Reducing bypass flow during land preparation of cracked rice soils.
1997
Cabangon R.
High water loss during land preparation of rice soils results from bypass flow through cracks. It was hypothesized that bypass losses could be reduced by measures which minimize the crack development or impede the flow of water through the cracks. The effect of straw mulching and shallow tillage during the fallow period on crack formation, total water required during land soaking and land preparation, and bypass losses was investigated at two Epicqualf sites (Bulacan and IRRI) with relatively permeable subsoil (saturated hydraulic conductivity, K sub s of 0.1 and 0.5 m/d, respectively) and in a Pellustert site (Nueva Ecija) with a less permeable subsoil (K sub s of 0.007 m/d) compared with the control, where no attempt was made to manage the soil during the fallow period, straw mulching reduced the mean crack width from 40 mm to 27 mm. Mean crack depth decreased only slightly, from 11.5 to 105 mm, resulting in a non-significant reduction in total water input. Shallow tillage reduced the total water input for land preparation by 31-48 percent. Most of the water savings came from a significant reduction (58-71 percent) in the seepage and percolation losses from land soaking to harrowing. Shallow tillage formed small soil aggregates which enhanced infiltration into the surface soil layer and reduced the amount of water to flow in the cracks and made the crack flow discontinuous. Shallow tillage offers a practical means for improving water use efficiency of an irrigation system.
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