Effects of water-saving superabsorbent polymer on antioxidant enzyme activities and lipid peroxidation in corn (Zea mays L.) under drought stress

BACKGROUND

Drought is the most important abiotic stress factor limiting corn (Zea mays L.) growth and productivity. Therefore efficient management of soil moisture and study of metabolic changes in response to drought are important for improved production of corn. The objective of the present study was to gain a better understanding of drought tolerance mechanisms and improve soil water management strategies using a water-saving superabsorbent polymer (SAP) at 30 kg ha(-1) under three irrigation levels (adequate, moderate and deficit) using a new type of hydraulic pressure-controlled auto-irrigator.

RESULTS

The results showed that relative water content and leaf water potential were much higher in corn treated with SAP. Although application of SAP reduced biomass accumulation by 11.1% under adequate irrigation, it increased the biomass markedly by 39.0% under moderate irrigation and 98.7% under deficit irrigation. Plants treated with SAP under deficit irrigation showed a significant decrease in superoxide dismutase, catalase, peroxidase, ascorbate peroxidase and glutathione reductase activities in leaves compared with control plants.

CONCLUSION

The results of this study suggest that drought stress causes the production of oxygen radicals, leading to increased lipid peroxidation and oxidative stress in plants, and the application of a superabsorbent polymer could conserve soil water, making it available to plants for quenching oxidative stress and increasing biomass accumulation, especially under severe water stress.

Effects of water-saving superabsorbent polymer on antioxidant enzyme activities and lipid peroxidation in oat (Avena sativa L.) under drought stress

BACKGROUND

Drought stress significantly limits oat (Avena sativa L.) growth and productivity. Thus an efficient management of soil moisture and study of metabolic changes in response to drought are important for improved production of oat. The objective was to gain a better understanding of drought tolerance mechanisms and improve soil water management strategies using water-saving superabsorbent polymer (SAP) at 60 kg ha(-1) under three irrigation levels (adequate, moderate and deficit) using a new type of hydraulic pressure-controlled auto irrigator.

RESULTS

The results showed that the relative water content and leaf water potential (ψ(1) ) were much higher in oats treated with SAP. Although the SAP had little effect on plant biomass accumulation under adequate and moderate irrigation, it significantly increased the biomass by 52.7% under deficit irrigation. Plants treated with SAP under deficit irrigation showed a significant decrease in superoxide dismutase, catalase, peroxidase, ascorbate peroxidase and glutathione reductase activities in leaves compared with control plants.

CONCLUSION

Our results suggested that drought stress leads to production of oxygen radicals, which results in increased lipid peroxidation and oxidative stress in the plant, and the application of SAP could conserve soil water, making same available to plants for increased biomass accumulation and reduced oxidative stress especially under severe water stress.

Impact of consumer-driven changes to crop production practices on lettuce drop caused by Sclerotinia sclerotiorum and S. minor

Increasing demands for value-added salad products have triggered revolutionary changes in the production practices of vegetable salad crops in recent years. One of the pivotal changes is the adaptation of 2-m-wide beds for increased vegetable biomass per unit area. The move away from the traditional 1-m-wide raised beds in cool-season vegetable production and the associated irrigation practices potentially can have a major influence on diseases affecting cool-season vegetables. To assess the potential impacts of this shift on lettuce drop caused by Sclerotinia minor and S. sclerotiorum, the two bed widths and different irrigation frequencies within each were compared in two separate field experiments over four lettuce crops in 2 years. Treatments included 1- and 2-m bed widths with twice-weekly, weekly and biweekly drip irrigation serving as subplot treatments that were begun immediately following thinning. Incidence of lettuce drop was evaluated weekly thereafter until maturity. For S. sclerotiorum, 36 half-liter soil samples were also collected once each season and assayed for the number of sclerotia, and apothecia were counted weekly in a 10-m(2) area for each plot. Regardless of the species, the effects of bed width and irrigation frequency were both significant. Twice-weekly irrigation and 2-m bed width resulted in higher lettuce drop incidence than other treatments. For S. sclerotiorum, twice-weekly irrigation and 2-m bed width also significantly increased the number of apothecia per unit area and the accumulation of soilborne sclerotia over multiple cropping seasons. Results demonstrated that the 2-m bed width combined with the practiced frequency of irrigations can result in higher lettuce drop caused by S. minor and increased incidence of airborne infection by S. sclerotiorum in the Salinas Valley where, historically, it has not been a serious threat. Increased incidence of S. sclerotiorum infection in commercial lettuce fields in the Salinas Valley between 2001 and 2006 validates these experimental results. These relatively new crop production practices can alter the balance of the two Sclerotinia spp. that has long existed in California.

