Influence of rice varieties, organic manure and water management on greenhouse gas emissions from paddy rice soils

The study is focused on impact of manure application, rice varieties and water management on greenhouse gas (GHG) emissions from paddy rice soil in pot experiment. The objectives of this study were a) to assess the effect of different types of manure amendments and rice varieties on greenhouse gas emissions and b) to determine the optimum manure application rate to increase rice yield while mitigating GHG emissions under alternate wetting and drying irrigation in paddy rice production. The first pot experiment was conducted at the Department of Agronomy, Yezin Agricultural University, Myanmar, in the wet season from June to October 2016. Two different organic manures (compost and cow dung) and control (no manure), and two rice varieties; Manawthukha (135 days) and IR-50 (115 days), were tested. The results showed that cumulative CH₄ emission from Manawthukha (1.084 g CH₄ kg^-1 soil) was significantly higher than that from IR-50 (0.683 g CH₄ kg^-1 soil) (P<0.0046) with yield increase (P<0.0164) because of the longer growth duration of the former. In contrast, higher cumulative nitrous oxide emissions were found for IR-50 (2.644 mg N₂O kg^-1 soil) than for Manawthukha (2.585 mg N₂O kg^-1 soil). However, IR-50 showed less global warming potential (GWP) than Manawthukha (P<0.0050). Although not significant, the numerically lowest CH₄ and N₂O emissions were observed in the cow dung manure treatment (0.808 g CH₄ kg^-1 soil, 2.135 mg N₂O kg^-1 soil) compared to those of the control and compost. To determine the effect of water management and organic manures on greenhouse gas emissions, second pot experiments were conducted in Madaya township during the dry and wet seasons from February to October 2017. Two water management practices {continuous flooding (CF) and alternate wetting and drying (AWD)} and four cow dung manure rates {(1) 0 (2) 2.5 t ha^-1 (3) 5 t ha^-1 (4) 7.5 t ha^-1} were tested. The different cow dung manure rates did not significantly affect grain yield or greenhouse gas emissions in this experiment. Across the manure treatments, AWD irrigation significantly reduced CH₄ emissions by 70% during the dry season and 66% during the wet season. Although a relative increase in N₂O emissions under AWD was observed in both rice seasons, the global warming potential was significantly reduced in AWD compared to CF in both seasons (P<0.0002, P<0.0000) according to reduced emission in CH₄. Therefore, AWD is the effective mitigation practice for reducing GWP without compromising rice yield while manure amendment had no significant effect on GHG emission from paddy rice field. Besides, AWD saved water about 10% in dry season and 19% in wet season.

Impact of treatment plant management on human health and ecological risks from wastewater irrigation in developing countries - case studies from Cochabamba, Bolivia

Wastewater irrigation is a common practice in developing countries due to water scarcity and increasing demand for food production. However, there are health risks and ecological risks associated with this practice. Small-scale wastewater treatment plants (WWTPs) intend to decrease these risks but still face management challenges. This study assessed how the management status of five small-scale WWTPs in Cochabamba, Bolivia affects health risks associated with consumption of lettuce and ecological risks due to the accumulation of nutrients in the soil for lettuce and maize crops. Risk simulations for three wastewater irrigation scenarios were: raw wastewater, actual effluent and expected effluent. Results showed that weak O&M practices can increase risk outcomes to higher levels than irrigating with raw wastewater. Improving O&M to achieve optimal functioning of small-scale WWTPs can reduce human health risks and ecological risks up to 2 log₁₀ DALY person^-1 year^-1 and to 2 log₁₀ kg nitrogen ha^-1 accumulated in soil, respectively.

Assessing the effect of irrigation on household water quality and health: A case study in rural Ethiopia

In areas with inadequate improved water supply, irrigation water serves as an alternative water source for domestic uses in addition to its prime purpose of agricultural production. This increased water availability for the household can generate positive hygiene and health impacts, but poor irrigation water quality can be a source of domestic water contamination and can be harmful to human health. Using primary household survey data from two rural districts of Ethiopia, this study seeks to disentangle these opposite effects: the results show that irrigation is associated with poor household water quality (adjusted odds ratio 1.68, 95%, CI 1.07-2.66) and a lower risk of diarrheal disease (adjusted odds ratio 2.07, 95%, CI 1.24-3.44). Domestic use of irrigation water, however, does not further degrade the microbial quality of household water. On the other hand, the domestic use of irrigation water reduces the burden of water collection (p < 0.01). Providing education and training programs to foster behavioral change towards sustainable improvements in water resource management, such as the safe use of irrigation water for domestic purposes through appropriate point-of-use water treatment, would be crucial to maximize the benefits of the domestic use of irrigation water and to minimize adverse environmental and health risks.

ERA5-based global assessment of irrigation requirement and validation

While only 20% of harvested lands are actually irrigated, 40% of global agricultural production originates from irrigated areas. Therefore, assessing irrigation requirements is essential for the development of effective water-related policies for an efficient management of water resources. Moreover, global-scale analyses are becoming increasingly relevant, motivated by globalized production and international trade of food as well as by the need of common strategies to address climate change.

In this study, a comprehensive model to estimate crop growth and irrigation requirements of 26 main crops at global scale is presented. The model computes a soil water balance using daily precipitation and reference evapotranspiration based on a high-resolution ERA5 reanalysis dataset from the European Copernicus Program. The irrigation requirement, defined as the minimum water volume to avoid water stress, is computed for year 2000 at the resolution of 5 arc-min (or 0.0833°) and aggregated at different spatial and temporal scales for relevant analyses.

The estimated global irrigation requirements for 962 km³ is described in detail, also in relation to the spatial variability and to the monthly variation of the requirements. A focus on different areas of the world (California, Northern Italy and India) highlights the wealth of information provided by the model in different climatic conditions.

National data of irrigation withdrawals have been used for an extensive comparison with model results. A crop-specific validation has also been made for the State of California, comparing model results with local data of irrigation volume and independent estimates of crop water use. In both cases, we found a good agreement between model results and real data.

