Abstract
Fracional factorial experiment using 8 lysimeters was applied to compare the effects of four operational factors in rice culture on the nitrogen outflow and balance (input by irrigation-outflow). Four factors and the two levels allocated to each factor are as follows : irrigation flow rate (10 and 20 mm/day) ; nitrogen concentration in irrigation water (+0 and +20 mg/l) ; phosphorus concentration (+0.0 and +2.0 mg/l) ; soil condition (fertilized in the past three years, not fertilized before). The lysimeters had little volume of percolated flow. The irrigation period was divided into 4 sub-period by their characteristics observed in the factorial effects on nitrogen outflow. Period I : high nitrogen concentration mainly affected positively, and in this particular level high flow rate had much outflow. Period II : high N concentration increased outflow significantly. Perion III : high flow rate, high N concentration, and non-fertilized soil increased outflow. Period IV : the most significant factor on increasing outflow was high flow rate. In no-irrigation period, nitrogen outflow was free from all factorial effects. Throughout those periods, no effects of P were observed. From the viewpoint of effects on nitrogen balance, in Periods I and II the high N concentration affected positively. Period III : high flow rate, high N concentration, and fertilized soil increased balance. Period IV : high N concentration and high flow rate increased balance. Throughout the irrigation period, effects by P were not significant. The conditions which increased the balance (removal), increased the crop. The conditions which promote the balance contradicted the conditions for decreasing outflow in many periods.
