Seaweed compost for agricultural crop production

• Published in: Journal of applied phycology Vol. 28; no. 1; pp. 629 - 642
• Main Authors: Cole, Andrew J., Roberts, David A., Garside, Alan L., de Nys, Rocky, Paul, Nicholas A.
• Format: Journal Article
• Language: English
• Published: Dordrecht Springer Netherlands 01.02.2016; Springer Nature B.V
• Subjects: Algae; Bagasse; Biomass; Biomedical and Life Sciences; Composts; Crop production; Ecology; Freshwater & Marine Ecology; Life Sciences; Nitrogen; Plant growth; Plant Physiology; Plant Sciences; Sugarcane; Ulva; Salt; Phosphorous; Agriculture; Electrical conductivity; Nitrogen; Macroalgae
• ISSN: 0921-8971; 1573-5176
• DOI: 10.1007/s10811-015-0544-2

This study manipulated the carbon-to-nitrogen ratio (C:N) of seaweed composts by varying the proportion of high N green seaweed ( Ulva ohnoi ) and high C sugarcane bagasse to assess their quality and suitability for use in agricultural crop production. Seaweed-bagasse mixes that had an initial C:N ratio greater than 18:1 (up to 50:1) could be transformed into a mature compost within 16 weeks. However, only composts with a high seaweed content and therefore low initial C:N (18 and 22:1) supported a consistently high rate of plant growth, even at low application rates. Sugarcane grown in these high seaweed composts had a 7-fold higher total above-ground biomass than low seaweed composts and a 4-fold higher total above-ground biomass than sugarcane grown in commercial compost that did not contain seaweed. Overall, the optimal initial C:N ratio for seaweed-based compost was 22:1 which corresponds to 82 % seaweed on a fresh weight basis. This ratio will produce a high quality mature compost whilst also ensuring that a high proportion of the nitrogen (>90 %) in the Ulva biomass is retained through the composting process.