Logo image
Back
NUISANCE SEAWEED BIOMASS AS AN AGRICULTURAL SOIL AMENDMENT – EFFECTS ON SOIL CARBON, SOIL FERTILITY, AND CROP YIELD
Thesis

NUISANCE SEAWEED BIOMASS AS AN AGRICULTURAL SOIL AMENDMENT – EFFECTS ON SOIL CARBON, SOIL FERTILITY, AND CROP YIELD

Nicole Jain Capizzi
Master of Science (MS), Washington State University
2026
pdf
8.13.26.Capizzi.MS.Thesis
Embargoed Access, Embargo ends: 04/06/2027

Abstract

Organic amendment Particulate organic matter Salinity Seaweed biomass Soil organic carbon
Agricultural soils are depleted from intensive management, increasing the interest in amendments derived from carbon-rich waste that can rebuild fertility and soil organic carbon (SOC) while supporting climate mitigation. Nuisance seaweed biomass (Ulva spp.)accumulates on shorelines and disrupts marine aquaculture and has potential in agriculture but its effects on soil fertility, salinity, and SOC remain uncertain. In a two-year, field trial on two farms in Washington state, unrinsed, dried seaweed was applied at five rates (0, 3, 6, 9, 12 Mg C ha-1) with either a one-time or two-time application. Seaweed increased soil NO₃-N, K, Mg, SO₄²⁻-S, B, and Zn, providing sustained fertility benefits across growing seasons. Although exchangeable Na and electrical conductivity increased with application, seasonal rainfall returned soils to normal condition by spring. Seaweed also increased C and N concentrations in both particulate organic matter (POM) and mineral-associated organic matter (MAOM) fractions, with repeated applications causing greater increases in the more stable MAOM pool. Bulk SOC stock increased only at the site with lower baseline SOC, following two applications at the highest rate. These findings demonstrate that Ulva can supplement crop fertility needs and alter SOC dynamics to improve C stabilization, while highlighting the importance of managing application timing and salt attenuation to optimize agronomic performance.

Metrics

1 Record Views

Details

Logo image