Growth of Naiad in Substrates with Varying Percentages of Sand and Controlled-release Fertilizer

Naiad (Najas guadalupensis) is a native aquatic plant in Florida. Very little has been published on its growth requirements. Many aquatic plants can be produced in submerged containers filled with sand.  Our objective was to compare naiad growth in substrates with varying percentages of sand and at 4 fertilizer rates.  Plants were placed in submerged containers filled with 100% sand, 75% sand 25% peat, 50% sand 50% peat, 25% sand 75% peat, and 100% peat. Each container had 0, 2.6, 5.2, or 10.4 grams of Osmocote 15N-9P2O5-12K2O incorporated into the containers prior to planting. We had four mesocosms for each fertilizer rate that held 1 container for each substrate. Containers were planted with three cuttings per container. Mesocosms were randomized and placed in a greenhouse for 8 weeks. Naiad shoot and root dry weight in 100% sand increased as the fertilizer rate increased from 0 to 5.2 and then decreased. Naiad shoot and root dry weight in 75% sand and 50% sand increased from 0 to 2.6 g and then decreased. In 25% sand and 0% sand, growth linearly decreased as fertilizer rate increased. Greatest growth was observed in 50% sand with 2.6 g of Osmocote.  It appears that with the addition of an organic substrate component, less fertilizer was required for naiad growth.