During my Kindergarten Practicum experience we needed to create lessons that revolved around a farm theme, and Minnesota Ag in the Classroom provided a plethora of resources that helped add on to the activities that my co-teachers and I had already generated. The link listed on the bottom here will take you to their website. There is also the national conference for Ag in the Classroom June 25-28 in Minneapolis.
http://www.mda.state.mn.us/kids.aspx