We don't need to convert cropland into pulpwood production. The idea, IMHO, is to use crop waste (which is discarded) into ethanol.
Much of sugar-cane production isn't used for ethanol, but burned because it's cellulose, and bacteria find it hard to degrade cellulose into its component sugar blocks.
If you get a cheap way to do this, you can produce much more ethanol per square meter. Be it from beet, soy, rice, sugar-cane or the grass you cut from your lawn.
"Kill the Wabbit, Kill the Wabbit, Kill the Wabbit!" -- Looney Tunes, "What's Opera Doc?" (1957, Chuck Jones)