also: はいつち
noun
ashes and earth; poor volcanic soil
Refers to soil mixed with volcanic ash, often infertile. The reading かいど is standard; はいつち is rare.
この地域の灰土は作物に適さない。
The volcanic ash soil in this area is not suitable for crops.
灰土を改良して肥沃な畑に変えた。
They improved the poor volcanic soil and turned it into fertile fields.
火山灰 refers specifically to volcanic ash itself, while 灰土 refers to soil mixed with ash, emphasizing the resulting poor soil.
Compound of 灰 (ash) and 土 (earth, soil). The reading かいど uses the on'yomi of both characters; はいつち is a mixed reading with はい (kun'yomi) and つち (kun'yomi), but it is rare.