Features of the AFFRC model for evaluating the relationship between the water cycle and rice production

This paper introduces the Agriculture, Forestry and Fisheries Research Council of Japan (AFFRC) model, an integrated model that predicts future rice production in the Mekong River basin by taking into account the effect of global warming on both the water cycle and the rice economy. The model focuses especially on the water balance of paddy fields for different farmland water use systems. We defined six categories of irrigated paddies and three categories of rain-fed paddies on the basis of their systems of water usage. We included a process-based model to predict future rice production, accounting for daily changes in available water resources such as precipitation. Many models of crop production treat rice in the same way as other crops; the particular characteristics of rice farming are considered in more detail in our model. Our results show that it is possible to estimate future rice production in the Mekong River basin by taking into account changes in available water, and to model the resultant effects on the grain market.     

Climate change impacts on agriculture and irrigation in the Lower Mekong Basin

According to hydrological simulations by the Mekong River Commission, average annual flow of the Mekong will not change significantly despite climate change. However, they projected increased variability in wet and dry season flows, which will tend to increase the flood and drought risks to crops. To learn the implications of climate change for rice farming in the Lower Mekong Basin (LMB), a lower part of the Basin from China-Lao PDR border to the South China Sea, climate and hydrological figures related to rice production were compared in between the baseline in 1985–2000 and the climate change scenario in 2010–2050. Special attention was given to their 10 and 90 % exceedance values, which are rough equivalence of 10 and 90 % cumulative probabilities, to see changes in the frequency and extent of extreme weather events. Major findings of this study include the followings: (1) evapo-transpirations will increase in both average and 90 % cumulative probability values, raising irrigation demand. (2) Deviation of the annual rainfall will become larger, causing water shortage in reservoirs more frequently in the future. (3) The transplanting date of rain-fed rice will be delayed more likely due to insufficient precipitation in the early wet season, which may result in decreasing rice production. (4) Longer dry spells will be observed during the wet season, raising the drought risk to rain-fed rice. (5) These changes will be generally observed across the LMB, while the extent of the changes varies among regions.

     

Climate change impacts on agriculture and irrigation in the Lower Mekong Basin

According to hydrological simulations by the Mekong River Commission, average annual flow of the Mekong will not change significantly despite climate change. However, they projected increased variability in wet and dry season flows, which will tend to increase the flood and drought risks to crops. To learn the implications of climate change for rice farming in the Lower Mekong Basin (LMB), a lower part of the Basin from China-Lao PDR border to the South China Sea, climate and hydrological figures related to rice production were compared in between the baseline in 1985–2000 and the climate change scenario in 2010–2050. Special attention was given to their 10 and 90 % exceedance values, which are rough equivalence of 10 and 90 % cumulative probabilities, to see changes in the frequency and extent of extreme weather events. Major findings of this study include the followings: (1) evapo-transpirations will increase in both average and 90 % cumulative probability values, raising irrigation demand. (2) Deviation of the annual rainfall will become larger, causing water shortage in reservoirs more frequently in the future. (3) The transplanting date of rain-fed rice will be delayed more likely due to insufficient precipitation in the early wet season, which may result in decreasing rice production. (4) Longer dry spells will be observed during the wet season, raising the drought risk to rain-fed rice. (5) These changes will be generally observed across the LMB, while the extent of the changes varies among regions.     

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.     

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.     

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 and water saving issues for Ningxia paddies,upper Yellow River Basin

In the Hetao Irrigation Districts of the Ningxia autonomous region, Upper Yellow River Basin, the continuous deep flooding irrigation method is used for the rice paddies. The field irrigation water use during the rice-growing season is two to three times higher than in other regions of North China where water-saving practices have been introduced. This paper, based on the data measured in experimental rice fields and sub-branch canal systems, presents main results concerning crop evapotranspiration, percolation and irrigation requirements for deep and shallow water irrigation. Causes for water waste relate to both the lack of regulation in supply and distribution canals and to the poor management of paddy fields. The potential for water saving is discussed using water balance data. Improved irrigation techniques and water management strategies, including the shallow water irrigation method, are suggested considering the expected impacts and benefits. Replacing the current continuous deep flooding with the shallow-ponded water irrigation method may reduce the growing season irrigation water use from 1,405 to 820 mm in average, with a likely increase in yields of 450 kg/ha. Water productivity would then increase from 0.49 to 1.03 kg/m³. Adopting improved canal management and modernization of regulation and control structures may lead to decreasing the gross irrigation demand from the present 3,100 mm to about 1,280 mm, which would highly benefit the environmental conditions in the area.     

