Whole orchard recycling in California's Central Valley: Benefits, management, and adoption.

Whole orchard recycling (WOR) has become a common practice in California (CA) orchards and vineyards due to declining options for agricultural biomass disposal. WOR is the process by which entire orchards or vineyards are shredded into chips, spread onto the soil surface, and incorporated into the soil before replanting a new crop. The paper summarizes current knowledge on WOR's impact on soils, crops, and the environment and outlines efforts to promote large-scale adoption across California. From 2008 to 2019, field trials were established at eight sites in the Central Valley to identify best management guidelines and measure changes in soil health, environment, and replanted orchard performance over time. Biomass incorporation ranged from 56 to 191 metric tons ha-1 across all sites. Results clearly show WOR increased soil organic carbon and improved crop yield. WOR improved soil water and nitrogen (N) retention and did not increase nitrate leaching. Carbon dioxide (CO2) emissions from biomass decomposition were highest in the first year following WOR but declined substantially thereafter, coinciding with soil carbon (C) sequestration and improvement of other soil properties. State incentive programs and outreach extension efforts have played a significant role in fostering acceptance of the practice and implementation. While the long-term benefits of WOR are clear, further research is needed to optimize water and fertilizer management in replanted systems. The outcomes of this research and the demonstrated success of WOR in California provide a model for sustainable orchard recycling practices in other regions facing biomass disposal and soil health challenges.