Characteristics of water balance in a rainfed paddy field in Northeast Thailand

Rice productivity in rainfed paddy fields varies with seasonal changes of water availability in which the conditions of flooding are affected by the water balance. Hydrometeorological measurements were performed in a rainfed paddy field in Northeast Thailand from July 2004 to December 2006 to analyze the water balance. As a result of our measurements, climatologically conditions were classified as semi-humid with an annual precipitation of 1,100 mm/year and annual potential evaporation of 1,660 mm/year in both the year. The surface layer of the paddy soil was clayey and the hydraulic conductivity was very low, so groundwater levels remained below the soil surface even under flooded conditions during the rainy season. Seasonal changes in the amount of soil water were very small, comprising only less than 16% of the total precipitation during the rainy season. Consequently, an effective precipitation of less than 180 mm was enough to establish standing water in the rainfed paddy field. Shinkichi Goto, Tsuneo Kuwagata and Pisarn Konghakote contributed equally to the paper.     

Nitrogen and phosphorus runoff modeling in a flat low-lying paddy cultivated area

Chiyoda basin is located in Saga Prefecture in Kyushu Island, Japan, and lies next to the tidal compartment of the Chikugo River to which the excess water in the basin is drained away. Chiyoda basin has a total area of about 1,100 ha and is a typical flat and low-lying paddy-cultivated area. The main environmental issue in this basin is total nitrogen (TN) and total phosphorus (TP) load management because TN and TP, which loaded from farmlands, degrade surface water as a result of anthropogenic eutrophication. This paper presents a mathematical model of TN and TP runoff during an irrigation period in Chiyoda basin in order to elucidate the pollutant fluxes that accompany water transportation in paddy fields and drainage canals, and to evaluate pollutant removal from the study area to the Chikugo River. First, the water flow and the algorithm of gate operation were simulated by a continuous tank model and the accuracy of the model was then evaluated by comparing the simulated water levels with observed ones during an irrigation period. The observed and simulated water levels were in good agreement, indicating that the proposed model is applicable for drainage and water supply analyses in flat, low-lying paddy-cultivated areas. Second, the TN and TP runoff during an irrigation period was simulated based on the TN and TP loads that were determined by observed data in paddy fields. For TN runoff, the simulated results and observed data were in good agreement whereas for TP runoff, the simulated results were higher than the observed data. However, if the settled TP within the paddy tank was calculated as 6%, then the simulated results and the observed data were in good agreement. We concluded that TN runoff from paddy field to the drainage canal system was not affected much by the sediment related process. The present study could provide farmers and managers with a useful tool for controlling the water distribution in an irrigation period, and the TN and TP loads in the downstream area as well as the Chikugo River.     

Nitrogen and phosphorus leaching losses from paddy fields with different water and nitrogen managements

While many water-saving rice production techniques have been adopted in China, the environmental effects of these techniques require further investigation. This study aims to assess nitrogen (N) and phosphorus (P) leaching losses under real conditions in different water and N managements. Two water and three N treatments are conducted in the Taihu Lake region of China. Results show that the total N leaching losses during the rice season under flooding irrigation (FI) are 12.4, 9.31, and 7.17 kg ha⁻¹ for farmers’ fertilization practices (FFP), site-specific N management (SSNM), and controlled-release nitrogen fertilizer management (CRN), respectively. Under controlled irrigation (CI), the respective losses were 7.40, 5.86, and 3.79 kg ha⁻¹ for the same management methods. The total P leaching losses during the rice season under FI were 0.939, 0.927, and 0.353 kg ha⁻¹ for FFP, SSNM, and CRN, respectively. Under CI, the losses were 0.424, 0.433, and 0.279 kg ha⁻¹, respectively, for the same management methods. Ammonium and nitrate N accounted for 42.2–65.5% and 11.8–14.7% of the total nitrogen leaching losses under different water and N management methods, respectively. Due to significant decrease of volumes of percolation water and nitrogen and phosphorus concentrations in percolation water, N and P leaching losses were reduced in the CI treatment compared to the FI treatment under the same N management. The reduction of N input and application of controlled-release nitrogen fertilizer can reduce N and P leaching losses from paddy fields.     

