Letter: Flexibility key to nitrate reductions

As water testing has increased, so have Iowans concerns over agriculture's contribution to pollutants, especially nitrates.

Des Moines Waterworks has filed a lawsuit against three drainage districts to recoup nitrate removal costs (limits are 10mg/L.) DMWW is an independently owned, publicly operated business permitted, however, to release nitrates back into waterways as brine. It also has been cited for discharging excessive sulfates and chloride. This just touches on the complexity of the issue.

Soil naturally has 1,0000 lbs. of nitrogen/acre and adds 7mg/L of nitrate to waterways alone. Fertilizers supplement only 1.5-2 percent of total nitrogen available thus comparable amounts of nitrate seep whether corn or soybeans (which go unfertilized) are planted. Farmland may have sandy soils which leach nitrates more easily into groundwater having eg 25 percent of the water capacity of clay/finer soils. Extreme weather events like drought or heavy rains/floods have increased, too, elevating the chance crops fail to take up nitrogen leaving nitrates to be further lost to percolation. Nitrates primarily leach in the late fall/early spring when vegetation is absent to fix nitrogen in warm, wet conditions. Big investments like cover crops, bioreactors, wetlands and saturated buffers alleviate nitrate problems as can rotations, field barriers and timely fertilizer applications. (Short growing seasons and poor soil and moisture may limit cover crop growth.)

Better land management decreases nitrate loss, but answers for each individual farmer are not, as the agrarian expression goes, always cut and dried. Flexibility is key.

Brent and Deb Donohoe

West Branch