[Differences in water consumption characteristics and grain yield of different wheat cultivars]

A field experiment with 10 wheat cultivars was conducted to study the water consumption characteristics at different growth stages and the differences in the grain yield of the cultivars. Three irrigation treatments were installed, i.e., no irrigation (W0), irrigation before sowing and at jointing stage (W1), and irrigation before sowing and at jointing and anthesis stages (W2), with irrigation amount 60 mm each time. Based on the cluster analysis with the parameters grain yield and water use efficiency (WUE) in the three treatments, the test ten cultivars could be divided into three groups, i.e., high yield and high WUE (Group I), high yield and medium WUE (Group II), and medium yield and low WUE (Group III). The average values of grain yield and WUE in each group were calculated to elucidate the water consumption characteristics of the three groups. In treatment W0, the total water consumption amount in the whole growth period, the water consumption amount from anthesis to maturing stages and its proportion to the total water consumption amount of Group I were lower than those of Group II and Group III, but the grain yield of Group I was the highest. In treatment W1, the water consumption amount from jointing to anthesis stages and its proportion to total water consumption amount of Group I were lower than those of Group II and Group III, but the water consumption amount from anthesis to maturing stages had no significant differences among Group I, Group II, and Group III. In treatment W2, the total soil water consumption amount, water consumption amount from jointing to anthesis stages and its proportion to total water consumption amount of Group I were lower than those of Group II and Group III, while the water consumption amount from anthesis to maturity stages and its proportion to total water consumption amount of both Group I and Group III were lower than those of Group II. In terms of high-yield and water-saving under the present experimental condition, it was implicated that the most appropriate cultivars might fall into the Group I with high yield and high WUE, and the most appropriate irrigation regime with high yield and low water consumption was treatment W1, i.e., irrigated 60 mm each time before sowing and at jointing stage.

[Effects of irrigation with treated wastewater on nutrient distribution in cucumber and tomato plants and their fruit quality]

A field experiment was conducted to investigate the effects of irrigation with treated wastewater on the nutrient distribution in cucumber and tomato plants and their fruit quality. Irrigation with treated wastewater promoted tomato growth significantly, but had definite inhibition effect on cucumber growth. After the irrigation with treated wastewater, the nitrogen in plants had the characteristics of upward translocation, potassium was easily to be accumulated in cucumber leaf but not accumulated in tomato root, and sodium was mostly accumulated in root but less enriched in leaf, not giving damage to the plants. No significant effects were observed on the distribution of calcium, magnesium, and chlorine in plants. Under the irrigation with treated wastewater, the overall quality of cucumber and tomato fruits was less affected. The nitrate concentration in cucumber and tomato fruits was increased by 5.3% and 32.9%, respectively, but still lower than the state food safety standard of China.

[Effects of irrigation amount and nitrogen fertilization rate on wheat yield and soil nitrate content]

A field experiment was conducted to study the effects of irrigation amount and nitrogen fertilization rate on wheat yield and soil nitrate content. With the increase of irrigation amount, the soil nitrate content in 0-200 cm layer at the same nitrogen fertilization rates had a trend of decrease -increase-decrease. Under irrigation, the soil nitrate content was significantly lower in 0-80 cm layer while significantly higher in 80-200 cm layer, compared with the control. As the irrigation amount increased, the translocation of soil nitrate nitrogen to deeper layers accelerated dramatically, with the content decreased in 0-80 cm layer, increased in 120-200 cm layer, and peaked in 120-140 cm layer. When the nitrogen fertilization rate increased from 210 kg x hm(-2) to 300 kg x hm(-2) the soil nitrate content at the same irrigation amounts increased significantly through anthesis, filling, and maturity stages. With the increase of irrigation amount, the grain yield decreased after an initial increase, being the highest when the irrigation amount in whole growth period was 60 mm. The grain yield, grain protein content, and grain protein yield all increased significantly with increasing nitrogen fertilization rate. Under the conditions of the present experiment, the treatment with nitrogen fertilization rate 210 kg N x hm(-2) and irrigation amount 60 mm (split into two times) had the highest grain yield, grain protein content, grain protein yield, and harvest index but the least NO3(-)-N leaching, being the more available irrigation and nitrogen fertilization mode for wheat production in the study area.

Assessment of wastewater effluent quality in Thessaly region, Greece, for determining its irrigation reuse potential

The objective of the present study is to assess wastewater effluent quality in Thessaly region, Greece, in relation to its physicochemical and microbiological burden as well as its toxic potential on a number of organisms. Wastewater may be used for agricultural as well as for landscape irrigation purposes; therefore, its toxicity potential is quite important. Thessaly region has been chosen since this region suffers from a distinct water shortage in summer period necessitating alternative water resources. During our research, treated effluents from four wastewater treatment plants operating in the region (Larissa, Volos, Karditsa, and Tirnavos) were tested for specific physicochemical and microbiological parameters [biochemical oxygen demand (BOD(5)), chemical oxygen demand (COD), total suspended solids (TSS), pH, electrical conductivity, selected metals presence (Cd, Co, Cr, Cu, Fe, Mn, Ni, Pb, Zn, As), and fecal coliforms' (FC) number]. The effluents were also tested for their toxicity using two different bioassays (Daphnia magna immobilization test and Phytotoxkit microbiotest). The findings were compared to relative regulations and guidelines regarding wastewater reuse for irrigation. The results overall show that secondary effluents in Thessaly region are generally acceptable for reuse for irrigation purposes according to limits set by legislation, if effective advanced treatment methods are applied prior to reuse. However, their potential toxicity should be closely monitored, since it was found that it may vary significantly in relation to season and location, when indicator plant and zooplankton organisms are used.

