A Tool for the Evaluation of Irrigation Water Quality in the Arid and Semi-Arid Regions

In the Mediterranean arid and semi-arid regions, large amounts of low quality waters could be used for crop irrigation, but the adoption of articulated classifications with too rigid quality limits can often reduce the recoverable quantities of water and make the monitoring of water quality too much expensive. Therefore, an evaluation of irrigation water quality based on only a few crucial parameters, which consider the crop species to be irrigated and the type of irrigation system and management adopted, can be an easy and flexible method for maximizing the reuse of wastewater and low-quality water for agricultural purposes. In this view, an irrigation water quality tool (IWQT) was developed to support farmers of arid and semi-arid regions on evaluating the use of low quality water for crop irrigation. The most significant and cheapest parameters of irrigation water quality were identified and clustered in three quality classes according to their effects on crop yield and soil fertility (agronomic quality indicators), human health (hygiene and health quality indicators), and irrigation systems (management quality indicators). According to IWQT parameters, a tool reporting a series of recommendations, including water treatment types, was implemented to guide farmers on the use of low quality irrigation water

Effect of injection depth of digestate liquid fraction on soil carbon dioxide emission and maize biomass production

The aim of this study was to evaluate, in open field conditions, the effect of injection depth of digestate liquid fraction (10 cm, 25 cm and 35 cm) in clay loam soil, on CO2 emission. An un-amended soil was considered as control. The study was performed in 2014 on a farm located in Terrasa Padovana, Veneto region (Italy) distributing digestate before maize sowing. Digestate injection determined a high soil CO2 emission in the first hour after application, followed by a progressive reduction in as early as 24 h, reaching significantly lower values, similar to those measured in the un-amended control, after 48 h. Gas emissions measured 1 h after digestate application decreased as injection depth increased with significantly higher emission values in the 10 cm treatment (median value 23.7 g CO2 m\u20132 h\u20131) than in the 35 cm one (median value 2.5 g CO2 m\u20132 h\u20131). In the 3 days between digestate distribution and maize sowing, soil CO2 emission was significantly higher in the amended treatments than un-amended one, with median values of 1.53 g CO2 m\u20132 h\u20131 and 0.46 g CO2 m\u20132 h\u20131 respectively. During maize growing season, no significant soil CO2 emission difference was monitored among treatments, with a median value of 0.33 g CO2 m\u20132 h\u20131. Digestate application significantly improved maize aboveground dry biomass with an average yield of 22.0 Mg ha\u20131 and 16.2 Mg ha\u20131 in amended and un-amended plots, respectively, due to the different amount of nutrients supplied

Greenhouse gas emissions from constructed wetlands and agronomic management of urban wastewater and digestate