Modeling the dependence of the crop calendar for rain-fed rice on precipitation in Northeast Thailand

Rain-fed lowlands are major agricultural ecosystems used for rice production in Northeast Thailand. Developing a tool to assess the effects of variable water conditions on the regional scale yield is also important to predict the effects of climate change on food supply. To estimate regional yields, we need a simple but accurate measure of the crop calendar (i.e., the distribution of planting dates), which has a strong influence on grain yield. In this article, we modeled the dependence of the crop calendar on rainfall patterns based on a survey of the region’s farmers as a part of an effort to provide a stronger basis for regional yield estimates. Our survey, conducted in 11 provinces for 2 years, confirmed the existence of large windows for sowing and transplanting versus narrow windows for heading and harvesting for rain-fed lowland rice culture in all the provinces. Variable water, soil, and toposequential conditions in the paddy fields were responsible for the large sowing and transplanting windows, whereas the use of photoperiod-sensitive varieties explained the narrow windows for heading and harvesting. The crop calendar was well expressed as a function of cumulative precipitation from June onward. When the crop calendar model was combined with a simple phenology-based model that uses growing degree-days adjusted by a day-length factor, we could estimate the rice crop calendar under rain-fed lowland conditions with acceptable accuracy. The model described in this article will be combined with a crop growth model to improve regional yield estimates for rain-fed lowland rice.     

A water balance model for characterization of length of growing period and water stress development for rainfed lowland rice

There is large year-to-year variation in rice production across the Mekong region (Laos, Cambodia and Thailand) due to uncertainty in the timing of the onset of the wet season and drought stress that may develop at any time during the growth of rainfed lowland rice. Unique to the nature of lowland water balance is a large component of deep percolation water loss, which depends on soil texture. The objectives of this study were to develop a soil water balance model for calculating the amount of water held in field storage (i.e. in soil and, if there is standing water, above the soil surface) and to apply it to determine the length of growing period (LGP) and water stress development in relation to soil type and rainfall pattern for the rice ecosystem. The water balance is computed separately for above-ground plus topsoil layer and subsoil layer. Components of the water balance are the existing amount of stored water, rainfall, evapotranspiration, deep percolation, and runoff. The deep percolation rate was determined from clay content in each soil layer. The model runs with daily or weekly weather data to estimate the soil water level for the growing period in the wet season. The model was validated with data collected from top, middle and bottom of rainfed lowland fields in Savannakhet province, Laos. The best correlation between the observed and simulated water level was obtained (r² = 0.41) for middle fields. The simulation results showed that LGP varied greatly from year to year, particularly in locations with sandy soils, due mostly to variation in monthly rainfall occurring at the early part of the growing season (April), but also to some extent by variation at the end of growing season (October). Soil texture on the other hand is shown to have a large influence on the end of the rice growing period and hence LGP, and also water stress development during growth. Sandy soils with clay content less than 7% that are prevalent in the province are shown to cause frequent water stress and early finish in rainfed lowland rice. The model accordingly provides reasonable outputs that can provide a geographical dimension of soil hydrological patterns for various rice growing environments, and also identify the spatial pattern of drought stress that is likely to occur. Model outputs can be used to provide guidelines for practical advice to the rice farmers and researchers for determination of appropriate crop management strategies (e.g. time of planting, varieties), and policy makers for investment decisions on inputs (e.g. fertilizer price) aimed at increasing rice productivity in this Mekong region.     

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.     

Effects of trees planted on levees on rice yields in rain-fed paddy fields of northeast Thailand

Trees are increasingly being planted on the levees of paddy fields of rice (Oryza sativa L.) in northeast Thailand. We investigated and compared the yields of rice grown in rain-fed paddies under and far from canopies of three different tree species: eucalyptus (Eucalyptus spp.), mango (Mangifera indica L.), and the indigenous neem tree (Azadirachta indica A. Juss). Rice yields tended to decrease near trees of all types at five sites, but there was no change in yields at the remaining 11 sites during the 3-year study. The reduced yields likely resulted from lower aboveground biomass, leading to fewer rice panicles and spikelets, particularly near trees with a dense canopy. Extremely low yields were observed near eucalyptus in paddy fields suffering from severe drought. These results, as well as information provided by farmers’, suggest that eucalyptus trees may have detrimental effects on rice and should not be planted on the levees of paddy fields with relatively low productivity.     

