Reliable detection and attribution of changes in nitrogen (N) runoff from croplands are essential for designing efficient, sustainable N management strategies for future. Despite the recognition that excess N runoff poses a risk of aquatic eutrophication, large-scale, spatially detailed N runoff trends and their drivers remain poorly understood in China. Based on data comprising 535 site-years from 100 sites across China's croplands, we developed a data-driven upscaling model and a new simplified attribution approach to detect and attribute N runoff trends during the period of 1990–2012. Our results show that N runoff has increased by 46% for rice paddy fields and 31% for upland areas since 1990. However, we acknowledge that the upscaling model is subject to large uncertainties (20% and 40% as coefficient of variation of N runoff, respectively). At national scale, increased fertilizer application was identified as the most likely driver of the N runoff trend, while decreased irrigation levels offset to some extent the impact of fertilization increases. In southern China, the increasing trend of upland N runoff can be attributed to the growth in N runoff rates. Our results suggested that increased SOM led to the N runoff rate growth for uplands, but led to a decline for rice paddy fields. In combination, these results imply that improving management approaches for both N fertilizer use and irrigation is urgently required for mitigating agricultural N runoff in China.

The groundwater environment changes under the influence of anthropogenic activities. Because of the construction of the Da’an irrigation area, the amount of irrigation and fertilizer there has changed. Achieving the coordinated development of groundwater resources and economic benefits requires a deeper understanding of the impact of the construction of irrigation areas on groundwater chemistry. In this study, the variations in groundwater chemistry characteristics were studied using statistics and hydrogeochemical methods. Further, the groundwater quality was assessed using the support vector machine method. The results show that the primary water chemistry type was the HCO₃ − Ca − Mg type, with local Fe³⁺ and F⁻ pollution. After the construction of irrigation area, the SO₄²⁻, HCO₃⁻, K⁺ + Na⁺, and Ca²⁺ contents decreased, but the Cl⁻ and Mg²⁺ contents increased. The main nitrogen source in phreatic water was anthropogenic activities, and the main pollution component was NH₄⁺. After the construction of the irrigation area, the NH₄⁺ concentration increased significantly, and the ratio of samples exceeding the standard increased by 37.5%. The over-standard regions spread to the northwest, east, and southeast of Da’an City and east and southeast of the irrigation area. The groundwater quality was predominantly grade IV and V, which accounted for an increase of 16.35%, widely distributed in the south, east, and southwest of the irrigation area and urban areas. The construction of the irrigation area reduced the suitability of phreatic water for agricultural irrigation in the southeast but increased in the west and north.

The use of wastewater for agricultural irrigation is a common practice worldwide; long-term use of wastewater can have adverse effects, such as the migration of the anthropogenic dissolved organic matter into the aquifer. Three-dimensional fluorescence spectroscopy (EEM) was used to investigate the characteristics of dissolved organic matter (DOM) in groundwater and irrigation wastewater, to establish the effect of intensive irrigation on the water quality from the aquifer that underlies the area. The fluorescence spectra showed the presence of humic and fulvic acids and anthropogenic organic compounds similar to aromatic proteins and soluble microbial products in wastewater resources. The significant fraction of DOM in groundwater samples are aromatic proteins and soluble microbial products, identical to wastewater. Chlorides and nitrate ion concentrations suggest a local flow system. High levels of TDS are associated with intensive irrigation with residual water and the return irrigation associated with a gradual increase in salts of CO₃²⁻, NO₃⁻, HCO₃⁻, Cl⁻, and SO₄²⁻. The anthropogenic DOM is a useful indicator of water quality management in groundwater based on origin tracking of DOM and changes in organic pollutants. Fluorescence spectroscopy can be used to investigate groundwater pollution characteristics and monitor DOM dynamics in groundwater.

The Nyabugogo natural wetland (Kigali City, Rwanda) receives all kinds of untreated wastewaters, including those from industrial areas. This study monitored heavy metal concentrations (Cd, Cr, Cu, Pb, and Zn) in all environmental compartments of the swamp: water and sediment, the dominant plant species Cyperus papyrus, and fish (Clarias sp. and Oreochromis sp.) and Oligochaetes. Cr, Cu, and Zn concentrations in the water were generally below the WHO (2008) drinking water standards, whereas Cd and Pb were consistently above these limits. Except Cd, all metal concentrations were below the threshold levels for irrigation. The highest metal accumulation occurred in the sediment with up to 4.2 mg/kg for Cd, 68 mg/kg for Cu, 58.3 mg/kg for Pb, and 188.0 mg/kg for Zn, followed by accumulation in the roots of C. papyrus with up to 4.2 mg/kg for Cd, 45.8 mg/kg for Cr, 29.7 mg/kg for Cu, and 56.1 mg/kg for Pb. Except Cu and Zn, other heavy metal (Cd, Cr, and Pb) concentrations were high in Clarias sp., Oreochromis sp., and Oligochaetes. Therefore, there is a human health concern for people using water and products from the swamp.

