INDONESIAN JOURNAL OF AGRICULTURAL SCIENCE

1-11

Authors: A. Wihardjakaa, S. Djalal Tandjungb, B. Hendro Sunarmintoc, and Eko Sugiharto

Incorporation of rice straw into soil is a common practice to improve soil productivity and increase inorganic fertilizer availability. However, this practice could contribute to methane (CH4) emission; one of the greenhouse gases that causes global warming. Nitrification inhibitors such as neem cake and carbofuran may reduce methane emission following application of rice straw. The study aimed to evaluate the application of rice straw and nitrification inhibitor to methane emission in rainfed lowland rice system. A factorial randomized block design was used with three replications. The first factor was rice straw incorporation (5 t ha-1 fresh straw, 5 t ha-1 composted straw), and the second factor was nitrification inhibitor application (20 kg ha-1 neem cake, 20 kg ha-1 carbofuran). The experiment was conducted at rainfed lowland in Pati, Central Java, during 2009/2010 wet season. Ciherang variety was planted as direct seeded rice with spacing of 20 cm x 20 cm in each plot of 4 m x 5 m. The rice straw was treated together with soil tillage, whereas nitrification inhibitor was applied together with urea application. Parameters observed were methane flux, plant height, plant biomass, grain yield, organic C content, and bacterial population in soil. The methane flux and soil organic C were measured at 25, 45, 60, 75, and 95 days after emergence. The results showed that composted rice straw incorporation significantly emitted methane lower (73.2 ± 6.6 kg CH4 ha-1 season-1) compared to the fresh rice straw (93.5 ± 4.0 CH4 ha-1 season-1). Application of nitrification inhibitors neem cake and carbofuran reduced methane emission as much as 20.7 and 15.4 kg CH4 ha-1 season-1, respectively. Under direct seeded rice system, methane flux level correlated with plant biomass as shown by linear regression of Y = 0.0015 X + 0.0575 (R2 = 0.2305, n = 27). This means that higher plant biomass produced more methane flux. The study indicates that application of nitrification inhibitors such as neem cake is prospective in decreasing methane emission from direct seeded rice cropping.

18-26

Authors: W. Setiawati, N. Gunaeni, T.S. Uhan, and A. Hasyim

Bemisia tabaci (Genn.) (Homoptera: Aleyrodidae) is one of the most serious pests on tomato. It is mainly controlled by chemical means, requiring some 25 sprays during the average growing season. The extensive and repeated use of insecticides has disrupted the natural balance between this pest and its natural enemies. In this study, Menochilus sexmaculatus F. was evaluated as a possible biological control agent of B. tabaci and its effect on gemini virus infestation. The study was conducted at the experimental station of the Indonesian Vegetables Research Institute (IVeGRI) in Lembang, West Java (1,250 m above sea level) from August to December 2008. The experimental plots consisted of 0.35 ha of tomato (± 100 m2 per plot) and spatially separated with four rows of maize (a minimum of 1 m) interplot distance to prevent cross-contamination among plots. The experiment was arranged in completely randomized block design with eight treatments and four replications. M. sexmaculatus were released at 24 days after planting. The treatments were designed according dosages and schedules at three released populations (i.e. 10 predators per plot, 20 predators per plot, and 10 predators per plot at vegetative stage followed by 20 predators per plot at generative stage); two places of release (center and edge of the plot); and two schedules of release (weekly and biweekly). Efficacy of the predator was measured in terms of the density of B. tabaci, both before and after release of the predator and its effect on gemini virus infestation. The result indicated the potential use of M. sexmaculatus to control B. tabaci and its effect on gemini virus infestation on tomato. Reductions in B. tabaci populations and subsequent tomato yields were significant. B. tabaci population in plots receiving 10 predators showed 73.62% and 75.75% reductions by the end of experiment. The incidence and intensity of gemini virus were consistently and significantly lowest and tomato yield gain was observed when 10 predators were released at weekly intervals. It is suggested that release of M. sexmaculatus against B. tabaci on tomato may be offered as an alternative solution to increase implementation of biologically-based B. tabaci management.

35-42

Authors: Dewa Ketut Sadra Swastika

Drying is a critical activity in rice postharvest handling. Any delay in drying will result in quality and quantity losses. Farmers and traders prefer to sell wet grain rather than dried grain of unhulled rice due to less attractive incentive for them to do drying. The study was conducted in Subang District, West Java, during March-June 2011 using survey method to analyze the financial feasibility of rice dryers. The respondents interviewed were 15 rice millers who have either sun-drying floor or mechanical dryer, or both. The main collected data were the investment cost, operational cost, maintenance cost, and the revenue of the dryers. The data were analyzed by using shortterm and long-term financial analyses to assess the profitability and feasibility of some drying technologies. The results showed that there were at least three drying technologies in the study area, namely sun-drying floor, flatbed dryer using gas fuel (gas dryer), and flatbed dryer using rice husk fuel (husk dryer). Under the mean capacity, the short-run MBCR of technological change from sun dryer to gas dryer was 1.29, while from sun dryer to husk dryer was 1.45. The long-run analysis showed that the IRRs were 44.44% for sun dryer, 233.47% for gas dryer, and 260.49% for husk dryer. These results showed that among the three drying technologies, husk dryer is the most profitable, most feasible, and most prospective to be adopted. Therefore, this type of dryer should be intensively promoted to the farmers’ group associations, rice traders, and rice millers. The government support in terms of rice dryers for farmers’ group associations should be focused on husk dryer.