Terraced paddy field rainfall-runoff mechanism and simulation using a revised tank model

Terraced paddy fields play important roles in water and soil conservation because their water storage effect reduces and delays flood peaks. This study applies the terraced paddy field rainfall-runoff mechanism to the tank model. Though the traditional four-section tank model can easily simulate rainfall-runoff in a terraced paddy field, it has many parameters that are difficult to calibrate. To address the shortcomings of the traditional four-section tank model, this study develops a revised tank model to simulate rainfall-runoff. This study selects a terraced paddy field located in Hsuing-Pu village in Hsiuing-Chu County as the experimental field. The field under investigation was equipped with automatic monitoring stations, water-stage, and rain gauges. These stations collected data on rainfall and water flow to simulate the rainfall-runoff model in that region. To simulate the runoff behavior of the experimental terraced paddy field, two rainfall events were selected from the gathered data and five normal evaluation indexes based on static and hydrological theory were applied to calculate the results of simulation simultaneously. The revised tank model performed better than expected, and precisely predicted the variations and trends in flow charge. Comparison with representation indexes proved that the revised tank model is an appropriate and valuable tool for rainfall-runoff simulation.     

Systematic assessment of flood mitigation in a tank irrigated paddy fields area

Flood mitigation in irrigation tanks and paddy fields is their favorable aspect though its practical effect is not known very well. A dynamic and systematic approach is presented to assess flood mitigation in a tank irrigated paddy fields area in the worst case where no static buffer function is expected. Based on the linear control theory, transfer function models for runoff process in catchments are identified. Hydraulic models are developed to represent flood dynamics in irrigation tanks, paddy fields, and drainage channels. These models are integrated as an ordinary differential equations system. Then, using the perturbed linear system, flood mitigation in each component of the system is examined in terms of frequency response. An application example demonstrates that a tank irrigated paddy fields area has a significant flood mitigation effect as a low-pass filter. This method has the advantage of assessing flood mitigation even in the case of an increase in the total runoff ratio.     

Fate and transport of bensulfuron-methyl and imazosulfuron in paddy fields: experiments and model simulation

Experiments were conducted to determine the fate of bensulfuron-methyl (BSM) and imazosulfuron (IMS) under paddy conditions. Initially, laboratory experiments were conducted and the photolysis half-lives of the two herbicides were found to be much shorter than their hydrolysis half-lives in aqueous solutions. In the aerobic water?Csoil system, dissipation followed first-order kinetics with water half-lives of 9.1 and 11.0?days and soil half-lives of 12.4 and 18.5 days (first phase) and 35.0 and 44.1 days (second phase) for bensulfuron-methyl and imazosulfuron, respectively. However, the anaerobic soil half-lives were only 12.7 and 9.8?days for BSM and IMS, respectively. The values of K _d were determined to be 16.0 and 13.8 for BSM and IMS, respectively. Subsequent field measurements for the two herbicides revealed that dissipation of both herbicides in paddy water involved biphasic first-order kinetics, with the dissipation rates in the first phase being much faster than those in the second phase. The dissipation of bensulfuron-methyl and imazosulfuron in the paddy surface soil were also followed biphasic first-order kinetics. These results were then used as input parameters for the PCPF-1 model to simulate the fate and transport of BSM and IMS in the paddy environment (water and 1-cm surface soil layer). The measured and simulated values agreed well and the mass balance error during the simulation period was ?1.2 and 2.8% of applied pesticide, respectively, for BSM and IMS.     

APEX-Paddy model simulation of hydrology,total nitrogen,and rice yield for different agricultural activities in paddy fields

Paddy and Water Environment - Existing agro-hydrological models to explore the effects of paddy management practices on hydrology and water quality suffer from multiple shortcomings because they...     

Nitrous oxide emission measurement with acetylene inhibition method in paddy fields under flood conditions

Nitrous oxide (N₂O) emission from flooded rice paddy fields was continuously measured by the closed chamber method at an experimental plot in Thailand for a whole cultivation period. To characterize the N₂O emission with regard to the denitrification N loss, the C₂H₂ inhibition method was applied. Flood water on the soil greatly suppressed the N₂O emission. The N₂O emission was mitigated considerably by even a thin film of the flood water. The overall average N₂O emissions under flood conditions for one crop season (83 days) at the control site and the C₂H₂ treated site were 10.3 and 11.8 μg N m⁻² h⁻¹, respectively. The N₂O emission from the C₂H₂ treated site was consistently higher than that from the control site and the N₂O emission from both sites followed the same diurnal and seasonal variation pattern, indicating the effect of denitrification inhibition by the supplied C₂H₂. The N₂O emission enhanced along with temperature increase when NO₃–N concentration in the soil water was above 0.4 mg N l⁻¹ and soil temperature was above 24°C, suggesting specific temperature influence over the emission. The increase in NO₃–N concentration and temperature in the soil affected only the N₂O emission while the difference in the emission at the C₂H₂ treated site and the control site was not so much affected. It was suggested that most of the actively produced N₂O under higher NO₃–N concentration and temperature would likely to quickly emit to the atmosphere rather than to undergo further reduction to N₂.     