Reduction of effluent nitrogen and phosphorus from paddy fields

In order to reduce nitrogen and phosphorous loads flowing out from paddy fields, the effects of no-puddling and coated fertilizer were examined. First, pot examination was performed in order to clarify the influence of puddling on nitrogen and phosphorous concentration in the ponding water on paddy soils. The experiment was conducted three times under the condition of puddling or no-puddling, as the condition of fertilizing or no-fertilizing. By using the result, the storage term of the ponding water after puddling was considered for four soils.Next, a field experiment was conducted to compare the effect of the coated urea division with the conventionally cultivated division and the no-fertilizing division. By using coated urea, it was possible to reduce the amount of nitrogen fertilizer to about 60% of the conventionally cultivated division; thus, it showed clearly that coated urea has a great effect on reducing effluent nitrogen. Although there was less yield of hulled rice than that of the conventionally cultivated division, it was proven by the palatability test that the flavor of the rice from the coated urea division was better than that of the conventionally cultivated division rice.     

闽江河口区稻田土壤和植物的C、N、P含量及其生态化学计量比

选取闽江河口区稻田为研究区域,对土壤和植物的C、N、P含量及其生态化学计量比进行测定和分析。研究表明：土壤C、N、P元素的变化范围分别为5.72-13.41、0.47-0.82和0.33-0.89 mg.g-1,平均值分别为9.50、0.62和0.56 mg.g-1,其C与N、C与P、N与P的比值分别为12.18-16.39、15.07-24.34和0.92-1.55,平均值分别为15.05、17.88和1.20;植物C、N、P元素的变化范围分别为28.62-38.99、0.65-1.52和0.13-0.32 mg.g-1,平均值分别为35.21、1.19、0.25 mg.g-1,其C与N、C与P、N与P的比值分别为24.54-44.10、94.05-258.93和2.13-10.55,平均值分别为32.11、160.07和5.47。土壤C、N含量低于植物,而P含量却高于植物,C与N、C与P、N与P的比值则表现为土壤低于植物。     

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.     

Analysis of runoff in the Han River basin by SSARR model considering agricultural water

This study begins to address the need for a runoff model that is able to simulate runoffs at control points in a dam’s upper and lower stream during the seasons of high and low water levels. We need to establish a synthetic management plan on water resources considering the runoff at the upper and lower streams to effectively manage the limited water resources in Korea. For this reason, we classified the Han River Basin into 24 sub-basins and arranged a great amount of rainfall data using 151 rainfall observation stations so as to prepare for the spatial distribution of precipitation. We chose several dams as subjects for this study, which includes the Chungju Regulating Reservoir, Soyang, Chungju, Hoengseong, Hwacheon, Chuncheon, Euiam, Cheongpyeong, and Paldang Dams as main controlling points. Also, we made up input data of this model, selecting the Streamflow Synthesis and Reservoir Regulation (SSARR) model as a runoff model in the Han River Basin. We performed a sensitivity analysis of parameters using hydrological data from the year 2002. And as a result, the findings of this study showed that, among many parameters related to the basin runoff, the following have revealed greater sensitivity than any other parameters: soil moisture index-runoff percent, baseflow infiltration index-baseflow percent, and surface-subsurface separation. On the basis of the above sensitivity analysis, we have used hydrological data between 2001 and 2002 when drafts and floods broke out in Korea to verify and calibrate the parameters of the SSARR model. Furthermore, we verified and calibrated the 2000 data using corrected parameters and performed an analysis of annual water balance in the Han River Basin from 1996 to 2005 considering agricultural water.     

