Nutrient cycling and greenhouse gas emissions from soil amended with biochar-manure mixtures

Abstract

Integrating biochar into cattle diets has recently emerged as a potential management practice for improving on-farm productivity. Yet, information concerning the cycling of biochar-manure mixtures is scarce. A 70-d incubation experiment was conducted within two surface (0–15 cm) Mollisols with contrasting textures, i.e., sandy clay loam (Raymond) and clayey (Lethbridge), to evaluate the effects of biochar (3 Mg ha–1) on cumulative greenhouse gas (GHG) emissions and related fertility attributes in the presence or absence of cattle manure (120 Mg ha–1). Five treatments were included: i) non-amended soil (control, CK), ii) soil amended with pinewood biochar (B), iii) soil amended with beef cattle manure (M) (manure from cattle on a control diet), iv) soil amended with biochar-manure (BM) (manure from cattle on a control diet, with pinewood biochar added at 20 g kg–1 of diet dry matter), and v) soil amended with B and M at the aforementioned rates (B+M). A total of 40 soil columns were prepared and incubated at 21 ° C and 60%–80% water-holding capacity. On average, total CO2 fluxes increased by 2.2- and 3.8-fold under manure treatments (i.e., M, BM, and B+M), within Raymond and Lethbridge soils, respectively, relative to CK and B. Similarly, total CH4 fluxes were the highest (P < 0.05) in Raymond soil under B+M and BM relative to CK and B, and in Lethbridge soil under M and BM relative to CK and B. In Lethbridge soil, application of BM increased cumulative N2O emissions by 1.8-fold relative to CK. After 70-d incubation, amendment with BM increased (P < 0.05) PO4 -P and NO3 -N + NH4 -N availability in Raymond and Lethbridge soils compared with B. A similar pattern was observed for water-extractable organic carbon in both soils, with BM augmenting (P < 0.05) the occurrence of labile carbon over CK and B. It can be concluded that biochar, manure, and/or biochar-manure have contrasting short-term effects on the biogeochemistry of Mollisols. At relatively low application rates, biochar does not necessarily counterbalance manure-derived inputs. Although BM did not mitigate the flux of GHGs over M, biochar-manure has the potential to recycle soil nutrients in semiarid drylands.