Multistage stochastic programming modeling for farmland irrigation management under uncertainty

Farmland management and irrigation scheduling are vital to a productive agricultural economy. A multistage stochastic programming model is proposed to maximize farmers’ annual profit under uncertainty. The uncertainties considered include crop prices, irrigation water availability, and precipitation. During the first stage, pre-season decisions including seed type and plant density are made, while determinations of when to irrigate and how much water to be used for each irrigation are made in the later stages. The presented case study, based on a farm in Nebraska, U.S.A., showed that a 10% profit increase could be achieved by taking the corn price and irrigation water availability uncertainties into consideration using two-stage stochastic programming. An additional 13% profit increase could be achieved by taking precipitation uncertainty into consideration using multistage stochastic programming. The stochastic model outperforms the deterministic model, especially when there are limited water supplies. These results indicate that multistage stochastic programming is a promising method for farm-scale irrigation management and can increase farm profitability.

A meta-analysis of the effects of crop residue return on crop yields and water use efficiency

After harvesting agricultural crops, the residue can be returned to the soil as mulch. This study performed a meta-analysis of previous research to investigate the effects of crop residue return and other factors on crop yields and water use efficiency (WUE). Overall, the results show that crop residue return increases crop yields by 5.0% relative to crops grown without it. The greatest increases in yield for crops grown with returned residue were associated with average annual temperatures < 10 °C (yield increase = 7.6%), rainfall ≥ 800 mm (9.5%), plowing depth ≥ 20 cm (6.5%), corn crops (8.0%), growth of a single crop per year (10.1%), no irrigation (11.9%), nitrogen (N), and potassium (K) fertilization (20.0%), and low nitrogen application rates of 0–100 kg N ha^-1 (10.8%). The effects of crop residue return on crop yields were found to vary according to the following soil properties: organic matter content ≥ 15 g kg^-1 (yield increase = 9.4%), available nitrogen content ≥ 100 mg kg^-1 (10.3%), and pH ≤ 6.5 (11.2%). The greatest magnitudes of increase in WUE associated with crop residue return were associated with corn (yield increase = 13.7%), medium nitrogen content (100–150 kg ha^-1; 23.3%), high soil organic matter (≥ 15 g kg^-1; 25.5%) and low air temperatures (< 10 °C; 19.9%). In addition, our results suggest that crop residue return might be most effective in increasing crop yields and WUE in corn crops, crops with a tillage depth ≥ 20 cm, crops grown with moderate nitrogen fertilization (0–150 kg ha^-1), growth of a single crop per year, high soil organic matter content (≥ 15 g kg^-1), and cold conditions (< 10 °C). Overall, the results of this meta-analysis suggest that crop residue return can increase crop yields and WUE, with the relationship being mainly affected by climatic conditions, plowing depth, fertilization management, crop types, and soil properties.

Climate adaptation by crop migration

Many studies have estimated the adverse effects of climate change on crop yields, however, this literature almost universally assumes a constant geographic distribution of crops in the future. Movement of growing areas to limit exposure to adverse climate conditions has been discussed as a theoretical adaptive response but has not previously been quantified or demonstrated at a global scale. Here, we assess how changes in rainfed crop area have already mediated growing season temperature trends for rainfed maize, wheat, rice, and soybean using spatially-explicit climate and crop area data from 1973 to 2012. Our results suggest that the most damaging impacts of warming on rainfed maize, wheat, and rice have been substantially moderated by the migration of these crops over time and the expansion of irrigation. However, continued migration may incur substantial environmental costs and will depend on socio-economic and political factors in addition to land suitability and climate.

U.S. farmers' opinions on the use of nontraditional water sources for agricultural activities

Water is a key resource for agricultural production in the United States. Due to projected changes in water availability across the country, long-term sustainability of agricultural production may rely on finding alternatives to traditional water sources. The aim of this study was to assess farmers' opinions on the use of nontraditional water sources (e.g., agricultural runoff, treated wastewater, recycled water, produced water, untreated surface water, and brackish surface and groundwater) for agricultural activities. A survey was distributed to farmers (n = 746) in the Mid-Atlantic and Southwest regions of the United States (U.S.) about water availability and nontraditional irrigation water perceptions. Chi-square, Fisher's exact tests, f-tests, and multinomial and ordinal logistic regression analyses were conducted. Of farmers surveyed, 80% (431/543) considered the use of nontraditional water sources to be at least moderately important and 61% (444/727) would use nontraditional water if given the option. Each of the following factors individually increased the likelihood that a farmer considered nontraditional water very important for agriculture: Farmers who lived in the Southwest region compared to the Mid-Atlantic, farmers who were concerned about water availability compared with those who were not, farmers with a graduate or professional degree compared to those with less education, farmers with access to nontraditional water, and farmers with some knowledge of nontraditional water compared to those with no reported knowledge. Concern about water availability and knowledge of nontraditional water sources were significantly associated with willingness to use these water sources (p < 0.001 for both). Water quality, food safety and health risks were the main concerns regarding nontraditional water use across both regions. Willingness to use nontraditional water increased significantly if the water quality was proven to be as good or better than farmers' current water sources (63% vs. 84%; p < 0.001). Projects focused on nontraditional water use in agriculture should be regionally tailored as our data found significant differences between farmers in two distinct U.S. regions.

