Reducing
Nitrogen Levels in Pasture Possible
|
|
When nitrogen fertilizer use was reduced or eliminated for several
years on some Ohio pastures, groundwater nitrogen levels returned
to acceptable levels.
“Grazing systems, unless there is a lot of nitrogen input to
optimize grass growth, are very environmentally benign,” said
Lloyd Owens, a soil scientist who conducted the study at the Agricultural
Research Service’s North Appalachian Experimental Watershed
Laboratory in Coshocton, Ohio.
Scientists have gathered data from watersheds in the area for more
than 60 years. The ARS land has been used as pasture for about 30
of those years. For 11 years prior to this study, Owens applied heavy
nitrogen fertilizer (150 pounds per acre) to see if it would produce
more and better grass without causing environmental harm.
But nitrate-nitrogen levels reached 13 to 26 parts per million (ppm).
The Environmental Protection Agency has set a guideline of 10 ppm
as the maximum safe level for nitrate-nitrogen in human drinking water.
“It seems if there is high mineral inputs, there is the potential
for high nitrates,” Owens said.
So he sought to see if he could lower nitrate levels by eliminating
commercial fertilizer for seven years. Two pastures where cattle grazed
were compared with two that used to cut and bale hay.
Nitrate-nitrogen levels were brought down to the same level (2 to
4 ppm)-- “very acceptable” --from both haying and grazing.
The lack of fertilizer caused only a slight decrease in grass growth.
These results showed it did not matter whether cattle were on the
land or not, he said.
Keeping nitrogen levels below 100 lb./per acre/per year seems to be
key for keeping nitrate-nitrogen levels in the acceptable range, he
explained. Producers should count all nitrogen sources—commercial
fertilizer, manure, legumes and feed inputs.
Owens just started a study of taking samples from tile lines in cattlemens’
pastures. Of the five herds sampled initially, just one had high nitrate
levels. That producer used a large amount of commercial fertilizer.
There has been little research in the United States on groundwater
nitrogen levels in pastures. But with the current interest on pasture
grazing, there will be a closer look at the environmental impact from
grazing. “Nitrate-nitrogen levels is certainly one of those
impacts,” Owens said. ©