Ammonia (NH₃) volatilization is one of the main pathways of N loss from farmland soil. Saline water irrigation can have direct or indirect effects on soil NH₃ volatilization, N leaching, and crop N uptake. This study was conducted to evaluate the effects of irrigation water salinity and urea-N application rate on NH₃ volatilization and N use efficiency in a drip-irrigated cotton field. The experiment consisted of three levels of irrigation water salinity: fresh water, brackish water, and saline water (electrical conductivities of 0.35, 4.61, and 8.04 dS/m, respectively). The N application rates were 0, 240, 360, and 480 kg/ha. The results showed that soil salinity and soil moisture content were significantly higher in the saline water treatment than in either the fresh or brackish water treatments. Irrigation water salinity significantly increased soil NH₄-N concentration, but NO₃-N concentration decreased as water salinity increased. The amount of N leaching varied from 5.0 to 25.5 kg/ha, accounting for 1.81 to 4.79 % of the urea-N applied under different water salinity and N application rate treatments. Both the amount of N leaching and the proportions of applied N lost through leaching significantly increased as water salinity increased. N application increased the amounts of N leaching, but the ratios of applied N were not affected by N application rate. Soil NH₃ volatilization increased rapidly after urea fertigation, and peaked at 1–2 days after N application, then decreased rapidly. The amount of NH₃ volatilization varied from 9.0 to 33.7 kg/ha, accounting for 3.2 to 3.8 % of the N applied in all treatments. Soil NH₃ volatilization was significantly higher in the saline water treatment than that in either the fresh or the brackish water treatments. Cotton N uptake increased significantly as N application rate increased, but decreased with irrigation water salinity increased. In conclusion, saline water irrigation with high N application rate induced high N leaching and NH₃ volatilization losses, thereby dramatically reducing the apparent N recovery (ANR) of cotton.

The present paper aims at planning the treated municipal wastewater reuse in fragile ecosystems of Messolonghion lagoon and Acheloos estuary, which are protected as a Natura wetland under the Ramsar Treaty. The need for environmental protection of the wetlands became necessary due to the continuing anthropogenic intervention, as well as to the climate changes that have been occurring in recent years. Relevant studies have shown that the lagoon of Messolonghion and Acheloos estuary are ecosystems that have been burdened by anthropogenic activities (pesticides, fertilizers, overexploitation of underground aquifers, intrusion and land use change), as well as by climatic changes (temperature, precipitation, sea level), which altogether have adversely affected the hydrodynamic and ecological balance of the entire ecosystem. The Messolonghion lagoon and Acheloos estuary are also the recipients of the wastewater processing plant effluents, operating locally, which have over-enriched the waters with macronutrients N, P and K, favouring eutrophication. The municipal wastewater reuse for crop irrigation grown in the protected area appears to be an environmentally acceptable solution for alleviating the natural water shortage, since it could save significant amounts of irrigation water as well as it could reduce the adverse effects of the treated effluents discharge into the aquatic ecosystem. This study describes the planning of the treated wastewater reuse in this ecologically sensitive area, on the basis of the geomorphologic and geotechnical characteristics, climatic factors, and crop irrigation water requirements grown in the area.

Phosphorus and nitrogen can leach from porous golf greens potentially causing degradation of ground water quality. Agreenhouse experiment was carried out with 52 cm columns (15 cm diam.) made to USGA green specifications and sodded to `Tifdwarf' bermudagrass to determine the effects of fertilizer sources at various rates on P and N leaching. Fertilizers were balanced soluble and controlled-release (polyand sulfur coated) sources at N rates of 0, 12, 24, and 49 kg N ha⁻¹ and at P rates of 0, 5, 11, and 21 kg ha⁻¹ every other week for a total of 6 applications. Controlled-release N was from NH₄ and urea and the soluble source N was from KNO₃, urea, and (NH₄)PO₄. Irrigation rate was 0.63 cm per day initially and increased to 1.25 cm per day at week 7. Weeklyleachate collections for 23 weeks were analyzed for P andNO₃-N. Concentrations of N and P were lower in the leachatefor the controlled-release source than for the soluble source. Leaching of P continued for the entire 23 weeks of theexperiment, whereas N was essentially exhausted by week 15indicating that P leaches at a slower rate than N. For the low Prate (5 kg ha⁻¹) for the controlled-release source there was no increase in P concentration in the leachate compared to control. Thus, low P rates will not result in degradation of water quality due to increased P. For the controlled-release source at the low rate <10% of the P added leached, whereasthe values for N were in the range of 20 to 45% for all ratesand sources. Control treatments resulted in N concentrations in the leachate as high as 26 mg L⁻¹. Results show thatP leaching is a potential problem only at high rates of solublesources and high irrigation, whereas N is more readily leached.

