Oil and gas extraction in the western United States generates significant volumes of produced water (PW) that is typically injected into deep disposal wells. Recently, crop irrigation has emerged as an attractive PW reuse option, but the impact on plant immune response is not known. In this study, we conducted a 3-month greenhouse pot study. Spring wheat (Triticum aestivum) was irrigated 3 times a week with 150 mL (∼80–100% of soil water holding capacity) with one of four irrigation treatments: tap water control, 10% PW dilution, 50% PW dilution, and salt water (NaCl50) control containing the same amount of total dissolved solids as PW50 to determine the effect on disease resistance. The wheat leaves were inoculated with either bacterial or fungal pathogens and changes in pathogenesis-related PR-1 and PR-5 gene expression were measured from the leaf tissue. PW50 experienced the largest relative suppression of PR-1 and PR-5 gene expression compared to noninfected wheat, followed by PW10, NaCl50, and the tap water control. A combination of PW contaminants (boron, total petroleum hydrocarbons, and NaCl) are likely reducing PR-gene expression by reallocating metabolic resources to fight abiotic stresses, which then makes it more challenging for the plants to produce PR genes to fight pathogens. This study provides the first evidence that plant disease resistance is reduced due to irrigation with reused PW, which could have negative implications for food security.

CORE IDEAS: Contributions are mainly from the 2017 International Soil Physics Workshop in China. Soils are fundamental in supplying food, energy, water (FEW), and ecosystem services. Interdisciplinary (convergence) approaches are needed to address FEW challenges. Soils are foundational to sustaining the food, energy, and water (FEW) systems and provide many essential ecosystem services. Soil degradation is a major threat to food security in China and elsewhere in the world. It is critical to advance soil science to improve the FEW systems so that FEW supplies can be provided to human populations in a sustainable and resilient manner. To do so, we must understand interactions among soil physical, chemical, and biological processes, as well as the role, function, and contribution of soil physical processes to delivering FEW supplies and ecosystem services. Soil processes and crop production are strongly controlled by physical processes such as soil water flow, aggregate stability, compaction, heat regime, irrigation and drainage, soil aeration, etc. Recognizing the importance of soil physics to the nexus of FEW systems, the collection in this special section mainly includes research presented at the International Workshop of Soil Physics and the Nexus of Food, Energy, and Water held on 3–5 Aug. 2017 at Shenyang, China. This special section covers diverse topics including fundamental soil physical properties and water flow, land use and agricultural management, soil organic carbon management, soil physical modeling, and transport of emerging contaminants. More future research using interdisciplinary (nexus or convergence) approaches should be undertaken to address challenges in many contemporary and emerging FEW issues.

This study presents an evaluation of the food-energy-water nexus (FEWn), complemented by a thorough life cycle assessment (LCA), of four young cacao production systems: two full-sun monocultures and two agroforestry systems under conventional and organic management. Land footprint (LF) for food production, non-renewable cumulative energy demand (NR CED) for energy, total water footprint (TWF) for water, and three efficiency indicators for the FEWn were all analysed. In addition, ten LCA impact categories were evaluated in relation to two functional units (kilograms of cacao output and kilograms of total crop output, i.e., cacao + other crops). The integrated analysis of the FEWn and the LCA framework reveals how agroforestry systems and organic management report better environmental performances for almost all indicators and impact categories considered, except for the TWF. However, given that the systems analysed have no irrigation, between 96.3% and 99.8% of the TWF corresponds to green water, i.e., soil moisture from precipitation. Green water has lower environmental impacts and opportunity costs than the water used to manufacture inputs (WFᵢₙₚᵤₜ). Accordingly, when the efficiency of the nexus is measured in relation to the WFᵢₙₚᵤₜ, organically managed systems produce more food/energy per unit of water used. Our results show how production diversification and organic and cultural management practices can improve energy efficiency and reduce the use of water associated with the inputs and, consequently, improve the nexus, as well as the rest of the environmental impacts analysed. The design of agricultural policies focused on sustainability should strongly favour the establishment of agroforestry systems, particularly those that are organically managed.

We manipulated the amount of food and water (soil moisture) available to natural populations of larval tiger beetles in Arizona. Supplemental food increased survivorship of first instars to the second instar in all species in at least one of two years. Supplemental soil moisture usually increased, but sometimes decreased, survival of first instars. Interaction of food and water treatments was significant in a few cases, but the nature of the interaction varied greatly among species and years. Significant mortality of first instars from natural enemies occurred, and may explain the anomalous cases of first—instar survival with food exclusion (since enemies were also excluded by this treatment). Food supplementation increased first—instar—to—adult survivorship for all species and third—instar—to—adult survivorship for most species; in contrast, water supplementation had no effect on most species. Food manipulation, but not water manipulation, also affected development time or size of adults (usually both) for all seven species tested. Supplemental food produced larger adults and resulted in more rapid maturation. Reduced food resulted in delayed development, and this usually resulted in death. The results of this study provide one of the few cases in which simultaneous effects of two major ecological factors have been analyzed for a large set of similar species in an array of habitats. The prevalence of food limitation and the frequent lack of a detectable consistent interaction between food availability and water availability in this system indicate that food limitation and resource competition may be the dominant factors controlling these organisms.

