Untreated Wastewater For Irrigation Research Articles

Response of soil health index to untreated wastewater irrigation in selected farms under different vegetable types

Crop irrigation with wastewater has drawn global attention in water-scarce areas as a strategy to offset water scarcity. However, the response of soil ecosystem functioning and soil health to long-term and continuous wastewater (WW) irrigation has not been well-understood. A total of 12 vegetable farms irrigated with WW and fresh water (FW) were analyzed to assess WW irrigation impacts on soil health using the minimum data set (MDS) and soil health index (SHI) framework. We determined the combination of soil physicochemical, nutritional, and biological indicators (22 soil indicators) along with linear SHI (L- SHI) and nonlinear SHI (NL- SHI) quantification approaches in the WW-irrigated fields versus the FW-irrigated fields. Significant changes were observed in most soil attributes in the WW-irrigated farms versus the FW-irrigated farms. These changes could mostly improve soil health (e.g., soil stability index, exchangeable cations, organic matter (OM), total N, and available P), but some of them have a degrading effect on soil health (e.g., electrical conductivity (EC), sodium absorption ratio (SAR), and heavy metals). Soil health indicators identified through the MDS approach were clay, EC, OM, exchangeable K, Pb, and soil microbial respiration, contributing to the SHI value by 40.6%, 40.6%, 23.8%, 23.8%, 20.8%, and 14.9%, respectively. The SHI values computed through the non-linear scoring technique were more sensitive to WW irrigation than those computed through the linear scoring technique, suggesting that NL- SHI would outperform L- SHI in representing variations in soil functions. The L- SHI and NL- SHI values were 17–31% and 21–32% higher in the WW-irrigated farms than in the FW-irrigated farms, respectively, suggesting a good improvement in soil capacity and functions after WW irrigation. To conclude, our results revealed that an integrated SHI, particularly NL- SHI, would be more instrumental for evaluating post-WW irrigation soil functions and soil health in the WW-affected croplands than single soil indicators.

Divergent effects of cerium oxide nanoparticles alone and in combination with cadmium on nutrient acquisition and the growth of maize (Zea mays).

The increasing use of cerium nanoparticles (CeO2-NPs) has made their influx in agroecosystems imminent through air and soil deposition or untreated wastewater irrigation. Another major pollutant associated with anthropogenic activities is Cd, which has adverse effects on plants, animals, and humans. The major source of the influx of Cd and Ce metals in the human food chain is contaminated food, making it an alarming issue; thus, there is a need to understand the factors that can reduce the potential damage of these heavy metals. The present investigation was conducted to evaluate the effect of CeO2-10-nm-NPs and Cd (alone and in combination) on Zea mays growth. A pot experiment (in sand) was conducted to check the effect of 0, 200, 400, 600, 1,000, and 2,000 mg of CeO2-10 nm-NPs/kg-1 dry sand alone and in combination with 0 and 0.5 mg Cd/kg-1 dry sand on maize seedlings grown in a partially controlled greenhouse environment, making a total of 12 treatments applied in four replicates under a factorial design. Maize seedling biomass, shoot and root growth, nutrient content, and root anatomy were measured. The NPs were toxic to plant biomass (shoot and root dry weight), and growth at 2,000 ppm was the most toxic in Cd-0 sets. For Cd-0.5 sets, NPs applied at 1,000 ppm somewhat reverted Cd toxicity compared with the contaminated control (CC). Additionally, CeO2-NPs affected Cd translocation, and variable Ce uptake was observed in the presence of Cd compared with non-Cd applied sets. Furthermore, CeO2-NPs partially controlled the elemental content of roots and shoots (micronutrients such as B, Mn, Ni, Cu, Zn, Mo, and Fe and the elements Co and Si) and affected root anatomy.

