Genesis 41:31

Or, they shall remember no more the plenty.

Geneva Bible (1599) marginal notes — public domain. Text via Bolls.life.

Verse 31. The plenty shall not be known in the land by reason of that famine following] As Egypt depends for its fertility on the flowing of the Nile, and this flowing is not always equal, there must be a point to which it must rise to saturate the land sufficiently, in order to produce grain sufficient for the support of its inhabitants. Pliny, Hist. Nat., lib. v., cap. 9, has given us a scale by which the plenty and dearth may be ascertained; and, from what I have been able to collect from modern travellers, this scale may be yet considered as perfectly correct. Justum incrementum est cubitorum xvi. Minores aquae non omnia rigant, ampliores detinent, tardius recedendo. HAE serendi tempora absumunt, solo madente, ILLAE non dant, sitiente. Utrumque reputat provincia. In xii. cubitis famen sentit. In xiii. etiamnum esurit; xiv. cubita hilaritatem afferunt; xv. securitatem; xvi. delicias. "The ordinary height of the inundations is sixteen cubits. When the waters are lower than this standard they do not overflow the whole ground; when above this standard, they are too long in running off. In the first case the ground is not saturated: by the second, the waters are detained so long on the ground that seed-time is lost. The province marks both. If it rise only twelve cubits, a famine is the consequence. Even at thirteen cubits hunger prevails; fourteen cubits produces general rejoicing; fifteen, perfect security; and sixteen, all the luxuries of life."

When the Nile rises to eighteen cubits it prevents the sowing of the land in due season, and as necessarily produces a famine as when it does not overflow its banks.

Adam Clarke's Commentary on the Bible (1810–1826) — public domain. Text from a community e-Sword/MySword module.

Let Pharaoh do this,.... Appoint such a person; who as a sovereign prince could do it of himself:

and let him appoint officers over the land; not Pharaoh, but the wise and discreet governor he should set over the land, who should have a power of appointing officers or overseers under him to manage things according to his direction:

and take up the fifth part of the land of Egypt in the seven plenteous years; not the officers appointed, but the appointer of them, the chief governor under Pharaoh, for the word is singular; it is proposed that he should, in Pharaoh's name, and by his order, take a fifth part of all the corn in the land of Egypt during seven years of plenty; not by force, which so good a man as Joseph would never advise to, whatever power Pharaoh might have, and could exercise if he pleased; but by making a purchase of it, which in such time of plenty would be bought cheap, and which so great a prince as Pharaoh was capable of. It is commonly asked, why an half part was not ordered to be took up, since there were to be as many years of famine as of plenty? and to this it is usually replied, that besides this fifth part taken up, as there might be an old stock of former years, so there would be something considerable remain of these seven years of plenty, which men of substance would lay up, as Pharaoh did; and besides, a fifth part might be equal to the crop of an ordinary year, or near it: to which may be added, that in times of famine men live more sparingly, as they are obliged, and therefore such a quantity would go the further; as well as it may be considered, that notwithstanding the barrenness of the land in general, yet in some places, especially on the banks of the Nile, some corn might be produced; so that upon the whole a fifth part might be judged sufficient to answer the extremity of the seven years of famine, and even to allow a distribution to other countries.

John Gill's Exposition of the Whole Bible (1746–1763) — public domain (CC PDM 1.0). Text via the HelloAO Bible API.

ולא יודע השבע AND THE PLENTY SHALL NOT BE KNOWN — this is the interpretation of (v. 21) “And it could not be noticed that they had eaten them up”.

Rashi on the Tanakh — English translations: “The Judaica Press complete Tanach with Rashi, translated by A. J. Rosenberg” (CC BY 4.0); “Pentateuch with Rashi's commentary by M. Rosenbaum and A.M. Silbermann, 1929-1934” (public domain); “The Metsudah Tanach series, Lakewood, N.J” (CC BY 4.0); and “The Book of Joshua, Metsudah Publications, 1997” (CC BY 4.0). Text via Sefaria.