Assessment of irrigation efficiencies and water productivity in paddy fields in the lower Mekong River Basin

Improving irrigation performance is a crucial issue for agriculture and irrigation development in the Lower Mekong River Basin to secure food production for people’s livelihoods. Irrigation efficiency is the most important indicator to determine the performance of an irrigation scheme. This study looks at water management practices and irrigation efficiency in three pilot sites in the Lower Mekong River Basin: the Numhoum scheme in Laos, the Huay Luang scheme in Thailand, and the Komping Pouy scheme in Cambodia. Irrigation efficiency and water productivity were analyzed using a water balance approach at the irrigation scheme level and results in the pilot areas show efficiencies that are definitely higher using this approach than by using the classical concept. Lower water productivity was observed at pilot schemes in areas of single cropping and higher productivity in areas where multiple agricultural activities were practiced. Strict and active water management is required to control and save water to meet agricultural demand and have sufficient water to expand cultivation areas while avoiding shortages. Promoting multiple uses of water for various agricultural activities in command area will increase water productivity.

Delivery management water requirement for irrigation ditches associated with large-sized paddy plots in Korea

Delivery management water requirement (DMWR) is the use of bypass water in paddy field irrigation to help maintain desired water levels in irrigation canals and to distribute water to paddy plots in a uniform manner. Diverted irrigation water (DIW), DMWR, and the DMWR/DIW ratio were investigated for concrete lined irrigation ditches with large-sized paddy plots (100 m×100 m) during irrigation periods (May to mid-September). DIW and DMWR were measured at 5- to 10-day intervals at the inlets and outlets of irrigation ditches on stable water supply days. The mean DMWR/DIW ratios in irrigation ditches L₁ and L₂ over 3 years were 36 and 34%, respectively. The mean DMWR/DIW ratios displayed month-to-month and year-to-year variation. The monthly mean DMWR/DIW ratios were highest (55 and 71%) in June and lowest (<20%) in August and September. The annual mean DMWR/DIW ratios during a dry year markedly decreased to 11%, compared with 42% in other years. The decrease was due to the small DIW and farmers water management to maximize capture of limited irrigation water during the drought. The DMWRs in May and June were significantly (p<0.01) correlated with the DIWs, indicating that high DMWR in May and June are attributed to excessive DIW.     

Crisis management of water shortage in an irrigation area with a pipeline network system

Problems caused by water shortage in a paddy-field district with a pipeline network system are different from those in a district with an open channel system. Abnormally low rainfall in Japan caused a very serious water shortage in 1994. A survey was carried out in the Hokuriku region, about 300 km in the north of Tokyo, and a typical paddy cultivation area, to determine problems in irrigation practices caused by water shortage and to find countermeasures for the problems. The following results were obtained. A tank model was proposed to estimate water requirements at the field level. The results showed that the amount of rainfall during the irrigation period in 1994 was only 27.1% of an average year and the rate of water sufficiency at the field level was 70.6%. Then, a simulation method was proposed to estimate hydraulic phenomena in a pipeline network system. The result showed that the pipeline network system distributed water to each hydrant unequally during water shortage. Based on simulations, the methods to equalize water supply to each hydrant and to set up reuse system of water were proposed.     

A combined technique of floodplain storage and reservoir irrigation for paddy rice cultivation

This paper introduces an irrigation system developed in the floodplain of a lake and studies the water management technique of the irrigation system by estimating the total water balance of the whole system. The system is characterized by a reservoir combined with a dike system in the floodplain of the Tonle Sap Great Lake and an irrigation system. Two main models are used for calculating the total water balance. The first model is the water balance of the reservoir. The inputs to the model are water level of the reservoir, precipitation, lake evaporation, infiltration, and area–volume curve of the reservoir. The outputs are inflow and outflow of the reservoir. The supply from the reservoir to paddy fields is computed from the outflow. The second model is the water balance of paddy fields, based on which the water requirement in paddy fields is derived. The reference evapotranspiration needed to calculate the water requirement is simulated for monthly time series using the FAO Penman–Monteith model. Since there is no drainage network in the irrigation system, surface drainage and runoff are not included in the calculation of the water balance, and seepage is considered negligible in the flat floodplain area. The evapotranspiration, rice variety, soil type and irrigated area are used to simulate water consumption in paddy fields. Finally, the two models are connected to produce the total water balance from the reservoir to paddy fields. The total outflow from the reservoir is estimated and the total water consumption for dry season cultivation is also determined. Finally, the efficiency of the whole system is examined.     

The effect of water stress in regulated deficit irrigation on soybean yield (Glycine max [L.] Merr.)

The objective of this research was to investigate the effect of water stress in regulated deficit irrigation (RDI) on the yield of soybean growing on Ultisol soil. This research was conducted under plastic house on the experimental farm of Lampung Polytechnique from August to November 2004. The water stress treatments in regulated deficit irrigation were ET₁ (1.0 × ET_c), ET₂ (0.8 × ET_c), ET₃ (0.6 × ET_c), ET₄ (0.4 × ET_c) and ET₅ (0.2 × ET_c), arranged in a randomized block design with four replications. ET_c means crop evapotranspiration under standard condition, which was well watered. For example, the ET₂ (0.8 × ET_c) treatment means that the amount of supplied water per a day is the same as the crop adjustment evapotranspiration (ET_cadj) with the value 0.8 of water stress coefficient (K _s). The RDI treatments were carried out just at vegetative phase and its treatments were stopped at the beginning of flowering phase, and afterwards the treatments were watered at 1.0 × ET_c. The results showed that since week II, the soybean experienced stress throughout the growth period except ET₂ treatment. ET₂ treatment started to be stressed at week V and continued to be stressed until the harvest time. At the ET₃ treatment, the critical water content (θ_c) of soybean was reached at week II, and the θ_c was 0.24 m³/m³ on the average. The RDI at vegetative period significantly affected the yield. The highest yield was ET₁ (35.2 g/plant), followed by ET₂ (31.0 g/plant), ET₃ (18.1 g/plant), ET₄ (7.6 g/plant), and ET₅ (3.3 g/plant). The optimal water management of soybean with the highest yield efficiency was regulated deficit irrigation with water stress coefficient (K _s) of 0.80 for vegetative phase.     

