Lasting effects of controlled irrigation during rice-growing season on nitrous oxide emissions from winter wheat croplands in Southeast China

Nitrous oxide (N₂O) emission from croplands in China is a serious environmental concern. Water management is an important factor in regulating N₂O emissions from croplands. In China, controlled irrigation (CI) is one mode of the water-saving irrigation for rice and is widely used. This study aims to assess the lasting effects of CI on N₂O emissions from winter wheat croplands in Southeast China, with traditional irrigation (TI) as the control. CI performed during the rice-growing season had obvious lasting effects on N₂O emissions of the subsequent winter wheat-growing season. Compared with TI, CI significantly increased the cumulative N₂O emission by 129.1 % during the rice-growing season (p < 0.05), but significantly decreased it by 47.7 % during the wheat season (p < 0.05). Continuous flooding of the TI during most of the rice-growing season resulted in an increase in N₂O emissions during the winter wheat-growing season. Over the whole annual cycle, the cumulative N₂O emission from the plots under CI during the rice-growing season was 5.3 kg N₂O–N ha^?1, which was 103.2 % of that under TI (p > 0.05). The results suggest that CI does not significantly increase the cumulative N₂O emission from the rice–winter wheat rotation systems while insuring rice and wheat yields. This study focuses on the lasting effects of water-saving irrigation mode during rice-growing season on N₂O emissions during the following wheat-growing season. Thus, it is a development and complement of the previous researches on the effects of water-saving irrigation on N₂O emissions from rice–winter wheat rotation croplands.     

New performance indicators for rice-based irrigation systems

Various indicators are used for evaluating the performance of different aspects of an irrigation system. This study proposes rice relative water supply (RRWS) and cumulative rice relative water supply (CRRWS) indicators to characterize the irrigation water delivery performance as the season advances in rice irrigation systems. These indicators were determined from field tests and evaluated. Traditionally, some standing water depth is kept in the field throughout the irrigation season. Some water is continuously delivered to maintain the standing water depth in the field due to the difference between the maximum standing water depth (WSmax _j ) and the present standing water depth (WS _j ). The widely used relative water supply (RWS) concept is found to incorrectly characterize an oversupply condition on irrigation deliveries for not considering the additional water supply to maintain standing water. Consequently, the cumulative relative water supply (CRWS) gives a wrong scenario in characterizing irrigation delivery performance throughout the season. The RRWS, on the other hand, distinctly characterizes the oversupply and undersupply condition on irrigation delivery as the season advances. A value of 1.0 for RRWS indicates an irrigation delivery that perfectly matches with the field water demand. Both in the main and off-season, RWS remains higher than RRWS during depletion periods (WS _j −WS _j ). On the other hand, the values of RWS and CRWS were higher than RRWS and CRRWS during 3rd to 6th weeks in the main season; and 3rd to 7th weeks in the off-season. The proposed indicators were found to be useful to enhance the decision-making and operational strategy for delivering the right amount of water to the fields for the upcoming period.     

Predicting future dry season periods for irrigation management in West Sumatra,Indonesia

Paddy and Water Environment - This paper proposes a new approach to predicting dry season periods by using annual cumulative rainfall for the past 35&nbsp;years to determine dry season...     

Effects of nitrogen fertilizer treatment and source and season on grain quality of IR64 rice

The effects of nitrogen fertilizer treatment and source (prilled urea, urea supergranule, fresh azolla, rice straw or sesbania or rice straw compost and their combinations) on grain quality were studied in the 1987 crops of variety IR64 at IRRI. Although fertilizer application improved grain yield, it improved protein content only in the case of urea supergranule, azolla and rice straw. Lysine contents of brown rice protein were similar in samples with no N fertilizer and those with the highest protein content in both seasons. Fertilizer treatment regardless of source tended to decrease weight and increase translucency of brown rice in both seasons. Effects on other grain properties were not consistent in both seasons. Season affected more grain properties than fertilizer treatment did, particularly translucency which was higher in the dry season than in the wet season.     

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.     

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.     

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.     

On-farm irrigation development and management in lower Myanmar: factors for sustainable rice production and collective action

The case study is aimed at assessing impacts of on-farm level irrigation development and management on dry season rice production in the main irrigated rice production area of Myanmar. The study was carried out from 2003 to 2009 in the middle reaches of the Ngameoeyeik irrigation area of 28,000 ha. In addition to collecting information on water management and institutional arrangement of the study area, hydrologic and agronomic parameters were monitored during the study period. Results showed the effectiveness of on-farm level infrastructural development for increasing rice productivity owing to increased amount of water delivery, increased flexibility of water distribution, and improved drainage conditions. Besides, encouraging the involvement of farmers in design and implementation of the development led to improved farmer participation in the operation and maintenance of the irrigation system. The outcomes of this study demonstrated the importance of balancing between infrastructural and institutional development in irrigation systems of Southeast Asia. Such infrastructural development should be in close association with institutional development and capacity building, and the interactions between those two aspects should be well understood.     

