Changes in Nitrogen Availability in Chernozemic Soils Amended with Anaerobically Digested Cattle Manure

Abstract

Anaerobically digested manure (ADM) is a nutrient-rich coproduct from manure-based biogas plants. The ADM is often separated into a solid fraction, known as solid digestate (SD), and a liquid fraction, which could be applied to cropland at rates equivalent to those for raw manure. Application of SD could result in different nitrogen (N) mineralization patterns compared to raw manure due to biophysicochemical changes occurring during anaerobic digestion. The objective of this laboratory incubation experiment was to characterize changes in the availability of N in a Dark Brown Chernozem (Typic Haploboroll clay loam) and a Black Chernozem (Typic Haplocryoll silty clay) amended with raw beef cattle (Bos taurus) feedlot manure, SD, pelletized SD (PSD), and urea plus monoammonium phosphate (UMAP) at rates equivalent to 400 and 800 mg N kg⁻¹ soil. Across rates, net mineralized N concentrations after 70 d in soils amended with UMAP, manure, SD, and PSD were 44, 18, −5, and -13% of added N, respectively, in the Dark Brown Chernozem and 45, 29, 6, and -18%, respectively, in the Black Chernozem. The lower N mineralization potential of SD and PSD compared with manure implies that anaerobic digestion alters the nutrient release patterns of manure and suggests that these digested manure forms may have to be either applied at higher rates compared with raw manure or should be supplemented with inorganic N fertilizer to ensure adequate N supply for plants.