Use of Invasive Algae as a Potassium (K) Source Affects Growth and K Content in Pak Choi (Brassica rapa cv. Bonsai, Chinensis Group) under Greenhouse Conditions

The application of locally available invasive algae biomass waste as a source of crop nutrients in Hawaii is a potential strategy to replace commercial chemical fertilizers, reduce production cost and increase grower profitability.  Two greenhouse trials were conducted at the University of Hawaii at Manoa Magoon facilities to study the effects of using invasive algae species as source of potassium (K) on growth, yield and nutrient content in the Pak choi (Brassica rapa cv. Bonsai,Chinensis group). In the first greenhouse trial, three algae species (Gracilaria salicornia, Kappaphycus alvarezii, Eucheuma denticulatum) were evaluated for growth and mineral evaluated for growth and mineral nutrition of pak choi plants with five rates of K(0, 84, 168, 252 & 336 kg*ha-1). The pak choi was directly seeded into 4L pots and grown in peat moss based media. In the 2nd greenhouse trial, pak choi was grown in peat and soil media at 5 rates of K provided through Eucheuma denticulatum and potassium nitrate (KNO3). Results from the 1st greenhouse trial showed no significant differences among the 3 species in yield or leaf K content. Plant yield & K concentration in plant tissue were significantly increased with application rates. The maximum yield and leaf K concentration were obtained when algae was applied at 252 kg*ha-1 K. In the 2nd greenhouse trial, KNO3 was significantly higher than Eucheuma for yields in soil but not in peat media. Highest yields & leaf K content in both experiments were observed when K was provided between 224 -284 kg*ha-1K.These results suggest that the use of invasive algae biomass is effective in increasing yield and improving K nutrition of pak choi. Further field studies are needed to validate the yield response curves developed from greenhouse trials.