Abstract
In the case of sprayed direct seeding of rice plant, the seed penetration is influenced by surface undulations of paddy eld after puddling. In this paper, the author grasp the influence of field undulations on the seed penetration, especially non-penetration, and consider the possibility to control the seed penetration from the viewpoint of leveling accuracy. As the results; 1) Surface soil hardness of paddy field quickly becomes harder when the soil exposed from the water surface because of undulations, and it causes expansion of the heterogeneity of surface soil hardness. 2) As water depth increases, the ratio of non-penetrating seeds increases because of the resistance of water. 3) The present standard of leveling accuracy, ±3.5cm, cannot avoid non-penetrating seeds completely. To avoid non-penetrating seeds, not only improvement of leveling accuracy is necessary but also precise water management when seeding, even though each of them are hard to practice.