Effects of Untreated Wastewater Irrigation on Peanut (Arachis hypogea) Productivity and Human Health

Effects of Untreated Wastewater Irrigation on Peanut (Arachis hypogea) Productivity and Human Health

Effect of untreated or reclaimed wastewater drip-irrigation for lettuces and leeks on yield, soil and fecal indicators

Sanitary and environmental impacts, as well as effects on agricultural yields constitute important parameters to be taken into account in wastewater reuse projects, and depend on the treatment applied to the wastewater. Extensive treatments or irrigation with untreated wastewater are rarely studied, although they represent a significant share of unplanned or indirect wastewater reuse in the world. The aim of this study was to contribute to the evaluation of chemical properties of soil, crop yields, and the fate of fecal indicators in soil and plants when vegetable crops (lettuces and leeks) are irrigated by drip-irrigation using untreated wastewater (UW), water reuse or treated wastewater by stabilization ponds (TW) and fresh water (FW). Over two years (2018 and 2019), three lettuces ( Lactuca sativa ) and two leeks ( Allium porrum ) growth cycles were performed in a greenhouse, and soil analyses show increases in electrical conductivity (EC), chlorine (Cl), sodium (Na) and nitrate nitrogen concentrations (NO 3 ) when TW and UW irrigation methods were compared to FW. As a result, FW irrigation and conventional fertilization lead to lower lettuce yields compared to TW (between 43 to 85% lower yields depending on the cultivation period) ( p -value < 0.05). However, trends are not clear for UW. Leeks irrigated with FW have also a smaller fresh mass compared to TW and UW (around 35 % and 45 % differences in the median for UW and TW, respectively, p -value < 0.05), which shows a possible positive effect of continuous nutrient supply against the risks associated with higher water conductivity. In addition, in the soil, the irrigation with TW and with UW increases some concentrations, especially EC, mainly due to Cl and Na values. Fecal indicators increased from 1 to 2 log with the used of UW but the decay of fecal indicators in topsoils was slow (less than 1 log for enterococcus load after 6h), as shown by culture-based and molecular techniques (qPCR, droplet digital PCR). Fecal indicators were found in plants irrigated with untreated wastewater. • Untreated and treated wastewater irrigation reuse were evaluated for lettuce and leek crops. • Fresh water irrigation produced lower yields compared to treated wastewater. • Untreated wastewater irrigation may negatively affect some soil properties. • Die-off rate of fecal bacteria was slow in topsoils irrigated by untreated wastewater. • Contamination by fecal indicators of crop roots irrigated by untreated wastewater.

Investigating and Managing the Impact of Using Untreated Wastewater for Irrigation on the Groundwater Quality in Arid and Semi-Arid Regions.

This study aims to investigate the impact of using untreated wastewater in irrigation. Different scenarios of management were applied by mixing it with treated wastewater or freshwater on groundwater quality. A hypothetical case study is presented. The numerical model of MODFLOW is used in the simulation by applying four stages (21 scenarios) including: different values of pumping rates, changing wastewater recharge rates, and a combination of the previous scenarios. Additionally, protection scenario for groundwater was applied by using different values of mixing of freshwater with wastewater. The simulation was carried out for the contamination of Chemical Oxygen Demand COD and the concentration reached 48.6 ppm at a depth of 25 m and 19.41 ppm at a depth of 50 m in the base case. The results showed a negative impact on groundwater quality had occurred due to increasing the pumping rates, wastewater recharge rates, and combination between two scenarios, which led to an increase of the contaminants in the aquifers. However, positive protection effects occurred due to mixing the wastewater with treated wastewater. The results of COD concentration in groundwater using treated wastewater reached 81.82, 77.88, 74.03, 70.12, and 66.15 ppm at a depth of 25 m and 53.53, 50.95, 48.43, 45.87, and 43.28 ppm at a depth of 50 m, at concentrations of 93, 88.52, 84.14, 79.7, and 75.19 ppm with constant pumping and recharge rates of 4320 m3/d and 547.5 mm/year, respectively. The using of treated wastewater could improve the groundwater quality to be used in the irrigation process and help to minimize groundwater contamination. Moreover, the abstraction of the groundwater should be optimized, and the qualities of wastewater should be constrained in agriculture to protect the groundwater quality.

