Nitrous oxide emissions from Chernozemic soils amended with anaerobically digested beef cattle feedlot manure: A laboratory study

摘要

Biogas production from beef cattle (Bos taurus) feedlot manure results in co-generation of anaerobically digested manure (ADM), a nutrient rich substrate with a solid fraction (SS) often applied to cropland. Application of SS to cropland may result in lower N2O emissions than raw manure due to biochemical changes occurring during anaerobic digestion. We tested this hypothesis using a laboratory incubation study in which N2O fluxes from two Alberta soils, being a Dark Brown Chernozem clay loam (Typic Haploboroll) and a Black Chernozem silty clay (Typic Haplocryoll) amended with raw beef cattle feedlot manure, SS, pelletized SS (PSS), and urea + monoammonium phosphate (UMP) were measured over 10 weeks. Amendments were applied at rates corresponding to 100 and 200 kg N/ha, with a ON control included for comparison. Amended soils were maintained near 70% of field capacity moisture content and incubated for 10 weeks at 22 degrees C. Gas samples were collected 0, 3 and 7 days after the start of the incubation and weekly thereafter for N2O and CO2 analysis by gas chromatography. The N2O fluxes differed among amendments with the differences dependent on soil, amendment application rate, and time. Across amendment rates, mean cumulative emissions from SS- (2.38 mg N/kg) and UMP amended soils (0.59 mg N/kg) did not differ, but were both lower than emissions from PSS amended soils (10.7 mg N/kg) and those from the higher manure rate (15.6 mg N/kg). The high N2O emissions from PSS amended soils were likely due to the concentrated microsites of N in pellets. A difference in cumulative N2O emissions between PSS and SS only occurred in Black Chernozem. Microbial activity as indicated by cumulative CO2 fluxes was highest in SS amended (6.7 g CO2-C/kg) and lowest in UMP amended soils (0.14 g CO2-C/kg). Post-incubation net mineral N content was highest in manure amended soils (144 mg N/kg), marginal in SS amended soils (23 mg N/kg), and lowest in PSS amended soils that had net N immobilization (-67 mg N/kg) due to low available N content in the pellets. Results suggest that field application of SS may reduce N2O emissions relative to raw manure.This article is part of the special issue entitled: Greenhouse Gases in Animal Agriculture Finding a Balance between Food and Emissions, Guest Edited by TA. McAllister, Section Guest Editors: K.A. Beauchemin, X. Hao, S. McGinn and Editor for Animal Feed Science and Technology, P.H. Robinson. Crown Copyright (C) 2011 Published by Elsevier BA/. All rights reserved.