Complex sentence: The main Bt crop being grown by small farmers in developing countries is cotton, and a 2006 exhaustive review of findings on Bt cotton by agricultural economists concluded, the overall balance sheet, though promising, is mixed.
Split into simpler sentences: The main Bt crop grown by small farmers in developing countries is cotton. A 2006 review of Bt cotton findings by agricultural economists concluded, the overall balance sheet, though promising, is mixed.