Total and organic soil carbon in cropping systems of Nepal
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The significance of soil organic matter (SOM) in sustaining agriculture has long been recognized. The rate of change depends on climate, cropping system, cropping practice, and soil moisture. A 3-yr on-farm study was conducted in two major agro-ecologies (hills with warm-temperate climate and plains with subtropical climate) of Nepal. The soils in warm-temperate climate are Lithic subgroups of Ustorthents with well-drained loamy texture, and in subtropical climate are Haplaquepts with imperfectly drained loamy texture. Farmers’ predominant cropping systems were selected from different cultivation length in addition to a reference sample collected from adjacent virgin forest. The objectives were to examine the effect of cultivation length and cropping system on total carbon, KMnO4-oxidizable soil C, C storage, and C/N ratio in two climatic scenarios: warm-temperate and subtropical. A large difference in KMnO4-oxidizable soil organic C was observed due to the effect of cultivation length and cropping system. However, TC remained similar during the 3-year study. The decrease in KMnO4-oxidizable C due to cultivation was more in the surface layer (43–56%) than in the subsurface layer (20–30%). Total C in uncultivated, < 10-year cultivated, and > 50-year cultivated soil was 22, 13, and 10 g kg−1 in warm-temperate climate and 10, 6, and 5 g kg−1 in subtropical climate, respectively. During the 3-year study period in both climates, large changes in soil C were observed for KMnO4-oxidizable C but not for TC, confirming our earlier work on the usefulness of the KMnO4 oxidized fraction for detecting a relatively short-term increase or decrease in soil C pool. The TC storage in uncultivated, < 10-year cultivated, and > 50-year cultivated soil was 38, 25, and 19 Mg ha−1 in warm-temperate climate and 22, 15, and 12 Mg ha−1 in subtropical climate, respectively. The rice–wheat and maize–potato cropping systems were good in storing soil C of 30 and 20 Mg ha−1 for 0–15-cm soil depth in warm-temperate climate. The rice–wheat cropping system was also good in storing soil C in subtropical climate (19 Mg ha−1) compared with other cropping systems studied.
KeywordsKMnO4-oxidizable carbon Total carbon Carbon storage C/N ratio Climate Cropping system
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This study was funded by the Rice–Wheat Consortium for the Indo-Gangetic Plain. The authors would like to thank S.L. Maskey, chief soil scientist, Soil Science Division, Nepal Agricultural Research Council, Lalitpur, Nepal; P. Hobbs, Cornell University, USA; and R.K. Gupta, Rice-Wheat coordinator, New Delhi, India, for their suggestions.
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