If the farmer is willing to accept a $1200 price, then what prevents the land owner from charging $1200 right now? All the factors you list which push the price up apply just as well for the current owner-renter negotiations.
The scenario you describe is possible only if there is a lot of land that's severely mispriced / underpriced - in which case the price should and would get corrected, and after that the arbitrage opportunity disappears because, as you say, the land owner can come in contact directly with the farmer and make arrangements.
The scenario you describe is possible only if there is a lot of land that's severely mispriced / underpriced - in which case the price should and would get corrected, and after that the arbitrage opportunity disappears because, as you say, the land owner can come in contact directly with the farmer and make arrangements.