Application of organic materials are fertilizers in Thailand sometimes resulted in the interruption of elongation of rapid decrease of the diameter of nodal roots along the axis at the early stage of rice growth. However, the damage caused to the roots at the early stage did not lead to the suppression of plant growth at later stages but rather resulted in high yield. The use of organic materials as fertilizers affected the amount of roots throughout the plant growth and increased the percentage of nodal roots that elongated to the deep soil layers. These effects on root growth were ascribed to the restrained uptake of the nitrogen released from organic materials at early stages of rice growth, whereas the application of nitrogen by chemical fertilizer may have caused excessive growth in vegetative phase.