HEALTH RISK ASSESSMENT AND HEAVY METAL CONTAMINATION LEVELS IN GREEN CHILLI DUE TO UNTREATED WASTEWATER IRRIGATION IN CHAK JHUMRA, FAISALABAD

To address the global issue of water scarcity, untreated wastewater irrigation has become a common practice in the developing countries to meet the emerging demand of irrigation water. It is a common practice in Pakistan as well to apply municipal wastewater for irrigation purposes, which is carrying high concentrations of heavy metals originating from industrial sources. The research was conducted in Chak Jhumra, Faisalabad, Pakistan to check the effect on health due to untreated wastewater. The purpose of this research work was to find out the concentrations of hazardous elements present in the wastewater and conduct health risk assessment of utilizing the contaminated vegetables, being grown on untreated effluent. The main parameters to be investigated for groundwater, wastewater, soil and vegetables were EC, TSS, SAR and Heavy metals like (Ni, Zn, Pb, and Cu). Concentrations of the targeted heavy metals were determined in these media and health risk assessment was conducted. It was finally concluded that the soil properties were greatly influenced by the supply of this wastewater. Zinc was found above safe limit, Cu was found within safe limit, Ni and Pb were above critical limits in all sites. Groundwater was found suitable and its values were within safe limits. Health risk assessment has also exhibited significant impact of the concentrations of heavy metals in the vegetables being utilized by the common man.

Decentralised approach of wastewater treatment and impact assessment of treated and untreated wastewater irrigation on agriculture land and its produce

A field experiment was conducted from October, 2015 – March, 2017 to investigate the effects of drip irrigation with wastewater, and treated wastewater on crop quality at the 12-C Research farm of Indian Agriculture Research Institute, New Delhi. A bioreactor was installed at 12-C field for the purpose of cleaning the wastewater for the irrigation. After wastewater irrigation, the level of metals in the wastewater irrigated field got increased with time in the soil. While in treated water irrigated soil, concentration of metals was very less. In case of crops, the level of heavy metals was found more in wastewater irrigated crops than the treated water irrigated crops. From the study, it can be concluded that unlike treated wastewater, untreated wastewater cannot be used in agricultural land for a long time. Further, use of treated wastewater for irrigation does not have a negative impact on the consumers’ health as well.

Development and performance evaluation of native microbial consortium for multi metal removal in lab scale aerobic and anaerobic bioreactor

Abstract Shortage of freshwater force farmers to use untreated wastewater for irrigation which leads to the accumulation of contaminants like heavy metals in the food chain and deteriorate the quality of produce and soil. Present study focused on bioremediation of multiple heavy metals (Cd, Cu, Cr, Zn. Pb and Ni) from wastewater used for irrigation of food crops using four continuous Stirred Tank Reactor (CSTR), two aerobic and two anaerobic. One set of bioreactor (aerobic and anaerobic) was fed with actual wastewater, showed heavy metal removal up to 30%–100%. Whereas other set fed with spiked with metal ion concentration showed removal up to 70%–100%, indicating the improvement in removal efficiency due to acclimatization of microbial consortia at higher metal concentration. Present study clearly shows the ability of native microbial consortia in removing even higher concentrations of heavy metals from actual wastewater under ambient conditions. The present bioreactors configuration can be scale up for the on-site wastewater treatment with further optimization of the removal process. It was recommended that after using the present treatment process, treated water is safe for irrational purposes.