Predicting water surface evaporation in the paddy field by solving energy balance equation beneath the rice canopy

The energy flux on the ground surface depends not only on climatological and biophysical controls in the vegetative canopy, but also on the available energy and energy partitioning beneath the canopy. Quantifying the evaporation and energy partitioning beneath the canopy is very important for improving water and energy utilization, especially in arid areas. In this study, we measured meteorological data, the net radiation and latent heat flux beneath the rice canopy, and then applied the radiation and energy balance equations to get the water surface temperature beneath the rice canopy. To apply the equations, we constructed shortwave and longwave radiation beneath the canopy sub-models and a bulk transfer coefficient sub-model. A plant inclination factor was parameterized with plant area index for the shortwave and longwave radiation sub-models. Bulk transfer coefficient was parameterized by plant area index and soil heat flux was predicted by the force restore model. With calculated water surface temperature and constructed sub-models, we reproduced net radiation and latent heat flux beneath the rice canopy. As a result, the reproduced water surface temperature, net radiation, and latent heat flux beneath the rice canopy were very close to the measured values and no significant differences were found according to 2-tail t test statistical analysis. Therefore, we conclude that these constructed sub-models could successfully represent water surface temperature, net radiation, and latent heat flux beneath the rice canopy.     

Study on the water and nitrogen balance in paddy fields with irrigation and drainage dual-purpose channel mode using the tank model

Paddy and Water Environment - In South China’s paddy irrigation area, irrigation and drainage dual-purpose channel mode (IDDCM) is applied to conserve farmland resources in rice cultivation...     

Evaluation of N and P mass balance in paddy rice culture along Kahokugata Lake, Japan, to assess potential lake pollution

Kahokugata Lake, a closed lake, has been subject to eutrophication. This research was conducted to clarify the actual phenomena and evaluation of the discharges of N and P from paddy test fields in the lowlands into Kahokugata Lake. A comprehensive mass balance of N and P was obtained from 4 years of study. About N, the mean value of harvested unhulled rice (79.9 kg/ha) was greater than mean controlled release fertilizer inputs (56.7 kg/ha). Other inputs and outputs include N in atmospheric acid deposition (21.4 kg/ha) and N fixation–denitrification (9.2 kg/ha). The rice straw recycled after harvest was balanced by straw produced in the succeeding year. The runoff and percolation losses discharged into the lake was 11.3 kg/ha, (8.6% of total inputs). Since the rice harvested was consumed domestically, which taking out from the farmland and, therefore, nitrogen pollutant into the lake was becoming small, paddy rice at this site is considered an “anti-polluting, purifying or cleansing” crop. The P content in harvested rice (39.4 kg/ha) was balanced by fertilizer inputs (36.4 kg/ha). Previous studies examining inflow–outflow relationships without considering a comprehensive mass balance may lead to erroneous conclusions. Our findings indicate paddy rice in lowlands could be an environmentally friendly crop and can play an important role in reducing pollution of lakes, and therefore should be considered in land use planning.     

Modeling of water and nitrogen balance in the ponded water of rice fields

A water and nitrogen balance model for the surface ponded water compartment of rice fields was developed. The model estimates the daily ponded water depth and the daily losses and the uses of NH₄–N and NO₃–N in their transformation processes. The model was applied with data obtained from two rice fields during 2005 at Thessaloniki plain in northern Greece. Significant amounts of applied irrigation water were lost with the surface runoff and deep percolation to groundwater. The gaseous losses of nitrogen (volatilization and denitrification) and nitrogen uptake by algae were the main processes of nitrogen reduction in the ponded water of rice fields. The study showed that the system of a rice field is a natural system where an important amount of influent nitrogen applied by irrigation water can be reduced. These processes decrease the possibilities of water resources contamination.     

Reduction of nitrogen,phosphorus, and suspended solids effluent loads from paddy fields by transplanting into retained ponding water using a GNSS-controlled rice transplanter

Paddy and Water Environment - We measured nutrient inflows and outflows on reclaimed land (157 km2, including 100 km2 of paddy fields) in Lake Hachiro. The net effluent loads...     

Storing and removing nitrogen in drainage from paddy field by using aquatic crops wetland

Paddy and Water Environment - Aquatic crop (Zizania latifolia Stapf–Ipomoea aquatica Forsk) wetlands were constructed to remove nitrogen (N) in drainage from paddy rice fields, with three...     

