Seagrass that washes ashore is an abundant, traditional amendment for crop production on Yap Islands, yet its potential for modern sweetpotato (Ipomoea batatas) cultivation remains largely unexplored. Traditionally, semi-decomposed seagrass is incorporated to create raised beds where sweetpotato is grown for several years. While compost and manure can be effective amendments to improve the conditions of the highly weathered, acidic volcanic soils of the Yap Islands, they are costly, labor intensive, and in short supply. By utilizing an abundant, free resource, this project seeks to improve crop yields and extend the productive life of agricultural lands. This study includes two field experiments that compare semi-decomposed seagrass with conventional commercial fertilizer for two sweetpotato cultivars in two production systems, raised-beds and grow-bags. Experiment 1 utilizes raised beds established on three farm sites with an improved sweetpotato cultivar, where treatments include medium and high application rates (by weight, approximately 40 and 60 kg N ha-1, respectively) of semi-decomposed seagrass and a control treatment using commercial fertilizer (10N-20P-20K) at N rate equivalent to the medium seagrass application. Each treatment is randomized in a complete block design, with six replicates per treatment. Experiment 2 is a split-plot design and compares a traditional vining and a modern sweetpotato cultivar (main plot treatment) in container cultivation using 10-gallon grow bags filled with a soil mix amended with seagrass at medium and high ratios compared to a commercial fertilizer control at N rate equivalent to the medium seagrass application (split-plot treatment). For both experiments, the seagrass is collected, washed, and piled to reduce salinity to acceptable thresholds, with leachate EC measured weekly. Seagrass is then shredded and piled to accelerate decomposition. Analysis results of semi-decomposed seaweed are 15% dry weight with 1.8% N on average, and application rates are 21 g and 32 g per sq foot of soil for N application rates of 40 and 60 kg.ha-1, respectively. Community buy-in and trust building are being achieved through collaboration with island-based agricultural educators and meetings with traditional leaders. This research has the potential to enhance sweet potato production on the Yap Islands, improve resource management, and provide an affordable soil amendment option for local farmers. The project promotes environmental stewardship and contributes to cleaner shorelines and sustainable agricultural practices. The findings will offer critical insights for local agricultural educators and policymakers in optimizing land use and advancing low-cost, high-yield cultivation methods in resource-limited settings.
