Using Seaweed As a Soil Amendment: Effects On Soil Quality and Yield of Sweet Corn (Zea mays L. var. rugosa).

As a practice that re-purposes waste materials, diversifies inputs, and relies on coastal resources, application of seaweed to manage soil fertility may be an effective and inexpensive agricultural practice in coastal agroecosystems. Seaweed may be a useful amendment for crop production and soil quality improvement due to provision of plant nutrients (e.g. N, P, K, Ca), and promotion of microbial activity, but may be limited by high S, salt, and heavy metal content. The objectives of this field study were to: (1) evaluate the effects of seaweed biomass application on soil physical, biological, and chemical properties; and (2) assess the sweet corn (Zea mays L.) yield obtained using seaweed amendment for soil fertility management. Low-dose seaweed (LDS), high-dose seaweed (HDS), and pre-formulated 8-1-9 (N-P-K) organic fertilizer (PFF) fertilization treatments were employed at 110, 152, and 113 kg total N/ha, with seaweed-derived N accounting for 40% and 55% of total N for LDS and HDS, respectively. Soil properties were assessed prior to seaweed application (October 2011) and throughout the growing season (April – September 2012) using recommended national and regional protocols. Physical properties, extractable Ca²⁺, total heavy metals, total nutrient elements, soil organic matter, earthworm abundance, nitrate, and phosphate did not differ among fertilizer treatments. Extractable K⁺, electrical conductivity, sulfate, and active C levels were increased with seaweed addition, and potentially mineralizable N decreased, though these effects varied in persistence. Yield, above-ground biomass, and dissolved soluble solids did not differ among fertilizer treatments, but average fresh ear weight was greater for LDS compared to PFF. Overall, yield results suggest that seaweed application, as a means of partially replacing total nutrient supply, may be a viable agricultural practice, but must be considered in light of potential yield enhancement value, persistence and magnitude of soil quality changes, and labor and transportation costs.