Infiltration properties of paddy fields under intermittent irrigation

Puddling and recurring intermittent irrigation, common praxis in wet rice cultivation, modify the soil structure and therewith cause a temporal variation of the infiltration properties. This study attempts to evaluate the temporal variation of the infiltration rates of plough pan (vertical infiltration) and paddy fields’ surrounding bunds (bund infiltration) by analyzing (i) the infiltration rate as a function of time, (ii) the relationship between ponding water depth and infiltration rate, and (iii) the influence of cultivation age on vertical water loss and cross-flow through bunds. Two experimental fields with respective cultivation ages of 30 (A) and 7 (B) years were investigated. The results revealed that the time series of vertical infiltration rate (IRv) was with time consistency and the persistency of the bund infiltration was uncertain. The mean infiltration rate into the plough pan of A and B was 3.34 and 1.01 cm d−1, respectively. A total water depth of 230 and 85 cm would be, respectively, lost in A and B through the plough pan during rice growing season. The correlation coefficient between ponding water depth and IRv was −0.48 and −0.81 in A and B, respectively, demonstrating that the dynamic IRv in the old paddy field was less affected by the drying and wetting cycles. It is concluded that rice paddies which have been taken into cultivation since only a few decades may contribute to water losses. Maintenance of equilibrium condition between ponding and drying stages and careful preparation of bunds may reduce water loss.