Project Objectives

This project aims to enhance the sustainability and resilience of California almond production by investigating WOR methods that can maximize environmental and economic benefits of orchard turnover, and by linking growers with the information they need to assess the potential for WOR in their own orchards.

Our specific objectives are:

  • Establish on-farm whole orchard recycling (WOR) research platforms representative of almond production regions and replant problems
  • This includes:

    Characterizing baseline soil properties, nematode populations, and potential for replant disease at orchards in the Central Valley prior to orchard turnover.

    Establishing trials in two of the orchards in Fall 2016, in which tree residues will be recycled or removed using a split plot design with five to six replicates per treatment combination:

    Main treatment:
    Whole tree grinding into large (4 to 18”) pieces and incorporated using land clearing equipment
    Whole tree chipping with a tub grinder (4 to 6”) and surface spreading
    Removal of aboveground biomass (Control)
    Sub treatment:
    Fumigated and non-fumigated control subplots will be randomly established on all three main treatments
    Replant orchards with almond trees in winter 2016/2017

  • Measure short- and long- term benefits of WOR for carbon sequestration and soil physical and chemical properties important for tree nutrition and soil health.
  • This includes:

    Measuring the short-term impacts of WOR strategies on soil carbon (organic matter, labile and recalcitrant carbon pools in aggregate fractions) and soil physical properties (aggregate stability, bulk density, crusting, soil structure and micropores) at the two trial orchards

    Assessing shifts in soil chemical properties (pH, EC, nutrients) after recycling

    Determining how WOR influences the amount and timing of nitrogen release from recycled tree organic matter and nitrogen immobilization and losses

    Measuring long term carbon sequestration in macro and micro aggregates from WOR at a research site recycled 8 years ago following similar experimental design and treatments

  • Determine impacts of WOR on soil biology and tree performance and health
  • This includes:

    Determining how WOR may affect the need for preplant soil fumigation

    Characterizing shifts in soil and root microbial communities (bacteria, archaea, fungi, oomycetes; including phytopathogens) with WOR, and with or without fumigation

    Evaluating the impacts of WOR on incidence of plant-parasitic nematodes (soil and root extraction methods) and phytopathogenic fungi and oomycetes (culture-based root system assays) twice a year after replant.

    Examining how WOR affects (i) soil suppression of phytopathogenic nematodes and fungi and (ii) incidence and severity of almond replant disease

    Measuring main and interactive effects of WOR and soil fumigation on tree growth

  • Measure impact of WOR on key plant-soil-water relationships, water use efficiency, and yield resilience to deficit irrigation.
  • This includes:

    Characterizing shifts in soil hydraulic properties at a research site recycled 8 years ago following similar experimental design and treatments

    Implementing replicated deficit irrigation scenario (50% after hull split) and a control 100% and monitor differences in soil moisture dynamics in the root zone.

    Measuring the impacts of WOR on water use efficiency and tree resilience to water shortages at the end of the season. 

  • Assess the environmental and carbon footprint of WOR methods using a Life Cycle Assessment framework
  • This includes:

    Consolidating data on (i) temporary and long term carbon storage in soil under orchard recycling scenarios, (ii) water and nutrient inputs (iii) disease incidence, and (iv) equipment use, transport, and fuel consumption of orchard end-of-life management practices from Objectives 1-4

    Using existing orchard Life Cycle Assessment models to assess the greenhouse gas balance, pollutants and resource consumption impacts of WOR under various alternative management and input-displacement scenarios

  • Extend project results to stakeholders in California and beyond
  • This includes:

    Conducting five field days for growers, crop advisors, and other extension professionals at each site to view equipment and present results on tree and soil health, nutrient cycling band input use. 

    Organizing and hosting a webinar for growers and extension on practices and benefits of WOR, based on project research results.

    Publishing the scientific results in peer-reviewed journals, and in professional scientific meetings