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.