Organic Matter in Submerged Soils

In data assembled by Greenland (1997), the mean level of organic carbon in the topsoils of wetland rice soils from across tropical Asia was 2%, and after excluding acid peaty soils the mean was 1 %. This compares with a range of 1.27-1.81 % for Oxisols and Ultisols of the Cerrado region of Brazil (Sanchez, 

1981) and 2.78-4.80 for Oxisols and Ultisols of the humid tropical forest zone of Sumatra (van Noordwijk et al., 1997). Under intensive multiple-rice cropping, the soil organic mater may increase until a new steady state level is reached after some years. Table 3.12 gives an example for a rice-rice system over five crops in 2 years compared with a maize-rice system. However, very large soil organic matter contents do not develop. 

Cropping system N fertilizer (kg ha ) Rice -rice Maize-rice  

Source Witt et al. (2000). Reproduced with kind permission of Kluwer Academic Publishers. 

Interchange of Solntes between Solid, Liqnid and Gas Phases 

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