Effects of different irrigation, drying and production scenarios on the productivity, postharvest quality and economic feasibility of Origanum syriacum, a species typically over-collected from the wild in Lebanon

BACKGROUND

The potential of Origanum syriacum L. to become a cultivated crop in Lebanon rather than being harvested from the wild was investigated at the production, postharvest and economic levels. Three irrigation schemes were tested on growth parameters of cultivated oregano plants. In order to identify the most quality-preserving drying technique, air-, oven (30 °C)- and freeze-dried oregano samples were assessed through sensory analysis. Cost/benefit analysis was used to compare the economic potential of O. syriacum in four production scenarios.

RESULTS

An irrigation scheme of 16 L per plant administered every 2 weeks (medium irrigation) during the dry period resulted in a doubling of the horticultural (56.34%) and hydro-distilled essential oil (55.22%) yields. Descriptive sensory analysis showed that air-dried material had the desired flavour, aroma and colour attributes. Net present values ranged from - 677 406.02 to 562 301.5 US$ and benefit/cost ratios from 0.5341 to 5.1993 for a 1 ha, 5 year life-cycle oregano farm.

CONCLUSION

Irrigating plants once every 2 weeks during the dry season optimised herbage and essential oil yields of oregano, while air drying of plant material preserved its organoleptic attributes as a spice. Three of the four production scenarios, namely Zaatar production, herbal tea and Zaatar production and essential oil production, were economically feasible, with the last of these having the highest economic feasibility.

Opportunities for woody crop production using treated wastewater in Egypt. I. Afforestation strategies

The Nile River provides nearly 97% of Egypt's freshwater supply. Egypt's share of Nile waters is fixed at 55.5 billion cubic meters annually. As a result, Egypt will not be able to meet increasing water demand using freshwater from the Nile and has been developing non-conventional wastewater reuse strategies to meet future demands. The USAID Mission in Cairo began promoting strategies for water reuse in 2004, and guidelines for safe and direct reuse of treated wastewater for agricultural purposes were approved in 2005 (Egyptian Code 501/2005). Twenty-four man-made forests were established that have been useful for assessing the efficacy of using treated wastewater for afforestation. At present, approximately 4,340 hectares are under irrigation with treated wastewater, utilizing a total daily volume of 467,400 cubic meters. Wastewater has been applied to trees along roads, greenbelts in cities, and woody production systems. Currently, a joint USDA Forest Service--Agricultural Research Service technical assistance team has been evaluating the feasibility of scaling up such afforestation efforts throughout Egypt. We describe information about: 1) suitable tree species that have been identified based on local soil characteristics, water quality, and quantity of water supply; 2) the benefits and consequences of using these species; 3) strategies to maximize the potential of afforestation with regard to improving water quality, maximizing resource production, increasing biodiversity, and limiting commercial inputs; and 4) potential long-term impacts on the natural resource base from afforestation. A companion paper addresses irrigation recommendations based on species and local conditions (see Evett et al. 2000).

[Simulation of soil water dynamics in triploid Populus tomentosa root zone under subsurface drip irrigation]

Based on the observed data of triploid Populus tomentosa root distribution, a one-dimensional root water uptake model was proposed. Taking the root water uptake into account, the soil water dynamics in triploid P. tomentosa root zone under subsurface drip irrigation was simulated by using HYDRUS model, and the results were validated with field experiment. Besides, the HYDRUS model was used to study the effects of various irrigation technique parameters on soil wetting patterns. The RMAE for the simulated soil water content by the end of irrigation and approximately 24 h later was 7.8% and 6.0%, and the RMSE was 0.036 and 0.026 cm3 x cm(-3), respectively, illustrating that the HYDRUS model performed well in simulating the short-term soil water dynamics in triploid P. tomentosa root zone under drip irrigation, and the root water uptake model was reasonable. Comparing with 2 and 4 L x h(-1) of drip discharge and continuous irrigation, both the 1 L x h(-1) of drip discharge and the pulsed irrigation with water applied intermittently in 30 min periods could increase the volume of wetted soil and reduce deep percolation. It was concluded that the combination of 1 L x h(-1) of drip discharge and pulsed irrigation should be the first choice when applying drip irrigation to triploid P. tomentosa root zone at the experiment site.

