Story written in the 80s, appeared in Analog or Fantasy & Science Fiction

This is one of Charles Sheffield's Traders stories; there were 4 published in Analog in the 1980s, but apparently never re-published:

• "Trader's Secret", Analog 1985 August;
• "Trader's Blood", Analog 1986 April;
• "Trader's Cross", Analog 1987 March;
• "Trader's Partner", Analog 1987 July.

Thanks to @user14111 the specific story in question is "Trader's Secret":

Suddenly we were looking down on a vast, geometric pattern. Endless kilometers of Farside lunar plain carried a regular, rectangular grid. And within each grid cell, beneath the soft blue-gray sheen of a continuous plastic canopy, I saw the bright green of growing plants.

Fields. We swept on over the surface, mile after mile after mile, and the pattern continued.

"First harvest in four months," said Li. Her voice was dreamy. "A generation's work. Twenty years, to prepare the surface, to modify the plant genetics, to drill for water, to add the protective canopy. And in four months we will see. the first full harvest."

[...]

"Self-sufficient," she repeated. "And now, some of us must ask the question: what will happen to Earth? Are we destroying Earth, to make a garden of the Moon? That must not happen. That is why I called on you for Trader's Oath, to tell us what will happen when the Yankees learn that we have our own food—and they have nothing to offer us in exchange for energy."

_{Analog, August 1985, p. 43}

(Note that the "Yankees," being among the regions that have suffered most from the war, have little to offer the blocs other than food.)

The protagonist is Mikal Asparian, a junior trader in the first story (who is handed a mission the Traders expect to fail, so it doesn't look bad on a more senior trader), who gains experience as the series progresses.

The world is divided into 4 power blocs after a nuclear war; the Chipponese (Japan+China/Korea), the Chill (Antarctica), the Strine (Australia) and [forget the name] (South America: Peru/Chile). Each of the power blocs has a jealously-guarded specialty (e.g. biotech for the Strines) and the traders exist separately, surviving as neutral negotiators.

The stories were fixed up into the novel Trader's World (1988).

The story you're asking about isn't "Trader's Partner"; in that one Mikal is sent to South America (specialty: recreation/pleasure) with a female partner to investigate a report that South America has managed to turn a VIP from another bloc. They are shooting needles into people's brains to hook them on direct stimulation of their pleasure centre; his partner saves him, but dies.