June 2009, Vol. 21, No.6


Irrigating With Swine Wastewater Can Increase Crop Yields

Bermudagrass hay crop yields were higher when irrigated with treated wastewater than bermudagrass crops irrigated with well water and amended with commercial fertilizer, according to a U.S. Agricultural Research Service (ARS) study.

However, the high nutrient content of wastewater from livestock can limit its use for irrigation, and spray irrigation can increase the emission of ammonia and other volatile organic compounds, according to an ARS news release.

Researchers Patrick Hunt, Ken Stone, and Matias Vanotti of the ARS Coastal Plains Soil, Water, and Plant Research Center in Florence, S.C., performed a 2-year study to see if subsurface drip irrigation with pretreated swine wastewater could eliminate emissions and increase effectiveness of irrigation, the news release says. The wastewater was pretreated to remove concentrations of ammonia, nitrogen, and phosphorus.

The study found that subsurface drip irrigation with treated wastewater reduces the amount of water draining through the soil, reducing the opportunity for nutrients to leach below the root zone, the release says. “These results imply that [subsurface drip irrigation] with treated swine wastewater provides forage crops with needed irrigation and fertilization that can equal — and even sometimes exceed — the benefits of feeding crops with commercial fertilizer,” the release says.

After assessing the yield and biomass of the crop and measuring the nutrient levels in the soil and soil water, the scientists found that yields did not vary significantly when irrigated with wastewater that only replenished 75% of the water lost to evapotranspiration. “This suggests that wastewater subsurface drip irrigation is often effective at lower application rates,” which reduces the amount of water needed for irrigation, the news release says.

Read more about this and associated research in the January 2009 issue of Agricultural Research magazine at www.ars.usda.gov/is/AR/archive/jan09/clean0109.htm

Using Graywater To ‘Green’ Landscapes

New Mexico State University (NMSU; Las Cruces) researchers are testing a filtering system’s ability to remove harmful substances from graywater in an effort to make the water suitable for home landscape irrigation.

“We are running out of water in New Mexico,” said Ryan Goss, assistant professor in NMSU’s Department of Plant and Environmental Sciences and a project researcher. “Water is clearly our most valuable resource, and anything we can do to help make our water supply more sustainable is important.”

The research aims to reduce the amount of water consumed in the area and to make it easier for homes to grow plants that improve air quality and reduce cooling costs, according to a university news release. “A family of four typically goes through as much as 100 gallons [380 L] of water a day,” the release says. NMSU researchers are attempting to find out how much of this is graywater coming from bathroom sinks, showers, and washing machines and how much can be used safely for irrigation.

Goss and his colleagues are studying a water pump and filtering system that attaches to a household’s wastewater line. System sensors are placed throughout the house to ensure that the pump only catches graywater. Black water from the kitchen sink and toilet is not pumped into the system, the release says.
Then graywater is sent through a series of filters and exposed to ultraviolet light to eliminate bacteria. After being processed, the water is made available for landscape irrigation. Phosphorus and chemicals from detergents that make it through the cleaning system are actually beneficial to landscaping plants, Goss added.

“This system has many unique engineering aspects that make it immediately useful to existing and future households,” Goss said. “Other systems require additional plumbing and therefore are not useful for retrofitting homes.”

The system is installed at NMSU’s Fabian Garcia Science Center family residence, sitting inside a small shed outside of the house. New Mexico water regulations require the treated graywater to be delivered by subsurface drip irrigation. At press time, the research group was scheduled to install a drip-irrigation system from the house to a portion of the neighboring university arboretum. According to the news release, future models may be small enough to fit inside a decorative landscape rock.