Improving water management practices to reduce nutrient export from rice paddy fields

Nitrogen (N) and phosphorus (P) loss from rice paddy fields represents a significant threat to water quality in China. In this project, three irrigation-drainage regimes were compared, including one conventional irrigation-drainage regime, i.e. continuous submergence regime (CSR), and two improved regimes, i.e. the alternating submergence-nonsubmergence regime (ASNR) and the zero-drainage irrigation technology (ZDIT), to seek cost-effective practices for reducing nutrient loss. The data from these comparisons showed that, excluding the nutrient input from irrigation, the net exports of total N and total P via surface field drainage ranged from -3.93 to 2.39 kg ha and 0.17 to 0.95 g ha(-1) under the CSR operation, respectively, while N loss was -2.46 to -2.23 kg ha(-1) and P export was -0.65 to 0.31 kg ha(-1) under the improved regimes. The intensity of P export was positively correlated to the rate of P application. Reducing the draining frequency or postponing the draining operation would shift the ecological role of the paddy field from a nutrient export source to an interception sink when ASNR or the zero-drainage water management was used. In addition, since the rice yields are being guaranteed at no additional cost, the improved irrigation-drainage operations would have economic as well as environmental benefits.

[Effects of canal-lining project on groundwater and ecological environment in Hetao Irrigation District of Inner Mongolia]

The canal-lining project in Hetao Irrigation District (HID) for water-saving irrigation has been implemented for many years. By using statistical method, ordinary Kriging, and software ArcGIS 9.0, this paper analyzed the spatiotemporal variation of groundwater table depth and salinity in HID in September, 2001 and 2009. In the meantime, the vegetation distribution on the both shores of the lining part and non-lining part of Yangjiahe channel was also investigated. After the many years implementation of the project, the water diversion amount in HID in 2009 was reduced to 44.5 x 10(8) m3. The region area of groundwater table with a depth of 2.5-3.0 m was increased from 1.2 x 10(4) hm2 in 2001 to 9.11 x 10(4) hm2 in 2009. The region area of groundwater table with a depth of 2.0-2.5 m in 2009 took 80% of the total area of HID. In the northwestern region of HID, the groundwater salinity had reduced from 5000-10000 mg x L(-1) to 3000-5000 mg x L(-1). In Wulate irrigation region, the areas of salt water belt and half-salt water belt were increasing. After the canal-lining of Yangjiahe channel, the plant species and diversity index on both shores reduced, and some herbaceous plants with shallow roots showed degradation signs. The implementation of the project and the reduction of water diversion for irrigation did not exert negative effects on the maintenance of water surface area of Wuliangsuhai Lake.

Opportunities for woody crop production using treated wastewater in Egypt. II. Irrigation strategies

An Egyptian national program targets annual reuse of 2.4 billion m3 of treated wastewater (TWW) to irrigate 84,000 ha of manmade forests in areas close to treatment plants and in the desert. To evaluate the feasibility of such afforestation efforts, we describe information about TWW irrigation strategies based on (1) water use of different tree species, (2) weather conditions in different climate zones of Egypt, (3) soil types and available irrigation systems, and (4) the requirement to avoid deep percolation losses that could lead to groundwater contamination. We conclude that drip irrigation systems are preferred, that they should in most cases use multiple emitters per tree in order to increase wetted area and decrease depth of water penetration, that deep rooting should be encouraged, and that in most situations irrigation system automation is desirable to achieve several small irrigations per day in order to avoid deep percolation losses. We describe directed research necessary to fill knowledge gaps about depth of rooting of different species in sandy Egyptian soils and environments, tree crop coefficients needed for rational irrigation scheduling, and depth of water penetration under different irrigation system designs. A companion paper addresses recommendations for afforestation strategies (see Zalesny et al. 2011, this issue).

Effects of different potato cropping system approaches and water management on soilborne diseases and soil microbial communities