Prevalence of Shiga-toxigenic and atypical enteropathogenic Escherichia coli in untreated surface water and reclaimed water in the Mid-Atlantic U.S

The microbial quality of irrigation water has increasingly become a concern as a source of contamination for fruits and vegetables. Non-traditional sources of water are being used by more and more growers in smaller, highly diversified farms in the Mid-Atlantic region of the U.S. Shiga-toxigenic E. coli (STEC) have been responsible for several outbreaks of infections associated with the consumption of leafy greens. Our study evaluated the prevalence of the "big seven" STEC serogroups and the associated enterohemorrhagic E. coli (EHEC) virulence factors (VF) genes in conventional and nontraditional irrigation waters in the Mid-Atlantic region of the U.S. Water samples (n = 510) from 170 sampling events were collected from eight untreated surface water sites, two wastewater reclamation facilities, and one vegetable processing plant, over a 12-month period. Ten liters of water were filtered through Modified Moore swabs (MMS); swabs were then enriched into Universal Pre-enrichment Broth (UPB), followed by enrichment into non-O157 STEC R&F broth and isolation on R & F non-O157 STEC chromogenic plating medium. Isolates (n = 2489) from enriched MMS from water samples were screened for frequently reported STEC serogroups that cause foodborne illness: O26, O45, O103, O111, O121, O145, and O157, along with VF genes stx1, stx2, eae, and ehxA. Through this screening process, STEC isolates were found in 2.35% (12/510) of water samples, while 9.0% (46/510) contained an atypical enteropathogenic E. coli (aEPEC) isolate. The eae gene (n = 88 isolates) was the most frequently detected EHEC VF of the isolates screened. The majority of STEC isolates (stx1 or stx2) genes mainly came from either a pond or reclamation pond water site on two specific dates, potentially indicating that these isolates were not spatially or temporally distributed among the sampling sites. STEC isolates at reclaimed water sites may have been introduced after wastewater treatment. None of the isolates containing eae were determined to be Escherichia albertii. Our work showed that STEC prevalence in Mid-Atlantic untreated surface waters over a 12-month period was lower than the prevalence of atypical EPEC.

Effects of temperature, precipitation and carbon dioxide concentrations on the requirements for crop irrigation water in China under future climate scenarios

Maize, rice, wheat and soybean-the major staple food crops in China-have a crucial role in national food security and economic development. Predictions of changes in the requirements for irrigation water in food crop production under climate change may provide scientific support for the optimum allocation of water resources and measures to mitigate climate change. We conducted a spatial grid-based analysis using projections of future climate generated by a bias-correction and spatial disaggregation multi-model ensemble for three representative concentration pathway scenarios (RCP2.6, RCP4.5 and RCP8.5) adopted by the fifth phase of the Coupled Model Intercomparison Project. We investigated the effects of climate change associated with increasing temperature, changed precipitation and increased concentrations of atmospheric carbon dioxide (CO2) on the irrigation water requirements of maize, rice, wheat and soybean in China at the end of the 21st century (2081-2100). Our results indicate that the irrigation water requirements of maize and wheat are driven by temperature and especially by CO2 concentrations in the northwest interior area as a result of the low rainfall and high rates of evaporation; the irrigation water requirement of soybean is influenced by a combined effect of temperature, precipitation and CO2 concentration, whereas the irrigation water requirement for rice is dominated by precipitation alone in the southern coastal region, which has high rainfall. The irrigation water requirements of crops decrease mainly as a result of the beneficial effects of CO2 on plant growth in China. The regions requiring vast amounts of irrigation water as a result of climate change are mainly concentrated in northwestern China. The effects of climate change affect the requirement for irrigation water, especially under high-emission scenarios, and should be studied further to design appropriate adaptation strategies for the management of agricultural water to maintain the sustainable development of agriculture.

Hydrochemical characteristics and quality assessment of groundwater for irrigation use in central and eastern Songnen Plain, Northeast China

The hydrochemical characteristics of groundwater in Songnen Plain's agricultural area were analyzed based on aquifer types and topography classification to evaluate irrigation suitability and factors influencing groundwater quality. Samples of different groundwater types and topographical conditions within the research area were collected and chemical indices, such as sodium adsorption ratio, %Na⁺, residual sodium carbonate, and magnesium hazard values, were calculated to assess the groundwater suitability for irrigation. The results indicated that groundwater was generally neutral, with low total dissolved solids and slightly high hardness; the dominant anion in groundwater was HCO₃^-, while Ca²⁺ was the relatively stable primary cation found in water samples from the high plain and river valley plain. The nitrate in groundwater significantly exceeded WHO drinking water standards, especially in the unconfined water of the high plain, which was due to the large-scale agricultural production activities in the eastern regions. The main reactions in the groundwater system were weathering and dissolution of carbonates and sulfates and ion-exchange reactions. Horizontal zoning in water chemical characteristics was prominent; from the high plain to river valley plain and low plain, the hydrochemistry gradually transitioned from HCO₃-Ca-Na to HCO₃-Na-Ca and HCO₃-Na. Based on the chemical indices, the majority of samples were suitable for agricultural irrigation except for some in the western area with high salinity and sodium hazards. Treatment measures to groundwater and soil should be taken to reduce the possibility of soil salinization and promote crop growth in these latter regions.

Impacts of irrigation water sources and geochemical conditions on vertical distribution of pharmaceutical and personal care products (PPCPs) in the vadose zone soils

Groundwater pollution by emerging contaminants, such as pharmaceutical and personal care products (PPCPs), has caused increasing concerns around the world. The vadose zone is an active zone where lithosphere, hydrosphere and biosphere interact. It is an important medium for PPCPs removal and entry into groundwater from irrigation using wastewater or polluted surface water. In the present study, the occurrence and distribution of eleven PPCPs in areas with a vadose zone (up to 16 m) was investigated from wastewater irrigated farmland, groundwater irrigated farmland and a seasonal river course in Beijing (China). Nine out of eleven PPCPs were detectable, and carbamazepine and caffeine had the highest detection frequencies, above 50%. The PPCPs were detectable deep in 16 m below ground level (bgl), and their concentrations ranged from <LOD (limit of detection) to 12.5 μg/kg. Compared to the vadose zone soils irrigated with groundwater, wastewater-irrigated vadose zone soils had significantly higher PPCPs detection frequencies and contamination levels, suggesting the important roles of irrigation water sources on PPCPs accumulation and transport in the vadose zone. Additionally, PPCPs vertical distribution presented a bell-shape pattern in the vadose zone soils with wastewater irrigation, peaking at 3-6 m bgl. Redundancy analysis (RDA) indicated a significant correlation between PPCPs concentrations in the vadose zone soils and geochemical variables, including available potassium and silt content. This study provides important evidence on the influential factors of PPCPs accumulation and migration in the vadose zone soils resulted from wastewater irrigation. The incomplete removal of PPCPs poses certain risks in subsurface environment, potentially challenging groundwater quality and drinking water safety.

