Evaluation of the effects of irrigation water on groundwater budget by a hydrologic model

Paddy and Water Environment - Groundwater is a valuable water resource, and it is used for domestic, industrial or agricultural use around the world. Especially, water use in paddy fields is very...     

Determination of the magnitudes and values for groundwater recharge from Taiwan's paddy field

Flooded paddy fields have many functions, including not only rice production, and ecological and environmental conservation. This work estimates the extent of paddy field infiltration in Taiwan by adopting a one-dimensional Darcy-based soil/water balance model SAWAH (Simulation Algorithm for Water Flow in Aquatic Habitats). A 10 cm thick plow sole layer with a hydraulic conductivity of 0.03 cm/day, coupled with the soil texture and irrigation data obtained from 15 irrigation associations, is used to estimate the volumetric amount of annual infiltration in Taiwan. Simulation results from SAWAH indicate that the plow sole layer controls the movement of infiltrated water, with a rate about 1.8 billion cubic meters annually. The estimated infiltration rate of 1.8 billion m³/yr comprises more than 40% of the annual infiltration recharge to ground water in Taiwan. Additionally, the amount of infiltration recharge to groundwater is equivalent to 20 billion Taiwan dollars NT$ (or 0.65 billion US$) while the yearly rice crop production is 35 billion NT$ (or 1.13 billion US$). It is evident that the infiltration from rice paddy is of great importance to the economy, environment, and water resources conservation in Taiwan.     

Experimental study on soil erosion characteristics in flooded terraced paddy fields

This experimental study assesses the effects of event rainfall on soil erosion characteristics in terraced rice paddy fields. A 0.75-ha terraced paddy field located in Northern Taiwan was used to investigate the soil erosion under the regular cultivation of rice during two crop seasons. The environmental changes were investigated in the neighboring areas in which terraced paddy fields have been converted to other land usages. The annual rate of soil erosion calculated from the observed rainfall runoff and suspended solid contained was 0.77 ton/ha, which is significantly less than the erosion rate associated with upland crop cultivation reported by other research conducted in Taiwan. Experimental results also showed that the terraced paddy field retained the highest percentages of clay, silt, and organic matter's content, as compared to those of other upland crops, indicating that the topsoil was less susceptible to rainfall erosion under flooded conditions of rice-cultivation. The results of this study show that the rice-planted terraced paddy offers the highest level of soil conservation. The function of soil and water conservation in terraced paddy fields could be further increased by effective maintenance of embankment and to raise the height of the bund. Poor management, abandoned cultivation, and converse to other upland crops of terraced paddy fields are regarded as major contributors to increased soil erosion in mountainous areas. The government in Taiwan should formulate effective measures and maintain sustainable rice cultivation in the terraced paddies.     

Impact of climate change on paddy field irrigation in southern Taiwan

Climate change can have a serious impact on water resources. The main agricultural product in southern Taiwan is rice, the planting of which consumes far more water than other crops. This makes agriculture in Taiwan especially vulnerable to climate change. In this study, we used the generalized watershed loading functions (GWLF) hydrological model to simulate the discharge of the Kaoping River under climate change scenarios A2 and B2 as released by the Intergovernmental Panel on Climate Change. We discussed the potential impact of climate change on water resources based on the results of GWLF simulations carried out using rainfall and temperature data from five general circulation models (GCMs). The simulation results indicate that river discharge in the wet season increases significantly, and decreases in the dry season. The discharge variations from using the various GCMs as inputs fall within the range of ?26 to +15 % for the dry season and ?10 to +82 % for the wet season. The variation in available water will seriously impact the first period rice farming (the period between the beginning of January and the end of May) in southern Taiwan. Consequently, effective reduction in conveyance loss in the irrigation canal systems and proper fallowing of paddy fields will be the main challenges to Taiwan’s agricultural sector for alleviating the impact of climate change. For further decision making, we show the effects of adapting to climate change by various degrees of the following two methods: fallowing paddy fields to various degrees and reducing conveyance loss in irrigation canal systems.     

