Issues of scale in water productivity in the Zhanghe irrigation system: implications for irrigation in the basin context

In the context of increased competition for water, growing more rice with less water will be one of the major challenges of the 21st century. This paper examines water savings and issues of scale in water productivity. The main objective is to understand if and how field-scale interventions scale up to subbasin-scale water savings in the Zhanghe Irrigation District (ZID) in Hubei Province, central China. Our results confirmed that on-farm water-saving practices result in higher water productivity per unit of irrigation water at the field scale due to lower irrigation water input. However, the question is, if these field-scale practices have led to real water savings; savings which can be transferred to other agricultural and non-agricultural uses without lowering existing production levels. To investigate this question, we examined water use and productivity at four different scales: field scale, meso scale, main canal command scale, and subbasin scale using the water accounting methodology. The study clearly demonstrates the high dependence on the scale of water use and productivity parameters. Depleted fraction and water productivity per unit of gross inflow and irrigation water varied dramatically across scale. Thus, it is not possible to conclude from field-scale observations that basin level water savings will or will not take place. The major reasons for these scale effects are the lateral flow of water across boundaries, differing land use patterns across scales, and changing water management patterns across scales. In the ZID, going from field and meso scale to even larger scales, water productivity per unit of irrigation increases to even higher levels than at the field scale. Here it becomes clear that the ZID, with its possibilities of reuse of drainage return flows and capturing rainfall and runoff in all the reservoirs within the system, is very effective in capturing and using water productively. Factors that influence water productivity and depleted fraction are on-farm water savings as well as the reuse of drainage water, effective capturing and utilization of rain, and canal water management. The scope for additional real water savings in the Zhanghe Irrigation District is limited. Only 13% of the combined rainfall and Zhanghe reservoir irrigation water releases flow out of the basin. A further reduction in drainage surface outflow from the ZID may have negative downstream effects on other water uses, including environmental uses. The main lessons learned are that (1) employing a combination of factors—on-farm practices, reuse, and canal operations—can be an effective means of conserving water resources within irrigation systems, (2) the scope for savings must be considered by an analysis at larger scales (i.e. irrigation system or basin scale), and may be less than thought because of the interactions of these factors. The results clearly indicate that scale effects are important for understanding and planning for water savings and water productivity.     

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.

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.     

Appropriation of Río San Juan water by Monterrey City, Mexico: implications for agriculture and basin water sharing

Monterrey metropolitan area’s growth has resulted in water transfers from the Río San Juan basin with significant impacts for downstream water users, especially farmers in the Bajo Río San Juan (BRSJ) irrigation district. El Cuchillo dam is the centerpiece of the basin’s water management infrastructure and has become the flashpoint of a multi-faceted water dispute between the states of Nuevo León and Tamaulipas as well as between urban and agricultural water interests in the basin. Subsequent to El Cuchillo’s implementation in 1994, the BRSJ irrigation district has been modifying its irrigation operations to adjust to the new water availability scenario. Compensation arrangements for farmers have been established, including crop loss payments on the order of US$ 100 per hectare un-irrigable due to the diversion of water to Monterrey plus 60% of the water diverted to be returned to farmers as treated effluent via the Ayancual Creek and Pesquería River, a process with its own water competition and environmental implications. The Mexican irrigation sector will continue to face intense competition for water given: (a) low water productivity in agriculture leading decision-makers to allocate water to higher productivity uses particularly in cities, (b) priority accorded to the domestic use component of municipal water supply, and in the BRSJ case, (c) Mexico’s national interests in meeting its water sharing obligations with the United States.     