Multiyear analysis of the dependency of the planting date on rainfall and soil moisture in paddy fields in Cambodia, 2003–2019

The dependencies of the planting date on rainfall and soil moisture in paddy fields in Cambodia were analyzed to quantify farmers’ empirical knowledge regarding their decision of the planting date. Remote sensing data from multiple satellites covering the 2003–2019 period were analyzed. The planting dates in rain-fed paddies ranged from April to August, with large spatial variations and year-to-year fluctuations. In years when planting was suppressed in April and May, planting was extensively enhanced in June and August compared to normal years, and vice versa. Over the northeastern side of Tonle Sap Lake and south of Phnom Penh city, the areas planted in April and May were found to have positive correlations with rainfall and soil moisture, suggesting that wetter-than-average conditions encouraged farmers to plant earlier in the season. In contrast, this relationship was unclear on the western side of Tonle Sap Lake, where the rainfall amounts were larger throughout the year than in other areas in Cambodia. In this region, the relationship between the planting area and soil water availability was either unclear or was even slightly negative from June to August. Since more frequent dry spells have been detected after the onset of the rainy season in recent years, further studies and disseminations of potential changes in dry spells are important for the agronomic adaptation of planting dates under climate change.

     

增氧处理对稻田土壤微生物量碳、氮和酶活性的影响

【目的】探讨增氧方式对稻田土壤微生物量碳、氮和土壤酶活性的影响。【方法】以中旱221(旱稻)、中浙优8号(水稻)和IR45765-3B(深水稻)为材料,研究微纳米气泡水增氧灌溉、干湿交替灌溉、淹水灌溉对稻田土壤微生物量碳、氮,土壤氮代谢作用强度和土壤氮素转化相关酶活性的影响。【结果】微纳米气泡水增氧灌溉和干湿交替灌溉可以显著提高稻田土壤微生物生物量碳、氮,中旱221、中浙优8号和IR45765-3B的增氧处理较淹水灌溉处理微生物生物量碳、氮分别增加了30.0%~46.1%和7.1%~92.1%,并且增氧处理降低了3个水稻品种的微生物量碳氮比;与淹水灌溉相比,微纳米气泡水增氧灌溉和干湿交替灌溉有助于提高稻田土壤脲酶、蔗糖酶、过氧化氢酶、蛋白酶、羟胺还原酶活性,降低硝酸还原酶活性和亚硝酸还原酶活性。【结论】微纳米气泡水增氧灌溉和干湿交替灌溉改善稻田土壤的氧化特性,提高土壤酶活性、微生物量碳、氮和硝化强度,有助于改善土壤环境和肥力状况,协调了C、N代谢的平衡。     

Impacts of climate change on rice market and production capacity in the Lower Mekong Basin

The supply of water is affected by climate changes. In addition, high economic growth in the lower Mekong River countries including two large rice exporters is expected to reduce the per capita consumption of rice as incomes grow. Consequently, the need exist to investigate changes in supply and demand using econometric models of rice markets in the countries, where water supplies are expected to change. The objective of this research is to clarify impacts of water supply changes on rice producers and consumers using supply and demand models of rice considering changes in the water supply to aid in producing agricultural policies and plans. The following two simulations were conducted in this assessment: (a) baseline and (b) CC_B2. The simulation of the baseline includes the assumption that the evapotranspiration (ET) of each province after 2000 is the average quantity of ET from 1995 to 1999. The simulation of the CC_B2 includes the assumptions that ET of each province after 2010 accords with the IPCC socioeconomic scenario B2. The simulation results suggest that climate change will depress wet season rice production in Cambodia and Mekong River Delta (MRD) region in Vietnam, and that of dry season rice in the MRD region in Vietnam and northeastern region (Isan) Thailand. The simulation results also indicate that climate change will increase farm prices of rice in Cambodia, Vietnam, and Thailand. The results suggest that climate changes will weigh on the livelihood of rice consumers, especially those of poor rural populations.

     

Impacts of climate change on rice market and production capacity in the Lower Mekong Basin

The supply of water is affected by climate changes. In addition, high economic growth in the lower Mekong River countries including two large rice exporters is expected to reduce the per capita consumption of rice as incomes grow. Consequently, the need exist to investigate changes in supply and demand using econometric models of rice markets in the countries, where water supplies are expected to change. The objective of this research is to clarify impacts of water supply changes on rice producers and consumers using supply and demand models of rice considering changes in the water supply to aid in producing agricultural policies and plans. The following two simulations were conducted in this assessment: (a) baseline and (b) CC_B2. The simulation of the baseline includes the assumption that the evapotranspiration (ET) of each province after 2000 is the average quantity of ET from 1995 to 1999. The simulation of the CC_B2 includes the assumptions that ET of each province after 2010 accords with the IPCC socioeconomic scenario B2. The simulation results suggest that climate change will depress wet season rice production in Cambodia and Mekong River Delta (MRD) region in Vietnam, and that of dry season rice in the MRD region in Vietnam and northeastern region (Isan) Thailand. The simulation results also indicate that climate change will increase farm prices of rice in Cambodia, Vietnam, and Thailand. The results suggest that climate changes will weigh on the livelihood of rice consumers, especially those of poor rural populations.     

