waving heads of grain
Refers to the visual effect of grain ears swaying in the wind like waves. Often used in poetic or descriptive contexts.
秋の田んぼに穂波が立っている。
Waves of grain heads are rippling in the autumn rice field.
風が吹くたび
Whenever the wind blows, golden waves of grain spread out.
Compound of 穂 (ho, 'ear of grain') and 波 (nami, 'wave'). The reading ほなみ is a straightforward combination.