Floriculture: alternate non-edible plants for phyto-remediation of heavy metal contaminated soils

Contamination of pre-urban arable land, by untreated municipal/industrial effluents derived heavy metals, is causing serious health hazards to human beings and abiotic components of the ecosystem. In this study, phytoremedial potential of four non-eatable floriculture plants, i.e. antirrhinum, pansy, calendula, and marigold, was explored by growing in heavy metal contaminated soil (collected from pre-urban area under untreated wastewater irrigation for more than 20 years) amended with bacterial inoculum and EDTA amended soils under greenhouse conditions for 75 days. Bacterial inoculation gave a maximum increase in the root (47.1%) and shoot (30.9%) biomass, while EDTA amendment gave 37.1 and 21.4%, respectively. However, EDTA application increases more metal concentrations in the root (65%) and shoot (36%) than that of bacterial inoculum, i.e. 37 and 27%, respectively. The values of bioconcentration factor (BCF) of all the plants for Cd, Cr, Ni and Pb were significantly increased by EDTA application and bacterial inoculum over control. The BCF values were either ≈1 or >1 in all the treatments in case of Cr. Ni and Pb. Contrarily, reduction in translocation factor (TF) values of all the flowering plants for all the metals were observed over control when the growth medium was treated with EDTA and bacterial inoculum.

Contamination of vegetables with heavy metals across the globe: hampering food security goal.

Food Security is a multifaceted aspect covering nutrition, availability, sufficiency, accessibility and safety. Millennium Development Goals as framed by United Nations focused to attain food security for all. The biggest hindrance in attaining food security was less productivity due to lack of enough resources. In order to increase the availability and produce sufficient food, malpractices like growing food on contaminated land or using untreated wastewater for irrigation came into play. Such practices have led to the transfer of heavy metals, pathogens and other harmful toxins to food crops. Various studies across the world have documented high concentration of heavy metals in vegetable crops. Root tubers and succulent stems are hyperaccumulators of heavy metals and thus tend to pose health hazard to the consuming population. In many instances the content of toxic metals in vegetables is much beyond permissible limits. Hazard quotient assessment in various studies has shown that consumption of these vegetables can be toxic to both adults and children. So, the question arises are we really attaining the global food security? There is a need to find a solution to produce sufficient, safe and nutritious food for the civilization so as to meet the goal of "zero hunger".

Epidemiological Evidence and Health Risks Associated With Agricultural Reuse of Partially Treated and Untreated Wastewater: A Review.

The use of partially treated and untreated wastewater for irrigation is beneficial in agriculture but may be associated with human health risks. Reports from different locations globally have linked microbial outbreaks with agricultural reuse of wastewater. This article reviews the epidemiological evidence and health risks associated with this practice, aiming toward evidence-based conclusions. Exposure pathways that were addressed in this review included those relevant to agricultural workers and their families, consumers of crops, and residents close to areas irrigated with wastewater (partially treated or untreated). A meta-analysis gave an overall odds ratio of 1.65 (95% CI: 1.31, 2.06) for diarrheal disease and 5.49 (95% CI: 2.49, 12.10) for helminth infections for exposed agricultural workers and family members. The risks were higher among children and immunocompromised individuals than in immunocompetent adults. Predominantly skin and intestinal infections were prevalent among individuals infected mainly via occupational exposure and ingestion. Food-borne outbreaks as a result of crops (fruits and vegetables) irrigated with partially or untreated wastewater have been widely reported. Contamination of crops with enteric viruses, fecal coliforms, and bacterial pathogens, parasites including soil-transmitted helminthes (STHs), as well as occurrence of antibiotic residues and antibiotic resistance genes (ARGs) have also been evidenced. The antibiotic residues and ARGs may get internalized in crops along with pathogens and may select for antibiotic resistance, exert ecotoxicity, and lead to bioaccumulation in aquatic organisms with high risk quotient (RQ). Appropriate mitigation lies in adhering to existing guidelines such as the World Health Organization wastewater reuse guidelines and to Sanitation Safety Plans (SSPs). Additionally, improvement in hygiene practices will also provide measures against adverse health impacts.

