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

日本要实现低成本的水稻生产，必须研究大规模稻田直接育苗法。我们主要研究了由于田间平整不良引起的种子萌发的异质性和由于幼苗密度引起的种子生长的异质性。第二年，我们继续第一年做的实验，并做了新的实验。1)几种直接育苗法的普及直接育苗法分为旱地直接育苗法、水田直接育苗法和水田直接育苗法。对三种方法进行了比较，即对三种方法的分布进行了调查，并对其原因进行了估计。2)发芽异质性调查大型水田直苗，收集平整、地下水、土壤水分、育苗方法、发芽条件等数据。然后，在人工气象室中进行了不同土壤、水分和幼苗条件下的发芽试验。在人工气象室内，在各种找平条件下进行干燥过程。该结果可用于估算种子的浸没距离，而浸没距离是影响种子萌发的重要因素。4)种子密度与生长的关系试验表明，存在最佳播种密度。5)大面积水田采用直播，需要更精确的平整。通过这些试验和讨论，我们发现了直接育苗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