The grains index ($DJAGR) on stockcharts.com has clearly rolled over. So far, we have fallen 30% from the highs (70 to 50 on the index). Historically, the lows for grains is 40 on the index. That's another 20% fall from these levels.Agrium and Potash track the grains index pretty well.AGU has fallen 30% from peak this year (~$100 to $70).POT has fallen 30% from peak this year (~$60 to $42).With another 20% downside, AGU target is $56 and POT target is $34. This is plausible as AGU has a gap at $54 to fill from July 2010 QE2 melt up. POT has a gap at $30.50 to fill from July 2010 also, not to mention the big gap from the BHP Billiton bid.