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.
In order to evaluate the application of seaweed biomass as a soil fertility management strategy, the overall objective of this study is to determine the effects of seaweed amendment on soil quality parameters and the yield of sweet corn (Zea mays) in a field experiment. The specific objectives and progress steps associated with each objective are listed below. 1) Characterize and prepare suitable amendment material from raw green seaweed biomass for field application Complete Fall and spring seaweed biomass collection Species identification and specimen preservation Field biomass application Carbon and nitrogen (C and N) composition analysis Trace nutrient and heavy metal analysis Notes In Rhode Island bays or estuaries (e.g. Warwick Bay), seaweed biomass accumulating on beaches is generally dominated by green seaweed species (e.g. Ulva spp.), and removal is often required. Consequently, the original study proposed use of green seaweed biomass. However, the abundance of beach-cast seaweed biomass, particularly in estuarine environments, is often affected by variation in factors such as temperature, wave activity, and wind strength (Merceron et al., 2007). Due to seasonal variability, beach-cast green seaweed from bays or estuarine sites in Rhode Island was limited during September and October 2011. In contrast, seaweed proliferation closer to the open ocean is generally less dependent on seasonal variability. Consequently, seaweed biomass for fall application was collected by hand from Watch Hill, Westerly, RI, on November 2, 2011. This seaweed biomass was largely composed of brown and red seaweed species. Additionally, seaweed biomass was collected and applied in late April 2012 from Mackerel Cove (Jamestown, RI) to supplement fall application. 2) Evaluate the effect of seaweed amendment on the yield (bushel/acre and biomass/cob) and quality of sweet corn, an economically important crop for local agricultural production, in comparison to a conventional inorganic fertilization treatment Complete Fall tillage for sweet corn plot preparation and weed management Seaweed biomass application and side-dress fertilizer application for seaweed amendment treatments (fall and spring) Pre-planting and side-dress fertilizer application for PFF treatment Sweet corn seeding and weed management Sweet corn pest control (Bacillus thuringiensis var. kurstaki application for corn borer) Sweet corn ear harvest (silk dry down), weighing, drying, and dissolved soluble solids (DSS) analysis Above-ground corn biomass collection, weighing and drying Data processing and analysis Notes The research proposal included a comparison between seaweed and inorganic chemical fertilizer. However, a pre-formulated, granulated organic 8-1-9 (N-P-K) fertilizer composed of poultry litter, peanut meal, and feather meal was used as the sole (PFF treatment) or supplemental (LDS and HDS treatments) nutrient supply. The reason for this substitution was to present results with application to organic or low-input sweet corn growers, a target audience generally interested in alternative organic amendment materials and practices. 3) Evaluate seaweed amendment effects on physical, chemical and biological soil quality parameters in comparison to a conventional inorganic fertilization treatment Complete Soil quality sampling Pre-seaweed application (October 2011), pre-corn seeding (May 2012), and post-harvest (September/October 2012) – Aggregate stability, bulk density, available water capacity, and infiltration Monthly (October-November 2011 and April-October 2012) – Soil respiration and earthworm abundance (in-field analysis); insect collection; bulk sample collection for soil pH, electrical conductivity (EC), nitrate (NO3-), ammonium (NH4+), phosphate (HnPO4n-3), potassium (K), active C, potentially mineralizable N (PMN), trace nutrients, sulfate (SO42-), soil organic matter (SOM), nematode abundance and community composition, and heavy metals Soil quality analyses (field and laboratory) Bulk density, available water capacity, infiltration, soil respiration, pH, EC, extraction for primary nutrients, trace nutrients and PMN, and total element/heavy metals 4) Assess the economic and practical feasibility of seaweed amendment for sustainable agriculture in coastal New England through synthesis of experimental findings, both from this and previous studies, and through discussions with local agriculturalists, Extension agents and agricultural economists Complete Documentation of time and cost requirements for seaweed location, collection, preparation and application Determination of potential yield improvement benefits Analysis of costs and potential changes in income based on yield improvements Informal assessment of farmer interest and current/prospective adoption Notes Estimated values for quantifiable expenses and benefits (e.g. fuel and labor requirements, crop yield enhancement) were used to generate an overall assessment of economic viability, but the difficulty in assigning monetary value to less quantifiable factors and externalities did not allow for comprehensive assessment of many complexities involved in the practice of seaweed amendment (e.g. fertilizer manufacture environmental impacts, improvement in soil quality).