The 137Cs activity concentration of suspended and dissolved fractions in irrigation waters collected from the 80 km zone around TEPCO's Fukushima Daiichi Nuclear Power Station

Fifty-four samples of irrigation water were collected in 2014 from agricultural ponds, rivers, and dams within the 80 km zone around TEPCO's Fukushima Daiichi Nuclear Power Station (FDNPS). The samples were filtered with a 0.45 μm pore-size membrane filter to produce suspended and dissolved fractions. The ¹³⁷Cs activity concentration of the suspended fraction varied from 1.5 to 300 Bq g^-1 dry weight and was significantly higher than that in the soil around each sampling site. The range of ¹³⁷Cs activity concentrations in the dissolved fraction varied over three orders of magnitude at 0.0075-6.7 Bq l^-1, which was a larger range than that of the suspended fraction; the higher values for samples were from within the 20 km zone. In the dissolved fraction 87 ± 9% of the ¹³⁷Cs (n = 37) was in a monovalent cationic form (Cs⁺) and therefore potentially mobile. The distribution coefficient (Kd) ranged from 4100 to 2,100,000; the geometric mean value (110,000) was higher than that reported by the IAEA (2010). The geometric mean Kd of samples collected from the 20 km zone was 61,000 (n = 27), which was significantly lower than that collected from 20 to 80 km zone (200,000, n = 27). The Kd-value was negative correlated with the concentration of stable ¹³³Cs and the electric conductivity in the dissolved fraction. This shows relatively higher mobility of radiocaesium in irrigation waters may occur when there are higher contents of cations present.

Field-based experimental water footprint study of sunflower growth in a semi-arid region of China

BACKGROUND

Field-scale changes in the water footprint during crop growth play an important role in formulating sustainable water utilisation strategies. This study aimed to explore field-scale variation in the water footprint of growing sunflowers in the western Jilin Province, China, during a 3-year field experiment. The goals of this study were to (1) determine the components of the 'blue' and 'green' water footprints for sunflowers sown with water, and (2) analyse variations in water footprints and soil water balance under different combinations of temperature and precipitation. Specific actions could be adopted to maintain sustainable agricultural water utilisation in the semi-arid region based on this study.

RESULTS

The green, blue, and grey water footprints accounted for 93.7-94.7%, 0.4-0.5%, and 4.9-5.8%, respectively, of the water footprint of growing sunflowers. The green water footprint for effective precipitation during the growing season accounted for 58.8% in a normal drought year but 48.2% in an extreme drought year. When the effective precipitation during the growing season could not meet the green water use, a moisture deficit arose. This increase in the moisture deficit can have a significant impact on soil water balance.

CONCLUSION

Green water was the primary water source for sunflower growth in the study area, where a scarcity of irrigation water during sunflower growth damaged the soil water balance, particularly in years with continuous drought. The combination of temperature and precipitation effected the growing environment, leading to differences in yield and water footprint. The field experiments in this area may benefit from further water footprint studies at the global, national and regional scale. © 2016 The Authors. Journal of The Science of Food and Agriculture published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Impact of Preservation of Subsoil Water Act on Groundwater Depletion: The Case of Punjab, India

Indian states like Punjab and Haryana, epicenters of the Green Revolution, are facing severe groundwater shortages and falling water tables. Recognizing it as a serious concern, the Government of Punjab enacted the Punjab Preservation of Subsoil Water Act in 2009 (or the 2009 act) to slow groundwater depletion. The objective of this study is to assess the impact of this policy on groundwater depletion, using panel data from 1985 to 2011. Results from this study find a robust effect of the 2009 act on reducing groundwater depletion. Our models for pre-monsoon, post-monsoon, and overall periods of analysis find that since implementation of the 2009 act, groundwater tables have improved significantly. Second, our study reveals that higher shares of tube wells per total cropped area and increased population density have led to a significant decline in the groundwater tables. On the other hand, rainfall and the share of area irrigated by surface water have had an augmenting effect on groundwater resources. In the two models, pre-monsoon and post-monsoon, this study shows that seasonality plays a key role in determining the groundwater table in Punjab. Specifically, monsoon rainfall has a very prominent impact on groundwater.

Water Footprint of crop productions: A review

Water Footprint is an indicator recently developed with the goal of quantifying the virtual content of water in products and/or services. It can also be used to identify the worldwide virtual water trade. Water Footprint is composed of three parts (green, blue and grey waters) that make the assessment complete in accordance with the Water Footprint Network and with the recent ISO14046. The importance of Water Footprint is linked to the need of taking consciousness about water content in products and services and of the achievable changes in productions, diets and market trades. In this study, a literature review has been completed on Water Footprint of agricultural productions. In particular, the focus was paid on crops for the production of food and bioenergy. From the review, the development of the Water Footprint concept emerged: in early studies the main goal was to assess products' water trade on a global scale, while in the subsequent years, the goal was the rigorous quantification of the three components for specific crops and in specific geographical areas. In the most recent assessments, similarities about the methodology and the employed tools emerged. For 96 scientific articles on Water Footprint indicator of agricultural productions, this literature review reports the main results and analyses weaknesses and strengths. Seventy-eight percent of studies aimed to quantify Water Footprint, while the remaining 22% analysed methodology, uncertainty, future trends and comparisons with other footprints. It emerged that most studies that quantified Water Footprint concerned cereals (33%), among which maize and wheat were the most investigated crops. In 46% of studies all the three components were assessed, while in 18% no indication about the subdivision was given; in the remaining 37%, only blue or green and blue components were quantified.

