I found this info, this is a snippet, but I think the main reason.
The lack of agriculture in the payroll survey, however, is almost certainly inconsequential. The absence of farms in the Bureau's payroll survey matters less to today's employment picture than it did during the early and mid 20th century. In 1930, 21.5 percent of the workforce worked in farming, and agricultural output represented nearly 8 percent of U.S. economic output. At the turn of the 21st century, less than 2 percent of the labor force worked in agriculture, a sector that now represents less than 1 percent of national economic output.
http://econblog.aplia.com/2009/05/why-do-monthly-job-loss-estimates.html
| 