Effects of Seaweed on Potato Yields and Soil Chemistry

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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.