Impact of Makowal type water system on crop productivity in Shivalik foothills of India

The availability of water through community based water harvesting structure has intensified agriculture and improved livelihood of the surveyed beneficiary households in the Shivalik foothills of India. Before the introduction of Makowal Type Water Harvesting System (before MTWHS), only 83.8% farmers in kharif and 79.7% during rabi season were growing crops but after its introduction (after MTWHS) the corresponding values improved to 100% and 97.3%, respectively, thus increasing cropping intensity from 145% to 189%. Introduction of MTWHS enabled farmers to take paddy and agro-forestry during Kharif, and vegetables and fodder during Rabi season. The increase in cultivated area due to MTWHS was to the tune of 46.1% in Kharif and 36.3% during Rabi, while increase in crop productivity ranged from 55.1% to 111.3% in kharif and 8.6 to 132.0% in Rabiseason. Better availability of irrigation changed varietal spectrum in favour of hybrids and high yielding varieties and farmers started adopting improved agronomic practices targeting better input-use efficiency. The MTWHS produced positive impact on the on-farm (crops, dairy and agro-forestry) sources of income and reduced the relative dependence on off-farm activities (labour, community forest area, etc.) for earnings. This system has brought drinking water very close to hutments of rural women thus reducing their drudgery and saving time. In general, rainwater harvesting from forest watersheds has resulted in quantum jumps in crop and milk production and acted as a catalyst to tie up the economic interest of communities, along with forest protection.

Reducing greenhouse gas emissions, water use, and grain arsenic levels in rice systems

Agriculture is faced with the challenge of providing healthy food for a growing population at minimal environmental cost. Rice (Oryza sativa), the staple crop for the largest number of people on earth, is grown under flooded soil conditions and uses more water and has higher greenhouse gas (GHG) emissions than most crops. The objective of this study was to test the hypothesis that alternate wetting and drying (AWD--flooding the soil and then allowing to dry down before being reflooded) water management practices will maintain grain yields and concurrently reduce water use, greenhouse gas emissions and arsenic (As) levels in rice. Various treatments ranging in frequency and duration of AWD practices were evaluated at three locations over 2 years. Relative to the flooded control treatment and depending on the AWD treatment, yields were reduced by <1-13%; water-use efficiency was improved by 18-63%, global warming potential (GWP of CH4 and N2 O emissions) reduced by 45-90%, and grain As concentrations reduced by up to 64%. In general, as the severity of AWD increased by allowing the soil to dry out more between flood events, yields declined while the other benefits increased. The reduction in GWP was mostly attributed to a reduction in CH4 emissions as changes in N2 O emissions were minimal among treatments. When AWD was practiced early in the growing season followed by flooding for remainder of season, similar yields as the flooded control were obtained but reduced water use (18%), GWP (45%) and yield-scaled GWP (45%); although grain As concentrations were similar or higher. This highlights that multiple environmental benefits can be realized without sacrificing yield but there may be trade-offs to consider. Importantly, adoption of these practices will require that they are economically attractive and can be adapted to field scales.

Effect of irrigation systems on temporal distribution of malaria vectors in semi-arid regions

Previous research models have used climate data to explain habitat conditions of Anopheles mosquitoes transmitting malaria parasites. Although they can estimate mosquito populations with sufficient accuracy in many areas, observational data show that there is a tendency to underestimate the active growth and reproduction period of mosquitoes in semi-arid agricultural regions. In this study, a new, modified model that includes irrigation as a factor was developed to predict the active growing period of mosquitoes more precisely than the base model for ecophysiological and climatological distribution of mosquito generations (ECD-mg). Five sites with complete sets of observational data were selected in semi-arid regions of India for the comparison. The active growing period of mosquitoes determined from the modified ECD-mg model that incorporated the irrigation factor was in agreement with the observational data, whereas the active growing period was underestimated by the previous ECD-mg model that did not incorporate irrigation. This suggests that anthropogenic changes in the water supply due to extensive irrigation can encourage the growth of Anopheles mosquitoes through the alteration of the natural water balance in their habitat. In addition, it was found that the irrigation systems not only enable the active growth of mosquitoes in dry seasons but also play an important role in stabilizing the growth in rainy seasons. Consequently, the irrigation systems could lengthen the annual growing period of Anopheles mosquitoes and increase the maximum generation number of mosquitoes in semi-arid subtropical regions.

Annual input fluxes of heavy metals in agricultural soil of Hainan Island, China

The accumulation of heavy metals in farmland has become an important issue related to food security and environmental risk. The annual inputs of heavy metals (As, Cd, Hg, Pb, Cr, Cu, and Zn) to agricultural soil for a full year in Hainan Island have been studied. Three fluxes through the cultivated horizon were considered: (1) atmospheric depositions, (2) fertilization, and (3) irrigation water. The corresponding samples were collected and analyzed on a large regional scale. The total input fluxes show obvious spatial variability among different regions. The inventory of heavy metal inputs to agricultural land demonstrates that agricultural soil is potentially at risk of heavy metal accumulation from irrigation water. The potential at risk of heavy metal accumulation from atmospheric deposition and fertilizer is relatively low compared to irrigation. The results indicate that Hg is the element of prior concern for agricultural soil, followed by Cd and As, and other heavy metal elements represent little threat to the environment in the study area. This work provides baseline information to develop policies to control and reduce toxic elements accumulated in agricultural soil.

Impacts of river water consumption on aquatic biodiversity in life cycle assessment--a proposed method, and a case study for Europe

In the context of climate change and food provisioning for a growing global population, the impacts of water consumption on aquatic biodiversity (e.g., river water consumption for irrigation) should be considered in Life Cycle Impact Assessment (LCIA). A previous LCIA method quantifying the potential impacts of river water consumption on fish biodiversity, using a species-discharge relationship (SDR), constituted an essential first step. This method is however limited in terms of regionalization and taxa considered, and predicts the potential risk of local species loss only. Here, we address these shortcomings by developing region-specific SDRs for Europe at various scales (continent, country, and eco-region), and including macro-invertebrate biodiversity. SDR exponents vary from 0.06 to 0.45 between regions, underlining the importance of such regionalization. Furthermore, we provide a new regionalized method which considers the location of water consumption within a river basin, by integrating the concept of longitudinal river zonation. This involves the use of a novel measure of potential loss of species richness, standardizing local species loss to an equivalent of global extinction and reflecting species vulnerability. The new method is applied in a Swiss case-study. The consideration of the location of water consumption within a basin was found to be of high importance in the assessment: potential species loss varied between 4.22 × 10(-3) and 3.95 × 10(-1) species (2 orders of magnitude) depending on location. This work thus provides enhancements in the assessment of potential impacts of river water consumption on aquatic biodiversity and contributes to the ecological relevance of the method.

