Zinc Adsorption in Relation to Soil Properties , Analysed with Langmuir and Freundlich Models in Soils of Kashmir Valley

The phenomenon of fixation of added zinc in soils considerably affects the availability and efficiency of applied zinc. Pertaining to this situation, different land-use soil samples across the valley were analysed for various physico chemical properties and adsorption capacities. The results showed that the soils were slightly acidic to alkaline in reaction and differ far and wide in other soil properties. Cation exchange capacity (CEC) of the soils showed little variation between the samples and varied from 13.3 to 17.2 cmol (p+) kg-1 with an average value of 15.1 cmol (p+) kg-1of soil. The maximum of zinc adsorption were greatly influenced by soil organic matter, clay content and CEC of the soils. The data was fitted to Langmuir and Freundlich equations and the results yielded that the Freundlich equation showed better fit to the sorption data at higher zinc concentrations. However, both the models were having satisfactory results for the obtained data. Current Agriculture Research Journal www.agriculturejournal.org ISSN: 2347-4688, Vol. 7, No.(1) 2019, pg. 68-73 CONTACT N. Z. Rehman zianaik@gmail.com Division of Soil Science, Sher-e-Kashmir University of Agricultural Sciences and Technology of Kashmir (SKUAST-K), Wadura Sopore, Jammu and Kashmir, India. © 2018 The Author(s). Published by Enviro Research Publishers. This is an Open Access article licensed under a Creative Commons license: Attribution 4.0 International (CC-BY). Doi: http://dx.doi.org/10.12944/CARJ.7.1.09 Introduction Zinc (Zn) is essential for the normal growth and development of plants however its content in soils is low compared with that of other essential nutrient elements.1 The deficiency of zinc is more common in calcareous than in non-calcareous soils, and its deficiency is having a profound economic impact in terms of yield loss.2 Various factors including pH,3 ionic strength as well as clay mineralogy have been shown to affect Zn availability4 however, zinc accessibility is likewise directed by adsorptiondesorption procedures and its parcelling between the arrangement and strong phases.5 Most examinations on Zn sorption and desorption by soils have been founded on balance conditions. Be that as it may, because of moderate compound responses, plant Article History Received: 17 October 2017 Accepted: 21 April 2019


Introduction
Zinc (Zn) is essential for the normal growth and development of plants however its content in soils is low compared with that of other essential nutrient elements. 1The deficiency of zinc is more common in calcareous than in non-calcareous soils, and its deficiency is having a profound economic impact in terms of yield loss. 2 Various factors including pH, 3 ionic strength as well as clay mineralogy have been shown to affect Zn availability 4 however, zinc accessibility is likewise directed by adsorptiondesorption procedures and its parcelling between the arrangement and strong phases. 5Most examinations on Zn sorption and desorption by soils have been founded on balance conditions.Be that as it may, because of moderate compound responses, plant take -up, manure expansion and different variables, horticultural soils are once in a while in a balance state concerning Zn sorption and discharge.Adsorption isotherms can be utilized to depict the equilibrium connection between the measures of adsorbed and broke down species at a given temperature 6 which considers force, amount and limit factors that are essential for anticipating the measure of soil supplement required for most extreme plant development.

Physico-Chemical Characteristics
The detailed physical characteristics of the soils are represented in figure-2 which reveals that the sand, silt and clay content are in the range of 18.20 to 25.90, 41.97 to 56.10 and 23.40 percent with mean value of 22.76, 50.80 and 26.71 percent, respectively.In general, the soils were slightly acidic to alkaline in reaction with the pH variation from 5.98 to 8.01.EC of the soils showed non-saline nature and ranged between 0.11 to 0.33 dSm-1.The organic carbon content of these soils showed a conspicuous variation and ranged from 0.59 to 0.94 percent with a mean value of 0.76 percent.The higher values in soils may be due to the continuous organic manuring, addition through vegetation and low mineralization rates in these soils. 8Cation exchange capacity of the soils showed little variation between the samples and varied from13.30to 17.21 cmol(p + ) kg -1 with an average value of 15.08 cmol(p + ) kg -1 of soil.The calcium carbonate content was present in meagre amounts in most of the soils with values ranging from 0.00 (S 9 ) to a maximum value of 0.72 percent (S 5 ) with a mean value of 0.27 percent in the soil.

Adsorption of Zinc by Soils
The aftereffects of zinc adsorption by the soils under examination obviously demonstrated that every one of the soil have proclivity for zinc adsorption.The measure of zinc adsorbed for every one of the soils was plotted against the equilibrium zinc concentration to get the adsorption isotherms (Figure-3), demonstrating the impact of zinc focus on zinc adsorption.The adsorption isotherm demonstrated that however the adsorption of zinc expanded with expanding focus in the balance arrangement, yet the level of adsorbed zinc diminished.This might be a direct result of an expansion in the proportion of adsorbate to adsorbent. 9The adsorption isotherms were L-shaped and showed that more destinations in the substrate were occupied 10 and in this way the solute atoms confronted extraordinary trouble to locate any empty site accessible.This prompts a proposal that either the adsorbed atom was not vertically situated or that there is no solid challenge from the solvent. 11The information on zinc adsorption by various soils demonstrated that the adsorption limit of various soils for zinc was extraordinary and the conduct of adsorption of zinc by various soils was not uniform in the entire focus run.Adsorption of zinc was observed to be most extreme in soils of Baramulla locale and this might be credited to the high soil substance and CEC of the soil.The soils of Shopian locale demonstrated least adsorption limit of zinc which is likely because of coarse surface and low CEC. 12From these outcomes, it could be inferred that adsorption of zinc was principally represented by soil substance and CEC of the soils which was affirmed factually since these soils demonstrated positive and critical connection with clay content (r = 0.884**) and CEC (r = 0.697**).
Langmuir adsorption isotherm was fitted to the information where a plot of C/(x/m) versus C gave a straight line with incline 1 / b and a block of 1 / kb.The adsorption maxima (b) esteem went from 41.66 to 76.92 µg Zn g -1 soil (Table -2).Most extreme value was found for the soils of Baramulla locale and least for Shopian region.The bonding energy constant (k) was most extreme (0.0378 ml g -1 ) in soils of Srinagar region and least of 0.018 ml g -1 in soils of Ganderbal locale.
The plot of zinc adsorbed against balance zinc focus on a log-log scale gave direct relationship in every one of the soils for Freundlich adsorption show.Freundlich k esteems extended broadly among soils, going from 2.22 to 3.55 µg g -1 (Table -2).This model was substantial for more extensive scope of zinc concentrations 13 as at higher groupings of connected zinc, multilayer adsorption and additionally precipitation responses seems to have occurred. 14In this way this came about a superior occurrence of information in Freundlich isotherms as contrast with Langmuir models.

Conclusion
Zinc adsorption information was tastefully portrayed by both Langmuir and Freundlich adsorption isotherms over the whole focuses utilized however Freundlich isotherms gave a best fit.Adsorption of zinc was principally represented by the clay content and CEC of soils.An endeavour was made in this examination to know the best fit numerical model to comprehend procedure of zinc adsorption which thusly can helps in advancing appropriate administration practices to defeat weaknesses of zinc in soils.Further research should be done to check the conduct of zinc discharge and alleviation to any issue emerging from abundance zinc adsorption process.

Fig. 1: Physico-chemical characteristics of different soils of Kashmir
7°C).After equilibration samples were centrifuged at 2500 rpm for 15 minutes and filtered.The Zn concentration in filtrate was determined by atomic absorption spectrophotometer.7Theamount of