A Study on Inorganic Fertilizers and Organic Materials to Increase the Productivity of Rice Crop (Oryza sativa L.) in Equatorial Agroecosystems

The aim is to determine the optimum combination of inorganic fertilizer and organic materials for increasing the productivity of rice crop (Oryza sativa L.). The experiment was conducted in February–June 2015 in Kebadu, Sanggau, West Kalimantan, Indonesia. The study area was located at 00°0.08,785′ N north latitude and 110°0.07,175′ E east longitude with ultisol soil; the altitude is 32 m above sea level, rainfall level ranges between 185–267 mm month⁻¹, and the solar radiation is 375.49–452.58 cal cm⁻² day⁻¹. This study used a factorial randomized block design. The first factor was the inorganic fertilization (without fertilizer, inorganic fertilizer 50%, 100%, and 150%) and the second factor was the addition of organic materials (EM₄ 2 l ha⁻¹, chicken manure 2 t ha⁻¹, and manure 2 t ha⁻¹ + EM₄ 2 l ha⁻¹). Results showed that the application of chicken manure and a combination of chicken manure + EM₄ could reduce the need for inorganic fertilizer NPK by up to 50% with productivity that ranged from 4.18–4.20 t ha⁻¹; this is relatively similar to 100% and 150% inorganic fertilizer NPK, and can increase the harvest by up to 68% compared to the no-NPK inorganic fertilizer.