Recent irrigation practices in the Upper East Bank of the Chao Phraya Delta

This study aims to investigate recent practices on water allocation and cultivation in the Upper East Bank of the Chao Phraya Delta in Thailand, by using data collected by RID local offices, questionnaires, and analyses of satellite images. As a result, we have identified the advantage that upstream areas of irrigation canals have enjoyed, namely the preferential water allocation over the downstream areas. This advantage was strongly associated with the intensive cropping patterns of rice: the upstream areas were estimated to conduct almost continuous rice cultivation throughout a year. In addition, the intensive rice cultivation would partly be supported by water from private shallow wells, which were mostly concentrated in the upstream areas of main canals. Those shallow wells would be used at the beginning of the dry season and in drought years, when farmers could not expect water supply from irrigation canals. The result indicated that the conjunctive use of surface and ground water would be practiced in this region.     

潜育化稻田品种耐潜性差异与栽培技术研究

于2012年选取潜育化典型田块为试验田,研究了部分适合于长江中下游地区种植的早晚稻的耐潜性。结果表明,耐潜型的早稻品种为湘早籼45和金优458,敏感型的早稻品种为中嘉早17和湘早籼3号;耐潜型的晚稻品种为湘晚籼13,敏感型的晚稻品种为黄华占和天优华占。通过翻耕及垄畦栽培的方式可提高潜育化稻田水稻品种的有效穗数和每穗粒数,进而提高产量。     

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.     

Greenhouse gases emission from paddy soil during the fallow season with and without winter flooding in central Japan

Many papers on measurements of greenhouse gases (GHGs) emission in rice paddies during a rice cropping season have been published. During a non-cropping season between Nov. and Apr., we investigated direct and indirect GHGs emissions in rice paddies. The indirect GHGs emission was evaluated as the amount of dissolved gases leaching from the paddy fields. Water management practices for the experiment were (1) continuous flooding (CF) and (2) non-flooding (NF). Although the direct CO₂ emission in the CF treatment was remained nearly zero during the non-cropping period, direct CO₂ emission in the NF treatment was continuously observed throughout the non-cropping period. The concentration of dissolved N₂O in the NF treatment was below the detection limit of the instrument during the non-cropping period except immediately after the flooding and before the drainage. The concentration of dissolved N₂O kept approximately 2 µg L^?1 during the non-cropping period in the CF treatment. The direct CH₄ emission and dissolved CH₄ were not observed during the non-cropping period. Total gas emission in the NF treatment was 10 times as large as that in the CF treatment. Direct CO₂ emission accounted for more than 90 % of the total emission in both treatments.     

谈谈两优培特的一季加再生栽培技术

两优培特是１个很有推广价值的两系法杂交组合，有极大的生态空间和应用领域。介绍了两优培特头季稻和再生稻的综合特性；一季加再生栽培的两种模式，即“早再式”和“中再式”的异同点和实施技术；一季加再生的开发利用。     

谈谈两优培特的一季加再生栽培技术

两优培特是 1个很有推广价值的两系法杂交组合 ,有极大的生态空间和应用领域。介绍了两优培特头季稻和再生稻的综合特性 ;一季加再生栽培的两种模式 ,即“早再式”和“中再式”的异同点和实施技术 ;一季加再生的开发利用     

Comparison of Different Methods of Rice Establishment and Nitrogen Management Strategies for Lowland Rice

Abstract

Shortage of labor and water are forcing farmers to explore the alternatives of transplanting. A field experiment was conducted at the experimental farm of International Rice Research Institute (IRRI), Philippines during the 2003 wet season and the 2004 dry season to (1) evaluate the effects of different crop-establishment methods and N management on yield and yield parameters of rice; (2) determine N-use efficiency and water-use efficiency under different methods of rice establishment; and (3) analyze the economics of different crop-establishment methods. Crop-establishment method did not influence grain yield during the wet or dry seasons, indicating the potential of the three variants of direct seeding as alternative methods of establishing lowland rice. Direct-seeded rice had shorter crop duration, required less water and therefore had higher water-use efficiency than the transplanting method. Crop establishment did not influence the various indices of nitrogen-utilization efficiency except partial factor productivity of N (PFPN) during the wet season. During the dry season, dry-seeded rice had the lowest recovery efficiency. In contrast, agronomic-use efficiency and recovery efficiency were significantly higher in the SPAD-based (soil plant analyses development) N management strategy during the dry season. PFPN was significantly higher in the SPAD-based N management strategy during the wet and dry seasons. The interaction effect of crop establishment and N management indicated that for smaller N input and higher efficiency of N usage, N requirement for direct-seeded rice should be based on SPAD N technique. The cost-and-return analysis showed that benefit-cost ratio was consistently higher in dry seeding rice than transplanted rice using a SPAD-based N management.     

