Charles Ellicott Commentary Psalms 65:9

"Thou visitest the earth, and waterest it, Thou greatly enrichest it; The river of God is full of water: Thou providest them grain, when thou hast so prepared the earth." — Psalms 65:9 (ASV)

You visit ... —Better, You have visited. Even if there is no reference to some particular season of plenty, yet with a glance back on the memory of such. Instead of “earth,” perhaps, here, “land.”

You water. —Or, you flood. The river of God stands for the rain. There is an Arabic proverb, “When the river of God comes, the river Isa (in Baghdad) ceases.” The Rabbis say, “God has four keys which He never entrusts to any angel, and chief of these is the key of the rain.” (Job 28:26; Job 38:28.) The expression “river” for rain is very appropriate for the downpour of a country that has its rainy season. (Compare to “the rushing of the river rain,” Tennyson’s Vivien.)

You prepare ... —The Authorised Version misses the sense, which is, you prepare their grain when you have prepared it (the land) so — i.e., in the manner now to be described. Thus Septuagint and Vulgate.