Laboratory Investigation of Plough Sole Reformation in a Simulated Paddy Field

The study aimed to determine the number of cultivation cycles required to reform the plough sole once it has been destroyed or removed from the paddy. An ad hoc infiltration column experiment, which is a cylinder of $50\mathrm{cm}$ in diameter and $140\mathrm{cm}$ long, was setup to simulate the processes of ploughing and compaction, the two major forces exerted by a tractor, for developing a plough sole in rice paddy. Three experimental conditions were investigated, namely developing the plough sole by ploughing, compaction, and a combination of ploughing and compaction. The results of the change in the infiltration rate, soil dry bulk density, and weight percentage of clay in an experimental soil column were measured and evaluated. The experimental results show that, the infiltration rate decreases to 63, 29, and 2% of its initial value with ploughing eight times, compaction 30 times, and combination of ploughing and compaction 14 times, respectively. Moreover, the soil bulk density increases from 1.51 to 1.53, 1.61, and $1.71\mathrm{g}{\mathrm{cm}}^{-3}$ , respectively. Finally, the weight percentage of clay in the plough sole as a result of clay particles moving down from above and increases from 6.2 to 8.2, 6.2, and 14.8%, respectively, over the experimental period. The ploughing rearranged clay content distribution and the compaction increased soil bulk density. Applying these two practices in sequence effectively increased the soil bulk density and reduced the infiltration rate. The results also indicate that after 14 ploughing and compaction the infiltration rate did not further decrease, suggesting that the soil structure could no longer be changed and the plough sole had successfully been reformed. The quantitative result of this work provides valuable information on how to rehabilitate a plough sole once it has been destroyed and needs to be reformed from the paddy field.