Post Soviet subsidy Cuba adapted quite well given the constraints it was under, greatly reducing the fossil fuel and industrial fertilizer it used to produce its food. The problem is that even with that adaptation it still had to use some of those, and it remained very heavily dependent on food imports.  

Here is an overview of the Cuban agriculture story in a form familiar to me from documentaries, first-hand testimony of friends who have done the susti ag tours, etc.  I note the intriguing excerpt:

Despite the embargo, in 2000, President Clinton signed the Trade Sanctions Reform and Export Enhancement Act (TSRA), which re-authorized the direct commercial export of food products and agricultural products via cash transactions from the United States to Cuba - but not from Cuba to the United States. [emphasis mine -- DeA]

In September 2002, after the U.S. Food and Agribusiness Exhibition took place in Havana, the Cuban government purchased more than $91.9 million in food and agricultural products from subsidiaries of U.S. companies based in Latin America and Canada and directly from U.S. companies.

Archer Daniels Midland (ADM), one of the world's largest exporters of cereal grains and oilseeds, signed a $19 million contract for soybean oil, soybeans, soy proteins, corn, margarine, and rice. In 2001, ADM's lobbying - combined with wreckage in Cuba after Hurricane Michelle - was the tipping point that persuaded the Bush Administration to allow the first sale of goods directly from the United States to Cuba since 1962.

The American Corn Growers Association (ACGA), which, to date, has not taken up trade negotiations with Cuba, would be interested in trade sometime in the future, said its chief executive officer.

"We should be exporting to any nation that needs food," said CEO Larry Mitchell.

With Cuba's well-documented ability to feed itself, why would the Cuban government be interested in spending $91.9 million on food imports?

John S. Kavulich II, president of the U.S. Trade and Economic Council based in New York City, said, "There is a strong political component to the Cubans' decision to purchase food products from us. Of the products purchased since 2001, nearly all of them are available from other sources at better prices."

Kavulich cited rice as an example. The Cubans could buy rice from Vietnam at a significantly lower price, but they choose to purchase from purveyors like ADM instead.

Food First's Rosset agrees. "I believe the Cubans are buying from the U.S. as a political gesture. They hope the food corporations will lobby the U.S. government on their behalf to lift the embargo."

Whether the Cubans bought food from american agricorps as a tit-for-tat deal in an attempt to get the travel and financial embargo lifted, or whether they faced any actual shortage of staple crops, I dunno.  I do know that for many USians of conservative persuasion, Castro is the Great Satan and Cuba is anathema:  nothing that Cuba does can be working.  As the last "actually existing socialism" on earth, it must be publicly proclaimed and proven a contemptible failure so that happy capitalists can dance on Marx's grave.  Op/eds appear regularly in US papers celebrating Castro's great age and infirmity and confidently predicting that "freedom" (meaning US domination) will come to Cuba just as soon as the old tyrant is dead.  

Recently a US op/ed joyfully announced that Raul Castro is likely to relax restrictions on private car ownership and permit real estate speculation -- hey, that sounds like democracy and freedom to me :-)  more like the stupidest possible moves to make at this particular historical moment, but -- as Chekov's protagonist muses at the end of "Three Years" -- we will live and we will see.

The difference between theory and practise in practise ...