Increasing water productivity for paddy irrigation in China

This paper introduces the research on practices to increase water productivity for paddy irrigation in China and summarizes the experience on implementation of the alternate wetting and drying (AWD) irrigation technique. The widespread adoption of the AWD practice on 40% of the rice growing area provides an opportunity for China to produce more food in the water-surplus south where it is wet and the traditional based paddy field agriculture is dominant. Physical and institutional measures leading to increasing water and land productivity in rice-based systems are discussed. Research studies show that AWD practice does not reduce rice yield, but does increase the productivity of water. Water use and thus water charges can be reduced. However, experience shows that demonstrations and training are needed to encourage farmer adoption. Furthermore, there are a range of complementary policies and practices, such as volumetric pricing or farm pond development, which provide incentives for adoption of AWD. Finally, there remain many scientific issues to be addressed. Application of the AWD technique in some regions is still very difficult because of both bio-physical and socio-economic problems. In conclusion, the widespread adoption of AWD is only a first step in the continuing effort to find practices that will increase water productivity for paddy irrigation in China.Dr. Yuanhua Li was a Professor and Dean in Wuhan University of Hydraulic and Electric Engineering from 1996 to 2000. After that, he has been a Professor and Deputy Director General of the National Centre for Irrigation and Drainage Development, Ministry of Water Resources, China. He has been doing research on irrigation principally for paddy since 1982.Dr. Randolph Barker is an agricultural economist and Professor Emeritus Cornell University. From 1966 to 1978 he served as head of the Economics Department, International Rice Research Institute, Los Banos, Philippines and from 1995 to 2004 was principal researcher, International Water Management Institute, Colombo, Sri Lanka.     

Application of system dynamics approach for time varying water balance in aerobic paddy fields

Increasing water scarcity has necessitated the development of irrigated rice systems that require less water than the traditional flooded rice. The cultivation of aerobic rice is an effort to save water in response to growing worldwide water scarcity with the pressure to reduce water use and increase water productivity. An accurate estimation of different water balance components at the aerobic rice fields is essential to achieve effective use of limited water supplies. Some field water balance components, such as percolation, capillary rise and evapotranspiration, can not be easily measured; therefore a soil water balance model is required to develop and to test water management strategies. This paper presents results of a study to quantify time varying water balance under a critical soil water tension based irrigation criteria for the cultivation of non-ponded “aerobic rice” fields along the lower parts of the Yellow River. Based on the analysis and integration of existing field information on the hydrologic processes in an aerobic rice field, this paper outlines the general components of the water balance using a conceptual model approach. The time varying water balance is then analyzed using the feedback relations among the hydrologic processes in a commercial dynamic modeling environment, Vensim. The model simulates various water balance components such as actual evapotranspiration, deep percolation, surface runoff, and capillary rise in the aerobic rice field on a daily basis. The model parameters are validated with the observed experimental field data from the Huibei Irrigation Experiment Station, Kaifeng, China. The validated model is used to analyze irrigation application soil water tension trigger under wet, dry and average climate conditions using daily time steps. The scenario analysis show that to conserve scarce water resources during the average climate years the irrigation scheduling criteria can be set as −30 kPa average root zone soil water tension; whereas it can be set at −70 kPa during the dry years, however, the associated yields may reduce. Compared with the flooded lowland rice and other upland crops, with these two alternatives irrigation event triggers, aerobic rice cultivation can lead to significant water savings.     

Modeling of continental-scale crop water requirement and available water resources

The relationship between agricultural water demand and supply has been of interest to government decision makers and scientists because of its importance in water resources management. We developed a water cycle model for eastern Eurasia that can estimate water requirements for crop growth and evaluate the demand–supply relationships of agricultural water use on a continental scale. To produce an appropriate water cycle, the model was constructed based on small drainage basins. To validate the model performance with respect to simulated runoff, which is here considered as the available water resource, we compared our outputs with those of other models and with observed river discharges. The results show that this model is comparable to other models and that it is applicable for the evaluation of water cycles at continental scale. We defined two types of crop water deficits (CWDs) as indicators of agricultural water demand. These were formulated by considering the physical processes of crop water use; we did not include water consumption that is dependent on cultivation management practices, such as water losses in irrigation systems. We assessed the reliability of our indicators by comparison with indicators from other studies and with published statistics related to agricultural water use. These comparisons suggest that our indicators are consistent with independent data and can provide a reasonable representation of water requirements for crop growth.     

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.     

