Phosphorus and potassium nutrition of a tropical waterlily (Nymphaea) used for commercial flower production

Abstract

Background and aims: Waterlilies (Nymphaea spp) are ancient iconic plants. Scientific knowledge of their nutrient requirements is scarce. We investigated plant responses to phosphorus (P) and potassium (K) nutrition in a cultivar of tropical waterlilies used for commercial flower production. Methods: Two studies with waterlilies were conducted simultaneously over 24 weeks. In Experiment 1, three amounts of fertiliser differing in P content were supplied either four, six or 12 times. Experiment 2 was similar, but fertiliser varied in K content. Flower production was recorded every two weeks, detailed plant measurements were made every six weeks and leaves were collected for nutrient analyses at week 20. At week 24, shoot biomass was harvested and weighed. Results: Total flower production increased with increasing P supply but decreased with increasing K supply. With increasing P supply, leaf P concentration increased from 1.3 to 2.0 mg g−1 dry weight. Increasing the K supply decreased leaf P concentration but had no effect on K concentration. In the P experiment, leaf calcium and magnesium concentrations were generally low as was the leaf zinc concentration. Final plant size increased with increasing P supply but declined with increasing K supply. Conclusion: Waterlily growth and flowering declined with increasing K supply and increased with increasing P supply. Fertiliser-P requirement was very high, and it is possible that plants would have responded to greater amounts of P than we used. This was partly due to the very high P-sorbing capacity of the soil we used. Inefficient nutrient uptake owing to the low capacity for P acquisition of waterlily roots at the near-neutral pH of flooded soil was also a likely factor.