In this lysimeter experiment, temporal changes of water percolation rate, irrigation requirement and No3 －-N leaching were investigated under different cultural practices that were no-till direct seeding on flooded paddy (NTDSF), till direct seeding on flooded paddy (TDSF), and transplanting. The highest water percolation rate of 3,001 l/m2 was measured in NTDSF. Others were 2,551 l/m2 and 2,210 l/m2 in TDSF and transplanting. Water percolation rate in NTDSF and TDSF was increased by 36% and 15% compared to transplanting. Water percolation rates in all cultural practices were increased remarkably from the reproductive growth stage and relatively large amount of water loss through percolation was measured even after the reproductive growth stage. A total irrigation requirement was 3,469 l/m2 in NTDSF and 2,898 l/m2 in TDSF. That was equivalent to 45% and 21 % of increase compared to 2,389 l/m2 in transplanting. The largest No3 －-N leaching through the entire rice growing period was 701 mg/m2 in NTDSF and was followed by 494 mg/m2 in TDSF and 465 mg/m2 in transplanting. The ratios to the total amount of No3 －-N leaching at the vegetative growth stage, reproductive growth stage and ripening stage were 31 %, 41 % and 28% in NTDSF; 21 %, 48% and 31 % in TDSF; and 18%, 48% and 35 % in transplanting.

The experiment was conducted to clarify irrigation requirement and percolation rate in rice paddy. The four rice cultural system of no-tin, till, transplanting, and direct seeding condition were treated in the lysimeter filled with sandy loam soil. The amounts of irrigation and soil percolation were measured daily, and irrigation requirement was estimated. The daily percolation was 19.5 l/~textrmm2 in no-till direct seeding on flooded paddy surface, 17.4 l/~textrmm2 in both of till-direct seeding on flooded surface and no-till transplanting, and 15.2 l/~textrmm2 in transplanting plot. This is equivalent to 19.5, 17.4, and 15.2 mm per day, respectively. Highest irrigation requirement was 3,770 l/~textrmm2 in no-till direct seeding plots. Others were 3,249, 2,577, and 2,321 l/~textrmm2 in till-direct seeding, no-till transplanting and transplanting plot, respectively. The estimated irrigation requirement of no-till transplanting, till-direct seeding and no-till direct seeding was increased by 11, 37, and 59% compared to till-transplanting plot. Percolation rate of no-till transplanting, till direct seeding and no-till direct seeding was increased by 12%, 40%, and 66%, respectively compared to the till-transplanting plot. The percolation rate in paddy soil was increased greatly after reproductive stage of rice.