The researchers looked at how farmers in tropical and subtropical regions grow crops more than once a year in a method called multiple cropping. They studied over 200 different cropping systems globally to see how much of the world's farmland is used for this. They found that about 12% of the world's farmland is used for multiple cropping, with a lot of it happening in irrigated areas. Crops like rice, wheat, and maize are often grown this way, showing that it's important for making lots of food. By harvesting these areas a second time, we could grow way more food without needing to use up more land. This method could help us produce more without harming the environment, but it depends on how well the crops grow in the second round and the costs involved.