Perbaikan Kesuburan Tanah Sawah Tadah Hujan dalam Pengembangan Kedelai Hitam melalui Aplikasi Pupuk Organik dan Anorganik Majemuk

Abstract

Increased land area can be done by utilizing vacant land or land that is not currently in production periods for example rainfed areas. Utilization of rainfed areas after the time of production of the rice such as black soybean planting assessed potential for development because it can increase the cropping index (IP). Black soybean planting, especially in North Sumatra is still very rare, whereas black soybean have a high economic value. If compared to yellow soybeans, black soybean varieties likes Detam-1 and Detam-2 showed a higher protein content. Black soybean planting in rainfed areas that potential drought was considered very risky. Coupled with other issues such as low soil fertility, high acidity, and the level of Al and Fe are high. Farmers usually have done fertilization using a single inorganic fertilizers maximally to increase production in rainfed areas. The reason for the use of inorganic fertilizers by farmers because the the famers can count themselves comparison of N, P, and K that was needed, but economically use of inorganic fertilizers less efficient because it was needed in large quantities. To improve the nutrient availability, the use of organic material in rainfed areas is very effective. The use of organic materials are needed in improving soil physical and chemical characteristics. The addition of organic material can be done by utilizing the organic matter available on the land (in situ) such as rice straw or with the use of organic fertilizer manufacturing results. Utilization of organic material in situ has disadvantages such as slow release and was needed in large quantities so that combining with organic fertilizer manufacturing results was considered appropriate to improve soil fertility. Petroganik fertilizer is one of the organic fertilizer manufacturing results. The advantages of fertilizer petroganik among others high C-organic content, water content 4-8 % so efficient in transportation and storage, compatible for all types of soil and plants, and granular form so easy in application. In an effort to increase the absorption of nutrients by plants in rainfed areas it is necessary to restorations the physical and chemical characteristics of soil from rainfed areas. Absorption of N, P and K would be more effective when combined with organic fertilizer . The purposes of the research are: (1) to obtain a combination of the type and dose of organic fertilizer petroganik and rice straw compost are the best to restorations the physical and chemical characteristics of the soil and growth and black soybean production in rainfed areas, (2) to evaluate the residual effect of the use of organic fertilizers and rice straw compost and inorganic compound Phonska fertilizer to restorations the physical and chemical characteristics of the soil and growth and black soybean production in rainfed areas. The study was conducted with two stages of research, The first stage (research I) were the application of organic fertilizers petroganik and rice straw compost on black soybean and the second stages (research II ) were monitoring residual effects of research I on black soybean crops was combined with the addition of inorganic compound fertilizer. Research I and II was conducted in the Suka Makmur village, District of Binjai, Langkat as soybean production center in North Sumatra. Research used randomized block design factorial. The first factor are the rice straw compost (J), which consists of four levels ie: JO = 0 tonnes ha-1 (control); JI = 2 tones ha-1 ; 12 = 4 tones ha-1 and J3 = 6 tones ha-1 . The second factor is the organic fertilizer petroganik consist of 4 levels, ie: Go= 0 tonnes ha-1 ( control); G1 = 0.5 tones ha-1 ; G2 = 1 tones ha-1 and G3 = 1.5 tonnes ha-1 . Research II was prepared using split plot design with main plot are inorganic compound fertilizer applications with 4 levels, ie: 0 kg ha-1 (Ao), 200 kg ha-1 (A1), 250 kg ha-1 (A2) and 300 kg ha-1 (A3). While the subplot are residual effects from the first research with number 16 combinations. Thus was obtained 64 combinations of treatment and research was repeated 3 times. The first research results indicated that in general didn't significant effect from applications organic fertilizer on growth, physical and chemical characteristics of the soil. The addition of organic fertilizer petroganik on the research I can improved number of pods, production per plant, and production per plot. Best dose for fertilizing soybean crop in rainfed areas are 6 t ha- 1 rice straw compost+ 1.5 t ha-1 organic fertilizer petroganik. The second research results indicated that residues of organic fertilizer in the next planting season be able to improve the content of C-organic, total N, P20 5 soil extracts 25 % HCl, K20 soil extracts 25 % HCl. Residues of organic fertilizer and inorganic compound fertilizer as a singly treatment showed the significanly effect to increase the number of pods and soybean production but in treatment interaction didn't significanly effect although generally found increasing of production in the treatment of 6 t ha-1 rice straw compost + 1.5 t ha-1 organic fertilizer petroganik + 250 kg ha-1 inorganic compound almost doubled compared to the controls.