i-adjective
fruitful; productive; successful
Describes efforts, work, or periods that yield good results or achievements. Often used for careers, research, or creative endeavors.
彼は実り多い研究生活を送った。
He led a fruitful research career.
今年は
This year was a productive one.
実り is a noun meaning 'harvest' or 'fruit', while 実り多い is an adjective meaning 'fruitful' or 'productive'.
多い is a standalone adjective meaning 'many' or 'much', but in 実り多い it combines with 実り to form a compound adjective.
Compound of 実り (harvest, fruit) + 多い (many, much). The combination yields the meaning 'having much fruit/harvest', extended to 'fruitful, productive'.