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Grass gets greener

When farmers and livestock producers think of nutrient loading of ponds
and streams or runoff, many probably imagine fertilizer or manure being
washed away from cultivated fields or draining from barnyard areas or
even seeping from mismanaged lagoons.
When farmers and livestock producers think of nutrient loading of ponds and streams or runoff, many probably imagine fertilizer or manure being washed away from cultivated fields or draining from barnyard areas or even seeping from mismanaged lagoons.

According to Iowa State University researcher Tom Isenhart, new research data is showing that 37 percent of phosphorous contamination in ponds, streams and rivers is actually coming from pasture and rangeland.

“Increasingly, we are seeing some impact from pasture,” he explained during a recent webinar hosted by the Livestock and Poultry Environmental Learning Center (LPELC). “An increase in pastureland can have a significant impact on the transport of sediments and the nutrients phosphorous and nitrogen.”

In light of this, researchers at ISU have been examining different grazing management methods in a bid to minimize pollution to pasture streams or ponds.
Jim Russell, a professor with ISU’s department of animal science, has been conducting research for several years on forage quality and beef cattle grazing, including examining the improvement of environmental quality through grazing management.

“We have found in our research that the percent of defecations or urinations … near a stream is directly related to the percentage of time the cattle are within that zone of the pasture,” he said, adding “the zone” is defined as within about 100 to 110 feet of the stream or pond.

When the researchers examined pastures at five farms in southern Iowa, they discovered the probability of the cattle being within 100 feet of a stream or pond varied from one percent to 40 percent, depending on the time of month and the temperature.

“While attempting to determine the reasons for this variation, we found that in these pastures the differences in distribution were not related to the percentage of tall fescues in the pastures or to the shade distribution in the pastures,” said Russell. “Rather, the most significant variable affecting cattle distribution was the percentage of pasture within 100 feet of the stream. In other words, if cattle have no choice but to be near a stream, that’s where they’ll be.”

Russell believes these findings may have important implications relative to further research and policy.

“It implies that all research investigating the use of grazing management to control non point source pollution should be evaluated in regards to pasture shape and size,” he said. “The treatments that appear to control non point source pollution seem likely to be most effective on small and/or narrow pastures than on large, wide pastures.

“It would certainly be nice to have more research on this hypothesis before implementing it but certainly our data appears to support that conclusion.”

To further investigate the issue, Russell and his research team decided to examine what effect different grazing management methods would have on cattle distribution and non point source pollution of pasture ponds and streams. An experiment was set up involving different 30-acre pastures, each bisected by a stream with a 463-foot reach. Global positioning (GPS) collars were mounted on the cattle to track their movements.

“We found that over a two-week period, the percentage of time the cattle were in a stream ranged from 0.2 percent in September to 2.3 percent in July and the percentage of time the cattle were within 110 feet of the stream ranged from 7 percent in August to nearly 14 percent in May, when offered unrestricted access to the stream.”

When researchers restricted the cattle’s access to the stream to a stabilized crossing with riparian buffers on either side, the percentage of time the cattle were either in or near the stream was “significantly reduced,” said Russell. “Restricting stream access by rotational stocking reduced the percentage of time the cattle were in the stream to essentially zero percent.”

Researchers also examined the use of an off-stream water source as a way to reduce the congregation of cattle near streams. While results from studies in Virginia and Oregon showed favorable results, studies in Georgia, Kentucky and North Carolina showed the different water source had no effect. Russell also utilized off-stream watering in his experiment pastures, placing them a minimum of 700 feet from the pasture stream.

“In 2006 and 2007, we found that off-stream water significantly reduced the percentage of time the cattle were within 110 feet of the pasture stream, if provided unrestricted stream access,” he said. “However, in 2008 the presence of off-stream water did not significantly affect cattle distribution in regards to the stream.”

According to Russell, it’s believed the difference in response to off-stream water in 2008 was likely caused by a large amount of precipitation that fell that season, resulting in a large number of natural off-stream sources.

Another issue affecting the usefulness of off-stream water could be temperature. According to Russell, research from Georgia shows that off-stream water could reduce the percentage of time cattle were within a riparian area as long as the temperature/humidity index was less than 72 Fahrenheit. “But if the temperature/humidity index is greater than 72 degrees, they found off-stream water to be ineffective,” he added.

Shade distribution may also have an effect, said Russell. “While shade distribution was not a significant variable affecting the distribution of cattle in pastures in southern Iowa, we believe this may have resulted from the large effects of pasture shape and size and the fact that the pastures were well shaded in both riparian and non-riparian areas. Because cattle will seek shade, particularly at temperatures of greater than 20 Celsius, shade distribution may still be effective in altering cattle distribution in a pasture.”

While Russell’s research has shown that grazing management does affect cattle distribution, there is some question as to whether it has a direct effect on water pollution. “We found no relationship between net annual stream bank erosion and the annual stocking rate of a pasture on streams in 13 pastures in southern Iowa,” he said.

“It would appear that stream bank erosion was more related to stream hydrology and stage of evolution than to grazing. We found no relationship between grazing and the concentration of fecal coliforms in water samples taken at upstream and downstream sites in these pastures. In fact, we sometimes had higher concentrations in upstream than downstream samples, even when the stream flows were coming from un-grazed land above the pastures we were testing. The coliforms appear to be coming from a number of hosts, which could be wildlife or humans as well as cattle.”

Even so, Russell believes grazing management can have an effect on water pollution, particularly if the management prevents the land within 110 feet of the stream bank from becoming bare. His research has found that allowing uncontrolled access to the stream banks increases the percentage of bare land adjacent to the stream and increases the percentage of land covered in manure, ultimately “increasing the risk of nutrient pathogen loading in precipitation runoff.”

During rainfall simulations on bare or vegetated areas on banks, “we found greater runoff, sediment loss and phosphorous loss from bare areas than vegetated areas, regardless of grazing management,” said Russell. “If we can control the percentage of bare areas by reducing the congregation of cattle near pasture streams through grazing management, we should be able to minimize non point source pollution.”

That would be good news to the U.S. Environmental Protection Agency (EPA), which recently released the first-ever baseline study of U.S. lakes. Of the 1,028 lakes randomly sampled in 2007, more than 40 percent were considered fair or poor with 20 percent showing high levels of nitrogen and phosphorous. According to the EPA, sampling of U.S. streams and rivers is currently underway. The results of that two-year study are expected in 2011.