CORVALLIS - "Biosolids," treated solids from western Oregon and Washington wastewater treatment plants, are proving to be effective fertilizer for winter wheat east of the Cascades in cooperative research by Oregon State University and Washington State University scientists.
OSU and WSU conducted their research on local dryland farms near Moro in Oregon and near Waterville and Ritzville in Washington state, with the cooperation of wheat growers. They used all of their normal production practices except for fertilization. Biosolids were applied during summer fallow to large on-farm plots using a manure spreader.
"Since 1992, we have evaluated biosolids application at eight field locations under a variety of weather and crop management regimes," explained Dan Sullivan, soil scientist with the OSU Extension Service.
In the dry Columbia Basin, biosolids performed quite as well, if not sometimes better than standard fertilization practices, said Sullivan. Growers generally apply about 50 pounds of nitrogen per acre, as anhydrous ammonia, in both wet and dry years.
"We measured increases in wheat yield, grain protein and changes in soil nutrient levels with several levels of biosolids application," said Sullivan. "Biosolids fertilization produced equal or higher yields."
"The biosolids supply both immediately available ammonium nitrogen, similar to that found in fertilizers and slow-release organic nitrogen," he added. "With biosolids, some nitrogen is available right away. And some is released slowly, in proportion to the amount of soil moisture available. So if there's more available soil moisture, there will be more available nitrogen. Nutrients are therefore in synchrony with available moisture."
Biosolids also provide phosphorus, sulfur, zinc and other nutrients that may limit wheat yields, especially on eroded soils, he said.
There may be additional benefits using biosolids as a fertilizer.
"Not only are there a broad range of nutrients available, there is increased organic matter, leading to better 'tilth,' or physical condition of the soil," he said. "I've seen biosolids stabilize soils out there."
The OSU and WSU research has helped identify biosolids application rates for growers that supply appropriate, but excessive amounts of nitrogen, explained Sullivan. They learned that too much nitrogen from biosolids, like too much conventional fertilizer nitrogen, can be detrimental to the crop and to the environment.
"With excessive nitrogen from biosolids application rates, we observed reduced crop yield from water stress, reduced crop quality from excessive grain protein and increased risk of nitrate movement below the root zone," he said. "If there is too much nitrogen provided by biosolids application, the plants produce more leaves instead of grain. They put on a lot of tillers, thereby taking more water out of the soil earlier in the year. There may not be enough water for good grain production."
Keeping transportation costs as low as possible is very important for economic feasibility of using biosolids for fertilizer, said Sullivan.
The closest supply of biosolids to the wheat fallow cropland of their studies near Moro in Oregon and near Waterville and Ritzville in Washington state, were wastewater treatment plants in the Willamette Valley and Puget Sound.
"The low precipitation zone, 10-14 inches per year, is the closest dryland wheat area to the big suppliers of biosolids, wastewater treatment plants in the Willamette Valley and Puget Sound," said Sullivan.
"In western Oregon, wet soils and annual cropping limit opportunities for biosolids application," he said.
Biosolids are quite different from raw sewage or sewage sludge, stressed Sullivan.
Wastewater treatment facilities remove raw solids from sewage and treat them, according to strict standards set by the U.S. Environmental Protection Agency. The Oregon Department of Environmental Quality oversees application of biosolids to land.