MSc

An investigation entitled ―Impact of agricultural land use systems on soil carbon pools in soil series of Thiruvananthapuram district‖ was carried out to study the soil carbon storage as different soil carbon pools and their distribution in different sized soil aggregates under different agricultural land use systems in soil series of Thiruvananthapuram district. The seven major soil series of Thiruvananthapuram district namely Vellayani, Amaravila, Trivandrum, Kazhakuttam, Nedumangadu, Kallar and Ponmudi were selected and three agricultural land use systems were identified in each soil series. Surface soil samples (0-15 cm) were collected and analysed for soil physico-chemical properties and soil carbon pools.
Examination of various soil parameters revealed that the soil texture in most of the soil series varied from sandy loam to sandy clay loam. The bulk density of soil varied from 1.10 to 1.59 Mg m-3. The highest BD was recorded in rice land use of Kazhakuttam series. The pH of various soil series ranged from 4.29 to 5.77. The highest value was recorded in tapioca land use of Trivandrum soil series. EC of the soils ranged from 0.02 to 0.13 dS m-1. The highest EC was recorded in rice land use of Kazhakuttam series. The CEC of the soil was significantly influenced by different land uses in all the soil series and the values ranged between 3.65 and 6.88 c mol (p+) kg-1. The highest CEC was possessed by vegetable land use of Vellayani series.
The effect of agricultural land use systems on the extent of different sized water stable aggregates viz., 5-8, 2-5, 1-2, 0.5-1, 0.25-0.5 and 0.1-0.25 mm were found to be significant. The highest total water stable aggregate of 95.08 % was registered in rubber land use system of Nedumangadu series.
Soil organic carbon (SOC) content in various soil series under different land use systems varied from 2.96 to 11.67 g kg-1. The agricultural land use systems viz.,
vegetable (8.73 g kg-1), coconut (7.96 g kg-1), rubber (9.37 and 9.93 g kg-1), homestead (7.30 g kg-1), rice (9.96 g kg-1) and tea (11.97 g kg-1) significantly increased SOC in various soil series. With respect to aggregate associated organic carbon, macro aggregates were found to be richer in carbon compared to micro aggregates in Vellayani, Amaravila and Trivandrum series. In the other soil series, micro aggregates were found to be richer in carbon. The agricultural land use systems viz., vegetable (1657 mg kg-1, 1400 mg kg-1), homestead (667 mg kg-1), rice (1725 mg kg-1), rubber (1132 and 1364 mg kg-1) and arecanut (1344 mg kg-1) significantly increased AAOC in various soil series.
Hot water soluble carbon in various soil series under different land use systems varied from 20.66 to 76.45 mg kg-1, where the highest value was recorded in rice land use system in Kazhakuttam series. With respect to labile carbon, the land use systems viz., vegetable (1997 mg kg-1), coconut (2541 mg kg-1), rubber (2211 and 1349 mg kg-1), coconut (2516 mg kg-1), rice (2187 mg kg-1) and tea ( 1241 mg kg-1) registered significantly higher content in various soil series. Particulate organic carbon (POC) in very fine fraction (<53 μm) was found to be higher than fine (53-250 μm) and coarse (>250 μm) fractions. Total POC in various soil series under different land use systems varied from 1130 to 3980 mg kg-1, where the highest value was recorded in rubber land use system of Kallar series. The mineralizeble carbon concentration was found to be the highest under rice land use of Kazhakuttam series (6.39 mg kg-1) and the lowest under coconut land use of Kallar series (2.86 mg kg-1).
The study revealed that vegetable land use system in Vellayani and Amaravila series, rubber in Nedumangadu and Kallar series, homestead in Trivandrum series, rice in Kazhakuttam series and tea and arecanut in Ponmudi series significantly contributed to soil organic carbon storage as different soil carbon pools in different sized aggregates compared to other land uses in the respective soil series.