Raised-bed plasticulture, an intensive production system used around the world for growing high-value crops (e.g., fresh market vegetables), faces a water-food nexus that is actually a food-water-energy-land-economic nexus. Plasticulture represents a multibillion dollar facet of the United States crop production value annually and must become more efficient to be able to produce more on less land, reduce water demands, decrease impacts on surrounding environments, and be economically-competitive. Taller and narrower futuristic beds were designed with the goal of making plasticulture more sustainable by reducing input requirements and associated wastes (e.g., water, nutrients, pesticides, costs, plastics, energy), facilitating usage of modern technologies (e.g., drip-based fumigation), improving adaptability to a changing climate (e.g., flood protection), and increasing yield per unit area.Compact low-input beds were analyzed against conventional beds for the plasticulture production of tomato (Solanum lycopersicum), an economically-important crop, using a systems approach involving field measurements, vadose-zone modeling (HYDRUS), and production analysis. Three compact bed geometries, 61cm (width)× 25cm (height), 45cm× 30cm, 41cm× 30cm, were designed and evaluated against a conventional 76cm× 20cm bed. A two-season field study was conducted for tomato in the ecologically-sensitive and productive Everglades region of Florida. Compact beds did not statistically impact yield and were found to reduce: 1) production costs by $150–$450/ha; 2) leaching losses by up to 5% (1cm/ha water, 0.33kg/ha total nitrogen, 0.05kg/ha total phosphorus); 3) fumigant by up to 47% (48kg/ha); 4) plasticulture's carbon footprint by up to 10% (1711kg CO2-eq/ha) and plastic waste stream by up to 13% (27kg/ha); 5) flood risks and disease pressure by increasing field's soil water storage capacity by up to 33% (≈1cm); and 6) field runoff by 0.48–1.40cm (51–76%) based on HYDRUS model simulations of 10-year, 2-h storm events in other major tomato production regions of California and Virginia.Re-designing the bed geometries in plasticulture production systems to be more compact is an example of win-win production optimization not only for traditional farms in rural areas but also for urban and peri-urban farms which are located closer to city centers. Compact beds could enable more plants per unit area, thus requiring less land area for the same production. Needing less area facilitates urban and peri-urban farming where land values can be high. Urban and peri-urban farming has several benefits, including reductions in transportation energy as production is closer to market and the ability for city wastewater to be reused for irrigation instead of freshwater withdrawals. Compact beds allow plasticulture to have smaller water, chemical, energy, carbon, waste, and economic footprints without impacting production. Improving agricultural systems in this way could enhance economic and environmental viability, which is essential for a sustainable food-water-energy-land-economic nexus.

Land Use Land Cover Change (LULCC) has a significant impact on water resources and ecosystems in sub-Saharan Africa (SSA). On the basis of three research projects we aim to describe and discuss the potential, uncertainties, synergies and science-policy interfaces of satellite-based integrated research for the Kilombero catchment, comprising one of the major agricultural utilized floodplains in Tanzania. LULCC was quantified at the floodplain and catchment scale analyzing Landsat 5 and Sentinel 2 satellite imagery applying different adapted classification methodologies. LULC maps at the catchment scale serve as spatial input for the distributed, process-based ecohydrological model SWAT (Soil Water Assessment Tool) simulating the changes in the spatial and temporal water balance in runoff components caused by LULCC. The results reveal that over the past 26 years LULCC has significantly altered the floodplain and already shows an impact on the ecosystem by degrading the existing wildlife corridors. On the catchment scale the anomalies of the water balance are still marginal, but with the expected structural changes of the catchment there is an urgent need to increase the public awareness and knowledge of decision makers regarding the effect of the relationship between LULCC, water resources and environmental degradation.