Transferring water from irrigation to higher valued uses: a case study of the Zhanghe irrigation system in China

The Zhanghe irrigation system (ZIS) is located in the Yangtze River Basin approximately 200 km west of Wuhan in Hubei Province. The reservoir was designed for multiple uses—irrigation, flood control, domestic water supply, industrial use, aquaculture, and hydropower. Over a period of more than 30 years a steadily increasing amount of water has been transferred from irrigation to other uses. Activities on the part of government, irrigation system managers, and farmers made this transfer possible with only modest decline in rice production. Most important factor was the steady increase in rice yields. The water pricing system provided an incentive for ZIS to reduce irrigation releases. With the steady decline in releases, farmers were forced to find ways to save water. Farmers improved existing ponds and built new ones to store water (improved infrastructure). Access to pond water on demand facilitated the adoption of alternate wetting and drying (technology) particularly in dry years. The establishment of volumetric pricing (price policy) and water user associations (institutions) may also have provided incentives for adoption of AWD, but more research is needed to establish their impact. These activities taken together can be seen as potentially complementary measures. Farmers received no direct compensation for the transfer of water, but recently farm taxes have been reduced or altogether abolished. Further reduction in water releases from the ZIS reservoir could adversely affect rice production in normal or dry years.     

The impact of on-farm water saving irrigation techniques on rice productivity and profitability in Zhanghe Irrigation System,Hubei, China

To optimize the use of limited water resources, surface irrigation systems in parts of China have introduced a new water saving irrigation method for rice termed alternate wetting and drying (AWD). The basic feature of this method is to irrigate so that the soil alternates between periods of standing water and damp or dry soil conditions from 30 days after crop establishment up to harvesting. However, many Chinese rice farmers still practice the continuous irrigation method with late- season drying of the soil.A comparative assessment of these two methods of on-farm water management for rice was conducted at two sites within the Zhanghe Irrigation System (ZIS) in Hubei province of China for the 1999 and 2000 rice crops. The objective was to evaluate the impact of AWD on crop management practices and the profitability of rice production. In conjunction with irrigation district officials, two sites within ZIS were selected for study, one where AWD was supposed to be widely practiced (Tuanlin, TL) and one where it had not been introduced (Lengshui, LS). It was found that farmers at both sites do not practice a pure form of either AWD or continuous flooding. However, farmers in TL did tend to let the soil dry more frequently than their counterparts in LS.Because most farmers practice neither pure AWD nor pure continuous flooding, an AWD score was developed that measures the frequency with which farmers allow their soil to dry. This AWD score was not significantly correlated with yield after controlling for site and year effects and input use. AWD scores were also not correlated with input use. We conclude that AWD saves water at the farm level without adversely affecting yields or farm profitability.     

More Rice,Less Water—Integrated Approaches for Increasing Water Productivity in Irrigated Rice-Based Systems in Asia

Abstract

The water crisis is threatening the sustainability of the irrigated rice system and food security in Asia. Our challenge is to develop novel technologies and production systems that allow rice production to be maintained or increased in the face of declining water availability. This paper introduces principles that govern technologies and systems for reducing water inputs and increasing water productivity, and assesses the opportunities of such technologies and systems at spatial scale levels from plant to field, to irrigation system, and to agro-ecological zones. We concluded that, while increasing the productivity of irrigated rice with transpired water may require breakthroughs in breeding, many technologies can reduce water inputs at the field level and increase field-level water productivity with respect to irrigation and total water inputs. Most of them, however, come at the cost of decreased yield. More rice with less water can only be achieved when water management is integrated with (i) germplasm selection and other crop and resource management practices to increase yield, and (ii) system-level management such that the water saved at the field level is used more effectively to irrigate previously un-irrigated or low-productivity lands. The amount of water that can be saved at the system level could be far less than assumed from computations of field-level water savings because there is already a high degree of recycling and conjunctive use of water in many rice areas. The impact of reducing water inputs for rice production on weeds, nutrients, sustainability, and environmental services of rice ecosystems warrants further investigation.     

