Fertilizer Rate for Kangkung (Ipomoea aquatica L.) Production in Ultisols of Nanggung, Bogor

Abstract

Nitrogen, phosphorus and potassium availabilities are the most limiting factors for maximum growth and yield. Kangkung (Ipomoea aquatica L.) is an important traditional leafy vegetable crop cultivated in Indonesia. Kangkung was grown to evaluate the optimum rates of N, P and K fertilizers in Ultisols of Nanggung, Bogor, with low pH (5.5), low organic C (1.54%), very-low total N (0.12%), low K content (0.29 me/100 g), but very high soil P20S concentration (19.2 ppm) to evaluate the best crop management practices with starter solution. The experiment was conducted in Hambaro village, Nanggung sub district, Bogor, Indonesia, from January to April 2008.• The treatments were: N, P, K fertilizer rates of 0%;• 50%, 100%, 150% and 200% from the fertilizer recommendation rates (100 kg/ha N, 135 kg/ha P20S and 135 kg/ha K20). This experiment used Randomized Complete Block Design with four replications (each farmer field as one replication): Total number of plots was 15 x 4 = 60, with plot size of 1.5 x 5 m. Kangkung (local variety) was planted in four rows per plot, 25 cm between rows and 15 cm within rows, at 10 seeds per planting. The application of N (200 kg/ha), P20S (270 kg/ha), and K20 (270 kg/ha) quadratically increased total and relative yields of kangkung. Based on Y = -0.0021x2 + 0.572x + 56.857 for N, Y = -0.0013x2 + 0.3673x + 72.102 for P20S, and Y = -0.000lx2 + 0.0959x + 84.102 for K20, the optimum rates for each nutrient was 136-141-674 kg/ha N-P2O5-K2O. The fertilizer recommendation based on K threshold (no K) was 41-40-0, on P threshold was 24-0-0 kg/ha N-P205-K20. However, no fertilizer was needed on N threshold. In the recommendation based on optimum yield (136-141-674), the percentage increase in cost (134.0) was higher than the expected increase in yield (19.28). Based on the yield vs. cost rule therefore, the most economical recommendation would be 41-40-0 kg/ha N-P20 S-K20 (K threshold).