Four different potato cropping systems, designed to address specific management goals of soil conservation, soil improvement, disease suppression, and a status quo standard rotation control, were evaluated for their effects on soilborne diseases of potato and soil microbial community characteristics. The status quo system (SQ) consisted of barley underseeded with red clover followed by potato (2-year). The soil-conserving system (SC) featured an additional year of forage grass and reduced tillage (3-year, barley/timothy-timothy-potato). The soil-improving system (SI) added yearly compost amendments to the SC rotation, and the disease-suppressive system (DS) featured diverse crops with known disease-suppressive capability (3-year, mustard/rapeseed-sudangrass/rye-potato). Each system was also compared with a continuous potato control (PP) and evaluated under both irrigated and nonirrigated conditions. Data collected over three potato seasons following full rotation cycles demonstrated that all rotations reduced stem canker (10 to 50%) relative to PP. The SQ, SC, and DS systems reduced black scurf (18 to 58%) relative to PP; SI reduced scurf under nonirrigated but not irrigated conditions; and scurf was lower in DS than all other systems. The SQ, SC, and DS systems also reduced common scab (15 to 45%), and scab was lower in DS than all other systems. Irrigation increased black scurf and common scab but also resulted in higher yields for most rotations. SI produced the highest yields under nonirrigated conditions, and DS produced high yields and low disease under both irrigation regimes. Each cropping system resulted in distinctive changes in soil microbial community characteristics as represented by microbial populations, substrate utilization, and fatty acid methyl-ester (FAME) profiles. SI tended to increase soil moisture, microbial populations, and activity, as well result in higher proportions of monounsaturated FAMEs and the FAME biomarker for mycorrhizae (16:1 ω6c) relative to most other rotations. DS resulted in moderate microbial populations and activity but higher substrate richness and diversity in substrate utilization profiles. DS also resulted in relatively higher proportions of FAME biomarkers for fungi (18:2 ω6c), actinomycetes, and gram-positive bacteria than most other systems, whereas PP resulted in the lowest microbial populations and activity; substrate richness and diversity; proportions of monounsaturated and polyunsaturated FAME classes; and fungal, mycorrhizae, and actinomycete FAME biomarkers of all cropping systems. Overall, soil water, soil quality, and soilborne diseases were all important factors affecting productivity, and cropping systems addressing these constraints improved production. Cropping system approaches will need to balance these factors to achieve sustainable production and disease management.

Volatile compounds and sensory attributes of wine from Cv. Merlot (Vitis vinifera L.) grown under differential levels of water deficit with or without a kaolin-based, foliar reflectant particle film

The volatile composition and sensory attributes of Merlot wines produced from vines under differing levels of water stress, with or without a foliar, kaolin-based particle film, were analyzed by stir bar sorptive extraction-gas chromatography-mass spectrometry (SBSE-GC-MS) and sensory evaluation. Vines were irrigated over consecutive vintages with 100, 70, or 35% of their estimated water requirements (ET(c)), or 35% until color change then 70% until harvest (35-70% ET(c)). Neither of the treatments consistently influenced ester concentrations or their relative amounts, though their concentrations varied from year to year. However, deficit irrigation had an effect on the concentration of terpene alcohols and norisoprenoids. Wines produced from vines under water deficit contained higher amounts of citronellol, nerol, geraniol, and β-damascenone, but linalool and β-ionone were not affected by deficit irrigation. Particle film did not affect volatile composition in the wine. Untrained panelists in 2007 and 2008 distinguished between wines from vines that received 100 or 35% ET(c) and between wines from vines that received 35 or 35-70% ET(c). Trained sensory panelists detected differences among wines for aroma, flavor, taste, and mouthfeel; however, significant interactive effects between particle film application and vine water status hindered interpretation of independent main effects.

Use of vegetated agricultural drainage ditches to decrease toxicity of irrigation runoff from tomato and alfalfa fields in California, USA

The current study investigated the potential of vegetated drainage ditches for mitigating the impact of agricultural irrigation runoff on downstream aquatic ecosystems. Water column toxicity to larval fathead minnow (Pimephales promelas),and the amphipod Hyalella azteca was measured for 12 h or less at the ditch inflow and outflow, using custom-built in situ exposure systems. In addition, water and sediment samples were subject to standard toxicity tests with Ceriodaphnia dubia and H. azteca, respectively. No acute toxicity to larval fathead minnow was observed; however, runoff was highly toxic to invertebrates. Passage through a 389- to 402-m section of vegetated ditch had a mitigating effect and reduced toxicity to some degree. However, runoff from an alfalfa field treated with chlorpyrifos remained highly toxic to both invertebrate species, and runoff from a tomato field treated with permethrin remained highly toxic to H. azteca after passage through the ditch. Predicted toxic units calculated from insecticide concentrations in runoff and 96-h median lethal concentration (LC50) values generally agreed with C. dubia toxicity measured in the laboratory but significantly underestimated in situ toxicity to H. azteca. Sediments collected near the ditch outflow were toxic to H. azteca. Results from the current study demonstrate that experimental vegetated ditches were unable to eliminate the risk of irrigation runoff to aquatic ecosystems. In addition, protective measures based on chemical concentrations or laboratory toxicity tests with C. dubia do not ensure adequate protection of aquatic ecosystems from pyrethroid-associated toxicity.

Spatial sap flow and xylem anatomical characteristics in olive trees under different irrigation regimes

The compensation heat pulse (CHP) method is widely used to estimate sap flow and transpiration in conducting organs of woody plants. Previous studies have reported a natural azimuthal variability in sap flow, which could have practical implications in locating the CHP probes and integrating their output. Sap flow of several olive trees (Olea europaea L. cv. 'Arbequina') previously grown under different irrigation treatments were monitored by the CHP method, and their xylem anatomical characteristics were analyzed from wood samples taken at the same location in which the probes were installed. A significant azimuthal variability in the sap flow was found in a well-irrigated olive tree monitored by eight CHP probes. The azimuthal variability was well related to crown architecture, but poorly to azimuthal differences in the xylem anatomical characteristics. Well-irrigated and deficit-irrigated olive trees showed similar xylem anatomical characteristics, but they differed in xylem growth and in the ratio of nocturnal-to-diurnal sap flow (N/D index). The results of this work indicate that transpiration cannot be accurately estimated by the CHP method in olive trees if a small number of sensors are employed and that the N/D index could be used as a sensitive water status indicator.

