Enhancement of manure composting by biochar: An emerging benefit to use biochar in animal feeding

Animal-derived organic matter (AOM) is a component of densely populated livestock regions and its occurrence within surface soil is now recognized as a key driver of global carbon-climate feedbacks. Feeding cattle biochar (BC) has recently been explored as an approach to mitigating the environmental footprint of beef production by reducing the intensity of enteric CH4 emissions. However, large-scale studies considering potential soil carbon (C) benefits of biochar-manure amendments have not been investigated.
A feedlot trial was conducted at the Lethbridge Research and Development Centre (Lethbridge, AB, Canada) within the context of the 2018-2021 project “Assessment of the potential for adding biochar to beef cattle diets to reduce greenhouse gas emissions in agriculture”. Heifers were offered a basal diet of 60% barley silage, 35% barley grain and 5% mineral supplement with BC added at 0%, 0.5%, 1.0% or 2.0% of dietary dry matter. Manure was collected from all pens (n=16) monthly (from January to July). Average (n=112) manure total %C increased linearly with the dietary addition of BC, whereas manure total %N displayed a quadratic trend. The pH and electrical conductivity of manure was similar among treatments. Characterization of manure with 0.0% and 2.0% BC by liquid- (UV-Vis absorbance) and solid-phase (DP MAS 13C NMR) analyses revealed differences in the aromaticity and functional group distribution of AOM. Manure from heifers supplemented with 0.0% or 2.0% BC was removed from pens in early-August and either composted (CM, turned three times) or
stockpiled (SP, not turned) until mid-November. Windrows were monitored hourly for temperature and weekly for greenhouse gas surface flux and concentration at 30, 60, and 90 cm below the windrow surface. Sub-samples of CM or SP were collected 14, 35, 62, and 91 d after the trial began. Preliminary results suggested that 2.0% BC manure decomposed slower than 0.0% manure as temperatures were frequently lower within windrows that contained biochar. Such differences translated to apparent higher cumulative CO2-C and CH4-C emissions from CM at 0.0% vs. 2.0% BC. From this initial report, we infer that the use of BC in animal feeding has the potential to improve the environmental performance of composting, increase the C quantity and quality of AOM, and augment the agronomic value of manure. On-going research efforts and future work regarding the application of biochar-manure to local soils will be discussed at the 57th annual ASSW.