Assessment of the camellia seed meal impact on loaches in paddy fields

In Taiwan, Camellia seed meal is often sprayed on rice paddies during rice transplantation season to stop the growth of Pomacea canaliculata. However, the application of camellia seed meal endangers muciferous mollusks and fishes in paddy fields. Though researchers have examined the effects of the saponin in the camellia seed meal on Pomacea canaliculata, previous studies ignore the effects of saponin on fish. Loaches often inhabit the rivers, lakes, ponds, paddy fields, and canals of low elevation where there have muddy layer with plant chips. This study uses vanillin-sulfuric acid method and field tests on loaches in paddy fields to determine the duration of camellia seed meal’s effect on loaches (Misgurnue Angullicaudatus). Results indicated that the best application to stop the growth of Pomacea canaliculata is to seal the rice field immediately after transplantation, apply the camellia seed meal, and then irrigate the field 2?days after camellia seed meal application for the summer transplantation, and 3?days for the spring transplantation. Water should not be drained from the paddy field after the application of camellia seed meal to reduce the chance of endangering loaches in irrigation canals. Field Tests show that high water temperature during summer also has a negative effect on loaches in paddy fields and irrigation canals.     

Characteristics of paddy irrigation in Taiwan

Paddy and water environment are closely related to each other in Asia. Developing agriculture by way of construction of farmland irrigation works has long been the principal objective of policies in Taiwan. Owing to significant temporal and spatial difference in rainfalls, natural river runoff has hardly corresponded with irrigation requirements. The cultivation of rice paddies and upland crops are practiced according to the state of the water sources, and cultivation patterns and irrigation systems are framed by placing the same importance on the role of irrigation and drainage management. In this article, the characteristics of paddy irrigation in Taiwan, distinguishable from the western arid farming, have been categorized and will be reviewed in terms of irrigation development, agricultural water utilization, equitable distribution management, farmland consolidation, and the Irrigation Association with its role as that of a public juridical body.Dr. Tsai is the Chief of Irrigation and Engineering Division, Council of Agriculture (COA), Executive Yuan, Taiwan, R.O.C, and also serves as the president of the Chinese Society of Agricultural Engineers (CSAE), the Vice-President of the International Society of Paddy and Water Environment Engineering, the vice-president of International Commission on Irrigation and Drainage (ICID) Chinese Taipei Committee, Managing Supervisor of Chinese Water Resources Management Society. He has an M.Sc. diploma in agricultural engineering from the National Taiwan University and in 1990 he received his Ph.D. degree in natural science and technology from Okayama University, Japan.     

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.     

A review on microbial and toxic risk analysis procedure for reclaimed wastewater irrigation on paddy rice field proposed for South Korea

Water shortage has become a major agricultural concern, and “The Sustainable Water Resources Research Program” in Korea is currently addressing this problem through the development of treatment systems for reclaiming wastewater and the assessment of human health risks associated with its reuse. Through this program, started in 2001, many studies have examined various water resources. Reclaiming wastewater is one way to alleviate water-shortage pressures, and one of the major potential uses of reclaimed water is irrigation. However, the main concern with reusing reclaimed wastewater is the increased likelihood of human contact that might result in exposure to pathogens and increased health risks. Relatively few studies have examined the toxic risks using reclaimed wastewater for irrigation in rice paddy fields. This study provides an overview of methods for quantitative microbial risk assessment and toxic risk assessment of heavy metal concentrations developed in the previous studies that can be applied to the evaluation of rice paddy fields irrigated with reclaimed wastewater in South Korea.     

Distribution of heavy metals in the sediments of agricultural fields adjacent to urban areas in Central Taiwan

In 2002, the Environmental Protection Administration of Taiwan began a detailed survey of heavy metals in soils, to determine the scope of the contaminated lands in the Changhua County’s agricultural fields. It was found that agricultural lands have been seriously polluted with Cr, Hg, Cu, Ni, and Zn, due to industrial wastewaters. This study, characterized the processes associated with heavy metal pollution by analyzing heavy metal contents in sediments within two periods, 2002 and 2010. This study employed geostatistical and multivariate statistics to obtain spatio-temporal variations of heavy metal pollution in paddy fields. The results indicate that, changes in industrial types have been altered the characteristics of pollutions, such as reducing the number of plants in industries (i.e., electroplating, surface treatments, metal works, chemicals, papermaking, etc.). Their wastewaters contained a large number of Ni, making the pollution composition of driven factors have been changed that can be indicated in this study. Pollution distribution and irrigation systems are positively correlated and concentrations of Cr, Cu, Ni, and Zn were inversely proportional to the scale of irrigation channels.     

Assessment of water quality in small agricultural ponds in Nara,Japan

Paddy and Water Environment - In Japan, since ancient times, numerous small- to medium-size agricultural ponds have been constructed to irrigate paddy rice fields. Economic growth and urbanization...     

