An Iowa State University researcher today (Monday) delivered his advice to a state board that’s considering limits on the amount of phosphorus that may be applied to farm fields. The issue’s heightened by the growing amount of liquid manure from large-scale livestock operations that’s being applied to corn and soybean fields. Manure has phosphorus in it. I-S-U agronomist Antonio Mallarino says for one thing, liquid manure should not be applied to frozen ground. He also says too many Iowa farmers are putting too much phosphorus on their ground and could use as little as one-fifth as much commercial fertilizer or manure as they’re applying. “About three-quarters of Iowa fields test optimal or high in phosphorus, and in some counties, the vast majority test high or very high,” he says. And manure was applied to most of those fields with high amounts of phosphorus, according to Mallarino. Mallarino says you CAN change the phosphorus content of manure by changing the diet of hogs. Mallarino shared his ideas with the State Environmental Protection Commission, the state panel that’s in the midst of writing rules for fertilizer application. “Of course, we scientists love to present charts and charts and graphs and data, but I feel we need some of those so we can support some of the things we recommend,” Mallarino said. Iowa Department of Natural Resources director Jeff Vonk says when phosphorus gets into streams or lakes, it stimulates the growth of plants. Vonk says aside from the look of murkier water, the plants demand more oxygen, robbing other acquatic life — like fish — of that oxygen. If water’s “super-saturated” with phosphorus, Vonk says it will smell.
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