Vegetable farmers' knowledge, attitude and drivers regarding untreated wastewater irrigation in developing countries: A case study in Iran

Untreated wastewater irrigation is a popular practice in developing countries, particularly those with poor wastewater treatment facilities. Whilst wastewater irrigation has harmful effects on the human health and the environment, little is known about knowledge and attitude regarding this source of water among farmers who use it as well as their reasons for irrigation using it. This cross-sectional survey study was conducted to explore knowledge and attitude of Iranian wastewater users towards this water resource. Also, their drivers for untreated wastewater irrigation were explored. Results indicated that farmers have a relatively high knowledge about the inappropriate quality of untreated wastewater and its negative effects. Although they were concerned about the health, environmental and social impacts of untreated wastewater, they believed that using this water resource is economically profitable for them. The Bayesian Network (BN) and Partial Least Squares (PLS) path modeling was used to clarify factors influencing attitude towards untreated wastewater irrigation. Analysis of the causal models specified that knowledge, moral norm and social cohesion significantly affects attitude towards untreated wastewater. Also, social cohesion moderated the effects of knowledge and subjective norm on attitude. The study clarified that the most important drivers for using untreated wastewater for irrigation by farmers were water scarcity, increasing crop yield, decreasing production costs, difficulty to access freshwater, saving freshwater and increasing soil fertility. The results of this study highlighted the need for planning to improve wastewater treatment along with appropriate policies and methods to improve farmers' commitment for the environmental conservation and the human health.

Survey of 218 organic contaminants in groundwater derived from the world's largest untreated wastewater irrigation system: Mezquital Valley, Mexico

The Mezquital Valley system is the world's oldest and largest example with regard to use of untreated wastewater for agricultural irrigation. Because of the artificial high recharge associated with the Mezquital Valley aquifers, groundwater is extracted for human consumption, and there are plans to use this groundwater as a water resource for Mexico City. Thus, this study analyzed 218 organic micro-contaminants in wastewater, springs, and groundwater from Mezquital Valley. Five volatile organic compounds (VOCs) and nine semi-volatile organic compounds (SVOCs) were detected in the wastewater used for irrigation. Only two SVOCs [bis-2-(ethylhexyl) phthalate and dibutyl phthalate] were detected in all the wastewater canals and groundwater sources, whereas no VOCs were detected in groundwater and springs. Of the 118 pharmaceutically active compounds (PhACs) and 7 reproductive hormones measured, 65 PhACs and 3 hormones were detected in the wastewater. Of these, metformin, caffeine, and acetaminophen account for almost sixty percent of the total PhACs in wastewater. Nevertheless, 23 PhACs were detected in groundwater sources, where the majority of these compounds have low detection frequencies. The PhACs sulfamethoxazole, N,N-diethyl-meta-toluamide, carbamazepine, and benzoylecgonine (primary cocaine metabolite) were frequently detected in groundwater, suggesting that although the soils act as a filter adsorbing and degrading the majority of the organic pollutant content in wastewater, these PhACs still reach the aquifer. Therefore, the presence of these PhACs, together with the high levels of the endocrine disruptor bis-2-(ethylhexyl) phthalate, indicate that water sources derived from the recharge of the studied aquifers may pose a risk to consumer health.

Health risk assessment and growth characteristics of wheat and maize crops irrigated with contaminated wastewater.

The present study evaluated the effect of untreated wastewater irrigation and its health risks in Triticum aestivum (wheat) and Zea mays (maize) cultivated at south Cairo, Egypt. Morphological measurements (stem and root lengths, number of leaves per plant, and dry weights of main organs) as well as soil, irrigation water, and plant analyses for nutrients and heavy metals were conducted in polluted and unpolluted sites. Wastewater irrigations leads to reduction in the morphological traits of the plants and reduced its vegetative biomass and yield production, with more negative impacts on maize than wheat. The concentrations of Pb, Cd, Cr, and Fe in roots and leaves of wheat were above the phytotoxic limits. Conversely, Pb, Cd, and Fe were significantly high and at phytotoxic concentrations in the leaves of maize at polluted site. The present study indicated that wheat plants tend to phytostabilize heavy metals in their roots, while maize accumulates it more in their leaves. Maize and wheat had toxic concentrations of Pb and Cd in their grains under wastewater irrigation. The health risk index showed values >1 for Pb and Cd in polluted site for both crops, in addition to maize in unpolluted site. Consequently, this will have greatest potential to pose health risk to the consumers.