三明各县（市）汛期特涝年气候特征分析

对福建省三明各县（市）1961—2008年汛期（5、6月份）的降水资料进行统计分析，揭示汛期雨量特多、特涝和异常偏涝年份的时间、地域分布特征和周期演变规律；用500hPa月平均高度场资料分析了2005年汛期异常偏涝的环流特征，并就2005年汛期异常偏涝与历史上特涝年的环流形势进行了对比分析。结果表明：5、6月份由于东亚大槽明显偏东，副高面积大、强度强，脊线明显偏南，印缅槽强度偏强，导致西风槽非常活跃，不断东移、南压，这是造成2005年三明各县（市）汛期异常偏涝的主要原因；5、6月份由于逐日副高脊线位置适中、稳定，导致三明各县（市）汛期开始早、结束迟、持续时间长，这是造成2005年汛期异常偏涝的原因之一。     

Infiltration properties of paddy fields under intermittent irrigation

Puddling and recurring intermittent irrigation, common praxis in wet rice cultivation, modify the soil structure and therewith cause a temporal variation of the infiltration properties. This study attempts to evaluate the temporal variation of the infiltration rates of plough pan (vertical infiltration) and paddy fields’ surrounding bunds (bund infiltration) by analyzing (i) the infiltration rate as a function of time, (ii) the relationship between ponding water depth and infiltration rate, and (iii) the influence of cultivation age on vertical water loss and cross-flow through bunds. Two experimental fields with respective cultivation ages of 30 (A) and 7 (B) years were investigated. The results revealed that the time series of vertical infiltration rate (IR _v) was with time consistency and the persistency of the bund infiltration was uncertain. The mean infiltration rate into the plough pan of A and B was 3.34 and 1.01 cm d^?1, respectively. A total water depth of 230 and 85 cm would be, respectively, lost in A and B through the plough pan during rice growing season. The correlation coefficient between ponding water depth and IR _v was ?0.48 and ?0.81 in A and B, respectively, demonstrating that the dynamic IR _v in the old paddy field was less affected by the drying and wetting cycles. It is concluded that rice paddies which have been taken into cultivation since only a few decades may contribute to water losses. Maintenance of equilibrium condition between ponding and drying stages and careful preparation of bunds may reduce water loss.     

杂交中稻留桩高度对再生稻米质的影响及其与头季稻米质的关系

以18个通过审定的三系杂交中稻品种为材料,于头季稻收割时设留高桩(40 cm)和低桩(15 cm)两个处理,研究高桩与低桩对再生稻米质的影响,及再生稻品质与头季稻品质的关系。结果表明,在6项主要品质指标中,再生稻的直链淀粉含量和整精米率2项指标比头季稻优;头季稻留高桩的处理与留低桩的处理相比,再生稻胶稠度和直链淀粉含量显著变优。多数品质指标头季稻与再生稻之间、再生稻不同留桩高度之间呈显著或极显著正相关,头季稻品种品质对再生稻品质有重要影响。     

Opportunities to increasing dry season rice productivity in low temperature affected areas

Rice is a major source of food for more than 2.7 billion people and planted on nearly 130 million hectares in which 10% is subjected to low temperature problems. Dry season (DS) rice cropping has been expanding in the high altitude lands in Asia and the low temperature is one of constraints to rice production. This study aims to quantify the potential for growing irrigated rice in DS, particularly in high altitude areas in northern Lao PDR where temperatures are low and pose problems for seedling establishment. Research focused on identifying sowing times to avoid the detrimental effects of low temperature, the optimal seedling age for transplanting, the potential of plastic covers and half burnt paddy husk layer to protect nursery seedbeds from low temperature and varieties suitable for this environment. Studies were conducted over 5 years and were examined at six locations. In two locations, where temperature was favorable for rice production throughout the DS, time of sowing was not critical. In higher altitude areas in northern Lao PDR, however, low temperature caused establishment problems in nurseries. In these areas, mid-November sowing before the onset of winter reduced the low temperature effects on seedling establishment while sowing in mid winter (December and January) increased the risk of failure. There were no significant effects of seedling age (25-, 35- and 45-day old) for transplanting on yield for DS rice. Using clear plastic to cover the nursery increased minimum temperatures on average by about 4 °C, which improved seedling growth and resulted in higher grain yield. The mean minimum temperature of 12 °C for 30 days after seeding is critical and temperature below 12 °C resulted in high risk of crop failure due to poor germination, poor seedling growth or insufficient seedlings. Rice needs to be sown at times where the mean minimum temperature exceeds 12 °C or plastic covers are required to protect seedlings. The current popular varieties did not show significant tolerance to extreme cold temperature.