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Water regimes play a central role in regulating methane (CH4) and nitrous oxide (N2O) emissions from irrigated rice field. Alternate wetting and drying (AWD) is a possible option, but there is limited information on its feasibility under local environmental conditions, especially for tropical region. We therefore carried out a 3-year experiment in a paddy field in Central Java, Indonesia to investigate the feasibility of AWD in terms of rice productivity, greenhouse gas (GHG) emission, and water use both in wet and dry seasons (WS and DS). The treatments of water management were (1) continuous flooding (CF), (2) flooding every when surface water level naturally declines to 15 cm below the soil surface (AWD), and (3) site-specific AWD with different criteria of soil drying (AWDS) established to find out the optimum for GHG emission reduction. Gas flux measurement was conducted by a static closed chamber method. Rice growth was generally normal and the grain yield did not significantly differ among the three treatments both in WS and DS. AWD and AWDS significantly reduced the total water use (irrigation + rainfall) as compared to CF. As expected, the seasonal total CH4emission was significantly reduced by AWD and AWDS. On average, the CH4emissions under AWD and AWDS were 35 and 38%, respectively, smaller than those under CF. It should be noted that AWD and AWDS were effective even in WS due partly to the field location on inland, upland area that facilitates the drainage. The seasonal total N2O emission did not significantly differ among the treatments. The results indicate that AWD is a promising option to reduce GHG emission, as well as water use without sacrificing rice productivity in this field. [ABSTRACT FROM PUBLISHER]

Recently, large areas of tropical peatland have been converted into agricultural fields. To be used for agricultural activities, peat soils need to be drained, limed and fertilized due to excess water, low nutrient content and high acidity. Water depth and amelioration have significant effects on greenhouse gas (GHG) production. Twenty-seven soil samples were collected from Jabiren, Central Kalimantan, Indonesia, in 2014 to examine the effect of water depth and amelioration on GHG emissions. Soil columns were formed in the peatland using polyvinyl chloride (PVC) pipe with a diameter of 21 cm and a length of 100 cm. The PVC pipe was inserted vertically into the soil to a depth of 100 cm and carefully pulled up with the soil inside after sealing the bottom. The treatments consisting of three static water depths (15, 35 and 55 cm from the soil surface) and three ameliorants (without ameliorant/control, biochar+compost and steel slag+compost) were arranged using a randomized block design with two factors and three replications. Fluxes of carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O) from the soil columns were measured weekly. There was a linear relationship between water depth and CO2emissions. No significant difference was observed in the CH4emissions in response to water depth and amelioration. The ameliorations influenced the CO2and N2O emissions from the peat soil. The application of biochar+compost enhanced the CO2and N2O emissions but reduced the CH4emission. Moreover, the application of steel slag+compost increased the emissions of all three gases. The highest CO2and N2O emissions occurred in response to the biochar+compost treatment followed by the steel slag-compost treatment and without ameliorant. Soil pH, redox potential (Eh) and temperature influenced the CO2, CH4and N2O fluxes. Experiments for monitoring water depth and amelioration should be developed using peat soil as well as peat soil–crop systems. [ABSTRACT FROM PUBLISHER]

The increasing human population requires greater rice production. However, rice cultivation contributes to global warming through greenhouse gas (GHG) emissions. Technologies for reducing GHG emissions in concert with the increased rice production from rice fields are needed. The objectives of this study were to evaluate the effects of steel slag applications on methane (CH4) and nitrous oxide (N2O) emissions and rice yields. Two study sites were established at the experimental farm belonging to Indonesian Agricultural Environment Research Institute (IAERI) in Jakenan and a farmer’s field in Wedarijaksa sub-district, Indonesia. Both field trials were conducted during the dry season (DS) of 2009 and the rainy season (RS) of 2009/2010. During the DS, a randomized block design was arranged with two treatments (a control and a steel slag application at 1 Mg ha−1), which were replicated five times. During the RS, the experimental plot with 1 Mg ha−1of steel slag treatment was split into two small sub-plots to accommodate the additional 1 and 2 Mg ha−1steel slag treatments. The results showed that there was a decreasing tendency in the CH4emissions at both sites and during both seasons after steel slag applications, although there was no statistical significance. During the RS in Jakenan, steel slag applications at rates of 1 and 2 Mg ha−1decreased the CH4emissions by 9.1 and 10.7%, respectively. In Wedarijaksa, steel slag applications at rates of 1 and 2 Mg ha−1decreased the CH4emissions by 12.6 to 18.7%, respectively. The N2O emissions were decreased by 34 and 38% following slag applications at the 2 Mg ha−1rate during the RS in Jakenan and Wedarijaksa, respectively. The iron content of steel slag could be used to reduce not only CH4but also N2O emissions. Increased level of electron acceptors suppresses CH4and N2O emissions. The application of steel slag at 1 and 2 Mg ha−1increased rice grain yields by approximately 4.8–5.6% in Jakenan and 0.3–4.7% in Wedarijaksa. It might be better to apply steel slag at higher rates for more than two growing seasons to reach reduction in CH4and N2O emissions. [ABSTRACT FROM AUTHOR]

Rainfed rice production needs to contribute more to the current and future world food security due to the increasing competition for limited water supplies including irrigation water. However, it is vulnerable to climate variabilities and extremes hence the utilization of climate predictions is crucial. In this study, the predictive accuracy and applicability of a seasonal climate predictions (SINTEX-F) were evaluated for rainfed rice areas where climate uncertainties are main constraints for a stable and high production. Outputs from SINTEX-F such as daily rainfall, maximum and minimum air temperatures, and wind speed were tested for Indonesia and Lao PDR through the cumulative distribution function-based downscaling method (CDFDM), which is a simple, flexible and inexpensive bias reduction method through removing bias from the empirical cumulative distribution functions of the GCM outputs. The CDFDM outputs were compared with historical weather data. Obtained results showed that discrepancies between SINTEX-F and the historical weather data were significantly reduced through CDFDM for both sites. ORYZA, an ecophysiological rice growth model that simulate agroecological rice growth processes, was used to evaluate the applicability of the SINTEX-F for grain yield predictions. Obtained results from on-farm field validation showed that the predicted grain yield was close to the actual grain yield that was obtained through optimum sowing timing given by the predictions. A normalized root mean square error between predicted and actual grain yield showed satisfactory model fit in predictions. This implies that SINTEX-F was applicable for improving rainfed rice production through CDFDM. However, CDFDM has a limitation in orographic precipitation, the high-resolution daily weather data or a sophisticated special interpolation method should be considered in order to improve the representation of the geographical pattern for the parameters derived from CDFDM. [ABSTRACT FROM AUTHOR]