A preliminary investigation for Cu distribution in paddy soil and rice plants in contaminated paddy fields

Paddy and Water Environment - The soil sample of a paddy field was found to be contaminated by copper (Cu). The application of wastewater as the nitrogen fertilizer was identified as the cause in...     

A novel method for controlling rice blast disease using fan-forced wind on paddy fields

Rice blast disease is one of the obstacles of rice production not only in Japan but throughout rice producing countries. The effects of fan-forced wind on the incidence of rice blast disease were studied in two successive seasons. Electric fans (5 KW, 110-cm blade diameter) set on the ridge of paddy fields at a height 5 m from the ground level were used to artificially generate wind. In season 1, the fan operated twice daily for 30 min periods at 11:00 pm and 4:00 am from June 15 to September 1. The blocks of the paddy fields were divided into 6 zones according to wind speed and distance from the fan. The wind speed ranged from 2.0 to >7.3 m/s. The incidence of both rice leaf and panicle blast was significantly lower in the zones receiving wind between 2.6 and 7.3 m/s; however, the zone that received a velocity >7.3 m/s was severely affected by leaf and panicle blast. The zone that received the a wind speed of 2.6 m/s or lower exhibited an inefficient reduction of leaf and panicle blast disease, but it was better than in the control fields. In season 2, a wind-forced fan was applied from June 16 to September 9, with the velocity adjusted between ca. 3.0 and 6.0 m/s. The incidence and severity of leaf and panicle blasts (chuff, rachis-branch and neck blast) were efficiently reduced in the wind-treated fields. Fan-forced wind was more effective than the application of conventional chemical fungicides for controlling rice blast disease. These data demonstrate the potential of fan-forced wind for controlling rice blast disease.     

Optimization model for cropping-plan placement in paddy fields considering agricultural profit and nitrogen load management in Japan

An optimization model for cropping-plan placement on field plots is presented for supporting decision-making on agricultural management by a farming organization. The mixed 0?C1 programming technique is employed to select the next planting crop at each field plot in a holistic manner. Reduction of total nitrogen discharged from field plots to the downstream end of the drainage canals is expressed as an objective function of the model to balance an achievement of economic goal and environmental conservation. Some Japanese governmental policies on regulating rice cropping areas and on promoting production of particular upland field crops can be formulated in the model. A computational example of cropping-plan placement on field plots managed under integrated policies is given by operating the optimization model with various weights associated with the objectives. The procured trade-off curve and corresponding patterns of cropping-plan could be useful in the decision-making by the farming organization.     

A new method for assessing land leveling to produce high quality consolidated paddy fields

The quality of leveling of 0.3-ha consolidated paddy fields in Japan was investigated. The leveling of normal consolidated plots was accurate to within 7 cm from a horizontal plane, with an average standard deviation of about 18 mm for the points measured throughout the plot. The investigated paddy fields had inclinations ranging from horizontal to quite steep; the average inclination was 0.56‰ (1/1,718). The traditional assessment method is based on a horizontal plane. Because it is difficult to use this method to assess the leveling conditions of paddy fields that have an inclined surface, a new assessment method that accurately evaluates the sloped plane of a paddy field is proposed. The new method assesses the leveling conditions within a field by means of a "state index" that considers both the inclination and the surface roughness. Using this state index not only allowed the conditions to be effectively evaluated, but also helped reduce the extra workload needed to level the field to the farmers' requirements after the initial consolidation. Electronic Publication     

宁远县中低产稻田工程改良治理研究

1999～2000年．对宁远县刘家洞的129hm^2冷浸潜育型低产稻田进行了工程改良。根据本地实际。对工程中的沟渠整体布局、沟渠结构及规格进行了具体的设计。通过对比试验分析．改良后的稻田地下水位降低．水温和泥温升高，土壤养分含量增加，早晚稻产量均大幅度提高，取得了明显的治理效果。     

Model development for surface drainage loading estimates from paddy rice fields

A field experiment was performed at two Korean research sites to evaluate water and nutrient behavior in paddy rice culture operations for 2 years. One site was irrigated with groundwater, whereas the other site was irrigated with surface water. Both sites received average annual rainfall of about 1,300 mm, and about 70–80% of it was concentrated during July–September coinciding with rice growing season. Although most of the nutrient outflow was attributed to plant uptake, nutrient loss by surface drainage was substantial. The simplified computer model, PADDIMOD, was developed to simulate water and nutrient behaviors in the paddy rice field. The model predicts daily ponded water depth, surface drainage, and nutrient concentrations. It was formulated with a few equations and simplified assumptions, but its application and a model fitness test indicated that the simulation results reasonably matched the observed data. It is a simple and practical planning model that could be used to evaluate nutrient loading from paddy rice fields alone or in combination with other complex watershed models. Further validation might be required for general application of the PADDIMOD to the simulation of paddy rice fields with various agricultural environments.     

