Abstract
To elucidate the relationship between root distribution in each soil layer and root lodging tolerance, the effects of root prunning and the laying of porous membrane (non-woven fabric) between topsoil and subsoil layer on pushing resistance were investigated using two root lodging tolerant USA rice cultivars (M-302 and Lemont) and two susceptible Japanese cultivars (Nipponbare and Hatsuboshi). Although pushing resistance was affected by root prunning to 5 cm under soil surface with inserting the steel plate, the reduction was more pronounced and significant when roots were pruned to a 1O cm depth. In addition, a remarkable decrease in pushing resistance was observed when a porous membrane was laid under the topsoil. This decrease was larger in the lodging-tolerant USA cultivars than susceptible Japanese cultivars. Comparison between the variances of pushing resistance and root dry weight induced by each treatment indicated that the contribution of unit root weight to lodging tolerance was higher in deeper (including subsoil)than in shallower soil layers. In the pot experiment, pushing resistance per unit dry weight of root was higher in rice plants grown on soil with higher bulk density than with lower bulk density. These results confirmed that the higher ability of root formation in rice into subsoil with a higher bulk density was one of the important characteristics for root lodging tolerance.
