Estimating the inverse demand function for transferring agricultural water in Taiwan

Changing climate has increasingly exacerbated droughts and floods in Taiwan; therefore, it is important to understand the actual demand of transferring Taiwan’s agricultural water. This estimation model could help the water resource agencies to develop appropriate mechanisms for transferring agricultural water, as well as bargaining tools for water-related negotiations. In this study, an inverse demand function estimation model for transferring agricultural water was established, and the water usage statistics derived from the water charge agreements, covering the period from January 1989 to December 2006 and including drought and non-drought periods, regarding the charging of water management fees and water usage fees, was applied to the estimation model in our empirical research. The agreements were made between irrigation associations and water companies, industrial water users, and science and industrial parks, for the purposes of strengthening irrigation management, building usage, and disposal of remaining water. The empirical research was conducted to estimate the demand for transferring agricultural water using double-log regression model for panel data, and analyzed with random effects models for regular conditions and drought periods. The results showed that the inverse demand function developed in this study was able to pass Largrange multiplier test, and adjusted R ² for the regression were high, fitting the random effects model showing good compatibility with the sample selection. From the results, we can verify the estimation models to forecasting models. The significant results not only prove that the model could provide important market information for the commercialization of water resources, but water resource agencies could also make use of this important information to develop suitable mechanisms for transferring agricultural water, as well as bargaining tools for negotiation of water transactions.     

Decision support system for reservoir operation considering rotational supply over irrigation blocks

This study aims not only to evaluate agricultural drought in paddy using the storage ratio of the corresponding reservoir, but also to develop a rotational irrigation scheduling system (RISS) for supporting both water supply scheduling and on–off control works for automated irrigation. From the present storage ratio of reservoir and an operation rule curve (ORC) as a guideline for releasing irrigation water, reservoir operators could determine the appropriate time to restrict the irrigation water supply, and calculate the deficient amount of irrigation water. The RISS based on the ORC and weekly rainfall forecasting information has been developed for decision support to minimize drought damage in irrigation districts during the irrigation period. The system was also applied to a test irrigation district with the Yedang irrigation reservoir, which is located in the mid-west of Korea. The RISS could be utilized as a water management program for irrigation reservoirs by interfacing with telemetering and telecontrol (TM/TC) technology.     

Potential rainwater storage capacity of irrigation ponds

From antiquity to the present, Japan has irrigated many paddy fields from irrigation ponds. There are some 64,000 such irrigation ponds with a benefit area of over 2 ha each. These irrigation ponds not only function as a water-source for the stable production of food, but also are thought to reduce flooding in lower regions through temporary storage of rainwater and catchment runoff because they are located upstream of paddy fields, upland fields and residential land. Centering our research on Kagawa and Osaka Prefectures, we assessed the potential of rainwater storage capacity created by free space in irrigation ponds resulting from irrigation at a macro level as an indicator of flood mitigation. In these prefectures, potential rainwater storage capacity of irrigation ponds in early September was 2.1 and 1.4 times that of the potential storage capacity of associated paddy fields in an ordinary year.     

水氮互作对百农207种子发芽特性及贮藏物质转运的影响

为了研究不同水氮处理下收获的百农207种子发芽特性和贮藏物质转运的差异,以百农207为材料,结合当地冬小麦灌溉施肥制度设置水氮两因素裂区试验,水分为主区,氮素为副区,设置W0(返青后不灌水)、W1(返青后灌拔节水)、W2(返青后灌拔节水和开花水)、W3(返青后灌拔节水、开花水和灌浆水)4个灌溉水平以及N0(不施氮)、N1(120kg·hm-2)、N2(180kg·hm-2)、N3(240kg·hm-2)4个施氮水平。在百农207收获后进行标准发芽实验,测定种子的发芽指数、活力指数、生长特性和贮藏物质转运等相关指标。结果表明,灌水和施氮对收获后的百农207种子活力指数、幼苗根冠比、贮藏物质转运率和转化效率的影响呈正向耦合效应。水分是决定收获后小麦种子活力指数、种子贮藏物质转运率和转化效率的主要因子;氮素是决定收获后种子发芽阶段根冠比的主要因子。高水肥处理(N3W3)的种子发芽指数和活力指数最高,水分和养分胁迫(N0W0和N1W0)下发芽阶段的根芽长比值较高。在一定施氮量范围内,增加灌水并不能促进收获种子在发芽阶段幼苗根冠比的增加。在W2和W3水平下,不同施氮处理的百农207种子贮藏物质转运率和贮藏物质转化效率均高于60%。种子发芽阶段幼苗生长相对最优的水氮处理为N2W2。这说明一定水分和氮素营养供应范围内降低氮肥用量,不会降低收获后百农207种子的贮藏物质转运率和转运效率,符合当前的减肥增效原则。     

