To provide modified soil which gives good results in growth of various plants when used as fundamental soil for gardening and the like or used as a mixture with a second soil, can be obtained utilizing inexpensive, readily available raw materials and is easily manufacturable and appropriate from the resource-saving and environmental aspects, and its raw materials composition.

Buckwheat chaff and/or chaff is kneaded and mixed with clay to give a raw material composition and the raw material composition is fired at a high temperature to give granular modified soil.