SEDIMENT TRAPPING BY TERRACED PADDY FIELD ON SLOPPING AGRICULTURAL LAND

Terraced paddy field is not only important for rural food security, but also for trapping sediment in the slopping land. The aims of this research were to quantify the amount of incoming and outgoing sediments and to study sediment movement behavior during harrowing and fertilizing under traditional irrigation of terraced paddy field system. This study was carried out at Keji Village, Semarang District, Central Java during two cropping seasons, a wet season 2003/04 and a dry season 2004. A paddy field with eight terraces was selected. The terraces were flat, different in size and descending to the river. Sediment samples were taken at harrowing and fertilizing activities. The results indicated that at harrowing, outgoing sediment was higher than incoming both during the wet and the dry seasons. About 0.53 and 0.27 t ha-1 day-1 of soil were eroded during harrowing in the wet and the dry seasons, respectively. However, a week before and after fertilizing, both in the wet and the dry seasons, the amounts of incoming sediment were higher than the outgoing one. In the wet season, the amounts of incoming sediments were three to four times higher than the outgoing one, both a week before and after fertilizing. During the wet season, about 0.31 and 0.34 t ha-1 day-1 of sediment was yielded a week before and after fertilizing, respectively. During the dry season, the incoming sediments were ten times higher than the outgoing one. On an average the sediment yields were about 0.07 and 0.08 t ha-1 day-1 a week before and after fertilizing, respectively. Terraces having greater areas deposited more sediment than those with smaller sizes. During a week before and after first fertilizing, the total amounts of incoming sediments were 6.44 and 1.19 t ha-1 for the wet and dry seasons, while that of outgoing sediments were 1.89 and 0.14 t ha-1 for the wet and dry seasons, respectively. This indicates that terraced paddy fields are not only producing rice, but also providing environmental service in term of sediment trapping. This external service minimizes sedimentation in the downstream.

Review of catalytic systems and thermodynamics for the Guerbet condensation reaction and challenges for biomass valorization

The Guerbet condensation reaction is an alcohol coupling reaction that has been known for more than a century. Because of the increasing availability of bio-based alcohol feedstock, this reaction is of growing importance and interest in terms of value chains of renewable chemical and biofuel production. Due to the specific branching pattern of the alcohol products, the Guerbet reaction has many interesting applications. In comparison to their linear isomers, branched-chain Guerbet alcohols have extremely low melting points and excellent fluidity. This review provides thermodynamic insights and unravels the various mechanistic steps involved. A comprehensive overview of the homogeneous, heterogeneous and combined homogeneous and heterogeneous catalytic systems described in published reports and patents is also given. Technological considerations, challenges and perspectives for the Guerbet chemistry are discussed

Modelling water-harvesting systems in the arid south of Tunisia using SWAT

In many arid countries, runoff water-harvesting systems support the livelihood of the rural population. Little is known, however, about the effect of these systems on the water balance components of arid watersheds. The objective of this study was to adapt and evaluate the GIS-based watershed model SWAT (Soil Water Assessment Tool) for simulating the main hydrologic processes in arid environments. The model was applied to the 270-km(2) watershed of wadi Koutine in southeast Tunisia, which receives about 200 mm annual rain. The main adjustment for adapting the model to this dry Mediterranean environment was the inclusion of water-harvesting systems, which capture and use surface runoff for crop production in upstream subbasins, and a modification of the crop growth processes. The adjusted version of the model was named SWAT-WH. Model evaluation was performed based on 38 runoff events recorded at the Koutine station between 1973 and 1985. The model predicted that the average annual watershed rainfall of the 12-year evaluation period (209 mm) was split into ET (72%), groundwater recharge (22%) and outflow (6%). The evaluation coefficients for calibration and validation were, respectively, R-2 (coefficient of determination) 0.77 and 0.44; E (Nash-Sutcliffe coefficient) 0.73 and 0.43; and MAE (Mean Absolute Error) 2.6 mm and 3.0 mm, indicating that the model could reproduce the observed events reasonably well. However, the runoff record was dominated by two extreme events, which had a strong effect on the evaluation criteria. Discrepancies remained mainly due to uncertainties in the observed daily rainfall and runoff data. Recommendations for future research include the installation of additional rainfall and runoff gauges with continuous data logging and the collection of more field data to represent the soils and land use. In addition, crop growth and yield monitoring is needed for a proper evaluation of crop production, to allow an economic assessment of the different water uses in the watershed

Sediment Trapping By Terraced Paddy Field On Slopping Agricultural Land

Terraced paddy field is not only important for rural food security, but also for trapping sediment in the slopping land. The aims of this research were to quantify the amount of incoming and outgoing sediments and to study sediment movement behavior during harrowing and fertilizing under traditional irrigation of terraced paddy field system. This study was carried out at Keji Village, Semarang District, Central Java during two cropping seasons, a wet season 2003/04 and a dry season 2004. A paddy field with eight terraces was selected. The terraces were flat, different in size and descending to the river. Sediment samples were taken at harrowing and fertilizing activities. The results indicated that at harrowing, outgoing sediment was higher than incoming both during the wet and the dry seasons. About 0.53 and 0.27 t ha-1 day-1 of soil were eroded during harrowing in the wet and the dry seasons, respectively. However, a week before and after fertilizing, both in the wet and the dry seasons, the amounts of incoming sediment were higher than the outgoing one. In the wet season, the amounts of incoming sediments were three to four times higher than the outgoing one, both a week before and after fertilizing. During the wet season, about 0.31 and 0.34 t ha-1 day-1 of sediment was yielded a week before and after fertilizing, respectively. During the dry season, the incoming sediments were ten times higher than the outgoing one. On an average the sediment yields were about 0.07 and 0.08 t ha-1 day-1 a week before and after fertilizing, respectively. Terraces having greater areas deposited more sediment than those with smaller sizes. During a week before and after first fertilizing, the total amounts of incoming sediments were 6.44 and 1.19 t ha-1 for the wet and dry seasons, while that of outgoing sediments were 1.89 and 0.14 t ha-1 for the wet and dry seasons, respectively. This indicates that terraced paddy fields are not only producing rice, but also providing environmental service in term of sediment trapping. This external service minimizes sedimentation in the downstream

