(taxpayer proposes to sell 99-year conservation easement on farmland; land acquired in 1991; taxpayer has owned undivided 1/4 interest in land until gifting 1/2 of such interest to spouse; portion of land enrolled in CRP from 1991 to 2010; balance of land farmed by taxpayer's sibling since 1991; taxpayer farmed other land and reported farm income on Schedule F; aggregation election could be made under Treas. Reg. Sec. 1.469-4(c) for all farming activities; test for material participation requirement of state law exclusion of capital gain upon sale of easement is whether totality of participation in all farming activities that are aggregated; material participation test satisfied overall even if not satisfied with respect to specific farmland at issue; as long as 10-year holding period satisfied, Iowa capital gain exclusion available).