The awareness of and interest in human activities environmental impact, in the framework of the ongoing climate change, has imposed the need to evaluate waste disposal in terms of greenhouse gases emission, in addition to the productive processes. Constructed wetlands (CW) are a low environmental impact technology to treat wastewater with little or no energy input, increasingly used as a natural-like treatment system that is applicable in urban and/or production contexts. CW systems reproduce the physical, chemical and biological self-purification process of the soil-plant-microorganism systems that characterize aquatic habitats and natural wetlands. Depuration processes, largely operated in these systems by rhizosphere microorganisms that contribute to the reduction of organic and nitrogen wastewater load, determine gaseous compounds release into the atmosphere, some of which act as greenhouse gases, in particular carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O). The evaluation of greenhouse gases (GHG) emission from CWs, influenced by CW and wastewater types and vegetation and species presence in the beds, has been investigated for about 15 years in CWs in central-northern European Countries, while few experiments, and mostly at laboratory scale, have been conducted in the Mediterranean Basin, and none in Italian CWs. With this in mind, the main aim of this PhD thesis was to evaluate the role of the main components used in the construction of CWs on GHGs emission in the more widespread (full scale or pilot plants) Italian CW systems. For this purpose in two different Italian bioclimatic contexts, Sicily and Veneto, two CW sites were selected that treated urban wastewater and digestate fluid fraction respectively. Particular attention was paid in the research to the role of vegetation on CWs GHGs emission studying different species (Arundo donax L., Phragmites australis (Cav.) Trin. Ex Steud., Cyperus papyrus L., Chrysopogon zizanioides (L.) Roberty and Mischantus x giganteus Greef et Deu.). The results obtained in the Sicilian context showed a species specific effect on CO2 and CH4 emissions. Significantly higher CO2 emissions (median value 16.5 g m-2 d-1) were monitored in the beds vegetated with A. donax, M. giganteus and P. australis, than those vegetated with C. papyrus and C. zizanioides and the unvegetated bed (median value 5.2 g m-2 d-1). The M. giganteus presence in the bed and the absence of vegetation both determined significantly higher CH4 emissions than those monitored with C. papyrus. At the end of the two trial years all vegetated beds showed a CO2(eq) positive balance with better values calculated for A. donax (21.4 kg CO2(eq) m-2), whereas the unvegetated bed showed a net emission into the atmosphere of 5.5 kg CO2(eq) m-2. The CW system in Veneto that treated digestate fluid fraction coming from an anaerobic digester for biogas production fed with livestock slurry and energy crops biomass, showed no significant depuration performance differences between P. australis and A. donax vegetation, but the latter did not regrow in the second year, thus determining a significant increase in CH4 emissions. The digestate fluid fraction, characterized by a high organic matter and nitrogen content, can also be considered as an agronomic resource in a region where land availability is not a limiting factor and considering the limit on its spreading imposed by Directive 91/676/EEC of 12 December 1991. In fact, the intensive mineral fertilization and deep soil tillage that were typical of Italian agriculture in the second half of last century, have caused some problems in the agro-ecosystems, including the loss of organic carbon. The addition of soil organic matter and the use of agricultural techniques to directly or indirectly reduce CO2 emissions, may be a response to soil organic carbon loss with a positive effect on the environment. Taking this into account, an additional investigation topic of the PhD research has been to evaluate the effect exerted by the digestate fluid fraction application on agricultural soil CO2 emissions by: 1) soil texture (sandy loam vs. clay loam) and preparatory tillage (plowing vs ripping) after splash-plate spreading; 2) the digestate fluid fraction injection depth into the soil (10, 25 and 35 cm). The results have shown a CO2 emission peak one hour after digestate distribution and emission values reaching those of un-amended soils after 3 days, using both application methods. Considering the splash-plate technique in the two weeks following spreading, significantly higher CO2 emissions were found in sandy loam than clay loam soil, the preparatory soil tillage showed no significant effect. Digestate fluid fraction soil injection determined after one hour of application, an opposite trend with injection depth, with lower emissions at increasing depth

Role of C3 plant species on carbon dioxide and methane emissions in Mediterranean constructed wetland

C3 plant species are widely used to vegetate constructed wetlands (CW), but so far no information is available on their effect on CW CO 2(eq) balance in the Mediterranean climate. The aim of this research was to study carbon dioxide (CO 2 ) and methane (CH 4 ) emissions and CO 2(eq) budgets of CW horizontal sub-surface flow pilot-plant beds vegetated with Arundo donax L. and Phragmites australis (Cav.) Trin. ex Steud. compared with an unvegetated bed in Sicily. The highest total plant biomass production was measured in the bed vegetated with A. donax (17.0 kg m –2 ), whereas P. australis produced 7.6 kg m –2 . CO 2 and CH 4 emissions and showed significant correlation with average air temperature and solar radiation for each bed. The CO 2 emission values ranged from 0.8±0.1 g m –2 d –1 , for the unvegetated bed in April, to 24.9±0.6 g m –2 d –1 for the bed with P. australis in August. The average CO 2 emissions of the whole monitored period were 15.5±7.2, 15.1±7.1 and 3.6±2.4 g m –2 d –1 for A. donax , P. australis and unvegetated beds respectively. The CH 4 fluxes differed significantly over the monitored seasons, with the highest median value being measured during spring (0.963 g m –2 d –1 ). No statistical differences were found for CH 4 flux among the studied beds. Cumulative estimated CH 4 emissions during the study period (from April to December) were 159.5, 134.1 and 114.7 g m –2 for A. donax , P. australis and unvegetated beds respectively. CO 2(eq) balance showed that the two vegetated beds act as CO 2(eq) sinks, while the unvegetated bed, as expected, acts as a CO 2(eq) source. Considering only the above-ground plant biomass in the CO 2(eq) budgets, P. australis and A. donax determined uptakes of 1.30 and 8.35 kg CO 2(eq) m –2 respectively

Extension of aquaponic water use for NFT baby-leaf production : mizuna and rocket salad

