I suggest more creativity in these markets. In a literal sense, there is no such thing as you are asking for.
In a thought out and extrapolated sense, I recommend you find the correlation of a broad index of equity stocks that have probably between $2.00 - $10.00 as their trading price, find their correlation to ag prices (probably +.5 is easy to find), and buy these stocks holding in perpetuity. They are priced as cheap as an option, and a broad recovery of the markets will likely enable these stocks with questionable (almost zero) equity positions to recover nicely with limited downside.
Other than that, buy whatever you are looking for outright with low leverage, and you are likely to do as well. There is no magic repository of zero risk that exists in these markets, at least for long.
Maybe another outside the box idea is some actual liquidated farmland. That is definitely a limited risk option on the agriculture market, as I see it. Your carrying cost can be equated with cost of money and property tax, with upside significant and most likely correlated.