Water reuse for irrigated agriculture in Jordan: challenges of soil sustainability and the role of management strategies

Reclaimed water provides an important contribution to the water balance in water-scarce Jordan, but the quality of this water presents both benefits and challenges. Careful management of reclaimed water is required to maximize the nutrient benefits while minimizing the salinity risks. This work uses a multi-disciplinary research approach to show that soil response to irrigation with reclaimed water is a function of the management strategies adopted on the farm by the water user. The adoption of management methods to maintain soil productivity can be seen to be a result of farmers' awareness to potentially plant-toxic ions in the irrigation water (70% of Jordan Valley farmers identified salinization as a hazard from irrigation with reclaimed water). However, the work also suggests that farmers' management capacity is affected by the institutional management of water. About a third (35%) of farmers in the Jordan Valley claimed that their ability to manage salinization was limited by water shortages. Organizational interviews revealed that institutional awareness of soil management challenges was quite high (34% of interviewees described salinization as a risk from water reuse), but strategies to address this challenge at the institutional level require greater development.

Increasing water productivity on Vertisols: implications for environmental sustainability

BACKGROUND

The availability and quality of irrigation water have become a serious concern because of global climate change and an increased competition for water by industry, domestic users and the environment. Therefore, exploring environmentally friendly water-saving irrigation strategies is essential for achieving food and environmental security. In northern Ethiopia, where traditional furrow irrigation is widely practiced, water mismanagement and its undesirable environmental impact are rampant. A 2-year field study was undertaken to compare the traditional irrigation management with surge and deficit irrigation practices on a Vertisol plot.

RESULT

Results have shown that surge and deficit irrigation practices increase water productivity by 62% and 58%, respectively, when compared to traditional management. The study also found out that these practices reduce the adverse environmental impacts (waterlogging and salinity) of traditional management by minimizing deep percolation and tail water losses. Total irrigation depth was reduced by 12% (for surge) and 27% (for deficit) when compared to traditional management.

CONCLUSION

Based on the results, the study concluded that surge and deficit irrigation technologies not only improve water productivity but also enhance environmental sustainability.

Seasonal changes in the concentrations of nitrogen and phosphorus in farmland drainage and groundwater of the Taihu Lake region of China

To reduce the harmful effects of irrigated agriculture on the environment, the evaluation of alternative irrigation water management practices is essential. The contents of total-phosphorus, nitrate nitrogen, and ammonium nitrogen in rural aquatic bodies typical of the Taihu Lake region (Yixing, Wangzhuang, and Xinzhuang) were determined during 2 years. The results showed that the concentrations of nitrogen and phosphorus during the rainy season were higher than in other months. The concentration of ammonium nitrogen in farmland drainage was higher than that of nitrate nitrogen. Ammonium nitrogen and nitrate nitrogen were the main pollution sources in rural groundwater. However, the pollution by ammonium nitrogen was worse than nitrate nitrogen. The annual average values of ammonium nitrogen in Yixing and Wangzhuang were 1.596 and 2.103 mg L(-1); with maximum values of 5.782 and 5.441 mg L(-1), respectively, exceeding the lower limit for type V water quality by a factor of 10. Concentrations of nitrate nitrogen in groundwater in Xinzhuang from May to September exceeded the limit value (10 mg L(-1)) for drinking water prescribed by the World Health Organization. Therefore, this groundwater was not suitable to drink. In Taihu Lake, the average concentration of phosphorus over 2 years was 0.492 mg L(-1) and pollution by phosphorus in Taihu Lake was worse than other farmland drainage because of the trend of total-phosphorus accumulation. In addition, the average concentrations of nitrate nitrogen and ammonium nitrogen in Taihu Lake were 2.152 and 2.885 mg L(-1), respectively over 2 years, indicating that the water in the Taihu Lake is constantly in danger of eutrophication. Because of the transformation of ammonium nitrogen to nitrate nitrogen, there was a connection between the concentrations of ammonium nitrogen in farmland drainage and nitrate nitrogen in groundwater. There was also a significant positive linear correlation between the concentrations of ammonium nitrogen in farmland drainage and in shallow groundwater.