Growth, yield and water productivity of zero till wheat as affected by rice straw mulch and irrigation schedule

Intensive cultivation of rice and wheat in north-west India has resulted in air pollution from rice straw burning, soil degradation and declining groundwater resources. The retention of rice residues as a surface mulch could be beneficial for moisture conservation and yield, and for hence water productivity, in addition to reducing air pollution and loss of soil organic matter. Two field experiments were conducted in Punjab, India, to study the effects of rice straw mulch and irrigation scheduling on wheat growth, yield, water use and water productivity during 2006-2008. Mulching increased soil water content and this led to significant improvement in crop growth and yield determining attributes where water was limiting, but this only resulted in significant grain yield increase in two instances. There was no effect of irrigation treatment in the first year because of well-distributed rains. In the second year, yield decreased with decrease and delay in the number of irrigations between crown root initiation and grain filling. With soil matric potential (SMP)-based irrigation scheduling, the irrigation amount was reduced by 75 mm each year with mulch in comparison with no mulch, while maintaining grain yield. Total crop water use (ET) was not significantly affected by mulch in either year, but was significantly affected by irrigation treatment in the second year. Mulch had a positive or neutral effect on grain water productivity with respect to ET (WP_ET) and irrigation (WP_I). Maximum WP_I occurred in the treatment which received the least irrigation, but this was also the lowest yielding treatment. The current irrigation scheduling guidelines based on cumulative pan evaporation (CPE) resulted in sub-optimal irrigation (loss of yield) in one of the two years, and higher irrigation input and lower WP_I of the mulched treatment in comparison with SMP-based irrigation scheduling. The results from this and other studies suggest that farmers in Punjab greatly over-irrigate wheat. Further field and modelling studies are needed to extrapolate the findings to a wider range of seasonal and site conditions, and to develop simple tools and guidelines to assist farmers to better schedule irrigation to wheat.     

Yield, water use efficiency and nitrogen uptake in potato: influence of drought stress

Summary A lysimeter experiment was performed to study the optimal allocation of limited water supply in potatoes. Irrigation regimes equal to 40, 60 and 80% of maximum evapotranspiration (ET) were evenly applied over the crop cycle. Other treatments involved withholding 80 mm of irrigation, based on ET, beginning at each of three designated growth stages (tuber initiation, early and late tuber growth). An irrigated control treatment, restoring the entire ET, was included for comparison. Continuous drought stress reduced photosynthesis as irrigation volumes were reduced. Plant biomass and tuber yield decreased almost proportionally to water consumption, so that WUE was roughly constant. N uptake was highest in the control and in 80% ET treatment. Withholding water during tuberisation severely hindered plant physiological processes and penalized tuber yield. Reductions in photosynthesis, total biomass and yield were the greatest when drought was imposed during tuber initiation. The earliest stress resulted in the lowest WUE and N uptake. A new crop water stress index (SI) was proposed, which combines atmospheric demand for water and canopy temperature.     

Farm level practices and water productivity in Zhanghe Irrigation System

China, the biggest rice-producing country in the world, has put considerable effort into finding ways to conserve water in rice cultivation. One very promising practice, intermittent submerged irrigation (ISI) was reported to be applied on farmers fields over a large area in the Zhanghe irrigation system (ZIS), which serves about 160,000 ha of irrigated land, which is intensively cultivated with rice. To better understand the actual farmer practices, the degree to which farmers adopt ISI, the resulting water productivity, and implications for farm and system water management, a water accounting methodology developed by IWMI was applied at farm and a larger meso scale. Two areas were observed: Tuanlin, where ISI was reported to be widespread (with ISI), and Wenjiaxiang, where farmers were reportedly not adopting ISI (without ISI). The field water level measurements demonstrate that farmers at the with ISI site follow a practice similar to the theoretical ISI techniques by letting ponding levels drop to the soil surface several times during the cropping season. At the without site, farmers keep higher water levels ponded, and do not let water levels drop to the soil surface as often as the with site. A major determinant of practice is ease of access to water. At the with site, farmers have access to a variety of sources such as ponds and drains. At the without site, access to water was primarily from canal water, without the degree of flexibility as areas that had a water source near the field. The process fraction of gross inflow at field scale (rice evapotranspiration divided by irrigation plus rain) ranged between 0.66 and 0.93, remarkably high values showing how effective farmers are in converting water sources to productive evapotranspiration. The on-farm water accounting results show that with ISI, the average values of irrigation water applied over two years 1999–2000 are 22% less than without ISI, and the yields approximately the same. The resulting water productivity values per unit of irrigation water (WP_irrigation) are 20% higher under ISI practices, but per unit of evapotranspiration water productivity results are similar. The meso site study yielded surprising insights into overall water management in the area. In the years 1999 and 2000, at the meso sites, the irrigation duty in Tuanlin (with ISI) was 29% and 21% less than in Wenjiaxiang (without ISI), respectively, resulting in WP_irrigation values of 24% and 26% higher at Tuanlin than Wenjiaxiang. But values of process fraction of gross inflow were considerably reduced at the meso scale ranging between 0.12 and 0.29, with considerable drainage outflow observed. Different land uses, trees, roads, villages, and ponds, begin to play an important role in overall water resource management at this scale. Drainage water from fields plus runoff served as supplies to ponds within the meso area as well as downstream reservoirs. Ponds play a very important role as an additional source of water, and in fact facilitate the uptake of ISI practices. This demonstrates that there are multiple strategies at play influencing water savings and productivity beyond ISI in the management of water within the area.     