Wastewater irrigation: past, present, and future

With population growth and social and economic development, water shortage is becoming a serious issue worldwide. As a key alternative water resource, wastewater can be used in agriculture to compensate for water shortages. Wastewater irrigation has a long development history and has undergone different phases in developing and developed countries. Untreated wastewater irrigation can come with numerous environmental problems. Strong management practices, such as the application of suitable treated and irrigated technologies, can be used to reap substantial benefits while minimizing risks. We discussed the major challenges associated with wastewater irrigation and its future use to help improve wastewater irrigation practices around the world.This article is categorized under: Engineering Water &gt; Sustainable Engineering of Water Engineering Water &gt; Water, Health, and Sanitation

Monitoring of indicator and multidrug resistant bacteria in agricultural soils under different irrigation patterns

The presence of multidrug-resistant bacteria has been proposed as an environmental impact indicator of wastewater use in agricultural soils. Nevertheless, the effect of untreated wastewater discharge on occurrence and persistence of these type of bacteria in soils is unclear. In this study, multidrug-resistant bacteria and microbial indicators of fecal contamination (coliforms and Salmonella) were determined at different depths (0–15, 15–30 and 30–50cm), in active agricultural soils under different untreated wastewater irrigation pattern (a zone with past and present wastewater irrigation; a zone with wastewater irrigation until 2003; and a zone that had never been irrigated with wastewater) in Chihuahua, Mexico. A total of 94 multidrug-resistant strains were recovered from all tested soil samples, even from those that have never been irrigated with wastewater. Higher presence (P<0.05) of multidrug-resistant bacteria was found in soils currently irrigated with untreated wastewater than in soils that has not been irrigated with wastewater for more than 10 years; the later had presence of multidrug-resistant bacteria that was statistically higher than soils that had never been irrigated with wastewater. Wastewater irrigation showed an impact on proliferation of antibiotic-resistant Gram negative bacteria in soils actually irrigated but not in Gram positive bacteria. No statistical difference was found for coliforms and Salmonella between the three soil groups. The effect of depth in multidrug-resistance bacteria presence was negligible. Although multidrug-resistant bacteria was also isolate from soils without wastewater irrigation, their persistence in a highest number in soils irrigated with wastewater suggest that use of untreated wastewater for irrigation enhance the proliferation of multidrug-resistant microorganisms which can be monitoring in soils even after a long period of time after the last irrigation.

Heavy metals in soil and plants after long-term sewage irrigation at Tianjin China: A case study assessment

Due to the constraints of freshwater for agricultural irrigation, sewage water has been used in farmland irrigation as an important supplement and alternative water resources during the past three decades in China, especially in northern areas. However, there is increasing concern about food safety and health risks, hence, a case study was undertaken to understand the long-term effect of sewage irrigation on heavy metal concentrations in soil and plants. Sewage sludge, soil and plant samples were collected and analyzed for heavy metals concentrations. Results showed that sewage irrigated soil contained much higher concentrations of Cd, Cu, Pb, Zn, Ni, Cr, As and Hg compared to clean water irrigated soil. The heavy metal content of the topsoil (0–20cm) was much higher than that of the subsoil. Significant heavy metal (Cd, Zn and Hg) pollution has occurred in soils of areas that had been using untreated waste water irrigation in Tianjin, China. There were significant accumulations of heavy metals in wheat that used sewage irrigation. Compared with the other parts of the wheat plants, the higher contents of Cd, Cr, Pb and As in the roots indicated that roots had a strong absorption ability and maybe cause an obvious barrier effect. Based on the soil to plant transfer factor of heavy metals, there is a strong accumulation effect of Cd in vegetables. Overall, the concentrations of Cd, Pb, Ni, Cr and As were lower than the national permitted safety limits in soil. Mean Cd, Pb and As concentrations in vegetables were higher than the national safety limits, whereas the mean concentrations of Cu, Zn and Cr were below Chinese national safety limits. Therefore, in order to ensure food safety and use of sewage for irrigation, continuous monitoring and pollution control is needed.