Mutagenicity and genotoxicity of tannery effluents used for irrigation at Kanpur, India

The tannery effluents at Kanpur (India) have been in use for irrigation since last many years, polluting soil directly while ground water and food crops indirectly. Gas chromatography-mass spectrometric analysis of the test samples revealed the presence of organic compounds including diisooctyl phthalate, phenyl N-methylcarbamate, dibutyl phthalate, bis 2-methoxyethyl phthalate, and higher alkanes. Tannery effluent extracts were prepared using XAD-4/8 resins, dichloromethane, chloroform, and hexane and tested with Ames Salmonella test and DNA repair-defective Escherichia coli K-12 mutants. In the presence of XAD-concentrated tannery effluent, TA98 found to be the most sensitive strain in terms of mutagenic index followed by TA97a whereas in terms of mutagenic potential TA102 was most responsive. The extracts were also found genotoxic as determined in terms of survival of E. coli K-12 mutants, suggesting the presence of DNA damaging compounds in the tannery effluents. In the light of results, precautious use of tannery effluents for irrigation is suggested.

[Contents and movement of phosphorus in soil of long term effluent irrigated land forest]

Treated sewage effluent from Rotorua City, New Zealand, has been spray-irrigated into Whakarewarewa Forest to minimize effluent-derived nitrogen (N) and phosphorus (P) entering Lake Rotorua. To assess the capacity of the ecosystem to assimilate the effluent derived nutrients, a long term field trial was established within the Rotorua land treatment system. The objective of this study was to determine the accumulation, redistribution and movement of P in the volcanic soil after 11 year effluent irrigation. The soil samples were analyzed. Soil pH, total phosphorus (TP), Olsen P, Mehlich-3 P(M3P), M3Ca and M3Mg had increased significantly (p < 0.05) in the top soil (0-10 cm) in all effluent treated plots compared with the control plots. Some significant increase had extended deeper soil layer (20-40cm) or much deeper soil layer. Most effluent-derived P had accumulated in top 40cm. Concentrations of soil Olsen P and M3P in the medium and high effluent treatments were over environmental threshold levels (Olsen P, 60 mg x kg(-1); M3P, 150 mg x kg(-1)) in the top 20 cm. The values of soil saturation ratio (M3PSR) show that it was nearly saturated of soil P sorption in top soil. It was suggested that there was a potential environment crisis for soil P to move downward with drainage water. Regular soil sampling and Olsen P measurement using 60 mg x kg(-1) as an environment threshold could provide a solution for monitoring the movement of P down the soil profile. Phosphorus saturation ratio index (M3PSR) calculated as the molar ratio of M3P to (M3Al + M3Fe) appeared to be inadequate as an indicator for downward movement of soil P in such land treatment system. A new Phosphorus saturation ratio index for this system will be one of future study work.

[Effects of sprinkler irrigation amount on winter wheat growth, water consumption, and water use efficiency]

In 2006-2008, a field experiment was conducted at the Tongzhou Experimental Base for Water-Saving Irrigation Research, Chinese Academy of Sciences, Beijing, aimed to study the effects of sprinkler irrigation amount on the growth, grain yield, water consumption, and water use efficiency of winter wheat. Different treatments were installed, with the irrigation amounts expressed by the multiples of the evaporation (E) from a standard 20-cm diameter pan placed above winter wheat canopy. The grain yield was the highest in treatment 0.75 E in 2006-2007 and in treatment 0.625 E in 2007-2008. In treatments with irrigation amount less than 0.25 E, winter wheat growth was subjected to water stress, and the yield loss was larger than 25%. The water consumption of winter wheat in the two growth seasons was in the range of 219-486 mm, and increased with increasing irrigation amount. The relationships between the grain yield and the water consumption and water use efficiency could be described by quadratic function. Sprinkler irrigation with an amount of 0.50-0.75 E was recommended for the winter wheat growth after its turning green stage in Beijing area.

Normal water irrigation as an alternative to effluent irrigation in improving rice grain yield and properties of a paper mill effluent affected soil

Rice crop (var. Luit) was grown under controlled conditions in paper mill effluent contaminated soil and irrigated with undiluted paper mill effluent as well as normal water and compared the results against a control treatment consisting of similar unaffected soil irrigated with normal water. The effluent was alkaline (pH 7.5), containing high soluble salts (EC 2.93 dS m(-1)), chloride (600 mg L(-1)) and total dissolved solids (1875 mg L(-1)). At maximum tillering (MT) stage effluent irrigation significantly (P < 0.05) reduced the leaf numbers per hill and leaf area by 19.8 and 36.4 %, respectively. Tiller number and maximum root length were reduced by 19.3% and 12.5%, respectively at fifty percent flowering (FF) stage. Effluent irrigated crop recorded significant reduction in the dry matter production (17.5-24.9%) and grain yield (19%). Unfilled grain was increased by 10.7%. Higher concentration of sodium, calcium and magnesium in the effluent irrigated soil affected K uptake. Available soil P was lowest while available N, K, S and exchangeable and water soluble Na, K, Ca, Mg were highest in effluent irrigated soil. Chloride content found to increase (3-7 folds) while microbial biomass carbon reduced (10-37%). The adverse effect of the paper mill effluent on the crop as well as on the affected soil could be reduced significantly through normal water irrigation.

