Development of labor saving operation technique by making large scale paddy field and direct seeding cultivation of rice in Tohoku district [Japan], 2: Development of technique for automatic precision laser-levelling system

1) Preparation for large scaled paddy fields and utilization of direct rice seeding cultivation are expected to be the key technologies for the low cost and labor saving large farm rice cultivation.To achieve this, the technique of land leveling for field operations have to be developed.A precise land leveling operation by a wheel tractor with laser-beam emitter and recever in a wet paddy field are developed.2) The automatic measur ament system of a rice paddy field surface level by a tractor that we developed was highly practical.After measured data are stored in a memory of handheld computer the standard deviation of a field height value is shown on the display. Also, measured data are exported to the personal computer and by RC232C, the contour map of the paddy field is draw quickly, which is useful for the land leveling work.3) Considering the relation between rice seed germination and water depth in the field, the priciseness of the field leveling for direct rice seeding is required to be under 1.5cm of standard deviation (s. d.). To realize this preciseness, a prototype leveling aparatus consisting a laser emitter, a laser receiver and dry land leveler pulled by a tracter, was developed and was tested the performance.The results of land leveling test at a field of 1ha indicated that the elevation difference of the field of 16cm was improved to that of 92% of ±2.5cm (1.58cm s. d.) after leveling work. The working efficiency was 0.57hour/10a. For a precise leveling work, the of the soil water content should be under the plastic limitation, under which less amoumt of soil adoheres to the blade of the leveler.The performance tests of the laser assisted leveling aparatus for a paddy harrowing work revealed that for an accuvate operation only a blade should be controlled by a hydaulic cylinder according to a laser beam.Since large amount of soil can not be handled by the aparatus, the leveling for a paddy harrowing work is recomended for a fine leveling work after a rough leveling work.