Multifunctionality of paddy fields in Taiwan

Paddy rice is the staple food in Taiwan, where rice farming always plays an important role in agricultural activities. The paddy fields and irrigation activities hold diversified functions, such as production, eco-environmental and living-associated functions. This paper is to provide information regarding the potential magnitude and monetary value of seven functions of paddy fields in Taiwan, including flood mitigation, fostering water resources, preventing soil erosion, purifying water, cooling air temperature, refreshing atmosphere and recreation. For quantification of the above values, replacement cost method (RCM), contingent valuation method (CVM), and the travel cost method (TCM) are adopted. In addition, the ratio of monetary value and their rice production commodity value (R) was also estimated. The results indicated that the flood mitigation function had a monetary value of US$ 389 million each year, and the ratio to the rice production value R was estimated at 37%. Water resource fostering function was US$ 501 million and R at 47%; soil erosion reduction function was US$ 433 million and R at 41%; water quality purification function was US$ 3 million and R at 0.3%; cooling air temperature function was US$ 961 million and R at 91%; refreshing air function was US$ 196 million and R at 19%, health and recreation function was US$ 987 million and R at 93%, respectively. Due to the significant importance of these externalities, it is recommended that the government should properly take into account the multifunctionalities in policy making to ensure sustainable development of agriculture.     

Environmental multifunctionality of Indonesian agriculture

Industrial and urban developments in Indonesia focus on the economic merits, but neglect agricultural services that, when disappear, will destabilize the environmental and livelihood systems. A series of 5-year study has evaluated various aspects of multifunctionality and implications of paddy field conversion on the disappearance of multifunctionality. Soil loss from a series of 18 terraced paddy fields in central Java is negligible. Only a few terraces located along the streams directly caused sedimentation. The functions of flood mitigation, water-resource conservation, erosion reduction, organic waste disposal, heat mitigation, and rural amenity of paddy fields in Citarum watershed in West Java were significant. The ‘replacement costs’ of such functions was about 51% ($92.67 million yr⁻¹) of the total price of rice of $181.34 million yr⁻¹ produced in the 156,000 ha paddy field. This amount could be considered as free services by the farmers to the society. However, because of society's negligence and unawareness, conversion has been accelerating while development of new paddy fields has been decelerating in the last few years. Low and fluctuating price of agricultural products, unavailability or non-affordability of agricultural supplies and inaccessibility to market are among the major disincentives faced by farmers. Because of appreciable multifunctionality they produce, farmers deserve various incentives for the sake of environmental sustainability and other services.     

Quantitative risk assessment for reclaimed wastewater irrigation on paddy rice field in Korea

Water shortage has become an important issue for Korean agriculture. Korea suffers from a limited agricultural water supply, and wastewater reuse has been recommended as an alternative solution. This study examined the concentrations of toxic heavy metals and Escherichia coli in a paddy rice field irrigated with reclaimed wastewater to evaluate the risk to farmers. Most epidemiological studies have been based on upland fields, and therefore may not be directly applicable to paddy fields. In this study, a Beta-Poisson model was used to estimate the microbial risk of pathogen ingestion. The risk value increased significantly after irrigation and precipitation. The results of the microbial risk assessment showed that risk values of groundwater and reclaimed wastewater irrigation were lower than the values of effluent directly from wastewater treatment plants. The monitoring results of heavy metals for each irrigated paddy fields did not show specific tendency. A risk assessment for toxic heavy metals was performed according to various exposure pathways; however, the results of the carcinogenic and noncarcinogenic risk estimation showed that the risk from reclaimed wastewater-irrigated paddy fields was the lowest.     

Evaluation of irrigation water requirements and crop yields with different irrigation schedules for paddy fields in ChiaNan irrigated area,Taiwan

Recent water shortages in reservoirs have caused such problems as insufficient water and fallow rice fields in Southern Taiwan; therefore, comparing irrigation water requirements and crop production of paddy fields using a technique that differs from the conventional flood irrigation method is important. Field experiments for the second paddy field with four irrigation schedules and two repeated treatments were conducted at the HsuehChia Experiment Station, ChiaNan Irrigation Association, Taiwan. Experimental results demonstrate that irrigation water requirements for the comparison method, and 7-, 10- and 15-day irrigation schedules were 1248, 993, 848, and 718 mm, respectively. Compared to the conventional method of flooding fields at a 7-day interval, the 10- and 15-day irrigation schedules reduced water requirements by 14.6 and 27.3 %, respectively; however, crop yields decreased by 7 and 15 %, respectively. Based on the results, it was recommended that the ChaiNan Irrigation Association could adopt 10 days irrigation schedule and plant drought-enduring paddy to save irrigation water requirements for the water resource scarcity in southern Taiwan. The CROPWAT model was utilized to simulate the on-farm water balance with a 10-day irrigation schedule for the second paddy field. A comparison of net irrigation water requirements with the 10-day irrigation schedule from model and field experiment were 818 and 848 mm, respectively, and the error was 3.54 %.     