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.

Evapotranspiration,irrigation water requirement,and water productivity of rice (<Emphasis Type="Italic">Oryza sativa</Emphasis> L.) in the Sahelian environment

Rice is the main crop produced in the Senegal River Valley under the semiarid Sahelian climate where water resource management is critical for the resource use sustainability. However, very limited data exit on rice water use and irrigation water requirement in this water scarcity environment under climate change conditions. Understanding crop water requirements is essential for better irrigation practices, scheduling and efficient use of water. The objectives of this study were to estimate crop water use and irrigation water requirement of rice in the Senegal River Valley at Fanaye. Field experiments were conducted during the 2013 hot and dry season and wet season, and 2014 hot and dry season and wet seasons. Three nitrogen fertilizer treatments were applied to rice variety Sahel 108: 60, 120, and 180 kg N ha^?1. Rice water use was estimated by the two-step approach. Results indicated that crop actual evapotranspiration (ETa) varied from 632 to 929 mm with the highest ETa obtained during the hot and dry seasons. Irrigation water requirement varied from 863 to 1198 mm per season. Rice grain yield was function of the growing season and varied from 4.1 to 10.7 tons ha^?1 and increased with nitrogen fertilizer rate. Rice water use efficiency relative to ETa and irrigation requirements increased with nitrogen fertilizer rate while rice nitrogen use efficiency decreased with the nitrogen fertilizer rates. The results of this study can be used as a guideline for rice water use and irrigation water requirement for the irrigation design projects, consultants, universities, producers, and other operators within rice value chain in the Senegal River Valley.     

稻—小龙虾—泥鳅绿色高效种养技术要点

稻虾鳅绿色高效种养模式能够提高稻田综合生产能力,实现农业增效及农民增收,是水稻种植和水产养殖结合后农业生态系统重建的典范模式.从田间工程改造、清沟消毒、施用基肥、投放有益生物、水稻品种选择、水稻栽培管理、放养苗种、饵料投喂、日常田间管理、水稻和水产品收获等方面介绍了稻虾鳅种养模式的关键技术.     

稻田高产节水灌溉方式的研究

 1984～1988年在中国水稻研究所实验场排水与其它农业措施相结合，采用节水灌溉措施和高产灌溉制度，综合考虑对田面水、土壤水、地下水和雨水的统一管理利用和合理调节控制，通过大田、小区、测坑试验和生产实践，提出了适合当地条件的节水高产灌排方式、地下水埋深度和排水量。这种水综合运用，既可节约灌溉用水量，减少灌水次数，还可降低排涝水量，减轻排涝能耗费用。     

Climate change’s impact on irrigation system and farmers’ response: a case study of the Plaichumpol Irrigation Project,Phitsanulok Province,Thailand

The Plaichumpol Irrigation Project, in Nan Basin of Thailand, is selected as a case study of impact study, where farmers depended on both surface and groundwater sources (especially in the dry year), to assess the impact on irrigation systems. The study used the MRI-GCM data to project the future climate condition and assess the impact on irrigation systems focusing on water shortage and groundwater pumping aspects in the selected consecutive dry years. The responses from farmers on the impact and adaptation were also gathered via site interviews and analyzed. Based on the bias-corrected MRI-GCM data, the annual rainfall in Nan Basin will decrease in the near future (2015–2039), compared with the past average data (1979–2006), while the rainfall will increase in the far future (2075–2099) compared with past. Water supply from dam will decrease in wet season and dry season, while water demand in both of near future and far future will increase in wet season and dry season. Less water shortage and groundwater pumping in both near-future and far-future periods are expected in the future consecutive dry years compared with the past, though the groundwater is still an important supplementary irrigation water source in the dry year. From the field interview, the farmers are ready to adapt to the changing situations and join in the water use meeting to follow up with irrigation officers about the adjustment of plant calendar and water allocation due to the climate change and to prepare adaptation measures as necessary.