be due to formation of Fe-Al-SO4 complex over a period of time which is relatively insoluble (Gowrisankar and Shukla, 1999).
The interaction effect of organic manures and incubation period had a significant influence on available S. In the case of pressmud (N1), continuous linear increase was observed with the advancement 2 of incubation period from 10 DAI to 70 DAI (13.1 to 19.4 mg kg -1 ). While in the case of FYM (N ) and vermicompost (N3), a progressive increase in available S was registered upto 40 and 60 DAI respectively beyond which it got declined. The difference in releasing pattern of S among the organic manures may be due to the S content of the organic manures. The pressmud contain higher amount of S (1.2%) and this organic S could have been released slowly over a period to the labile pool.

Effect of inorganic S and incubation time on S availability
The rate of release of applied S was more at higher concentration as compared to the lower levels and it ranged from 9.8 to 18.7 mg kg-1 ( Table  2). The highest available S content of 18.7 mg kg-1 was registered with the application of 80 kg S (M4) closely followed by 60 kg S ha-1 (M3) however, they were statistically on par with each other. At lower concentration, the rate of adsorption of sulphate over the soil colloidal complex would be higher to satisfy the positive charges exist on the soil colloidal complex (Sammi Reddy et al., 2001). As the experimental soil belonging to the sub group Typic Hyplustalf with 12.8 per cent sesquioxide, the applied S would have been adsorbed over sesquioxide and this could have been the possible reason for lower concentration of S at lower levels of S. The incubation time also had a significant influences on the availability of S and it ranged from 12.9 to 16.1 mg kg-1. A progressive increase in available S was noticed upto 40 days beyond which it got declined irrespective of levels of S. This might be due to continuous adsorption of sulphate over Fe-Al colloidal complex over a period of time as the experimental soil belong to the sub group Typic Haplustalf with 12.8 per cent sesquioxide content. Decrease in available S in labile pool over a period of time have already been confirmed by Athokpam et al. (2007). Similar to the individual effect, the interaction effect of levels of S and incubation time also had a significant influence on S availability. The availability of S followed a quadratic relationship over a period of time irrespective of levels of S.

Effect of organic manures and inorganic S on availability of S
The data depicted in Table 3 revealed that both organic manures and inorganic S had a significant effect on release of S at different days of incubation. The rate of release of applied S was more at higher concentration as compared to the lower levels and it ranged from 9.8 to 18.7 mg kg-1. The highest available S content of 18.7 mg kg-1 was registered with the application of 80 kg S ha-1. Since at lower concentration, the rate of adsorption of sulphate over the sesquioxide would be higher to satisfy the unsatisfied positive charges exist on the soil colloidal complex (Tiwari and Gupta, 2006). In the case of organic manures, the available S content varied from 12.8 to 17.2 mg kg-1 and the higher available content of 17.2 mgkg-1 was registered with the application of vermicompost (N3) closely followed by pressmud (16.9 mg kg-1).Interaction effect of organic manures and inorganic S was prominent on the release of S irrespective of the days of incubation. The double combination of vermicompost with 80 kg S ha-1 registered the highest available S content (21.3 mg kg-1) closely followed by pressmud with 80 kg S ha-1. This might be due to higher S content of vermicompost (1.1%) and pressmud (1.2%) which would have favoured the long term release of S into the labile pool. The positive relationship between S content, Arylsulphatase activity and release of S was reported by Shriner and Henderson (1978).

Adsorption of sulphur
The data on S adsorption revealed that amount of S adsorbed follows the order as Control (N0) > FYM (N 1 ) press mud (N 2 ) > vermicompost (N 3 ). An increase in S adsorption was noticed upto 16.0, 18.0 and 16.0 mg l -1 for press mud, FYM and vermicompost treatments respectively beyond which it got declined  (Table 2). Soil belonging to the manured treatments possessed lower S adsorption capacity (55%) than the unmanured one (71%). However, among the organic manures the lowest S adsorption was registered in vermicompost (50.6%) followed by press mud (52.9%) and FYM (61.7%). This may be attributed to the narrow C:S ratio (41:1) and active carbon pool present in vermicompost. The lowest amount of adsorption of S in manured soils may be attributed to the competition between the organic anions and SO 2for the same adsorption sites. Evans (1986) reported that the SO 2and the low molecular weight organic anions compete for the similar adsorption sites.

