Use of Almond Hull and Shell as Organic Matter Amendments in Advanced Orchard Management

Standard almond harvest in California utilizes an on-ground approach which requires multiple machinery passes to shake trees, sweep nuts into row alleys after drying, and collect the crop. This relies on fruit contact with a bare orchard floor, limiting application of organic matter amendments (OMA). This high protein crop requires high nutrient inputs. Inefficient fertilizer use can lead to nutrient leaching, groundwater contamination, and financial losses. Almond huller/processors face management decisions concerning increasing hull and shell biomass. Harvest machinery can disturb topsoil and create dust. Accessible strategies are needed to improve soil health, optimize crop nutrient use, mitigate environmental issues, and optimize hull and shell value.

This project addresses the need for advanced nutrient and harvest management through orchard trials using food-safe OMA to improve soil health and provide nutrients. This creative solution will produce results that guide recommendations using hulls and shells as OMA (HS OMA) to address critical issues currently limiting orchard sustainability. This research will examine complementary off-ground catch frame harvesters to minimize soil disturbance and promote nutrient mineralization.

Research questions will investigate effects of HS OMA management strategies on soil health, plant nutrition, economic value, and environmental impacts:

1. How does almond HS OMA application affect components of soil health?

2. How does HS OMA decomposition and nutrient mineralization impact plant-available nutrients, crop nutrition, and yield?

3. What are the nutrient values, application costs, and associated potential yield effects from HS OMA in different production contexts?

4. What are the broad environmental implications of HS OMA practices?

Research components will utilize randomized complete block design (RCBD) at three sites to evaluate the effects of HS OMA. At one site, a split-plot design will be added to RCBD treatments to compare catch frame harvest to conventional on-ground harvest. Each site will be a case study, independent in location and distinct in design. Outreach and collaboration will share findings among growers, crop advisors, Extension educators, and the public. At on-site field days, growers will discuss practices and guide orchard walk-throughs, prompting dialogue and farmer-to-farmer education. Researchers will present results using posters and engaging take-home materials. A final workshop will integrate feedback and present aggregated data. Researchers will creatively deliver outreach using a decentralized social media approach, engaging existing platforms with partners to provide content through active media outlets such as blog posts, podcast episodes, and videos. At conferences, researchers will present findings and promote social media outlets. Pre/post surveys will assess educational outcomes at events and a stakeholder-developed survey will assess barriers to practice adoption.

This project will promote change in the almond industry by integrating self-generated OMA with nutrient management to improve almond orchard soil health and nutrient management. Assessing benefits and barriers to adoption will ensure research directly assists growers. Results will inform recommendations to improve the sustainability of the almond industry and lay groundwork for future studies. Recommendations will be widely accessible and a variety of management options will allow growers to tailor practices to unique regional contexts.

Project objectives:

Soil Health Objective: Assess impacts of almond HS OMA and advanced orchard management strategies on soil health, nutrient mineralization over time, and soil microbial activity related to HS OMA decomposition. Monitor and evaluate changes in soil health measures in three separate case study orchards. Assess broad potential environmental implications of HS OMA and advanced orchard management strategies by evaluating potential changes in soil health and nutrient retention.

Plant Nutrition Objective: Assess the impacts of almond HS OMA and advanced orchard management on almond tree nutrient uptake and crop productivity. Monitor and evaluate HS OMA decomposition over time. Measure changes in crop nutrition by analyzing July leaf samples annually. Analyze annual yield data across treatments. Assess findings in plant nutrient use to characterize crop nutrient uptake from OMA.

Economic Objective: Assess the economic value of HS OMA inputs. Quantify the nutrient value of potassium in HS OMA and compare to potassium content in fertilizer sources. Compare costs of HS OMA practices to current fertilizer costs. Use annual yield data to assess potential economic benefits from HS OMA effects. Document and compare costs of HS OMA and fertilizer application and labor at each site. Document and compare the costs of on-ground and off-ground harvest at Tracy field site.

Educational Objective: Aggregate research data in engaging outreach documents and media that characterizes HS OMA management strategies to facilitate grower adoption. Demonstrate and discuss potential costs and benefits through presentations at conferences, three field days at trial sites, and a final workshop. Prompt discussion among growers and advisors to improve research. Use surveys to identify learning outcomes at all events. During the first year, use an online stakeholder-developed survey to assess potential barriers to adoption for conventional and organic almond growers. Integrate survey findings into outreach activities.

Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture or SARE.