Sulphur status of major uplands of south Kerala
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Date
1991
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Department of Soil Science and Agricultural Chemistry, College of Agriculture, Vellayani
Abstract
A study has been made to determine the different forms and distribution of sulphur, and its relationship to relevant soil parameters in the major upland soils of South Kerala representing sandy, redloam, laterite midland, laterite midupland and forest soils. An attempt was made to study the plant available sulphur by conducting Neubauer technique using paddy as the test crop. Available sulphur in the soils was also estimated using different extractants. The results of the experiments were summarised and appropriate conclusions drawn.
The study revealed that the forms of sulphur varied considerably from soil to soil. The soils in general were not deficient in this element. The content of different forms of sulphur was maximum in the forest and minimum in sandy soils. Sulphur content decreased from forest to sandy soils through laterite midupland, laterite midland and redloam soils. Organic sulphur registered more than 90 % while sulphate sulphur less than 10 % of the total sulphur in all the soils. The leaching loss of sulphate sulphur in the humid tropical soils may be accounted for the lower contribution of sulphate sulphur to total sulphur.
In all the soil types both total and organic sulphur decreased with increasing depth. Except for sandy soils sulphate sulphur also showed the same trend in distribution in all the soils. Accumulation of sulphate form in the subsurface layers of sandy soils may be attributed to its coarse textured nature.
Of the four extractants used for the determination of available sulphur in soils, Morgan’s reagent was proved to be the best extractant followed by neutral normal ammonium acetate, normal hydrochloric acid and water in the descending order in all the soils.
Sulphur uptake as determined by Neubauer technique recorded the highest value in forest and lowest in sandy soil, laterite midupland, laterite midland and redloam coming in between in the descending order. Neubauer values reflected the actual amount of sulphur in the soils. The significant correlation between the Neubauer values and available sulphur determined by the different extractant was also established.
The different forms of sulphur were positively and significantly correlated with the soil characteristics viz. silt, clay, organic carbon, total contents of nitrogen, phosphorus, calcium, magnesium and sesquioxides and negatively correlated with soil pH. The relationship among the various forms of sulphur was also found to be significantly positive.
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