Is this not exactly what you would expect in a free market? All arable farming land will produce whatever crop brings in the best return; no arable land will be

Is this not exactly what you would expect in a free market? All arable farming land will produce whatever crop brings in the best return; no arable land will be left fallow long term. But just because we are using all of it doesn't mean we need all of it or else starve. Vast quantities of crops are used to produce biofuel, or feed for livestock, or raw materials for other non-food products.