Effects of AB-mix Rates and Watering Time on the Growth and Yield of Black Potato Crops (Plectranthus rotundifolius)

Black potato (Plectranthus rotundifolius) has been used as a source of carbohydrate for diabetic people. In Java, it is usually planted during a long period of dry season where water is barely available and without fertilizer application. Two experiments were run at the greenhouse, arranged in a completely randomized design (CRD) and replicated 9 times. The first experiment was conducted to evaluate the effect of fertilizer rates (0%, 50%, 100%, and 150% of the AB-mix solution) on the growth and yield of black potato crops. The second experiment was to evaluate the effect of watering times (every 1, 5, 9, and 13 days) on the growth and yield of black potato crops. Germinating seeds were seeded in a polybag, filled with 10 kg of media, a mix of top soil, manure, and rice paddy charcoal (3:1:1). The crops were fertilized with AB-mix solutions weekly. The crop growth and yield were observed. The results showed that the interaction between fertilizer rates and watering increments did not significantly affect crop growth and yield. Likewise, fertilizer rates did not significantly affect crop growth and yield. Finally, watering time significantly affected crop growth, with longer watering time reduced crop growth. However, it did not significantly affect crop yield. We concluded that black potato might grow well and produce a good yield in marginal soil.