Biochar–compost mixture and cover crop effects on soil carbon and nitrogen dynamics, yield, and fruit quality in an irrigated vineyard

Effects of biochar–compost (B+Com) mixture and cover crop were assessed on soil and grapevine productivity in an irrigated Merlot ( Vitis vinifera L.) vineyard in Okanagan Valley, British Columbia (BC), Canada, from 2017 to 2020. The experimental design was a factorial arrangement of control, B+Com, cover crop, and combination of cover crop and B+Com (cover crop/B+Com) treatments in alleys with four replications. The B+Com comprised a 1:1 ratio of biochar and compost and was applied at a rate of 22 Mg ha −1 dry weight basis in May 2017 and 2019. The cover crop consisted of a dryland forage mixture and bird’s-foot trefoil ( Lotus corniculatus L.). B+Com treatment did not affect cover crop biomass or tissue C and N concentrations except for a 12% reduction in 2019 biomass. B+Com and cover crop/B+Com increased soil C content averaged across sampling dates by 11% and 17% ( P < 0.05), respectively, only at the 0–15 cm soil depth compared with the control. Cover crop treatment did not affect ( P < 0.05) soil C content at two soil depths in all sampling dates. Soil N content was not affected by B+Com, decreased by an average of 12.5% at both soil depths with cover crop, and increased with cover crop/B+Com by 4% only at the 0–15 cm soil depth averaged across sampling dates ( P < 0.05). Grape yield was increased by 32% by cover crop/B+Com relative to control only in 2020. The cover crop reduced petiole N and pruning weights in one or two years out of three.