Are small-scale irrigators water use efficient? Evidence from lake Naivasha basin, Kenya

With increasing water scarcity and competing uses and users, water use efficiency is becoming increasingly important in many parts of developing countries. The lake Naivasha basin has an array of different water users and uses ranging from large scale export market agriculture, urban domestic water users to small holder farmers. The small scale farmers are located in the upper catchment areas and form the bulk of the users in terms of area and population. This study used farm household data to explore the overall technical efficiency, irrigation water use efficiency and establish the factors influencing water use efficiency among small scale farmers in the Lake Naivasha basin in Kenya. Data envelopment analysis, general algebraic and modeling system, and Tobit regression methods were used in analyzing cross sectional data from a sample of 201 small scale irrigation farmers in the lake Naivasha basin. The results showed that on average, the farmers achieved only 63 % technical efficiency and 31 % water use efficiency. This revealed that substantial inefficiencies occurred in farming operations among the sampled farmers. To improve water use efficiency, the study recommends that more emphasis be put on orienting farmers toward appropriate choice of irrigation technologies, appropriate choice of crop combinations in their farms, and the attainment of desirable levels of farm fragmentation.

Research on the drought index of irrigation district with multi-time scales

The empirical mode decomposition method is applied to analyze fluctuating periods and local features of the annual drought index and the drought index in the irrigation and non-irrigation periods from 1956 to 2010 in the Yinchuan irrigation district. In order to understand the uncertainty between these variables, the set pair analysis method is used to present the identity, discrepancy, and contrary of the drought index with multi-time scales. The results reveal that the annual drought index and the drought index in the irrigation and non-irrigation periods have a complex relationship which may be related to El Niño, the air-sea intersection, and the long period of solar activity. The drought index in the irrigation and non-irrigation periods presents mainly the contrary and the discrepancy; the fluctuating shapes of the annual drought index and drought index in the irrigation period are the same on their different period levels. The original annual drought index and its intrinsic mode function components have a certain connection degree; they mainly present the discrepancy.

Accumulation of Cd in agricultural soil under long-term reclaimed water irrigation

Safety of agricultural irrigation with reclaimed water is of great concern as some potential hazardous compounds like heavy metals may be accumulated in soils over time. Impacts of long-term reclaimed water on soil Cd pollution were evaluated based on the field investigation in two main crop areas in Beijing with long irrigation history and on simulation results of STEM-profile model. Under long-term reclaimed water, Cd content in the top 20 cm soil layer was greatly elevated and was more than 2 times higher than that in the deep soil layer. There was very small differences between the field measured and model simulated Cd content in the plow layer (top 20 cm) and entire soil layer. Long-term model prediction showed that reclaimed water irrigation had a low environmental risk of soil Cd pollution, but the risk would be aggravated when there were high metal loading from other sources. The risk is also depending on the soil and plant properties.

Use of multivariate indicator kriging methods for assessing groundwater contamination extents for irrigation

Multivariate geostatistical approaches have been applied extensively in characterizing risks and uncertainty of pollutant concentrations exceeding anthropogenic regulatory limits. Spatially delineating an extent of contamination potential is considerably critical for regional groundwater resources protection and utilization. This study used multivariate indicator kriging (MVIK) to determine spatial patterns of contamination extents in groundwater for irrigation and made a predicted comparison between two types of MVIK, including MVIK of multiplying indicator variables (MVIK-M) and of averaging indicator variables (MVIK-A). A cross-validation procedure was adopted to examine the performance of predicted errors, and various probability thresholds used to calculate ratios of declared pollution area to total area were explored for the two MVIK methods. The assessed results reveal that the northern and central aquifers have excellent groundwater quality for irrigation use. Results obtained through a cross-validation procedure indicate that MVIK-M is more robust than MVIK-A. Furthermore, a low ratio of declared pollution area to total area in MVIK-A may result in an unrealistic and unreliable probability used to determine extents of pollutants. Therefore, this study suggests using MVIK-M to probabilistically determine extents of pollutants in groundwater.

[Effects of reclaimed water recharge on groundwater quality: a review]

Reclaimed water recharge to groundwater is an effective way to relieve water resource crisis. However, reclaimed water contains some pollutants such as nitrate, heavy metals, and new type contaminants, and thus, there exists definite environmental risk in the reclaimed water recharge to groundwater. To promote the development of reclaimed water recharge to groundwater and the safe use of reclaimed water in China, this paper analyzed the relevant literatures and practical experiences around the world, and summarized the effects of different reclaimed water recharge modes on the groundwater quality. Surface recharge makes the salt and nitrate contents in groundwater increased but the risk of heavy metals pollution be smaller, whereas well recharge can induce the arsenic release from sedimentary aquifers, which needs to be paid more attention to. New type contaminants are the hotspots in current researches, and their real risks are unknown. Pathogens have less pollution risks on groundwater, but some virus with strong activity can have the risks. Some suggestions were put forward to reduce the risks associated with the reclaimed water recharge to groundwater in China.

Estimation of agricultural water consumption from meteorological and yield data: a case study of Hebei, North China

Over-exploitation of groundwater resources for irrigated grain production in Hebei province threatens national grain food security. The objective of this study was to quantify agricultural water consumption (AWC) and irrigation water consumption in this region. A methodology to estimate AWC was developed based on Penman-Monteith method using meteorological station data (1984-2008) and existing actual ET (2002-2008) data which estimated from MODIS satellite data through a remote sensing ET model. The validation of the model using the experimental plots (50 m(2)) data observed from the Luancheng Agro-ecosystem Experimental Station, Chinese Academy of Sciences, showed the average deviation of the model was -3.7% for non-rainfed plots. The total AWC and irrigation water (mainly groundwater) consumption for Hebei province from 1984-2008 were then estimated as 864 km(3) and 139 km(3), respectively. In addition, we found the AWC has significantly increased during the past 25 years except for a few counties located in mountainous regions. Estimations of net groundwater consumption for grain food production within the plain area of Hebei province in the past 25 years accounted for 113 km(3) which could cause average groundwater decrease of 7.4 m over the plain. The integration of meteorological and satellite data allows us to extend estimation of actual ET beyond the record available from satellite data, and the approach could be applicable in other regions globally where similar data are available.

