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Carbon status and structural stability of soils from differing land use systems in the K ingdom of T onga
Author(s) -
Manu V.,
Whitbread A.,
Blair N.,
Blair G.
Publication year - 2014
Publication title -
soil use and management
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.709
H-Index - 81
eISSN - 1475-2743
pISSN - 0266-0032
DOI - 10.1111/sum.12135
Subject(s) - environmental science , tillage , soil water , soil carbon , vegetation (pathology) , soil fertility , carbon fibers , secondary forest , agronomy , forestry , hydrology (agriculture) , agroforestry , soil science , geography , geology , biology , mathematics , medicine , geotechnical engineering , pathology , algorithm , composite number
Maintenance of soil carbon stocks is vital for the environment at large and for maintenance of soil chemical, physical and biological fertility. Tonga represents a country in agricultural transition from subsistence to commercial production and whilst this is good for the national economy the impact on soil resources is less clear. The major cropped soils, fallow vegetation types and forest systems of Tonga were identified in each island group and samples of representative soils (0.15 m depth) from each land use unit were taken. Total carbon ( C T ) and δ 13 C were measured and labile carbon ( C L ) determined by oxidation with 333 m m KM nO 4 . These data were used to determine the carbon management index ( CMI ) and the proportion of carbon from C4 species in the C T pool. Relative to primary forest, the soil C T and C L generally declined with changes in vegetation and more intense mechanical tillage. The contribution of C4 plants to soil C increased with intensity of mechanical tillage and the prevalence of C4 guinea grass ( P anicum maximum J acquin) fallow. The changes in soil C were reflected in the CMI , and C L was a more sensitive indicator of change than C T . These data indicates that all land use systems have experienced a large net loss of soil C relative to the forest systems. Soil mean weight diameter ( MWD ) decreased significantly with increased intensity of mechanical tillage and to a lesser extent with the intensity and length of cropping. The relationship between soil MWD and soil C was similar with soil C T and C L . Grass fallow was as effective as permanent vegetation systems in improving soil MWD and lowering the micro‐aggregate (<125 μ m) fraction.