The IRS has posted some FAQ's regarding this. 

https://www.irs.gov/businesses/small-businesses-self-employed/conservation-reserve-program-annual-re...

CRP “annual rental payments” may be includible in net income from self-employment for purposes of the self-employment tax

Unless the taxpayer is receiving Social Security retirement or disability benefits, CRP “annual rental payments” are includible in net income from self-employment subject to self-employment tax. Note: Payments that are for the permanent retirement of cropland base and allotment history are not includible in net income from self-employment subject to self-employment tax because they are for the sale of section 1231 property or a capital asset.