Nitrate Leaching from Fertilization of Three Douglas-fir Stands with Biosolids

Abstract —In many forest systems the limiting criterion for land applications of biosolids (municipal sewage sludge)is the amount of nitrogen added to a soil. N applications, which exceed the assimilative capacity of soil and plantson a site, will result in excess ammonification of organic N, nitrification of ammonium, and nitrate leaching. Manystudies that have observed high levels of NO 3– leaching utilized rates of biosolids application exceeding 250 dry Mgha -1 . This study investigated NO 3– leaching from three different Douglas-fir stands in the Pacific Northwest thatreceived single and multiple annual applications of 47 dry Mg ha -1 of biosolids, so that predictions could be made ofappropriate application rates based on N. Plate lysimeters under continuous vacuum of 0.01 MPa were used tocollect monthly samples of soil solution before and after biosolids application. Tree stand age had a major impacton NO 3– leaching losses. Average solution concentrations during the first year were 57 mg 1