Abstract
In the case of reclamation of peat land for the purpose of utilization as upland field, drainage and acid neutralization are the most important practices. On the other hand, for the purpose of utilization of peat land as paddy field for rice cultivation, the practice of soil putting (which means to put the mineral soil on the surface of peat soil about 10cm in thickness) is important, next to drainage. This practice was taught by experience, because good rice yield has been obtained in the case of peat land covered with mineral soil by inundation of river. So, the authors intended to make clear the meaning of soil putting from the standpoint of soil science and plant nutrition. Three experimental fields were prepared, viz., peat soil, mineral soil and peat soil with mineral soil putting, in Bibai, Hokkaido. First authors compared the growth of rice plant in each plot as described in Table 12,subdividing each plot into 4 small plots, complete fertilizer, no nitrogen, no phosphorus and no potassium, respectively. From the above Table it will be clear, that in the case of peat soil the yields of ear are in the following order : no nitrogen<no potassium<no phosphorus<complete; while in the case of peat soil put by mineral soil the order is : no potassium<no phosphorus<no nitrogen<complete. Moreover, in the case of soil putting, no-nitrogen plot gave the same yield as complete-fertilizer plot. These phenomena seem to be due, as stated in the 1st report, to the fact that in the case of peat soil, the seasonal change of available nitrogen does not cope with the demands of rice plant for nitrogen, so the rice plant suffers from a disturbance in its normal growth. But, as the result of soil putting, soil temperature increases markedly, and the decomposition proceeds comparatively quickly in early stage and liberates available ammonia comparatively early before the formation of flower primordia of rice plant. So, even in the case of no-nitrogen plot, a great yield was produced comparatively to that of the complete-fertilizer plot. In the case of no-potassium, the yield is very low even in the case of soil putting. The peat soil contains a very small amount of potassium and at the same time is low in the power to fix it. Among the elements derived from the mineral soil which was put on the peat soil, only silicic acid exerted a beneficial effect directly on the growth of rice plant. So, the meaning of soil putting will be summarized as follows : 1. It increases volume weight of soil. 2. It increases soil temperature quickly. 3. So, the decomposition proceeds quickly and liberates available nitrogen at the period just suitable for the growth of rice plants. 4. It supplies silicic acid to the rice plant and increases the strength of the plant. 5. It supplies no potassium, but increases the power of soil to absorb potassium and protects soil from loss by drainage. 6. It precipitates active iron and aluminium and increases the activity of phosphoric acid.
