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From Farmer to Shrimper: The Dead Zone
(pg 4 of 8)

Why the increase? Largely because of the changing nature of agriculture in the upper basin.

In the early 1900s, agriculture in the upper Mississippi watershed consisted of mixed crops of wheat, oats, barley, rye, alfalfa, and pasture. Numerous wetlands and small lakes trapped nearly all the nitrogen that ran off of farm fields.

Since then, Midwestern grain farmers have switched to corn and soybeans. Corn requires large amounts of nitrogen fertilizer. Soybeans capture nitrogen from the air and fix it to the soil. Furthermore, artificial drainage in farm fields short circuits the filtering of nitrogen through groundwater and flushes it directly to surface waters. Excess soluble nitrate remains in soil and groundwater, to be flushed out by high precipitation. Minnesota soil scientist Gyles Randall has calculated that nitrogen losses from corn and soybean fields can be 30 to 50 times higher than from land planted to perennial plant systems such as hay or grass (Randall et al., 1997).


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Whitewater
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Valley Creek
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