Salinisation of rivers: an urgent ecological issue

Secondary salinisation of rivers and streams is a global and growing threat that might be amplified by climate change. It can have many different causes, like irrigation, mining activity or the use of salts as de-icing agents for roads. Freshwater organisms only tolerate certain ranges of water salinity. Therefore secondary salinisation has an impact at the individual, population, community and ecosystem levels, which ultimately leads to a reduction in aquatic biodiversity and compromises the goods and services that rivers and streams provide. Management of secondary salinization should be directed towards integrated catchment strategies (e.g. benefiting from the dilution capacity of the rivers) and identifying threshold salt concentrations to preserve the ecosystem integrity. Future research on the interaction of salinity with other stressors and the impact of salinization on trophic interactions and ecosystem properties is needed and the implications of this issue for human society need to be seriously considered.

[Ecological risks of reclaimed water irrigation: a review]

Wastewater reclamation and reuse have become an important approach to alleviate the water crisis in China because of its social, economic and ecological benefits. The irrigation on urban green space and farmland is the primary utilization of reclaimed water, which has been practiced world widely. To understand the risk of reclaimed water irrigation, we summarized and reviewed the publications associated with typical pollutants in reclaimed water including salts, nitrogen, heavy metals, emerging pollutants and pathogens, systematically analyzed the ecological risk posed by reclaimed water irrigation regarding plant growth, groundwater quality and public health. Studies showed that salt and salt ions were the major risk sources of reclaimed water irrigation, spreading disease was another potential risk of using reclaimed water, and emerging pollutants was the hot topic in researches of ecological risk. Based on overseas experiences, risk control measures on reclaimed water irrigation in urban green space and farmland were proposed. Five recommendations were given to promote the safe use of reclaimed water irrigation including (1) strengthen long-term in situ monitoring, (2) promote the modeling studies, (3) build up the connections of reclaimed water quality, irrigation management and ecological risk, (4) evaluate the soil bearing capacity of reclaimed water irrigation, (5) and establish risk management system of reclaimed water reuse.

Pollution by organochlorine pesticides in Navachiste-Macapule, Sinaloa, Mexico

The lagoon system of Navachiste-Macapule is located in northern Mexico, in the state of Sinaloa, with an area of 24,000 ha. The main economic activity in the area is agriculture, and the lagoon lies next to the irrigation district ID-063 which covers 116,615 ha. The purpose of this study is to evaluate the levels of pollution generated by organochlorine pesticides (OC) in the surface sediments of the lagoon and in the agricultural drains of the ID-063 that are supposedly transported into the system as a result of agricultural activities and runoff from adjacent land. For this, between 2006 and 2007, 45 surface sediment samples were collected (warm dry, rainy and cold dry) from 15 sampling sites, during the three climatic seasons. Of these, eight were located inside the lagoon in marine conditions (salinity >31 PSU) and seven in the agricultural drains of the ID-063 in freshwater conditions (salinity <5 PSU). The average concentration of the OC in the sediments was 44.75 ng g(-1), among which the group of the alicyclic compounds presented the greatest concentrations. The average value of the total organic carbon (TOC) in the sediments of the system was 0.90%. The sediments collected inside the lagoon had an average OC concentration of 18.97 ng g(-1), and the predominant type of sediment was fine to very fine sand. The average OC concentration in the sediments collected in the agricultural drains was 75.69 ng g(-1), where fine sediments (silt) were predominant. The presence of methoxychlor, endrin and heptachlor suggested that these compounds were continuously used in the system, even though their use is forbidden in Mexico.

Identifying the cause of soil cadmium contamination with Monte Carlo mass balance modelling: a case study from Potosi, Bolivia

The Chayanta river in Potosi, Bolivia is polluted by present and past mining activities in the districts of Siglo XX and Llallagua. The river water, which is enriched with cadmium (Cd), is used for irrigation in the Quila Quila and Asiruri valleys where the median soil Cd concentration is 20 mg kg(-1), well above the background value of < 0.5 mg kg(-1). The objective of this study was to predict current soil contamination using a retrospective mass balance. Monitoring data were collected on Cd concentrations in irrigation water, irrigation application rates, crop yield and composition, and soil properties including pore water composition. The mass balance was made assuming constant model parameters since the start of upstream mining operations about 85 years ago (1920). The parameter uncertainty was taken into account with a Monte Carlo analysis. The current annual Cd input by irrigation is 800 g ha(-1). The annual output of Cd through removal of the crop harvest and leaching is less than 10 g ha(-1). The predicted soil Cd concentrations after 85 years of contamination (geometric mean: 21.9 mg x kg(-1), 10th and 90th percentile 7.2-65.1 mg kg(-1) respectively) matched the distribution of observed values (geometric mean: 18.6 mg kg(-1); 10th and 90th percentile 4.7-65.9 mg kg(-1) respectively; n = 56). This study confirmed that irrigation water is the prime source of soil Cd enrichment in that area. The Monte Carlo analysis is a convenient way of including parameter uncertainty in mass balance modelling and of estimating spatial variability of the contamination.

Dietary intake of pollutant aerosols via vegetables influenced by atmospheric deposition and wastewater irrigation

Pot culture experiments were conducted to study dietary intake of heavy metals via vegetables, spinach (Spinacia oleracea L.), radish (Raphanus sativus L.) and tomato (Lycopersicon esculentum Mill) grown under the influence of atmospheric deposition and wastewater irrigation. The results indicated substantial accumulation of heavy metals in vegetables, which contribute significantly to dietary intake of total heavy metals ranging from 1.34 to 110.40 μg g⁻¹ through leaves (spinach), 1.04 to 105.86 μg g⁻¹ through root (radish) and 0.608 to 82.19 μg g⁻¹ through fruits (tomato). Concentration of Cd, Ni and Pb in vegetables exceeded the safe limits of Prevention of Food Adulteration Act 1954. Health risk index for Cd and Pb exceeded the safe limits set by the United States Environmental Protection Agency. The study indicated that the atmospheric depositions as well as wastewater irrigation have significantly elevated the levels of heavy metals in dietary vegetables presenting a significant threat for the health of users.