Factors impacting yields in rain-fed paddies of the lower Mekong River Basin

The Mekong River Basin (MRB) is the biggest basin in Monsoon Asia. About 80% of the agricultural lands, which occupy about 40% of the basin are rain-fed paddy rice area. Therefore, it is assumed that changes in rain-fed paddy rice production affect the total agricultural production to a great degree in the Mekong River Basin. While there are many factors affecting the productivity of rain-fed paddies, such as climate, water use, rice varieties, applications of manure, fertilizer and agro-chemicals, sowing date and other agronomic practices, this paper focuses on the relation between rainfall and yields of rain-fed paddies. Agricultural statistics and rainfall data were collected and analyzed for all 24 provinces in Cambodia for the years 2001 and 2002. Factors such as soil fertility and other natural conditions were removed by comparing the yield and rainfall in one province for different years. Special attention was given to the relation between yields of paddy in the wet season and rainfall, considering factors such as rice varieties, soil fertility, irrigation ratio and the ratio of area damaged by flood, drought, and insect. Although it is not easy to assess those impact factors on yields because they are organically interactive, the following results were obtained: (1) The ratio of high yielding varieties (HYV), soil fertility, and irrigation ratio among many factors that affect yields individually, especially if they are combined, (2) Total rainfall did not have a significant influence on rice yields even for the rain-fed paddies if it was over 700 mm in wet season, and one of the reasons for this would be that there exist supplementary water uses through small ponds and water ponding in local land depressions in and around paddies.     

吉林半干旱区不同灌溉方式对土壤水分变化及玉米产量的影响

通过对常规垄灌溉、固定隔沟灌溉和交替隔沟灌溉的试验对比,交替隔沟灌溉水量仅为常规沟灌的1/2,有一半左右的地表面处于相对干燥状态,水分渗入率较大,提高了土壤对灌溉水和自然降雨的储存与利用,有利于对有限的水资源进行合理分配和充分利用。运用交替隔沟灌溉技术能提高作物对垄两侧土壤中养料、水分等的利用效率,作物根系进行干湿交替锻炼后,刺激根系生长,提高根系活力,一定程度增强植株抵御干旱的能力,更利于作物健康生长,交替隔沟灌溉是具有较强实用性的大田节水灌溉方法。     

The reasonable scale of water reuse system in irrigation area: a case study of Chitong irrigation district in Taiwan

The aim of this study is to assess the potential of the irrigation return-flow in a water reuse system, for the supply of other local water users. Both field survey and water-budget analysis were conducted, and the Chitong irrigation district in Taiwan was selected as the case study area. The results indicate that through the regulation of a pond with the effective capacity of 20,000 m³, a stable supply of 10,000 CMD of reuse water can be generated if the return-flow from the irrigation area of 200 hectares, which is about the size of a rotation plot, is intercepted. However, as the irrigation and effective rainfall are low from December to March, which are considered high risk for water supply, the irrigation return-flow decreases accordingly, and a series of responding measures are also suggested.     

Water quality and limnology of Korean reservoirs

Reservoirs are the predominant type of lentic ecosystem in Korea, and they account for a considerable proportion (~59%) of the agricultural water uses. There are 18,797 reservoirs in Korea; most (~90%) are small (storage capacity <1,000,000 m³), and most provide irrigation water for paddy farming. Characteristics of Korean agricultural reservoirs are high watershed-reservoir area ratios, shallow depth, unstable hydrodynamics, and eutrophic conditions. Many agricultural reservoirs are relatively old; 54% of all reservoirs were constructed more than 50 years ago. As a result, they have a considerable amount of organic matter accumulation on the sediment, which may contribute to the internal loading of nutrients. Deterioration of water quality and ecosystem health, resulting from cultural eutrophication and harmful algal blooms, are common problems in most Korean agricultural reservoirs. Environmental considerations about reservoirs, especially their ecological functions, have largely been ignored in past management plans. Limnology, the multidisciplinary study of lakes and reservoirs, can provide conceptual models of reservoirs and fundamental information needed to determine causes and potential solutions for environmental stresses. Problems prevailing in Korean reservoirs, such as cultural eutrophication and harmful algal blooms, are complicated ecosystem-level phenomena with many factors interacting with each other. Thus, limnological understanding is a prerequisite to identifying sound solutions and to making wise judgments about reservoir management and restoration. Cooperation with other related disciplines is necessary to establish the proper management plans and applications. Also, international cooperation is suggested to solve environmental problems in agricultural reservoirs, particularly among the countries with similar agricultural practices, climate, geology, and water uses. Electronic Publication     

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.     

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.     

