I have a new situation: Bubba and Dean are two farmers which realized the benefits of having AM fungi in their soil. Dean, however, took active steps in helping the growth of AM fungi so he grew cover crops on his lands.  But I can use this background: Since AM fungi are biotrophic, they are dependent on plants for the growth of their hyphal networks. Growing a cover crop extends the time for AM growth into the autumn, winter, and spring. Promotion of hyphal growth creates a more extensive hyphal network. The mycorrhizal colonization increase found in cover crops systems may be largely attributed to an increase in the extraradical hyphal network that can colonize the roots of the new crop (Boswell et al. 1998). The extraradical mycelia are able to survive the winter, providing rapid spring colonization and early season symbiosis (McGonigle and Miller 1999). This early symbiosis allows plants to tap into the well-established hyphal network and be supplied with adequate phosphorus nutrition during early growth, which greatly improves the crop yield.  What is an answer for this question: Which farmer didn't increase the extraradical hyphal network that can colonize the roots of the new crop?

Bubba