Unfortunately during these times, slavery was a big thing for people in the south of the United States. In the south, slaves were forced to do agriculture all the time. In the north, there werent many slaves so the south and north would fight all the time. This meant that the amount of crops were high in the south, so the possible explanation can be that agriculture grew due to slavery during this time. (It grew because the slaves were forced into the agriculture labor which meant the agriculture numbers were higher in the south during these years.) I really hoped this helped you understand a bit.