Abstract
Early sowing of spring wheat often increases the risk of frost injury in early spring due to accelerate jointing, it is therefore necessary to delay the jointing stage. Ground rolling has the effect of delaying apical development and may reduce the risk of frost injury by delaying the jointing stage. In this study, to clarify optimal conditions for effectively delaying the jointing stage by rolling, the effect of two types of rolling machines on delaying apical development was examined, and the relationship between soil data collected before and after rolling and apical development was analyzed. The results showed that both types of machines delayed apical development, and there was a high negative correlation between soil volumetric water content before rolling and the degree of delay in the jointing stage. To obtain the effect of delaying apical development in the field in this study （upland field converted from a paddy field, soil volumetric water content of surface soil is approx. 50% of field water capacity, approx. 34% of plastic limit, and approx. 20% of permanent wilting point）, the soil volumetric water content must be at least 27% or less before rolling.