Effect of short term irrigation with treated and untreated wastewater on growth and physio-biochemical parameters of wheat

Pot experiments were conducted to evaluate the possibility of use of treated and untreated wastewater for irrigation. Wastewater samples collected from electroplating, steel processing industrial units and common effluent treatment plant (CETP) were treated with Salvinia biomass. Wheat (Triticum aestivum), the staple food crop was chosen for the study. Seeds were sown in pots and irrigated with treated and untreated wastewater. Plants irrigated with tap water were designated as control. The growth of wheat was assessed at seedling and pre-flowering stages using various physiological and biochemical indices. The results obtained from the studies conducted for two consecutive seasons in net house indicated that levels of total chlorophyll, glucose, protein and photosynthetic efficiency was not significantly affected in plants irrigated with treated wastewater in comparison to those irrigated with tap water at both seedling and pre-flowering stages. In contrast, plants irrigated with untreated wastewater showed significant alteration in all the parameters at all the growth stages in comparison to control. The studies suggested that the treated wastewater can be used for irrigating crop plants as plant growth was not significantly affected.

Assessing nitrogen fertilizer rates and split applications using the DSSAT model for rice irrigated with urban wastewater

When reclaimed wastewater containing more nutrients than conventional irrigation water is used for irrigation, alternative fertilization practices are required for agricultural productivity and environmental sustainability. The objective of this study was to assess the effect of the nitrogen (N) fertilizer rates and split N fertilizer application on rice yields grown in paddy fields irrigated with reclaimed wastewater using the Decision Support System for Agrotechnology Transfer (DSSAT) v4.5 model. The experimental plots employed a randomized complete block design with three treatments and four replications. The three treatments included ground water irrigation plots (GW), untreated wastewater irrigation plots (WW), and reclaimed wastewater irrigation plots (RWW). The input data for the DSSAT model, including weather data, irrigation amount, irrigation water quality, soil data, cropping practice data, and rice yields, were monitored and collected between 2006 and 2009. The DSSAT model was calibrated and validated with observed yield data using the root mean square error (RMSE), normalized RMSE (nRMSE), and the index of agreement (d) for the statistical indices. The values of RMSE, nRMSE, and d were 269–645kgha−1, 4.1–11.7%, and 0.94–0.95, respectively, for the calibration period. The calibrated model showed good agreement with the observed rice yields, and the values of RMSE, nRMSE, and d were 155–538kgha−1, 2.6–10.4%, and 0.95–0.98, respectively, for the validation period. The simulation results showed that the optimal N fertilizer rate for paddy field rice irrigated with reclaimed wastewater was considered to be 20–50% less than the standard fertilizer rate (SFR). Adjusting the split N fertilizer application rate was demonstrated as being enough to satisfy the target rice yield and resulted in an additional 10–20kgha−1 reduction in the amount of N fertilizer used.

Farmers' Perception and Knowledge of Health Risks in Wastewater Irrigation

This paper uses cross-sectional survey data to evaluate the farmers’ perception and knowledge of health risks in urban wastewater irrigation in Nairobi, Kenya. In order to identify the determinants of farmers’ perception on health risks of wastewater irrigation to farm workers and consumers of produced vegetables, analysis of the study used the ordered probit model. The results show urban and peri-urban farmers are aware of health hazards attributed to untreated wastewater irrigation.