Study on Appropreate Seeding Density and Levelling Accuracy of Paddy Field Surface in Direct Seedling of Paddy Rice.

为实现日本水稻的低成本生产，应研究大面积水田直播育秧法。第二年，我们继续进行了第一年的试验，并进行了新的试验。1)几种直接育苗方法的普及性。直接育苗方法分为旱地DS法、水田DS法和水田DS法。对3种方法进行了比较，即调查了3种方法的分布，并对其原因进行了分析。2)调查了大田直播秧苗的异质性，收集了平整、地下水、土壤水分、秧苗方法和发芽情况等资料。然后，在人工气候室中，在不同的土壤、水分和苗木条件下进行发芽试验。3)灌后排水田的土壤硬度在人工气候室中，在各种平整条件下进行干燥过程。4)种子密度与生长关系的试验表明，存在最佳播种密度；5)大面积水田直播需要更精确的平整。通过试验和讨论，找出了直播存在的问题和改进的方向

Direct seedling method in large-sized paddy field should be researched for low-cost rice production in Japan. Our research was focused on the heterogenity of germination caused by bad levelling of the field and that if growing caused by seedling density.In the second year, we continued experiments done in the first yearand made new ones.1) Popurarity of several direct seedling methodsDirect seedling methods are categorized as DS in dry field, DS in ponding field and DS in wer field. Three methods are compared, i. e. the distribution of three methods is surveyed and the reason is estimated.2) Heterogenity of germinationDirect seedling in large-sized paddy field is surveyed, and the data of levelling, groundwater, soil moisture, seedling method and germination condition are collected. Then, in the artifitial weather chamber, germination experiments were done in various conditions of soil, water and seedling conditions.3) Soil hardness of drained field just after puddingIn the artifitial weather chanber, drying process is pursued in various levelling conditions. This result well be utilized for the estimation of the submergence distance of seed, which is an important factor of germination.4) Experiment on relations between seed density and growth shows the existence of optimum density of seeding.5) To apply direct seeding for large-sized paddy field, more precise levelling is neede.After these experiments and discussions, we've found the problems of direct seedling and directions for the improvement