It's not been implemented yet, it will come in Q1 with land 1.75 when only grain producing land terrain types will produce grain. At that point there will be much less grain produced and much more demand for it, however there is a VERY large stockpile of grain in existence now, so it may take a while for this play to bear fruit.
In the meantime, I am building a position in the DEC:Grain LP to capture the increase in fees for swapping that will be generated as more ppl need to buy grain and as a result and to grow my qty of DEC in the LP as the grain price in the LP rises
So voucher DEC is going into DEC, which is being split between grain and DEC and added to the LP over time
Looks like a very cool and solid strategy! LPs are a bit tricky because you always have to track the token prices to avoid excessive impermanent loss, but if you can leverage them you surely are going to get back a nice ROI :)