Water quality mapping and assessment, and weathering processes of selected aflaj in Oman

There are more than 4,000 falaj (singular of a peculiar dug channel) distributed in different regions in Oman. The chemical characteristics of the water in 42 falaj were studied to evaluate the major ion chemistry; geochemical processes controlling water composition; and suitability of water for drinking, domestic, and irrigation uses. GIS-based maps indicate that the spatial distribution of chemical properties and concentrations vary within the same region and the different regions as well. The molar ratios of (Ca + Mg)/Total cations, (Na + K)/Total cations, (Ca + Mg)/(Na + K), (Ca + Mg)/(HCO₃ + SO₄), and Na/Cl reveal that the water chemistry of the majority of aflaj are dominated by carbonate weathering and evaporite dissolution, with minor contribution of silicate weathering. The concentrations of most of the elements were less than the permissible limits of Omani standards and WHO guidelines for drinking water and domestic use and do not generally pose any health and environmental problems. Some aflaj in ASH Sharqiyah and Muscat regions can be used for irrigation with slight to severe restriction because of the high levels of electrical conductivity, total dissolved solids, chloride, and sodium absorption ratio.

The function of constructed wetland in reducing the risk of heavy metals on human health

Irrigation with polluted water from the upper Yellow River (YR) channel of Northwest China has resulted in agricultural soil being contaminated by heavy metals (HMs). This causes major concerns due to the potential health risk to the residents in this area. The present study aims to assess the efficiency of constructed wetland (CW) in reducing the heavy metal contamination in irrigation water and food crops, thus in reduction of potential health risk to the residents. The associated risk was assessed using hazard quotient (HQ) and hazard index (HI). The results showed a potential health risk to inhabitants via consumption of wheat grain irrigated with untreated water from YR. However CW could greatly reduce the human health risk of HMs contamination to local residents through significantly decreasing the concentrations of HMs in wheat grain. In theory, the reduction rate of this risk reached 35.19% for different exposure populations. Therefore, CW can be used as a system to pre-treat irrigation water and protect the residents from the potential HMs toxicity.

Projected water consumption in future global agriculture: scenarios and related impacts

Global stress on water and land resources is increasing as a consequence of population growth and higher caloric food demand. Many terrestrial ecosystems have already massively been degraded for providing agricultural land, and water scarcity related to irrigation has damaged water dependent ecosystems. Coping with the food and biomass demand of an increased population, while minimizing the impacts of crop production, is therefore a massive upcoming challenge. In this context, we developed four strategies to deliver the biotic output for feeding mankind in 2050. Expansion on suitable and intensification of existing areas are compared to assess associated environmental impacts, including irrigation demand, water stress under climate change, and the productivity of the occupied land. Based on the agricultural production pattern and impacts of the strategies we identified the trade-offs between land and water use. Intensification in regions currently under deficit irrigation can increase agricultural output by up to 30%. However, intensified crop production causes enormous water stress in many locations and might not be a viable solution. Furthermore, intensification alone will not be able to meet future food demand: additionally, a reduction of waste by 50% along the food supply chain or expansion of agricultural land is required for satisfying current per-capita meat and bioenergy consumption. Suitable areas for such expansion are mainly located in Africa, followed by South America. The increased land stress is of smaller concern than the water stress modeled for the intensification case. Therefore, a combination of waste reduction with expansion on suitable pastures generally results as the best option, along with some intensification on selected areas. Our results suggested that minimizing environmental impacts requires fundamental changes in agricultural systems and international cooperation, by producing crops where it is most environmentally efficient and not where it is closest to demand or cheapest.

Environmental impacts of water use in global crop production: hotspots and trade-offs with land use

Global crop production is causing pressure on water and land resources in many places. In addition to local resource management, the related environmental impacts of commodities traded along international supply chains need to be considered and managed accordingly. For this purpose, we calculate the specific water consumption and land use for the production of 160 crops and crop groups, covering most harvested mass on global cropland. We quantify indicators for land and water scarcity with high geospatial resolution. This facilitates spatially explicit crop-specific resource management and regionalized life cycle assessment of processed products. The vast cultivation of irrigated wheat, rice, cotton, maize, and sugar cane, which are major sources of food, bioenergy, and fiber, drives worldwide water scarcity. According to globally averaged production, substituting biofuel for crude oil would have a lower impact on water resources than substituting cotton for polyester. For some crops, water scarcity impacts are inversely related to land resource stress, illustrating that water consumption is often at odds with land use. On global average, maize performs better than rice and wheat in the combined land/water assessment. High spatial variability of water and land use related impacts underlines the importance of appropriate site selection for agricultural activities.

What weight should be assigned to future environmental impacts? A probabilistic cost benefit analysis using recent advances on discounting

Cost-benefit analysis is a standard methodological platform for public investment evaluation. In high environmental impact projects, with a long-term effect on future generations, the choice of discount rate and time horizon is of particular relevance, because it can lead to very different profitability assessments. This paper describes some recent approaches to environmental discounting and applies them, together with a number of classical procedures, to the economic evaluation of a plant for the desalination of irrigation return water from intensive farming, aimed at halting the degradation of an area of great ecological value, the Mar Menor, in South Eastern Spain. A Monte Carlo procedure is used in four CBA approaches and three time horizons to carry out a probabilistic sensitivity analysis designed to integrate the views of an international panel of experts in environmental discounting with the uncertainty affecting the market price of the project's main output, i.e., irrigation water for a water-deprived area. The results show which discounting scenarios most accurately estimate the socio-environmental profitability of the project while also considering the risk associated with these two key parameters. The analysis also provides some methodological findings regarding ways of assessing financial and environmental profitability in decisions concerning public investment in the environment.