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

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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.