Michael Sipiora* and Miguel Garcia
*Treasury Wine Estates; Napa Resource Conservation District, 1000 Pratt Avenue, 1303 Jefferson St. , St. Helena; Napa, CA, 94574; 94558 
(michael.sipiora@tweglobal.com)

The objective of this trial was to determine the effects of a biochar (10 tons per acre), a compost application (20 tons per acre), and a combined application of biochar and compost (10 + 20 tons per acre) on soil health and vine performance in a Cabernet Sauvignon vineyard in Napa. Soil amendments were applied in fall of 2021. The average level or soil organic matter (SOM) for control treatment was 2.13%. There was a tendency for SOM to increase with either biochar (2.29%) or compost application (2.31%), and the SOM of combined application was 2.69%. Neither total carbon nor active carbon increased significantly with either biochar or compost application. Soil respiration rates were not significantly impacted by either application, although there was an indication that biochar depressed soil respiration rates. Total nitrogen (%) was not significantly increased by any treatment, but potentially mineralizable N was significantly increased by compost application. The percentage of water-stable aggregates was not influenced by either the biochar or compost application. There were no significant treatment effects on soil pH, CEC, or EC. Neither application of biochar or compost affected bloom petiole macronutrient (N, P, K, Mg, Ca) concentrations the following spring, but there were significantly lower concentrations of petiole Na, S, Al, and Zn where biochar was applied. There was no significant yield response to either a biochar of compost this first year after application, nor was there a significant impact of either biochar or compost on vine pruning weights in 2022. There were significantly lower total soluble solids (TSS) near harvest in plots with compost application. The average TSS (Brix) of fruit from plots with biochar (25.6), compost (25.2), or biochar + compost (24.5) was 1 to 2 Brix lower than in fruit from control plots (26.7) at harvest.

Funding Support: The National Institute of Food and Agriculture and the Western Sustainable Agriculture Research and Education program