The first project in this category was initiated in 1975 and sought to investigate the use of anaerobically digested sewage sludges and poultry manure as fertilizers for sweet corn, winter cereals, and grass or pasture crops. This project was supported by the cities of Portland and Salem, and the Unified Sewerage Agency of Washington County, as well as Agricultural Experiment Station funds. The primary purposes were to determine how much of the nitrogen normally applied to each crop could be replaced with sludge or manure nitrogen, the degree of availability to the crops of the organic nitrogen in the waste materials, and the degree of accumulation of sludge-originated phytotoxic heavy metals in the crops. Three years yield and tissue analysis data have now been obtained for each crop. The next few growing seasons will be devoted to refinement of data for grain crops and further vegetable research will not be undertaken until the 1981 or 1982 growing season.
Another related project, supported by the U. S. Environmental Protection Agency, originated in 1978 and seeks to demonstrate the efficacy of chrome tannery waste as a fertilizer for vegetables and grass crops. As with sewage sludge, this material contains significant quantities of nitrogen but the use may be limited by the 0.8 to 3 percent chromium content.
Methods
In both the sludge and tannery waste experiments, commercial nitrogen fertilizers, usually ammonium nitrate or ammonium sulfate, were applied at rates from 0 to 300 pounds/acre to provide a comparison for the organic fertilizers. Sludge or waste applications were made about two weeks prior to planting at rates of up to 700 pounds of total nitrogen per acre, plowed under, and the seedbeds prepared. Jubilee sweet corn was the only vegetable crop in the sludge-poultry waste experiments; Jubilee corn and Spartan Arrow bush beans were used in the tannery waste experiments. Thirty-inch row spacing was used for corn and beans, and pesticide, cultivation, and irrigation practices were similar to those commonly used in the Willamette Valley. For both crops, harvest was near time of optimum maturity for the earliest maturity treatments. Especially for corn, this may have accentuated yield differences among treatments because of earlier maturity of certain treatments, e.g. where phosphorus was banded at planting.
Results
In 1978, for the first time in three years, sewage sludge additions greater than 150 pounds per acre of total nitrogen resulted in a significant increase in corn yields. In previous years, commercial nitrogen applications increased yields up to a rate of 200 pounds/acre, but 300 to 400-pound applications of sludge nitrogen yielded no more than 150 to 200-pound applications. In 1978, low rates of sludge were equally as efficient as equivalent rates of commercial nitrogen but higher rates were only about 80 percent as efficient. Maximum sludge-fertilized yield was about 10 tons/acre compared to 12 tons/acre for commercial nitrogen. Unfertilized check plots yielded 4 to 5 tons/acre. Plant tissue analysis data for the 1978 crop are not yet available, but in 1976 and 1977, heavy metal accumulation did not appear to be a problem. In 1976, sweet corn grown on plots fertilized with Portland sludge had higher leaf tissue levels of cadmium and other metals than did corn from plots grown on U.S.A. or Salem sludge, but levels were not in a range considered to be dangerous. In 1977, after two consecutive sludge applications, cadmium levels were generally lower in plants from sludge amended plots than from commercial nitrogen plots. Poultry manure has been considerably less effective as a sweet corn fertilizer than either the sewage sludge or commercial nitrogen.
In the first year of the tannery experiment, the waste was only about 50 percent as effective as commercial nitrogen as a sweet corn fertilizer when expressed on the basis of equal weights of total nitrogen (180 pounds/ acre) applied. Both low and very high (720 pounds/acre of N) rates of tannery waste appeared to suppress corn yields. In the bean experiments, yields from check plots, commercial N plots, and low rates of tannery waste did not differ significantly. But the highest rate of tannery waste depressed yields well below those of unfertilized check plots. At least one more year will be devoted to refining data from these field plots. Results of plant tissue analyses are not yet available.