With the implementation of the “Grain-for-Green” program, artificial vegetation was introduced on the Loess Plateau, which resulted in high soil water content (SWC) depletion. Currently, lack of soil water recharge is one of the most serious challenges on the Loess Plateau. Soil drying and wetting processes are critical for the sustainability of soil water recycling, but this has not been well studied. There is also a lack of physical definition of the upper bound SWC of dried soil layers (DSL). In this study, soil water dynamics – the change of SWC affected by precipitation and vegetation transpiration – were studied under converted vegetation. In-situ SWC measurements from the 0–5 m or 0–8 m deep profile over consecutive wet years (from 2016 to 2018 with an average precipitation of 660.9 mm) were analyzed to understand soil water depletion and restoration processes. Results showed distinct differences in soil water dynamics in the soil profiles and soil water balances under different vegetation types. SWC under continuous perennial alfalfa (Medicago sativa) had greater fluctuations between 0 and 300 cm than below 300 cm, and a DSL was observed below 300 cm. After converting from alfalfa to soybean (Glycine max), SWC increased greatly during the three wet years. Soil water storage (S) increased at an average rate of 35.8 mm year⁻¹ m⁻¹ within the top 500 cm of the soil profile, average evapotranspiration (ET) was 482.0 mm year⁻¹, and maximum restoration depth of soil water extended to 660 cm. However, SWC gradually decreased over time after replacing food crop with alfalfa. S declined at an average rate of 21.4 mm year⁻¹ m⁻¹ within the top 500 cm of the soil profile, average ET was 680.4 mm year⁻¹ and the maximum depth of soil water depletion extended to 360 cm. These results suggest that SWC in deep layers can be depleted and replenished quickly, and the processes were dominated by vegetation types and precipitation. Taking vegetation types and soil texture into consideration, the calculation of upper bound SWC of DSL was redefined. Given the long-term effects of high water demand from vegetation such as alfalfa on the soil water balance, ET of vegetation should be reduced through conversion to less water-intensive vegetation types or biomass control (i.e. reduced planting density appropriately) in arid areas of the Loess Plateau.

Groundwater is a precious freshwater resource heavily relied upon by agricultural activities in many parts of the world, and especially by countries with limited water resources located in arid regions. Groundwater resources are under severe pressures due to population increase, urbanisation and socio-economic development, with potential for causing long-term threats to human life and natural ecosystems. This study attempts to investigate the impacts of local and regional climatic trends, and establish key forcing functions that have changed local groundwater resources. The main questions answered through this study include: Are these changes beneficial or detrimental? If they are detrimental, what is the future outlook for impacts on the ecosystem? What are the corrective actions needed to avert the long-term risks in arid environments? In view of this, the methodology developed in this study focuses on a joint time-series statistical analysis using ground data as well as Gravity Recovery and Climate Experiment (GRACE) satellite data. Results show a substantial depletion in the groundwater thickness (0.24 ± 0.20 cm/year) during the period of observation (2002–2020). Long-term temperature data indicates that the annual mean temperature increased significantly by 1.02 °C between 1987 and 2016, while total rainfall exhibited a slight decreasing trend. In addition to groundwater extraction, fluctuations in monthly rainfall, soil moisture, evapotranspiration and relative humidity support the groundwater thickness reduction of GRACE datasets. The use of desalinated water and wastewater reuse in the agriculture sector may reduce the pressure on groundwater resources. Optimization, adaptation and mitigation in the EWF nexus will further improve the sustainability of the EWF resources.

The Ecosystem Restoration Project (ERP) is a critical and urgent practice to achieve the land degradation neutrality (LDN) targets. However, an insufficient understanding of the balance between contrasting sectors of the food-water-ecosystem nexus results in ineffectiveness in supporting complex environmental management (CEM), leading to undesirable ERP failures. The Ordos Plateau case identified the nexus evolution and the non-linear interactions between sectors, which were expected to support adaptive strategy formulations for CEM and achieve win-win outcomes. Revegetation in drylands substantially boosted ecosystem restoration, alleviating soil erosion. However, the excessive reliance on returning cropland to woodland and grassland has caused a significant loss of arable and grazing land. During the initial period of ERPs, this exacerbated decline in grain and meat productivity. In addition, aggressive revegetation activities have also reduced runoff yield and depleted soil water resources. Water scarcity is recognized as the most challenging issue in dryland ecosystem restoration, heavily influencing the interactions between sectors and threatening the long-term sustainability of ERPs. To accommodate for regional water carrying capacity, ERPs should adopt and properly allocate the use of suitable plant species with a proven anti-drought capability and high survival ratios without additional human interventions. In addition, the evolution regimes, driving factors, critical thresholds, and complex feedbacks between the nexus sectors should be fully understood to address the water resources constraints and reconcile trade-offs. This would enable the prevention of ecosystem shifts to undesirable failures and inform timely and cost-effective CEM to achieve the LDN targets.

Groundwater pollution with nitrate of agricultural origin is a major problem in many countries. A great deal of effort is focused on finding ways to reduce leaching from agricultural land. In this study, different land management scenarios were evaluated with the SWAT model in order to determine which are the most effective in reducing nitrate leaching on specific soil types in the Krška kotlina alluvial plain (Slovenia). The area is very important both for agriculture production and drinking water resources. The model was calibrated for three soil moisture field trial sites, each representing one major soil type of the area. Simulated soil moisture values were in good agreement with the observed values (PBIAS (percent bias) ±25%). Of the nine land management scenarios that were evaluated, vegetable rotation caused the most nitrate leaching on all soil types, but it fared better on Cambisol than on Fluvisol. Orchards on the other hand leached the least amount of nitrate, but also fared better on Cambisol. Presented studies should be considered as a preliminary stage in the study of nitrate pollution in the investigated area. Results show that nitrate leaching varies for different land management scenarios on different soil types. Further work should concentrate on field trials to evaluate the impacts of reduced fertilization on nitrate leaching and both crop yield and quality on different soil types.