Nitrogen Recovery from Heat‐Dried and Dewatered Biosolids Applied to Forage Grasses

Abstract

AbstractBiosolids are stabilized solids from municipal wastewater treatment that meet federal criteria for land application. Limited information exists on N availability from biosolids treated to meet Class A standards for pathogen reduction. We conducted a 2‐yr field study at two locations in western Washington: (i) to evaluate N recovery from Class A biosolids applied to two cool‐season perennial grasses, and (ii) to make practical recommendations for biosolids application rates for intensive production of these grasses. We surface‐applied two types of Class A biosolids (heat‐dried and thermophilically digested‐dewatered) at three rates to a well‐drained soil planted to tall fescue (Festuca arundinacea Schreb.) and to a poorly‐drained soil planted to perennial ryegrass (Lolium perenne L.). Each location also had N fertilizer (34‐0‐0) and zero‐N control treatments. Grass was harvested at 30 to 50 d intervals during the growing season. The two types of biosolids were similar in their ability to supply N to the grasses. At the well‐drained site, application of 1100 to 1250 kg ha−1 of biosolids N over 2 yr produced similar grass yield and apparent N recovery as 540 kg ha−1 ammonium (NH4) nitrate (NO3)‐N. At the poorly‐drained site, application of 750 to 830 kg ha−1 biosolids N over 2 yr produced similar yield and apparent N recovery as 340 kg ha−1 NH4 NO3‐N. Residual soil NO3 in the fall was low at both locations and was not affected by the biosolids treatments. Comparison with other literature suggests that these materials are as effective as liquid biosolids at supplying N to forage grasses.