稻田油菜免耕直播密度与播种期探讨

为完善稻田油菜免耕直播技术，探讨其在本地的最适播种期和最佳密度，2002～2003年度在安乡进行了播期和密度试验。通过分析播期、密度与产量及其构成因素的关系，认为稻田油菜免耕直播在9月底到10月份均可播种，都能获得一定的产量，且播期越早，产量越高；播种密度以每公顷36万～45万株时为最佳。     

Modeling irrigation return flow for the return flow reuse system in paddy fields

This research is to construct a water balance model to estimate the amount of return flow in an irrigation system. A simple computation framework for the model was established to include various irrigation applications in cropping seasons. The model was able to estimate evapotranspiration, deep percolation into groundwater aquifer, and return flow. Return flow can be split into two parts, which are surface and subsurface return flows. The water balance model was then applied at the irrigation system (rotational block No. 11-2 of five paddy field units) which is operated by the Taoyuan Irrigation Association in Taiwan as an example. Two study cases were simulated, in which one was for using return flow and the other one was for using no return flow. The study period for the model simulations is the first rice cropping term in 2010 which was from February 16 to July 10. As a result, return flows calculated by the model were 27, 27, 34, and 39% of outflows for sandy loam, sandy clay, clay loam, and light clay soil, respectively. Irrigation water at the downstream field unit with use of return flow was supplemented by the upstream field units, and the amount is 5?C8% of irrigation water for using no return flow. Furthermore, it can be seen from the simulations that increases in irrigation water provide increases of return flow. Increases of irrigation water result in slight increases of subsurface return flow, while increases of irrigation water cause nearly none of change in deep percolation.     

Application of system dynamics approach for time varying water balance in aerobic paddy fields

Increasing water scarcity has necessitated the development of irrigated rice systems that require less water than the traditional flooded rice. The cultivation of aerobic rice is an effort to save water in response to growing worldwide water scarcity with the pressure to reduce water use and increase water productivity. An accurate estimation of different water balance components at the aerobic rice fields is essential to achieve effective use of limited water supplies. Some field water balance components, such as percolation, capillary rise and evapotranspiration, can not be easily measured; therefore a soil water balance model is required to develop and to test water management strategies. This paper presents results of a study to quantify time varying water balance under a critical soil water tension based irrigation criteria for the cultivation of non-ponded “aerobic rice” fields along the lower parts of the Yellow River. Based on the analysis and integration of existing field information on the hydrologic processes in an aerobic rice field, this paper outlines the general components of the water balance using a conceptual model approach. The time varying water balance is then analyzed using the feedback relations among the hydrologic processes in a commercial dynamic modeling environment, Vensim. The model simulates various water balance components such as actual evapotranspiration, deep percolation, surface runoff, and capillary rise in the aerobic rice field on a daily basis. The model parameters are validated with the observed experimental field data from the Huibei Irrigation Experiment Station, Kaifeng, China. The validated model is used to analyze irrigation application soil water tension trigger under wet, dry and average climate conditions using daily time steps. The scenario analysis show that to conserve scarce water resources during the average climate years the irrigation scheduling criteria can be set as −30 kPa average root zone soil water tension; whereas it can be set at −70 kPa during the dry years, however, the associated yields may reduce. Compared with the flooded lowland rice and other upland crops, with these two alternatives irrigation event triggers, aerobic rice cultivation can lead to significant water savings.     

Development of a user friendly water balance model for paddy

A water balance model for paddy is developed primarily based on the principle of conservation of mass of soil–water within the root zone. The water balance for paddy is different from that of field crops because paddy requires standing water in the field during most of its growth period. This model requires soil, crop and meteorological data as inputs. This user friendly model was developed using computer programmes C and Visual Basic (VB) 6.0. It simulates various water balance components such as evapotranspiration, deep percolation, surface runoff and depth of irrigation water and ponding depth in the field on a daily basis. For estimation of deep percolation loss, physically based saturated and unsaturated flow processes are incorporated into the model to consider ponding (if there is standing water in the field), saturation (if moisture content of soil is in between field capacity and saturation) and depletion (if moisture content of soil is below field capacity) phases of paddy field. This article presents development of a user friendly water balance model for paddy and also its validation using published data.     

A decision-making model for rice paddy cropping in an urbanizing area of the Lao PDR

In Southeast Asia, economic and population growth are expected in the near future. Rapid change is anticipated especially in the Lao PDR. Concern has been expressed that population growth will lead to an increased demand for food and economic growth to changes in the use of land. For food production to keep pace with the growth of population, it is very important to understand decision-making in rice paddy cultivation in urbanizing areas; for this reason, this study with the SEM model was conducted. The original data were collected by a questionnaire survey in some Lao villages; the survey included questions on various conditions, such as the availability of water in the dry season (irrigation), the access to a city, and job opportunities other than farming. The findings of the study demonstrate that the planting of a second rice crop was related to such factors as the productivity of rain-fed rice and cash crops and, most importantly, job opportunities other than farming.