Yield response,water productivity,and seasonal water production functions for maize under deficit irrigation water management in southern Taiwan

As the challenges toward increasing water for irrigation become more prevalent, knowledge of crop yield response to water can facilitate the development of irrigation strategies for improving agricultural productivity. Experiments were conducted to quantify maize yield response to soil moisture deficits, and assess the effects of deficit irrigation (DI) on water productivity (water and irrigation water use efficiency, WUE and IWUE). Five irrigation treatments were investigated: a full irrigation (I₁) with a water application of 60 mm and four deficit treatments with application depths of 50 (I₂), 40 (I₃), 30 (I₄), and 20 mm (I₅). On average, the highest grain yield observed was 1008.41 g m^?2 in I₁, and water deficits resulted in significant (p < .05) reduction within range of 6 and 33%. This reduction was significantly correlated with a decline in grain number per ear, 1000-grain weight, ear number per plant, and number of grain per row. The highest correlation was found between grain yield and grain number per ear. The WUE and IWUE were within range of 1.52–2.25 kg m^?3 and 1.64–4.53 kg m^?3, respectively. High water productivity without significant reduction in yield (<13%) for I₂ and I₃ compared to the yield in I₁ indicates that these water depths are viable practices to promote sustainable water development. Also, for assessing the benefits of irrigation practices in the region crop water production functions were established. Maize yield response to water stress was estimated as .92, suggesting the environmental conditions are conducive for implementing DI strategies.     

Effect of water saving management practices and nitrogen fertilizer rate on crop yield and water use efficiency in a winter wheat–summer maize cropping system

Deficit irrigation (DI) is a water-saving irrigation strategy in which irrigation water is applied at amounts less than full crop-water requirements. Some researchers have suggested that greater increases in water use efficiency (WUE) could be realized if DI was used in combination with water conservation or rainwater harvesting techniques. The objective of this six-year field study was to determine the effect of DI in combination with straw mulch (SM) or plastic film-mulched ridge and straw-mulched furrows (RF) on grain yield and WUE in a winter wheat-summer maize rotation. Interactive effects between the water-saving management practices and N fertilizer rate were also investigated. Results indicated that maize yields in the RF + DI and SM + DI treatments were as much as 1.6 times those in the DI and conventional furrow irrigation (CFI) treatments. Over the six-year study, total maize yield in the RF + DI treatment was 5580 kg/ha more than in the CFI treatment and 6500 kg/ha more than in the DI treatment. Wheat yields in the RF + DI and SM + DI treatments were similar to the CFI treatment but slightly more than in the DI treatment. At harvest, there was no significant difference in water storage in the 0-200 cm soil profile among the RF + DI, SM + DI, DI, and CFI treatments. Nitrogen fertilizer application significantly increased maize and wheat yield compared to the unfertilized treatment; however, there was no further yield response when the N application rate exceeded 120 kg N/ha. In summary, these results indicated that DI in combination with SM or RF practices increased crop yield and WUE in the winter wheat-summer maize crop rotation. Compared to CFI practices, the SM + DI and RF + DI practices reduced the amount of irrigation water applied over a six-year period by about 350 mm.     

