Spatial and temporal changes of soil C after establishment of a pasture ona long-term cultivated vertisol (Martinique)

In 1991 in Martinique (F.W.I), a Digitaria decumbens pasture was establishe d on a vertisol that had supported a market-gardening culture for more than 10 years. Organic matter stock restoration was investigated by measuring c arbon contents (C contents) and carbon/nitrogen (C/N) ratios each year from 1992 to 1997. Relations between and soil properties (particle-size distrib ution, soil depth) and C contents were studied. Furthermore, geostatistical analyses of C contents were realised in order to characterise the C storag e in soil at plot scale. The increase of C contents from 1992 (Y-0) to 1997 (Y-5) was 5 g C (kg soil)(-1) in the topsoil (0-10 cm) and 2.5 g C kg soil (-1), or 7.5 Mg C ha(-1), in the 0-30-cm layer. The intensity of organic C storage had a spatial pattern, although the C/N ratio remained homogeneous across the plot. However, there was no correlation between the C increase a nd the particle-size distribution or the depth of the soil. In the topsoil, the local variability of the C contents increased with time until 1995 and then there was a gradually spreading of this local variability. Plant-cove r distribution and physical structure of vertisol could explain the evoluti on of spatial structure of the soil C content. (C) 2000 Elsevier Science B. V. All rights reserved.