Kinetics of water‐extractable zinc release from seaweed (Fucus serratus) as soil amendment

Soil fertilization with trace‐metal rich organic fertilizers such as Fucus serratus seaweed may be an effective way to combat micronutrient deficiency. In this study the kinetics of zinc release from Fucus serratus seaweed was investigated in a packed soil column leaching experiment over 1,776 h. The release of zinc from control (soil only) and treatment (soil + seaweed; equivalent zinc application rate of 1.42 kg ha−1) columns, measured by ICP‐MS, demonstrated two distinct release stages. The cumulative zinc release data for each phase were fitted to five kinetic models: zero order, first order, Elovich, power function and parabolic diffusion. In the first stage (0–400 hours) the release of zinc from both control and treatment was best described by a parabolic rate law, indicating release of zinc from a soluble soil reservoir. In the second stage (400–1,776 h) zinc release followed a zero order rate law indicative of slow release from an essentially insoluble reservoir. The modelled difference between the amount of zinc released from treatment and control columns in stage 1 (230 ± 11 µg) represented the total amount of zinc added via seaweed. The parabolic rate constant for seaweed zinc release was 12.09 µg g−1 h−0.5. In summary, the addition of F. serratus to soil is a viable source of labile zinc and a low cost agronomic option for mitigating zinc deficiency in soils.