GIS analysis of conjunctive water resource use in Nganjuk district, east Java, Indonesia

Water shortages during the dry season threaten sustainable agricultural production in Nganjuk District, East Java, Indonesia. To mitigate this problem, farmers adopted conjunctive use of surface water and groundwater, but the sustainability of this practice has not been investigated. This study temporally and spatially assessed water allocation in Nganjuk District when conjunctive irrigation was used. In particular, the land cover, water balance, and irrigation well density (IWD) were analyzed using time series GIS and remote sensing data to obtain their temporal and spatial distributions. First, the land cover was analyzed to determine cropping intensity, and the water balance was analyzed temporally and spatially. IWD was introduced to facilitate the water balance analysis. Second, the land cover, water balance, and IWD results were overlaid. Third, the effectiveness of the IWD method, the magnitude of water shortages, and the sustainability of groundwater resources were considered. Temporal and spatial water shortages in irrigation blocks were observed during the dry season. The change of storage showed a surplus during the wet and early dry seasons and a shortage during the late dry season. The annual water balances indicated that the southern part had a surplus, and the northern part experienced water shortages, especially downstream of the Widas River. Conjunctive use during the late dry season was predominant and concentrated in the southern part (83% of southern blocks). IWD was appropriate for examining groundwater use trends and was effective for expressing average withdrawal data (R ² = 0.87).     

Crop water use indicators to quantify the flexible phenology of quinoa (Chenopodium quinoa Willd.) in response to drought stress

Models can play an important role in agricultural planning and management. Thermal time accumulation is a common way of describing phenological development in crop models, but the sensitivity of this concept to water stress is rarely quantified. The effect of pre-anthesis droughts on the timing of anthesis and physiological maturity was assessed for quinoa (Chenopodium quinoa Willd.) var. ‘Santa Maria’, with the help of two field experiments (2005–2006 and 2006–2007) in the central Bolivian Altiplano. Various treatments with different sowing dates and irrigation applications were considered. To evaluate the effect of drought stress on crop development, drought stress during the first 60 days after sowing was assessed with three different stress indicators: the number of days that the soil water content of the root zone was above a threshold, the average relative transpiration, and the sum of daily actual transpiration, standardized for reference evapotranspiration (∑(T_a/ET₀)). The best indicator to quantify the effect of pre-anthesis drought stress on phenological development was ∑(T_a/ET₀) cumulated until 60 days after sowing. This indicator showed a significant logarithmic relation with the time to anthesis and time to physiological maturity. Correlations of the drought stress indicator with thermal time accumulation were better than with calendar time accumulation. Due to an effect of post-anthesis droughts, the correlations of the drought stress indicator with the time to anthesis were stronger than with the time to physiological maturity. It was also demonstrated that deficit irrigation can contribute to a better agricultural planning due to a better control of the phenological development of quinoa. The proposed relations can be used for modeling phenological development of quinoa in drought prone regions and for efficient deficit irrigation planning.     

Feasibility and sizing of unlined on-farm pond for partial rice substitution in rainfed uplands of eastern India

Rice (Oryza sativa L.)-dominated rainfed uplands of eastern India are facing two major problems such as lack of irrigation water sources and low productivity. In fact, unlined on-farm pond (OFP) technology in this terrain could prove to be an effective agricultural drought mitigation measure for monsoon crops but failed to ensure supplemental irrigation (SI) to the next winter crops. Consequently, the OFP technology could not pick up in the region. In order to overcome the shortcomings in the technology, the location of the OFP has been changed and a new concept of partial rice substitution (PRS) has been introduced in the present study to provide SI for the second crop in winter. Maize (Zea mays L.) and rice crops at upper and lower compartments of the field, respectively, were tried at various crop substitution ratios (CSR) of 70:30, 60:40, 50:50, 40:60, and 30:70 during monsoon season. Rainfall excess from both the compartments was harvested in an unlined OFP located in between the compartments and used for providing SI. In winter, black gram (Vigna mungo L.) and mustard (Brassica campestris) were taken in the upper and lower compartments, respectively, based on availability of water in the OFP. Water balance models were used to simulate the soil moisture in crop root zone as well as storage of water in the OFP. The optimal size of such unlined OFP for average land holdings (1200 m²) in rainfed uplands and under 60:40 CSR was found to be occupying 6 % area of the crop field.     

Utilizing rainfall and alternate wetting and drying irrigation for high water productivity in irrigated lowland paddy rice in southern Taiwan

Taiwan’s average annual rainfall is high compared to other countries around the world; however, it is considered a country with great demand for water resources. Rainfall along with alternate wetting and drying irrigation is proposed to minimize water demand and maximize water productivity for lowland paddy rice cultivation in southern Taiwan. A field experiment was conducted to determine the most suitable ponded water depth for enhancing water saving in paddy rice irrigation. Different ponded water depths treatments (T_2 cm, T_3 cm, T_4 cm and T_5 cm) were applied weekly from transplanting to early heading using a complete randomized block design with four replications. The highest rainwater productivity (2.07 kg/m³) was achieved in T_5 cm and the lowest in T_2 cm (1.62 kg/m³). The highest total water productivity, (0.75 kg/m³) and irrigation water productivity (1.40 kg/m³) was achieved in T_2 cm. The total amount of water saved in T_4 cm, T_3 cm and T_2 cm was 20, 40, and 60%, respectively. Weekly application of T_4 cm ponded water depth from transplanting to heading produced the lowest yield reduction (1.57%) and grain production loss (0.06 kg) having no significant impact on yield loss compared to T_5 cm. Thus, we assert that the weekly application of T_4 cm along with rainfall produced the best results for reducing lowland paddy rice irrigation water use and matching the required crop water.     