Irrigation water scheduling is crucial to make the most efficient use of ever-decreasing water. As excessive irrigation decreases yield, while imprecise application also causes various environmental issues. Therefore, efficient management of irrigation frequency and irrigation level is necessary to sustain productivity under limited water conditions. The objective of the current study is to assess the water productivity at various irrigation regimes during peanut crop growing seasons (2014 and 2015) in Eastern Mediterranean, Turkey. The field experiments were conducted with treatments consisting of three irrigation frequencies (IF) (IF₁: 25 mm; IF₂: 50 mm; and IF₃: 75 mm of cumulative pan evaporation (CPE)), and four irrigation water levels (WL₁ = 0.50, WL₂ = 0.75, WL₃ = 1.0, and WL₄ = 1.25). WL₁, WL₂, WL₃, and WL₄ treatments received 50, 75, 100, and 125 of cumulative pan evaporation. The CSM-CROPGRO-Peanut model was calibrated with experimental data in 2014 and evaluated with second-year experimental data (2015). The model simulated seed yield and final biomass (dry matter) reasonably well with low normalized root mean square error (RMSEₙ) in various irrigation intervals. The model simulated reasonably well for days to anthesis (RMSE = 2.53, d-stat = 0.96, and r² = 0.90), days to physiological maturity (RMSE = 2.55), seed yield (RMSE = 1504), and tops biomass dry weight at maturity (RMSE = 3716). Simulation results indicated good agreement between measured and simulated soil water content (SWC) with low RMSEₙ values (4.0 to 16.8% in 2014 and 4.3 to 18.2% in 2015). Further results showed that IF₂I₁₂₅ irrigation regime produced the highest seed yield. Generally, model evaluation performed reasonably well for all studied parameters with both years’ experimental data. Results also showed that the crop model would be a precision agriculture tool for the extrapolation of the allocation of irrigation water resources and decision management under current and future climate.

Given a critical water scarcity in arid and semi-arid Tunisian areas and aiming to reduce irrigation water request, it is crucial to identify and apply the best water-saving practices in these irrigated areas. Tomato is a high-water-requiring vegetable crop, thus increasing the pressure on water resources and environment. Its sustainable cultivation in such alarming conditions requires an adaptation of on-farm irrigation water-saving strategies preserving also the crop yield and leading to a fruit quality improvement. This study aimed to explore the effects of the regulated deficit irrigation (RDI) as an irrigation water-saving strategy, on yield, fruit quality, and physiological behavior of greenhouse grown potted tomato crop (Solanum lycopersicum L.) during three identified growth stages. The managed water regimes were (i) full irrigation (FI) ensuring 100% of the estimated water crop requirements, (ii) RDI1-25 and RDI1-50 ensuring respectively 75% and 50% of FI water supplies during the vegetative crop stage (stage I), (iii) RDI2–25 and RDI2–50 ensuring respectively 75% and 50% of FI water supplies from first truss blossom until first harvest (stage II), and (iv) RDI3-25 and RDI3-50 ensuring respectively 75% and 50% of FI supplies during the rest of the harvest period (stage III). The results showed that the substrate moisture vary significantly with the water deficit regime applied under different growth stages, thus providing different levels of substrate water content. Under RDI2, the tomato yield was the highest when compared with FI, RDI1, and RDI3 regimes. Indeed, saving the water by 20% under RDI2-50 reduced only 3% of tomato yield. Deficit irrigation under ripening fruit and flowering stages, mainly with 50% of water supplies shortage, resulted in higher fruit skin color, firmness, and refractometry index (°Brix) when compared to FI and RDI1. Physiological traits measurements indicated that FI exhibited the highest leaf stomatal conductance (gs) and chlorophyll index (CI) values while RDI3 exhibited the lowest gs and CI values among all the RDI treatments. Results are valuable in considering gs and CI as an efficient indicators of tomato plant water status. The results are also an important contribution to identify the second tomato growth stage as the best period that tomato plant tolerate water shortage without significant yield decrease, as well a rather fruit quality improvement. These results help to reach the challenge “more crop per drop” and can contribute to water scarcity remediation.

Water scarcity constrains global cotton production. However, partial root-zone drying (PRD) and mulching can be used as good techniques to save water and enhance crop production, especially in arid regions. This study aimed to evaluate the effects of mulching for water conservation in an arid environment under PRD and to further assess the osmotic adjustment and enzymatic activities for sustainable cotton production. The study was carried out for 2 years in field conditions using mulches (NM = no mulch, BPM = black plastic mulch at 32 kg ha⁻¹, WSM = wheat straw mulch at 3 tons ha⁻¹, CSM = cotton sticks mulch at 10 tons ha⁻¹) and two irrigation levels (FI = full irrigation and PRD (50% less water than FI). High seed cotton yield (SCY) achieved in FI+WSM (4457 and 4248 kg ha⁻¹ in 2017 and 2018, respectively) and even in PRD+WSM followed by BPM>CSM>NM under FI and PRD for both years. The higher SCY and traits observed in FI+WSM and PRD+WSM compared with the others were attributed to the improved water use efficiency and gaseous exchange traits, increased hormone production (ABA), osmolyte accumulation, and enhanced antioxidants to scavenge the excess reactive oxygen. Furthermore, better cotton quality traits were also observed under WSM either with FI or PRD irrigation regimes. Mulches applications found effective to control the weeds in the order as BPM>WSM>CSM. In general, PRD can be used as an effective stratagem to save moisture along with WSM, which ultimately can improve cotton yield in the water-scarce regions under arid climatic regions. It may prove as a good adaptation strategy under current and future water shortage scenarios of climate change.