ANALYSIS OF INTERSTITIAL WATER DURING CULTURE OF HYDRILLA-VERTICILLATA WITH CONTROLLED-RELEASE FERTILIZERS

The dioecious strain of hydrilla (Hydrilla verticillata (L.f.) Royle) was cultured outdoors with fertilizer placed as a layer in a sand root ing medium, Plant dry weight averaged 77 g per culture container after 12 weeks of summer growth and was more than three times that for plan ts cultured for the same length of time during the following winter se ason, Concentrations of nitrate, ammonia-nitrogen, and phosphate-phosp horus in interstitial water after 12 weeks of hydrilla growth were 90, 88, and 47% lower, respectively, than in containers without plants, H owever, potassium in interstitial water was 61% higher after 12 weeks of plant growth as compared to containers without plants suggesting hy drilla was transporting this nutrient from the upper ambient pond wate r to the root zone, Results for the winter season were similar but dif ferences in nutrient concentrations between containers with and withou t plants were not as great as during the summer season.