Aquaponics is a recirculating technology that combines aquaculture with hydroponics. It allows nutrients from fish waste to feed plants and thus saves water and nutrients. However, there is a mismatch between the nutrients provided by the fish waste and plant needs. Because of this, some nutrients, notably N, tend to accumulate in the aquaponic water (APW or AP water). The aim of this study was to investigate how APW, which is depleted of P and K but still rich in N, could be further utilized. APW was used in a mesocosm and compared with APW from the same source that had been supplemented with macro-nutrients (complemented AP water or CAPW) and a hydroponic control (HC). Mizuna (M) and rocket salad (R) were used as short-cycle vegetable crops in a NFT system. The results revealed that the low production potential of APW was mainly caused by the lack of P and K. If these were supplemented, the yields were comparable to those in the HC. M yield in CAPW was significantly higher than that of HC, probably due to biostimulant effects connected to the organic components in the water as a result of fish farming. Water type, cultivation density, and intercropping significantly influenced the qualitative characteristics of the crop in terms of antioxidant compounds and minerals. Nitrate content in vegetables was lower than European regulation limits. The extended use of APW is viable if the missing nutrients are supplemented; this could be a strategy to increase the efficiency of water and nitrogen use, while further reducing environmental impact

Vegetable intercropping in a small-scale aquaponic system

This paper reports the results of the first study of an aquaponic system for Pangasianodon hypophthalmus production that uses Lactuca sativa L. (lettuce) and Cichorium intybus L. rubifolium group (red chicory) intercropping in the hydroponic section. The experiment was conducted in a greenhouse at the Zurich University of Applied Sciences, W\ue4denswil, Switzerland, using nine small-scale aquaponic systems (each approximately 400 L), with the nutrient film technique (NFT). The intercropping of vegetables did not influence the water temperature, pH, electric conductivity (EC), oxidation\u2013reduction potential, nor O2 content. Intercropping with red chicory increased the lettuce sugar content (+16.0% and +25.3% for glucose and fructose, respectively) and reduced the lettuce caffeic acid content ( 1216.8%). In regards to bitter taste compounds (sesquiterpene lactones), intercropping reduced the concentrations of dihydro-lactucopicrin + lactucopicrin ( 1242.0%) in lettuce, and dihydro-lactucopicrin + lactucopicrin ( 1222.0%) and 8-deoxy\u2013lactucin + dihydro-lactucopicrin oxalate ( 1218.7%) in red chicory, whereas dihydro-lactucin content increased (+40.6%) in red chicory in regards to monoculture. A significantly higher organic nitrogen content was found in the lettuce (3.9%) than in the red chicory biomass (3.4%), following the intercropping treatment. Anion and cation contents in vegetables were affected by species (Cl 12, NO3 12, PO43 12, SO42 12, and Ca2+), intercropping (K+ and Mg2+), and species 7 intercropping interactions (NO2 12 and NH4+). Experimental treatments (monoculture vs intercropping and distance from NFT inlet) did not exert significant effects on leaf SPAD (index of relative chlorophyll content) values, whereas the red coloration of the plants increased from the inlet to the outlet of the NFT channel. Intercropping of lettuce and red chicory affected the typical taste of these vegetables by increasing the sweetness of lettuce and changing the ratio among bitter taste compounds in red chicory. These results suggest intercropping as a possible solution for improving vegetable quality in aquaponics. Although the results are interesting, they have been obtained in a relatively short period, thus investigations for longer periods are necessary to confirm these findings. Further studies are also needed to corroborate the positive effect of the presence of red chicory in the system on fish production parameters

Hydroponic systems and water management in aquaponics : a review

Aquaponics (AP), the integrated multi-trophic fish and plants production in quasi-closed recirculating system, is one of the newest sustainable food production systems. The hydroponic component of the AP directly influences water quality (in turn influencing fish growth and health), and water consumption (through evapotranspiration) of the entire system. In order to assess the role of the design and the management of the hydroponic component on the overall performance, and water consumption of the aquaponics, 122 papers published from 1979 to 2017 were reviewed. Although no unequivocal results were found, the nutrient film technique appears in several aspects less efficient than medium-based or floating raft hydroponics. The best system performance in terms of fish and plant growth, and the highest nutrient removal from water was achieved at water flow between 0.8 L min–1 and 8.0 L min–1. Data on water consumption of aquaponics are scarce, and no correlation between the ratio of hydroponic unit surface/fish tank volume and the system water loss was found. However, daily water loss was positively correlated with the hydroponic surface/fish tank volume ratio if the same experimental conditions and/or systems were compared. The plant species grown in hydroponics influenced the daily water loss in aquaponics, whereas no effect was exerted by the water flow (reciprocating flood/drain cycle or constant flow) or type (medium-based, floating or nutrient film technique) of hydroponics