Effects of water-saving irrigation on weed infestation and diversity in paddy fields in East China

The purpose of the article is to investigate the effects of water-saving irrigation on weed infestation and diversity in paddy fields; a two-year field experiment was conducted in Gaoyou Irrigation District, China. The responses of two irrigation treatments, controlled irrigation (CI) and traditional irrigation (TI), were observed and compared. The irrigation water use, yield, weed density, coverage ratio, height, species richness, density, dominant species, Shannon–Wiener index, and Pielou index were examined to analyze the water productivity, weed infestation, and diversity in paddy fields under the two treatments. The results showed that the water conditions were similar before the late tillering stage, and thereafter the CI fields were alternatively dry and wet with shallow standing water and low soil water content, while the TI fields were mostly continuously flooded by deep standing water and high soil water content. Irrigation water use for CI was 46.8% lower than TI. The CI treatment reduced weed density by 38.0%, decreased coverage ratio by 13.8%, and resulted in a 39.0% increase in weed height. Fewer species were found in CI fields than TI fields. The Shannon–Wiener index decreased by 11.5%, and the Pielou index increased by 3.2%. The changed water regime under CI not only impeded the growth of dominant species but also placed the whole weed community at a relatively stable level with reduced weed density. Meanwhile, aquatic weeds were well controlled; however, semi-aquatic weeds became the dominant species. In general, CI effectively reduced the risk of weed outbreaks, and weed diversity also decreased when it reduced irrigation water use.     

Effect of irrigation schedule on growth and seed yield of camelina (Camelina sativa L.) in Tarai region of central Himalaya

Camelina(Camelina sativa)has emerged as a potential biofuel crop globally with its suitability even as a jet fuel source with 75–80%less greenhouse gas emissions compared to common petroleum fuels.The crop has originated from Mediterranean region and belongs to Brassicaceae family.DIBER,DRDO has made initial and pioneer efforts in successful introduction of this crop to India and its agro-technology standardization.Being a short duration crop with lesser input requirement,it fits well in the cropping pattern of hilly states of Indian Himalaya.These areas experience fallow land due to shortage of irrigation water for growing other crops.The present study revealed that irrigation at flowering stage is more beneficial.Irrigation at this stage(if only one irrigation is available)exhibited grain yield of 1.004 kg·m^-2which was 21 and 80%higher over pod setting and rosette stage irrigation,respectively.The maximum seed yield was observed under treatment where irrigation was provided at all three crop growth stages(2.044 kg·m^-2).It was 50%higher over T6 treatment(where two irrigations were given at rosette and flowering stage)and 104%higher over T3(where only one irrigation was given at flowering stage).     

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

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

宁夏引黄灌区滴灌玉米4种光响应曲线模型比较

为探讨宁夏引黄灌区滴灌玉米光合响应机制,采用Li-6400XT气体交换测量系统测定2年玉米大喇叭口期的光响应曲线,选取4种通用的光响应曲线模型分别对玉米光响应过程进行分析、拟合与比较,筛选出6个不同氮素处理下最优光响应模型,并利用最优模型计算分析玉米光合生理特征参数。结果表明,滴灌玉米功能叶片光合能力随着施氮量的增加呈递增趋势。通过模型误差计算与分析,4种光响应曲线模型拟合精度存在差异,且直角双曲线、非直角双曲线和指数模型对于高氮处理的光响应曲线拟合度均高于低氮处理。相对其他3种模型,直角双曲线修正模型拟合精度最高,可作为最优光响应曲线模型模拟引黄灌区水肥一体化玉米光响应动态。由最优模型对各氮素处理光响应生理参数计算分析表明,360 kg/hm^2氮处理玉米叶片的光响应参数均高于其他氮处理,有利于提高玉米对强光的适应范围和光能利用效率,增强光合作用。