Soil organic carbon changes in cracking clay soils under cotton production as studied by carbon fractionation

Abstract

This study examined soil carbon levels across a wide range of cracking clay soils used for growing cotton in Australia by using a simple carbon fractionation procedure. The soils studied included reference and cropped sites. The procedure employed determines soil carbon fractions based on their ease of oxidation to obtain the labile (C_L) and non-labile (C_NL) carbon components. Based on the total carbon (C_T), labile carbon (C_L), and non-labile carbon (C_NL) of a cropped soil relative to a reference soil, various monitoring indices were developed. It was found that cultivation has generally led to a decrease in the organic carbon status of the soils. The effect of cultivation was found to be more pronounced in the C_L and the carbon management index (CMI) than in the C_T and C_NL. The changes in the ratio of C_L to C_NL as a result of cultivation have been variable. The CMI has generally declined during cultivation, and since the CMI has incorporated the changes taking place in C_T, C_L, and C_NL, the use of this index can provide very useful results in monitoring of organic matter status of soils.