Commodities prices are famously unpredictable, but many on Wall Street are nevertheless predicting these tangible investments can only continue to lag as a result of the global economic slowdown.

The Dow Jones-UBS Commodity Index, a broad index comprising 19 physical commodities including energy, agriculture and industrial and precious metals, has fallen nearly 15 percent for the year, one of the worst performances of any investment class. But in characteristic style, the same index has shot up nearly 10 percent over the past month, largely as a result of agricultural commodities within the index that have surged as a result of drought conditions limiting supply.

In fact, the corn crop has been so battered that pork producer Smithfield Foods has taken the unusual and counterintuitive step of importing corn from Brazil, where even the addition of expensive shipping costs results in a lower price than corn offered in the U.S. market, long the world's No. 1 corn producer.