Reuse of greywater for irrigation has surged due to increasing urban freshwater scarcity. Greywater sources differ in ease and cost of reuse, with limited studies on the effects of irrigation with different sources on soil properties and subsequent rainwater remediation. Thus, this study compared the effect of four major household greywater sources (shower (SH), dishwasher (DW) and liquid and powdered laundry detergent (LLD and PLD)) on soil properties and rainwater remediation potential of two contrasting (albic Planosol (bleached) and Lixisol (rhodic)) topsoils under Mediterranean climate conditions. Summer irrigation with the greywater and tap water sources was simulated (370 mm) followed by winter rainfall simulation (370 mm). Soil chemical, physical and microbial properties were determined after each simulation. Irrigation with SH and LLD greywaters was least harmful to soil chemistry; however, LLD decreased soil infiltration rate by 48-53%, and SH resulted in hydrophobic crusting. Irrigation with PLD and DW greywater was most damaging, resulting in alkalisation, sodification and salinisation accompanied by soil structural degradation, decreasing infiltration by 85-100%. All treatments reduced soil bacterial diversity and species richness. Rain simulation was only able to reduce sodicity and salinity associated with PLD and DW application on the rhodic soil, as the clay fraction was more stable, permitting some infiltration. Therefore, PLD and DW greywaters should not be used directly for irrigation, especially on bleached soils, as this can halt rainwater percolation. Furthermore, use of less chemically harmful SH or LLD liquid greywaters could result in undesirable soil physical problems in the long term.

Inappropriate fertilisation results in the pollution of groundwater with nitrates and phosphates, eutrophication in surface water, emission of greenhouse gasses, and unwanted N deposition in natural environments, thereby harming the whole ecosystem. In greenhouses, the cultivation in closed-loop soilless culture systems (CLSs) allows for the collection and recycling of the drainage solution, thus minimising contamination of water resources by nutrient emissions originating from the fertigation effluents. Recycling of the DS represents an ecologically sound technology as it can reduce water consumption by 20-35% and fertiliser use by 40-50% in greenhouse crops, while minimising or even eliminating losses of nutrients, thereby preventing environmental pollution by NO3- and P. The nutrient supply in CLSs is largely based on the anticipated ratio between the mass of a nutrient absorbed by the crop and the volume of water, expressed as mmol L-1, commonly referenced to as uptake concentration (UC). However, although the UCs exhibit stability over time under optimal climatic conditions, some deviations at different locations and different cropping stages can occur, leading to the accumulation or depletion of nutrients in the root zone. Although these may be small in the short term, they can reach harmful levels when summed up over longer periods, resulting in serious nutrient imbalances and crop damage. To prevent large nutrient imbalances in the root zone, the composition of the supplied nutrient solution must be frequently readjusted, taking into consideration the current nutrient status in the root zone of the crop. The standard practice to estimate the current nutrient status in the root zone is to regularly collect samples of drainage solution and determine the nutrient concentrations through chemical analyses. However, as results from a chemical laboratory are available several days after sample selection, there is currently intensive research activity aiming to develop ion-selective electrodes (ISEs) for online measurement of the DS composition in real-time. Furthermore, innovative decision support systems (DSSs) fed with the analytical results transmitted either offline or online can substantially contribute to timely and appropriate readjustments of the nutrient supply using as feedback information the current nutrient status in the root zone. The purpose of the present paper is to review the currently applied technologies for nutrient and water recycling in CLSs, as well as the new trends based on ISEs and novel DSSs. Furthermore, a specialised DSS named NUTRISENSE, which can contribute to more efficient management of nutrient supply and salt accumulation in closed-loop soilless cultivations, is presented.