fallow vs ploughland

fallow and ploughland both are nouns.

Word	Noun	Adjective	Verb	Adverb
fallow	Yes	Yes	No	No
ploughland	Yes	No	No	No

As nouns, ploughland is a hypernym of fallow; that is, ploughland is a word with a broader meaning than fallow:

fallow: cultivated land that is not seeded for one or more growing seasons
ploughland: arable land that is worked by plowing and sowing and raising crops

Other hypernyms of fallow include cultivated land, farmland, plowland, tillage, tilled land, tilth.

fallow (noun)	ploughland (noun)
cultivated land that is not seeded for one or more growing seasons	arable land that is worked by plowing and sowing and raising crops

fallow (adjective)	ploughland (adjective)
undeveloped but potentially useful
left unplowed and unseeded during a growing season