Agricultural term, especially for rice; refers to a crop that has not filled out well, resulting in low yield or poor grain quality.
This year's poor crop is due to the low summer temperatures.
The harvest decreased significantly because of the poor crop.
不作 is a more general term for a poor harvest or crop failure, while 稔実不良 specifically refers to poor grain filling, often used in agricultural contexts.
Compound of 稔実 (ねんじつ, 'ripening of grain') and 不良 (ふりょう, 'poor, bad'). The exact historical derivation is uncertain, but the term is used in modern agricultural contexts.