Evaluating the tolerance of young hybrid poplar trees to recycled waters high in salinity and boron

The successful adoption of water recycling strategies in many arid regions will require crops able to tolerate poor-quality waters. We evaluated different clones for salt and boron (B) tolerance within each of seven genetically distinct genomic groups (e.g., deltoides, deltoides x nigra, trichocarpa x deltoides, trichocarpa x deltoides x maximowizcii, trichocarpa x deltoides x nigra, trichocarpa x nigra, trichocarpa x maximowizcii). During each evaluation period, different clones within each of the groups were irrigated with high sodium chloride (NaCl) salinity (i.e., 10-30 dS m(-1)) and B (i.e., 10 mg L(-1)) water up to a maximum of 150 days, for a 4-year testing period under micro-field plot conditions. Excessive accumulation (up to 6%) of chloride (Cl) likely caused toxicity symptoms (necrosis of the leaves) observed in the less tolerant clones, while leaf B concentrations rarely exceeded 300 mg kg(-1) DM in any clone. Increased soil salinity likely hindered the uptake of B by the clones. Our results show that a wide range of selected Populus clones, of parentage trichocarpa x nigra, followed by deltoides x nigra show potential salt and B tolerance as young trees to recycled waters high in salinity and B.

[Stomatal response of spring wheat and related affecting factors under different irrigation treatment]

Taking three spring wheat cultivars as test materials, a field experiment was conducted to study the effects of different irrigation treatments on the stomatal conductance of the cultivars during their growth period, with the relationships between the stomatal conductance and the environmental factors analyzed. On the basis of winter irrigation with 1800 m3 x hm(-2) of water, three irrigation treatments, i. e., irrigating three times (T1), two times (T2), and once (T3) during spring wheat growth period, were installed, with 1050 m3 x hm(-2) of irrigation water each time. All irrigation treatments had greater effects on the stomatal conductance, which was decreased with the decreasing times of irrigation, and varied with the cultivars. From jointing stage to florescence, the stomatal conductance in all treatments had the same variation trend, i. e., decreased after an initial increase, and reached the peak at heading stage. After florescence, difference occurred among the treatments. In treatment T1, the stomatal conductance of all test cultivars increased after an initial decrease; in treatment T2, the variation patterns of stomatal conductance differed with cultivars; while in treatment T3, the conductance of all cultivars decreased all along. Among the environmental factors, relative atmospheric humidity had the greatest effects on the stomatal conductance, and their correlation coefficient in treatments T2 and T3 reached significant (0.82) and very significant (0.92* *), respectively. The stomatal regulation mechanism of spring wheat adapting to water deficit in Hexi corridor was of feedback manner.

[Effects of alternate partial root-zone subsurface drip irrigation on potato yield and water use efficiency]

Field experiment was conducted to investigate the effects of alternate partial root-zone subsurface drip irrigation (APRSDI) on the physiological responses, yield, and water use efficiency of potato. Compared with conventional drip irrigation (CDI), APRSDI had less negative effects on the potato leaf photosynthesis rate (P(n)), but decreased the transpiration rate and stomatal conductance significantly. The slightly higher P(n) under CDI was at the expense of consuming more water. No significant difference was observed in the potato yield under APRSDI and CDI, but APRSDI saved the irrigation amount by 25.8% and increased the irrigation water use efficiency and total water use efficiency by 27.5% and 15.3%, respectively, suggesting that APRSDI would be a feasible water-saving irrigation technique for the planting of potato.

Minimizing health risks during secondary effluent application via subsurface drip irrigation

Health risks posed on consumers due to the use of agricultural products irrigated with reclaimed wastewater were assessed by numerical simulation. The analysis is based on defining of an Exposure Model (EM) which takes into account several parameters: (i) the quality of the applied wastewater, (ii) the irrigation method, (iii) the elapsed times between irrigation, harvest, and product consumption, and; (iv) the consumers' habits. The exposure model is used for numerical simulation of human consumers' risks by running the Monte Carlo simulation method. Although some deviations in the numerical simulation which are probably due to uncertainty (impreciseness in quality of input data) and variability due to diversity among populations reasonable results were accepted. Accordingly, there is a several orders of magnitude difference in the risk of infection between the different exposure scenarios with the same water quality. The variability indicates the need for setting risk-based criteria for wastewater reclamation, including the application method and environmental conditions, rather than single water quality guidelines. Extra data is required to decrease uncertainty in the risk assessment. Future research needs to include definite acceptable risk criteria, more accurate dose-response modeling, information regarding pathogen survival in treated wastewater, additional data related to the passage of pathogens into and in the plants during irrigation, and information referring to the consuming habits of the human community.