Table 4. Effect of organic manures and inorganic S on adsorption and desorption of S in soils
The unmanured soil recorded higher percentage of adsorption of added S. This may be attributed to the specific adsorption of SO 2by the hydrous oxides (R 2 = 0.94**). Fox (1982) compared four adsorption equations to explain the SO 2adsorption and the highest regression coefficient was noticed with Langmuir equations. Similarly Sammi Reddy et al. (2001) andSaravana Pandian andSaravanan (2012) reported that the Langmuir equation gave the best fit over Freundlich equations. As regard the Langmuir adsorption equation, the SO 2sorption maxima (b) of Fe and Al (Singh, 1984). The experimental soil is belonging to the sub group Typic Haplustalf with ranged from 484 mg kg -1 4 in vermicompost to 654 mg 12.8 per cent sesquioxide. Due to high sesquioxide, more amount of SO 2would have been retained in the unmanured soil. Neary et al. (1987) reported that the amount of inorganic fractions of soil matrix, amorphous and crystalline forms of Fe and Al found to control the SO 2retention kinetics of podzols. A kg -1 in unmanured control treatments respectively. The highest and the lowest SO 2sorption maxima were registered in control and vermicompost treatments respectively. Among the manurial treatments, the highest SO 2adsorption maxima was recorded in FYM (N2) followed by press mud 4 2-(N ) and vermicompost (N ) treatments. Similar to significant relationship between the SO 4 adsorption 1 3 and Fe 2 O 3 (r= 0.820**) and Al 2 O 3 (r=0.859**) was reported by Dolui and Nandi (1987). The result showed that adsorption of S increased with the increasing concentration of added S upto 800 mg kg -1 beyond which it got declined except in unmanured soil (N0). The percentage of adsorption of S was found to be higher at the lower concentration of S (100 mg kg -1 ) and decreased gradually with the corresponding increase in the concentration. These results are in line with the earlier works of Bhogal et al. (1996) who found that the adsorption of SO 2decreased with the increasing concentration of added S in Calciorthents.

Adsorption isotherm
The adsorption data were fitted to two adsorption isotherms viz., Langmuir and Freundlich equations. The results revealed that the S adsorption was fitted well in the Langmuir adsorption isotherm by registering higher R 2 values (0.96**) than the Freundlich isotherm the adsorption maxima, the bonding energy (k) values were extended from 0.288 to 0.357. The highest k value was noticed in unmanured control (N0) (0.357) followed by FYM (N2) treatments. This may be due to the high sesquioxide content, the SO 2would have been adsorbed strongly over the Fe and Al oxides to satisfy their positive charges. Johnson and Todd (1983) and Stankogolden et al. (1994) observed a positive relationship between the SO 2adsorption maxima and the sesquioxide in laterite soils. The lower values of adsorption maxima and bonding energy coefficient in manure added soil may be attributed to the saturation of adsorption sites by organic anions (Kodama and Schnitzer, 1980).
In the case of Freundlich adsorption isotherm, the constants viz, K and 1/n values varied from 2.35 to 2.50 and 0.329 and 0.603 respectively. The highest and the lowest K values were registered with unmanured control (N0) and vermicompost (N3) treatments respectively. In general, the K values were higher in unmanured treatments than the manured ones. As regards the manurial treatments, the highest K value of 2.50 was recorded in N0 followed by 2.44 in N2 treatments. The concentration exponent (1/n) values were higher in the treatments received organic manures as compared to the unmanured control and the highest and lowest values of 0.603 and 0.329 were recorded in vermicompost and unmanured control respectively.

Desorption of sulphur
The data on desorption of added S indicated that it extended from 18.5 to 115.5, 27.0 to 125.0, 24.5 to 121.5 and 28.5 to 128.0 mg kg -1 in control (N 0 ), press mud (N 1 ) FYM (N 2 ) and vermicompost (N3) treatments respectively. The results showed that the lowest amount of desorption was registered in unmanured control (N0) whereas, the highest quantity was recorded in N3 (vermicompost). It was observed that the amount of desorption was higher in the manured soils which may be due to presence of SO 2in an adsorbed from over organic colloidal constituents which would be released at a faster rate upon equilibrium with 0.15% CaCl2 2H2O. Besides, due to the high content of organic colloids in the manure added soils, the organic anions would have chelated the metallic cations like Fe and Al which inturn released the SO 2to the labile pool. Evans and Anderson (1990) observed a positive relationship between the organic matter and desorption of SO 2 . Among the manured soils, the highest rate of desorption was registered in vermicompost added soils than the others. This may be attributed to narrow C: S ratio (41; 1) of vermicompost.

Conclusion
From this study, it is concluded that the SO 2--S get adsorbed strongly over sesquioxides in Typic Haplustalf To supply the SO 2continuously for the