Two brothers

Two brothers were raised on a farm, one brother moved to town. Every year, the city brother would come out to visit the farmer brother. Every time he came out, the farmer brother was complaining about his crops. It was too hot or too cold, too wet or too dry, prices were low, the crops looked bad. As the city brother was driving out one year, he noticed the crops looking great. He had the radio on and crops were hitting an all time high. As he got out to the farm, here was the farmer brother sitting in a rocking chair with a grumpy looking on his face. The city brother asked why he was in a bad mood. The crops looked great, the right amount of rain, temp., and prices were setting records highs. The farmer brother said, you know what a crop like this takes out of the soil?