The development of a coupled model (PCPF-SWMS) to simulate water flow and pollutant transport in Japanese paddy fields

A new coupled model (PCPF–SWMS) was developed for simulating fate and behavior of pollutant in paddy water and paddy soil. The model coupled the PCPF-1, a lumped model simulating pesticide concentrations in paddy water and 1 cm-surface sediment compartment, and the SWMS-2D, a finite element numerical model solving Richard's and advection-dispersion equations for solute transport in soil compartment. The coupling involved improvements on interactions of the water flow and the concentration the pollutant of at the soil interface between both compartments. The monitoring data collected from experimental plots in Tsukuba, Japan in 1998 and 1999 were used to parameterise and calibrate hydraulic functioning, hydrodynamic and hydrodispersive parameters of the paddy soil. The analysis on the hydraulic functioning of paddy soil revealed that the hard pan layer was the key factor controlling percolation rate and tracer transport. Matric potential and tracer monitoring highlighted the evolution of saturated hydraulic conductivity (K _S) of hard pan layer during the crop season. K _S slightly decreased after puddling by clay clogging and strongly increased after mid term drainage by drying cracks. The model was able to calculate residential time in every soil layers. Residential time of tracer in top saturated layers was evaluated to be less than 40 days. It took 60 days to reach the unsaturated layers below hardpan layer.     

Effect of irrigation method and N-fertilizer management on rice yield, water productivity and nutrient-use efficiencies in typical lowland rice conditions in China

Alternate wetting and drying irrigation (AWD) has been reported to save water compared with continuous flooding (CF) in rice cultivation. However, the reported effects on yield varied greatly and detailed agro-hydrological characterization is often lacking so that generalizations are difficult to make. Furthermore, it is not known how AWD modifies nutrient use efficiencies and if it requires different N-fertilizer management compared with CF. This study quantified the agro-hydrological conditions of the commonly practiced AWD and compared the impact of AWD and CF irrigations at different N-fertilizer management regimes on rice growth and yield, water productivity, and fertilizer-use efficiencies in five crop seasons in 1999 and 2000 at two typical lowland rice sites in China (Jinhua, Zheijang Province and Tuanlin, Hubei Province), with shallow groundwater tables.Grain yields varied from 3.2 to 4.5 t ha^–1 with 0 kg N ha^–1 to 5.3–8.9 t ha^–1 with farmers N-rates (150 kg N ha^–1 in Jinhua and 180 in Tuanlin). In both sites, no significant water by nitrogen interaction on grain yields, biomass, water productivity, nutrient uptakes and N-use efficiency were observed. Yield and biomass did not significantly differ (P >0.05) between AWD and CF and among N timings. The productivity of irrigation water in AWD was about 5–35% higher than in CF, but differences were significant (P <0.05) only when the rainfall was low and evaporation was high. Increasing the number of splits to 4–6 times increase the total N uptake, but not total P-uptake, and total K-uptake compared with farmers practices of two splits. Apparent Nitrogen recovery (ANR) increased as the number of splits increased, but there was no significant difference in ANR between AWD and CF. During the drying cycles of AWD irrigation, the perched water table depths seldom went deeper than – 20 cm and the soil in the root zone remained moist most of the time. The results suggest that in typical irrigated lowlands in China, AWD can reduce water input without affecting rice yields and does not require N-fertilizer management differently from continuous flooding. The results can be applied to many other irrigated lowland rice areas in Asia which have a shallow groundwater table.     

Deficit irrigation management for rice using crop growth simulation model in an optimization framework

Optimization of irrigation water is an important issue in agricultural production for maximizing the return from the limited water availability. The current study proposes a simulation–optimization framework for developing optimal irrigation schedules for rice crop (Oryza sativa) under water deficit conditions. The framework utilizes a rice crop growth simulation model to identify the critical periods of growth that are highly sensitive to the reduction in final crop yield, and a genetic algorithm based optimizer develops the optimal water allocations during the crop growing period. The model ORYZA2000, which is employed as the crop growth simulation model, is calibrated and validated using field experimental data prior to incorporating in the proposed framework. The proposed framework was applied to a real world case study of a command area in southern India, and it was found that significant improvement in total yield can be achieved by the model compared to other water saving irrigation methods. The results of the study were highly encouraging and suggest that by employing a calibrated crop growth model combined with an optimization algorithm can lead to achieve maximum water use efficiency.     

Measuring the implicit value of paddy irrigation water: application of RPML model to the contingent choice experiment data in Japan

For efficient use of water as a limited resource, evaluation on the water value is critical, but there is little information in Asian paddy irrigation. This paper proposes the method for measuring implicit price of paddy irrigation water by using the choice experiment (CE) data with contingent scenarios. Empirical results demonstrated that (a) the estimated implicit price of water showed reasonable value as compared to the production indexes, (b) the random parameter multinomial logit model was more suitable than the conventional multinomial logit model to treat the CE data, and (c) the implicit price is much lower than the full cost price, indicating that full cost pricing probably damages and ruins rice production too seriously in Japan. As seen above, the method proposed here is useful for decision making on water pricing policies and easy to apply to different irrigation systems under limited data of water value.