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.     

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.     

Long-term changes in nitrogen loads of a stream in the vicinity of an earthen waste storage pond

It is not sufficiently known for how long earthen waste storage ponds that are no more in use continue to affect surface water quality. In 2006, we carried out an investigation on the water quality and hydrology at the outlet of a small agricultural catchment area (area A) by estimating the in-stream nitrogen loads and nitrogen inputs. In this area, swine waste had been retained in an earthen waste storage pond, which was not in use since 1990. Similar investigations were conducted at the same location in 1992 and 2002, and the results of all these three studies were compared. The average nitrate nitrogen (NO₃-N) concentrations were 26, 4.9, and 4.0 mg L⁻¹ in 1992, 2002, and 2006, respectively. Despite 76% of the land use of area A being forest, the average NO₃-N concentration was relatively high, indicating that effluents from the earthen waste storage pond continued to affect surface water quality in 2006. The ranges of in-stream nitrogen loads derived from the earthen waste storage pond were estimated to be 154 to 207, −14 to 39, and 14 to 74 kg ha⁻¹ for 1992, 2002, and 2006, respectively. The results suggested that although the effects of effluents from the earthen waste storage pond on water quality decreased over 14 years, they still continued in 2006.     

分根区灌溉和氮肥处理对星油藤幼苗的影响

探讨分根区灌溉和氮肥对盆栽星油藤幼苗生长的影响。试验设置3个因素，灌水量、灌溉方式和氮肥，共7个处理，测量了幼苗生长、光合和水分利用效率等指标。结果表明：与充分灌溉相比，分根区灌溉的处理，生物量降低5％，节水75％，水分利用率高出60％，表现出极大的节水效益。重度干旱条件下，施氮肥的处理，根冠比增加达30％，但分根区灌溉处理叶面积指数下降38％，光合速率下降9％，生物量下降18％，分根区灌溉在严重干旱条件不适宜施氮肥。总之，在适度干旱条件下，分根区灌溉降低蒸腾，提高水分利用率，是一种有效的节水灌溉技术。     

Using water quality variables to predict light attenuation coefficient: case study in Shihmen Reservoir

The amount of photosynthetically active radiation (PAR) in the water column is of fundamental importance in determining the growth of aquatic plant and aquatic primary production. Light attenuation in aquatic ecosystems has important ecological implication and water quality applications. In the present study, the light attenuation through the water column in the Shihmen Reservoir, Taiwan was measured. A light attenuation coefficient (K _e) can be derived from the PAR measurements at each stations. The linear regression analysis reveals that Secchi disk depth is a sample alternative measure of light transmitability and provides a reasonable estimate of the light attenuation coefficient in the Shihmen Reservoir. We conducted multiple-regression analysis for the K _e, chlorophyll a, and total suspended solids (TSS). Because the concentration of chlorophyll a is roughly <5 μg/L in the Shihmen Reservoir, the chlorophyll contribution to the attenuation coefficient will be <0.1 m⁻¹, which is negligible. K _e correlated with TSS concentration yields a good correlation, indicating the TSS should be a good water quality variable for predicting water column light attenuation coefficient in the Shihmen Reservoir.     

吉林省玉米生产中水分高效农艺技术途径与模式探索

近年来，吉林省粮食产量逐步提升，已连续8年总产量稳定在350亿kg以上，对保障国家粮食安全做出了重要贡献。吉林省水资源总量相对贫乏，虽然自然降水相对丰富，但时空分布不均，加之气候暖干化，导致的季节性干旱是吉林省农业发展的主要制约因素。此外，长期重用轻养的生产方式造成耕层土壤结构恶化，水分蓄、保、供能力下降，致使粮食增产与水资源紧缺的矛盾十分突出。针对上述生产与技术问题，围绕“以高效利用自然降水为主，节水补充灌溉为辅”的技术原则，开展玉米丰产高效栽培机理和关键技术创新，在半湿润区提出了“蓄水保墒”自然降水高效利用技术，在半干旱区提出了“蓄水保墒+节水补灌”水分高效利用技术，构建了7套适于吉林省半干旱、半湿润区的栽培技术模式，并在生产中示范推广应用。