Clarification of adsorption and movement by predicting ammonia nitrogen concentrations in paddy percolation water

We noted that ammonia nitrogen was not adsorbed by the cultivated layers of highly permeable paddy fields during the initial fertilization period, but reached the lower layers relatively early. In our study, we considered an exponential equation from an aqua-environmental perspective with the goal of obtaining good growth of rice plants in order to estimate the concentrations and integrated volume of ammonia nitrogen accompanying paddy percolation. Using this exponential equation, we were able to derive a relation between time and concentrations of paddy percolation water, and hypothesized that if percolation rates were less than 10 mm/day, percolation would have no effect on rice growth, while simultaneously helping to maintain the good water quality of the extra-paddy environment. We also clarified the differences between the potential ammonia nitrogen adsorption volume derived from the CEC value and the integrated amount of ammonia nitrogen water in soil, and considered the causes from the perspectives of solute movement and water movement. Electronic Publication     

Numerical simulation on effect of irrigation conditions on water temperature distribution in a paddy field

Water management methods regulate water temperature in paddy fields, which affects rice growth and the environment. To understand the effect of irrigation conditions on water temperature in a paddy field, water temperature distribution under 42 different irrigation models including the use of ICT water management, which enables remote and automatic irrigation, was simulated using a physical model of heat balance. The following results were obtained: (1) Irrigation water temperature had a more significant effect on paddy water temperature close to the inlet. As the distance from the inlet increased, the water temperature converged to an equilibrium, which was determined by meteorological conditions and changes in water depth. (2) Increasing the irrigation rate with higher irrigation water amount increased the extent and magnitude of the effects of the irrigation water temperature. (3) When total irrigation water amount was the same, increasing the irrigation rate decreased the time-averaged temperature gradient effect over time across the paddy field. (4) Irrigation during the lowest and highest paddy water temperatures effectively decreased and increased the equilibrium water temperature, respectively. The results indicate that irrigation management can be used to alter and control water temperature in paddy fields, and showed the potential of ICT water management in enhancing the effect of water management in paddy fields. Our results demonstrated that a numerical simulation using a physical model for water temperature distribution is useful for revealing effective water management techniques under various irrigation methods and meteorological conditions.

     

Prediction of the environmental concentration of pesticide in paddy field and surrounding surface water bodies

Pesticides are very important in European rice production. For appropriate environmental protection, it is useful to predict the potential impact of pesticides after application, in paddy fields, in paddy runoff, and in the surrounding water, by calculating predicted environmental concentrations (PECs). In this paper, a joint simulation is described, coupling a field-scale pesticide fate model (RICEWQ) and a transportation model (RIVWQ) to evaluate the potential for predicting environmental concentrations of pesticides in the paddy field and adjacent surface water bodies and comparing the predicted values with the monitoring data. The results demonstrate that the application of the calibrated field-scale RICEWQ model is a conservative method to predict the PEC at the watershed level, overestimating the observed data; the coupled RICEWQ and RIVWQ models could be adequately used to predict PECs in the surrounding water at watershed level and in the higher tier risk assessment procedure.     

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.     

Estimation of supplementary water to paddy fields in the lower Mekong River basin during the dry season

Efficient management of water resources in paddy fields requires an understanding of the volume of supplementary water used. However, quantifying the volume is laborious due to the large amount of data that must be collected and analyzed. The purpose of our study was to estimate the volume of supplementary water used in paddy fields, based on several years of available statistical data, and to provide information on how much water can be supplied to paddy fields in each target area. In this study, the lower Mekong River basin of northeast Thailand, Laos, and Cambodia was selected as the study area. In the first step, we used agricultural statistics for each country, rainfall data acquired from the Mekong River Commission Secretariat (MRCS), and the value of virtual water required per unit of rice production. Because several years of data were used for dry season harvested areas and rice production in each country, the supplementary water to paddy fields in each province was calculated using virtual water and rainfall. This method made it possible to estimate changes in supplementary water in each province. Through this study, the supplementary water to paddy fields during the dry season in three countries was approximated from the minimum number of data sets. Moreover, for cases in which it is not possible to procure agricultural water use data for a hydrological model simulation, an alternative solution is proposed.