STUDY ON LIMITING FACTORS FOR LENGTH OF LONGER SIDE IN LARGE SIZED PADDY FIELD

1.指出机械作业效率、地面排水和土地平整是限制大面积水田长边长度的主要因素。但灌溉的水坑没有被指出的因素。在许多稻田中采用无积水撒播可增加底土层的渗透性。在这种情况下，必须将水田长边长与灌水量的关系作为水田长边长的限制因子。2.对两块长边长为100 m的水田进行了试验。一个具有透水性底土层，另一个具有不透水层。通过对水田积水进行灌水，以等时间间隔观测其前进距离。在有不透水土层的稻田中，可根据土壤气相体积和积水深度估算推进距离;在有透水土层的稻田中，可根据渗透率估算推进距离。进水流量与长边长度的关系是限制大面积稻田的主要因素之一。3.从机械系统和田间条件的角度研究了租赁耕作的最小和最大规模，明确了较大规模养殖系统的养殖场规模可以是20- 4.通过对两个规模化农业的实例研究发现，耕作机械的使用决定了一块地的最小边长，一块地的边长越大越有利于机械作业。

1.Efficiency of farm machine work, surface drainage and land leveling have been indicated as main limiting factors for the length of longer side in a large sized paddy field. But irrigation for puddling has not been pointed out as the factor. Introduction of unponding broadcasting in many paddy fields may increase permeability of subsoil layrs. In this case, the relation between inlet flow rate of irrigation for puddling and length of longer side of paddy plot must be marked as the limiting factor for the longer side.2.Two paddy fields with the longer side of 100m were tested. One had permeable subsoil layr and the other had impermeable one. Through irrigation for puddling in the paddy fields, the advance distances were observed at equal intervals of time. In the paddy with impermeable subsoil layr, the advance distance can be estimated from gaseous phase volume of soil and ponding water depth, and in the paddy with permeable subsoil layr, it can be estimated from percolation rate with the above factors. The relation between inlet flow rate and length of longer side in paddy is one of the limiting factor for large sized paddy fields.3.The minimum and maximum size of a rental farming that was investigated from the viewpoint of machines system and field condition, make cleared that the farm size of larger scale farming system can be 20-100 ha.4.By the case study of two large scale farming it was found that the machines used for farming work decides the minimum side of one plot and larger side of one plot is better for operating machines.