Nutrient retention, availability and greenhouse gas emissions from biochar-fertilized Chernozems

Abstract

Amending soil with pyrogenic-C (biochar) has emerged as a potential best management practice to accumulate organic matter (OM), reduce greenhouse gas (GHG) emissions and increase nutrient retention among degraded, marginally-productive croplands. Nevertheless, the impact of biochar application on intensively cropped prairie eco-regions is not well documented, particularly when co-applied with chemical fertilizer. Our objective was to determine the effect of biochar on cumulative CO2-C, N2O-N and CH4-C emissions, water-extractable OM, and available N (AN; NH4-N + NO3-N) and P (AP; PO4-P) in the presence or absence of NP-fertilizer. Biochar was applied to two surface Chernozems (0–15 cm) of contrasting texture [i.e., sandy clay loam (Raymond) and clayey (Lethbridge)] at six rates (0, 0.15, 0.5, 3, 10 and 20 Mg ha−1) in combination with (+NP) or without (−NP) urea-N (150 kg N ha−1) and KH2PO4 (50 kg P ha−1). A total of 72 soil columns were incubated at 21 °C for 86 d. Biochar addition increased soil total C up to 24.9 g kg−1 and 28.7 g kg−1 in Raymond and Lethbridge, respectively, but did not affect water-extractable OM. Cumulative N2O-N and CH4-C emissions were not influenced by biochar, regardless of whether or not NP-fertilizer was added (p > 0.05). Cumulative CO2-C emissions varied between soil textures and were increased or decreased non-linearly by biochar addition under –NP only. Available P increased within +NP soil with increasing biochar rates reaching 43.9 mg kg−1 in Raymond and 79.5 mg kg−1 in Lethbridge when biochar was applied at 20 Mg ha−1. A similar but less pronounced response was observed for AN. Our results indicate that biochar-only application is not a practical management approach for improving soil fertility and nutrient cycling in surface Chernozems. Nevertheless, co-applying biochar with NP-fertilizer appears to improve soil P availability in the short-term.