Changes in soil chemistry associated with the establishment of forest gardens on eroded,acidified grassland soils in Sri Lanka |
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Authors: | Ilyas Siddique Caroline Gutjahr Gamini Seneviratne Broder Breckling Sudheera W Ranwala Ian J Alexander |
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Institution: | (1) School of Biological Sciences, University of Aberdeen, Cruickshank Building, Aberdeen, AB24 3UU, UK;(2) Institute of Fundamental Studies, Hantana, Kandy, Sri Lanka;(3) Center for Environmental Research and Technology, University of Bremen, POB 330440, 28334 Bremen, Germany;(4) Present address: School of Integrative Biology, Hines Building, The University of Queensland, Brisbane, QLD, 4072, Australia |
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Abstract: | Topsoil properties were determined in forest gardens established about 20 years ago on eroded grassland soils (abandoned tea
lands) in the wet zone of the Sri Lankan highlands. They were compared with adjacent, eroded grasslands (abandoned tea lands)
on strongly weathered soils vs soils at earlier stages of pedogenic development in a two-way analysis of variance. Soil pH
in forest gardens was, on average, 6.1, nearly one unit higher than in the adjacent grasslands. In the garden soils, the cation
exchange capacity (CEC measured at pH 4.8) was nearly double, exchangeable calcium concentrations five times and exchangeable
magnesium three times as high as in the grasslands soils. Total soil N content was found to be nearly 40% higher in the gardens.
Topsoil gravel contents in the gardens were less than half as high as in the grasslands. The increases in exchangeable bases
and N in gardens, relative to grasslands, were attributed to increased nutrient retention and acquisition. Higher retention
was partly due to the higher CECpH4.8, and probably to reduced erosion and increased, continuous fine root density in the garden topsoils. Higher field CEC in
gardens was likely to result from generally higher C contents and from the reversal of acidification, presumably caused by
base accumulation and decomposition processes. Our results suggest that forest garden establishment on degraded grasslands
can lead to accumulation of mobile nutrients in the topsoil, probably due to increased nutrient retention, subsoil uptake
and litter input exceeding nutrient uptake by the standing biomass. |
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Keywords: | Soil acidity Exchangeable bases CEC at low pH Multistrata agroforests Tropical tree fallows |
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