There has been a big change in what farmers do. Traditional farmers both raised crops (such as corn and soybeans) and raised animals (such as hogs, beef cattle, chickens, dairy cows). This is a year around operation. Nowadays there is much greater specialization. If you just raise crops you are busy in the spring (planting) and in the fall (harvesting) and do some work in the summer (controlling weeds) and very little in the winter. So this leaves a lot of time for a part time job. Raising animals has become both specialized (one type of animal) and these being mostly very large, fulltime operations.