Study on the Application of Seaweed Extract and NPK Fertilizer on the Growth of Black Potato (Plectranthus rotundifolius)

Abstract

Black potato (Plectranthus rotundifolius) is a potential alternative food crop to substitute rice. However, its low productivity in Indonesia currently averaging around 15 tons/ha is influenced by factors such as sub-optimal nutrient supply and limited availability of high-quality planting materials. This study aims to examine the effect of applying seaweed extract as a biostimulant along with NPK fertilizer (16-16-16) on the growth and yield of black potato. The research was conducted at the Experimental Farm of the Faculty of Agriculture, UNISRI, Surakarta (130 m a.s.l.). A 4 x 4 factorial Completely Randomized Design (CRD) with three replications (totaling 48 experimental units) was employed. The first factor was the dosage of seaweed extract (0, 1, 2, and 3 mL/L), and the second factor was the NPK dosage (0, 200, 400, and 600 kg/ha). Data were analyzed using Analysis of Variance (ANOVA) followed by Honestly Significant Difference (HSD) test at the 5% significance level. The results showed a significant interaction between seaweed extract and NPK fertilizer on plant height, with the best combination observed at 3 mL/L seaweed extract and 600 kg/ha NPK (34.6 cm). Meanwhile, no interaction was found for the number of branches; however, each single factor had a significant effect. The single treatment of 3 mL/L seaweed extract produced the highest number of branches (15.5 branches), while 600 kg/ha NPK alone yielded 15.1 branches.