The methods to consolidate scattered tenanted lots into large rice paddy lots by the land consolidation projects in Japan

Today in Japan, agricultural productivity of rice cropping farmers is low. In order to get sufficient agricultural productivity, Japanese government is encouraging enlarging core farmers' farm sizes to 10–20 ha by borrowing farm lots from retiring farmers of small farms and carrying out the land consolidation projects to construct large rice paddy lots. In order to realize large rice paddy lots of more than several hectares, it is necessary to consolidate small scattered leased farm lots of core tenant farmers, but it is supposed to be very difficult. In order to clarify how to consolidate those leased lots into large rice paddy lots, I investigated five land consolidation project areas in which large rice paddy lots of more than several hectares were constructed for core tenant farmers. The result shows that (1) large rice paddy lots for core tenant farmers were settled in relatively inferior areas of the project areas, for instance, far from the land owners' residence area. (2) Basically land lenders do not accept their substitute lots settled into large rice paddy lots in such inferior areas, (3) but some land lenders who were eager to lend their farmland to core farmers accepted their substitute lots in such inferior areas. (4) Even in cases that tenant farmers could not consolidate substitute lots of their tenant land into large rice paddy lots, they could consolidate their cultivating lots by adjusting user rights, that is, exchange of user rights of lots between land lenders whose substitute lots were located outside of a large rice paddy lot area and owner farmers whose substitute lots were located in the area. (5) Owner farmers accepted this adjustment on their farmland as they could cultivate superior lots, consolidate their scattered cultivating lots into one place and so on.     

The role of paddy rice in recharging urban groundwater in the Shira River Basin

Agricultural fields in the middle Shira River basin play an important role as a source of groundwater recharge; however, the water balance between the agricultural water and river water is unclear. This study was conducted to investigate the water balance in the fields by measuring the stream flow of agricultural water channels, which draw water from the Shira River. The flow rate of water channels was found to increase in the beginning of May, which corresponded to the cultivation of paddy rice fields. During summer, the total agricultural intake was comparable to the river flow observed in the middle Shira River Basin. Determination of the water budget for the targeted area revealed that most of the recharged water was dependent on agricultural irrigation from the river. The annual recharge of the overall target area was estimated to be as high as 15,300 mm. In addition, the infiltration rate was as high as 170 mm/day in the paddy fields during summer, and as high as 30 mm/day in the upland fields during winter. In order to recover the groundwater recharge in this region, it is necessary to extend the submerged period to include periods in which the stream water in the Shira River is not subject to heavy rainfall as well.     

Analysis of the water balance and the nitrogen and phosphorus runoff pollution of a paddy field in situ in the Taihu Lake basin

Paddy and Water Environment - Nitrogen (N) and phosphorus (P) runoff loads of paddy fields in situ under conventional water and fertilizer management measures caused severe water pollution in the...     

The price elasticity of transferring agricultural water to industrial water during non-drought period in Taiwan

In this study, the demand function for the transferring agricultural water to industrial water during non-drought period covering from January 1998 to December 2008 in Taiwan was estimated, and the water usage statistics derived from the short-term water charge agreements, regarding the charging of water management fees and water usage fees from the irrigation associations, were applied to the estimation in the empirical model. The results of the research are presented as follows: (a) the demand for transferring agricultural water into industrial water is non-elastic; the price elasticity is −0.368; (b) the transferred water volume decreases when the water price rises; (c) the transferred water volume also decreases when the wholesale price index of domestic products rises; (d) the buyer’s industry classification was the significant factor influencing the transfer water demand; (e) the different title of transferred water including: “building utilization cost” or that in “costs for enhanced irrigation management” was the significant factor influencing the transfer water demand; (f) type of repository of irrigation association for transferred water was the significant factor influencing the transfer water demand; (g) whether irrigation association enhances irrigation management was the significant factor influencing the transfer water demand; (h) the source of transferred water was the significant factor influencing the transfer water demand; (i) the method for water transfer was the significant factor influencing the transfer water demand; (j) more water transferred by the industry when the total population of Taiwan increases; (k) the transferred water volume rises when the groundwater level of the water transferred area rises; and (l) the areas for water transferred was the significant factor influencing the transfer water demand.     

Enhancing field scale water productivity for several rice cultivars under limited water supply

Paddy and Water Environment - Rice production is one of the largest consumer of water in agriculture. In general, the irrigation water productivity (WPI) is low in paddy fields. In order to improve...