Effect of Small-Scale ‘Crashing and Compaction Method’ on Controlling Water Percolation in Paddy Fields with Volcanic Ash Soil

Abstract

Effect of ‘crashing and compaction method’ by using farming machineries on reduction of water percolation was examined in paddy fields with volcanic ash soil. After removing plow layer, 27 experimental plots, each of which has a combination of treatments: tillage depth (0, 10, 20cm), compaction intensity (L, M, H) were allocated in the paddy field following split-plot experimental design. Saturated hydraulic conductivity was measured by using closed-type infiltrometers just after and 3 months after the construction of the layer for percolation controlling, to compare the effect of the factors by ANOVA. The study revealed clear effect of tillage before compaction. Although the hydraulic conductivity of hardpan kept no less than 140mm/d by the compaction treatment alone, it decreased to 15 to 22mm/d in average by the combination of tillage and compaction. However the 10cm of tillage was too thin to make a layer for the stable percolation control under the two months of drying and freezing circumstance. Tillage to 20cm and moderate compaction was evaluated to be adequate for controlling excess seepage under normal farming management.