Effects of Seaweed on Potato Yields and Soil Chemistry

Abstract

In parts of northwest Spain, seaweeds have traditionally been used as fertilizer for potatoes. In the work reported here, a potato field was divided into plots which were fertilized with seaweed (20, 40 or 80 t ha⁻¹), or fertilized by conventional means (46.5 t ha⁻¹ cattle manure plus 1 t ha⁻¹ NPK 8:24:16), or not fertilized. Soil properties were monitored before planting and at the “end of season” phase. Fertilization with seaweed reduced the acidity, which was demonstrated as a pH increase from 0.3 to 0.6 in the plots fertilized with seaweed; the concentration of exchangeable Ca doubled, when compared to the traditional fertilizer, and the percentage of Al saturation decreased to 4.5% for the dose of 80 t ha⁻¹ of seaweed, with respect to the initial values (19.2%). Assimilable K levels rose significantly, from 0.41 to 0.68 cmol kg⁻¹ with 80 t ha⁻¹ seaweed which did not cause salinization (E.C. < 0.5 dS m⁻¹). Crop yield in plots which received 80 t ha⁻¹ of seaweed was significantly higher than in all other plot types (11.6 t ha⁻¹) against 5.5 t ha⁻¹ in unfertilized plants and 8.2 t ha⁻¹ in conventional plots, significant differences which are also evident in the single-potato weight.