noun
fully matured compost
Agricultural term for compost that has completely decomposed and is ready for use as fertilizer.
完熟堆肥を畑にまいて土を改良する。
Spread fully matured compost on the field to improve the soil.
堆肥 is general compost, while 完熟堆肥 specifically refers to compost that has fully matured.
Compound of 完熟 (fully ripe/mature) and 堆肥 (compost).