Rainfed rice soils

Figure 7.3 Typical annual nutrient balances for rainfed rice soils from probable inputs (left side of each graph) and outputs (right side) (data from Greenland, 1997). Inputs come from R = rainfall, F = floodwater and irrigation, S = sediments, N = nitrogen fixation and M = manures and fertilizers. Outputs are due to removals in Cg = rice grain, Cs = rice straw. Cl = legume crop, S = seepage and percolation and G = gaseous emission...

Despite the burning of crop residues in the productive, irrigated rice areas of tropical and subtropical Asia, and their removal for other purposes in the low-producing rainfed rice areas, soil carbon levels are largely constant (Bronson et al., 1998). In any case, the amount of carbon in the shallow puddled layer of ricefields amounts to only a few per cent of the amount in natural wetlands. 

Flood-prone. Distinguished from rainfed lowland rice by extent and duration of flooding. Fields are flooded to at least 100 cm and often much more for at least 10 consecutive days in tiie growing season. Crop is transplanted in puddled soil or direct seeded on ploughed dry soil soil may alternate between oxic and anoxic conditions during season. 

Tripathi BP, Ladha JK, Timsina J, Pascua SR. 1997. Nitrogen dynamics and balance in intensified rainfed lowland rice-based cropping systems. Soil Science Society of America Journal 61 812-821. 

Panda, M. M., Reddy, M. D., and Sharma, A. R. (1991). Yield performance of rainfed lowland rice as affected by nursery fertilization under conditions of intermediate deepwater (15-50 cm) and flash floods. Plant Soil 132 65-71. 

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