In a nutshell: almond hull and shell organic matter amendments increase soil and tree potassium status

Project Type: Research and Education
Funds awarded in 2020: $349,807.00
Projected End Date: 12/31/2023
Host Institution Award ID: G126-21-W7899
Grant Recipient: University of California Davis
Region: Western
State: California
Principal Investigator:
Dr. Sat Darshan Khalsa
University of California Davis
Dr. Patrick Brown
University of California Davis
Dr. Amelie Gaudin
University of California, Davis
Crop residues used as organic matter amendments have been shown to release potassium (K) into the soil, promoting K cycling in agronomic systems. Orchard field trials are needed to evaluate K dynamics under almond hull and shell amendments, which contain high K concentrations.

Three field trials in commercial almond orchards were conducted to assess the effects of surface-applied almond hull and shell amendments on K cycling within plant and soil systems. Amendment K concentrations over time, soil exchangeable K, and tree K status were measured as well as decomposition rate and crop yield.

Hulls and shells released K rapidly under irrigation and rainfall, significantly increasing soil exchangeable K in the upper 0–10 cm soil within 2–7 weeks. Amendments increased tree leaf K status within the first 1–3 years to varying degrees depending on site. Initial amendment K concentrations decreased by at least half by dry weight within the first 25.4 cm (10 inches) of water (irrigation and precipitation) within the irrigated zone.

Almond hulls and shells can increase soil and plant K status when used as amendments on the soil surface. This practice can address byproduct utilization issues, recycle potassium (K), and reduce orchard K fertilizer demand by replacing the majority of tree K demand. Growers can tailor application rates to meet orchard-specific K management goals. Off-ground harvest preserved the hull/shell organic layer over time and maximized K cycling. Hull/shell amendments applied on the soil surface cover more soil area within the irrigated wetted zone compared to banded K fertilizer. This practice can reduce reliance on K fertilizers and reduce associated costs while providing a convenient outlet for hulls and shells.
Peer-reviewed Journal Article
Ellie Andrews, UC Davis
Daniel Rivers, UC Davis
Amelie Gaudin, UC Davis
Daniel Geisseler, UC Davis
Patrick Brown, UC Davis
Sat Darshan Khalsa, UC Davis
Target audiences:
Educators; Researchers
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.