COMPARATIVE EVALUATION OF PHYSICO-CHEMICAL CHARACTERISTICS OF LATERITE SOIL

* Binoy T Thomas, Saranya Mol S T, Reshma Rajan and Bhagya M V. Department of Botany, Phycotechnology Lab, Catholicate College, Pathanamthitta, Kerala. ...................................................................................................................... Manuscript Info Abstract ......................... ........................................................................ Manuscript History


ISSN: 2320-5407
Int. J. Adv. Res. 5 (6), 1748-1753 1749 (Soil Survey Organization 2007). The major objective of this study was the analysis of sensitive fertility characteristics of laterite soils of Pathanamthitta District, Kerala during three different seasons.

Materials and methods:-
Area of study:-Soil samples were collected in triplicate from Catholicate College, Pathanamthitta District (9 0 16'N 76 0 47'E),Kerala during the three different seasons viz southwest, northeast and summer seasons. The climate of the Pathanamthitta District is humid with a short summer (January to April) and plentiful rainfall (average annual rain fall in the district is 2610.3 mm) available in two monsoon seasons -the southwest (May to August) and the northeast (September to December) monsoons. The annual average temperature of the area is 28.00 ºC (Soil Survey Organization, 2007).Among the three types of laterite soils in the State the soil under the current investigations belonged to a shallow soil type of less than 50 cm depth, having indurated laterite and laterite outcrops. This soil has five different series such as the Airavon, Adoor, Ayroor, Kumaranperur and Gudarakal. The study sites of the present investigation were distributed in the Ayroor series in the district (Soil Survey Organization, 2007).
Soil samples were collected from 10 different sites of the study area. Soil sampling and physico-chemical analyses were carried out as per standard methods (Jackson, 1973).Soil samples from 1-2 cm layer were taken for the analysis by using a sterilized blade. For physico-chemical studies, soil samples were randomly taken in each season. The different random samples were thoroughly mixed together to a general composite sample of about 500 gm and carried to the lab in separate cotton bags for further studies. Altogether 30 composite samples belonging to the three different seasons were collected from the study area for physico-chemical studies of soils.
Certain physico-chemical characteristic features of the soil viz. pH, total soluble salt, temperature, organic carbon,available phosphorous and potassium were analyzed. Soil pH and TSS were measured from 1:2 (neutral distilled water) soil pastes of air dried sample. Soil pH was measured using a pH meter (Systronics 324) and TSS using an electrical conductivity bridge (Systronics Conductivity Bridge 303). The temperature of the soil samples were measured directly from the field using a thermometer. Organic carbon, Available phosphorous (P) and available K were estimated as per Jackson (1973).

Results and Discussion:-
The variations in physico-chemical characteristics viz. pH, total soluble salt, temperature, organic carbon, available phosphorous and potassium of tropical laterite soils have been studied and the data were summarized in the table 1.

Soil Temperature:-
In all the spots, average temperature of the soil was highest during summer seasons (37 0 c) and least was observed during southwest (32 0 c) and northeast monsoon seasons. Similar results were observed in all other sites. Temperature is one of the soil forming factors which help in weathering and soil development (Sandeep et al. 2014).
Soil pH:-Data on soil pH reveals that soils were acidic to neutral and alkaline in reaction; lowest pH was noted during the summer seasons (6.8) and highest pH was observed at monsoon seasons (7.5).The pH of all the sites varied from 6.5 to 7.5 and 4.6 to 7.0. The lower pH of certain sites was mainly due to leaching of bases by rainfall. Higher pH of certain sites may be due to the accumulation of bases.
The slightly acidic pH in the tropical soil (4.6) is similar to the previous reports elsewhere in the region (Soil Survey Staff 2007). In general, such soils are found to be more favorable than alkaline soils to support the diverse vegetation (Diaz-Maroto and Vila-Lameiro 2007). Since soil pH influence fertility management of tropical soils and the knowledge of its variations in soils enable understanding of the rate at which the laterisation precedes in a particular land use system (Byju 2001), the present study is useful to assess the ecology of soil fertility of tropical laterite soils in general.

TSS (Total Soluble Salts):-
Total soluble salts of all the study sites were quite same as 0.1ds/m. It indicates that low salt content was present in all the studied soil.

Organic Carbon:-
The data on organic carbon content ranged from 1.87 to 2.8 %. All soils of the study area fall under low to medium content category. During southwest monsoon season organic carbon was low (1.87) and slightly elevated in northeast monsoon and summer seasons (2.8). The differences in the amount of organic carbon are probably due to the differences of litter decomposition rate. The good percentage of organic carbon in the study sites was due to deposition processes and low soil erosion. This observation is in accordance with the results of Tsui et al (2004). The range in variations of soil organic carbon observed currently in the soils is comparatively higher than the observations of Karthikakuttyamma et al. (1998). But according to Sheikh et al. (2009) low amount of organic carbon in soils is due to wider spacing between trees, resulting in lower litter input. Balagopalan et al. (1992) found that higher organic carbon and exchangeable bases in soils depends on both the vegetation as well as climate, altitude and soil minerals.

Available Potassium:-
The average rate of available potassium in all the sites was 400 kg/ha -1 in all the seasons. In general laterite soil is considered to be poor in Potassium (Ambily et al.2000). But a general increase in the amount of available Potassium noticed in all the regions in all the seasons, which agrees with the observations of Anu and Sabu (2007) in similar soil systems.
In general, physico-chemical characteristics of soils vary in space and time because variation in topography, climate, weathering processes, vegetation cover, microbial activities and several other biotic and a biotic factors. Plant tissues are the main source of organic matter, which influences the physico-chemical characteristics of soil (Johnston 1986). Abbreviations: S1 to S10-The ten different spots, SWM-South West Monsoon, NEM-North East Monsoon, Sum-Summer seasons, C-Organic Carbon, P-Available Phosphorous, K-Available Potassium, TSS-Total Soluble Salts

Conclusion:-
After the investigation it is clear that physic-chemical parameters of the soil vary significantly with seasons. During the transition of southwest monsoon to northeast monsoon, the temperature was almost stable; however high temperature was observed at the summer seasons. There was a significant increase in the soil pH observed during the transition of seasons. There was an increase in phosphorous and organic carbon content in season transition while the potassium content was varied.