Determinação de coeficientes de cultura para o milho durante um experimento de evapotranspiração em um oxisol do Brasil

Soil water balance components were measured during two periods (from 1989 to 1991) on a Dark Red Latosol (oxisol) in Piracicaba,SP, Brazil. The change in soil water storage and the soil water fluxes at the lower limit of the rooting zone were calculated for a transect of 25 observation plots. Hydraulic head gradients were determined by tensiometer measurements. Soil water flux densities were estimated through Darcy's equation. The actual evapotranspiration of the crops and weeds and the actual evaporation of bare soil were obtained from the water balance equation and this for two periods under different crop rotations. For the first period the sequence was bare soil-corn-weeds and for the second period it was stubble mulch-weeds-corn. For assessing the crop coefficients the potential evapotranspiration was calculated according to two different methods. The first method was based on the modified Penman equation with grass as a reference crop, to obtain this way reference coefficients, and the second method was based on the pan "A" evaporation data in order to obtain pan coefficients. These coefficients were compared with the tabulated crop coefficients. In general when there was no shortage of water during the corn growth, the crop coefficients k c"A" and k c ref were very close to the k c values.Os componentes do balanço hídrico foram medidos durante dois períodos (de 1989 a 1991) em terra roxa estruturada, em Piracicaba,SP, Brasil. As variações de armazenamento de água e os fluxos de água no solo no limite inferior da zona radicular foram calculados para uma transeção de 25 parcelas experimentais. Gradientes hidráulicos foram determinados por meio de medidas tensiométricas. Densidades de fluxo de água foram estimadas através da equação de Darcy. A evapotranspiração atual das culturas e das ervas daninhas e a evaporação atual do solo nú foram obtidas da equação do balanço hídrico, para dois períodos, sob diferentes rotações de cultura. Para o primeiro período a seqüência foi solo nú - milho - ervas daninhas e para o segundo cobertura morta - ervas daninhas - milho. Para determinar os coeficientes de cultura, a evapotranspiração potencial foi calculada por dois métodos. O primeiro foi baseado na equação de Penman modificada, com a grama como cobertura de referência, obtendo assim os coeficientes de referência, e o segundo baseado no tanque de evaporação tipo classe "A", obtendo os coeficientes de tanque. Estes coeficientes foram comparados com os coeficientes de cultura tabulados. De uma forma geral, em períodos sem falta de água para a cultura, os coeficientes de referência e de tanque se assemelharam bastante aos coeficientes de cultura

Using an inverse modelling approach to evaluate the water retention in a simple water harvesting technique

In arid and semi-arid zones, runoff harvesting techniques are often applied to increase the water retention and infiltration on steep slopes. Additionally, they act as an erosion control measure to reduce land degradation hazards. Nevertheless, few efforts were observed to quantify the water harvesting processes of these techniques and to evaluate their efficiency. In this study, a combination of detailed field measurements and modelling with the HYDRUS-2D software package was used to visualize the effect of an infiltration trench on the soil water content of a bare slope in northern Chile. Rainfall simulations were combined with high spatial and temporal resolution water content monitoring in order to construct a useful dataset for inverse modelling purposes. Initial estimates of model parameters were provided by detailed infiltration and soil water retention measurements. Four different measurement techniques were used to determine the saturated hydraulic conductivity (<I>K</I><sub>sat</sub>) independently. The tension infiltrometer measurements proved a good estimator of the <I>K</I><sub>sat</sub> value and a proxy for those measured under simulated rainfall, whereas the pressure and constant head well infiltrometer measurements showed larger variability. Six different parameter optimization functions were tested as a combination of soil-water content, water retention and cumulative infiltration data. Infiltration data alone proved insufficient to obtain high model accuracy, due to large scatter on the data set, and water content data were needed to obtain optimized effective parameter sets with small confidence intervals. Correlation between the observed soil water content and the simulated values was as high as <I>R</I><sup>2</sup>=0.93 for ten selected observation points used in the model calibration phase, with overall correlation for the 22 observation points equal to 0.85. The model results indicate that the infiltration trench has a significant effect on soil-water storage, especially at the base of the trench

Enrichment of Organic Carbon in Sediment Transport by Interrill and Rill Erosion Processes

Erosion and loss of organic carbon (OC) result in degradation of the soil surface. Rill and interrill erosion processes on a silt loam soil were examined in laboratory rainfall and flume experiments. These experiments showed that rill and interrill erosion processes have contrasting impacts on enrichment of OC in transported sediment. Rill erosion was found to be nonselective, while for interrill erosion the enrichment ratio of OC, EROC, varied between 0.9 and 2.6 and was inversely related to the unit sediment discharge. At unit sediment discharge values >0.0017 kg s(-1) m(-1), the EROC remained equal to 1. The enrichment process was not influenced by raindrop impact. Enrichment of OC by "aggregate stripping" was found to be unimportant in our study. This was attributed to the low aggregate stability of the soil and the equal distribution of OC within the different soil aggregate classes