Figures (2)  Tables (4)

    • Figure 1. 

      Illustration of two hydroponic systems. (a) Nutrient film technique. (b) Deep water culture. Figure created by Dario Rueda Kunz using BioRender.com.

    • Figure 2. 

      Illustration of one type of aeroponic system with the reservoir outside the root chamber. Figure created by Dario Rueda Kunz using BioRender.com.

    • SystemLocationCropTreatmentEquationWUEUnitConversion
      (g Fw/L)      		Main findingsRef.
      Drip recirculating hydroponicsKashiwanoha, JapanTomato (Solanum lycopersicum) cv. Momotaro YorkDifferent cultivarsFruit weight/total water uptake per plant0.015kg/kg15WUE was dependent on cultivar.[5]
      Tomato (Solanum lycopersicum) cv. Jaguar0.03333
      NFT systemNaples, ItalyLettuce (Lactuca sativa) cv. Red SalanovaDifferent cultivarsFW/Volume of water consumed92g/L92WUE was dependent on cultivar.[12]
      Lettuce (Lactuca sativa) cv. Green Salnova80.880.8
      Deep flow techniqueBahia, BrazilCoriander (Coriandrum sativum) cv. Tabocas & VerdaoTwo Nutrient solution depths: 0.02 and 0.03 m
      Three recirculation intervals: 0.25, 12 and 24 h      		FW/Total water consumed29.43 @ 15 min intervalg/L29.43Recirculation interval significantly affected WUE, with higher WUE at 15 min intervals.[18]
      25.93 @ 2 cm25.93A 2 cm depth of water had higher WUE.
      Closed loop- NFTBari, ItalyTomato (Solanum lycopersicum) cv. Diana, Jama (Beef steak)
      Naomi, Conchita (Cherry)      		NFTFruit yield/Water supplied31−45
      		g/L38NFT had higher WUE.
      Cultivation system and tomato type were significant.
      WUE varied among different seasons.      		[15]
      Open loop- drip fertigationRockwool23−2524
      SoilSoil31−37
      		34
      Deep water cultureGrossbeeren, GermanyTomato (Lycopersicon esculentum) Mill. Cv. CounterNutrient form and concentrationDW/water used1−3.5g/kg2.25Nutrient form and concentration affected WUE.[16]
      Drip systemPunjab, IndiaCucumber (Cucumis
      sativus) var. Kafka,
      Multistar & PBRK-4      		Three fertigation levels (100%, 85% and 70%)Irrigation WUE: Yield/Irrigation water appliedIrrigation WUE: 34.5−51.4kg/m342.95Both variety and nutrient solution significantly affected WUE.[13]
      Crop WUE: Yield/Crop Water useCrop WUE: 120.6−179.9150.25
      Closed system-NFTAhvaz, IranTomato (Solanum lycopersicum) cv. V4-22 & AmiraClosed systemFruit yield/cubic meter water appliedWater productivity: 33.7
      Water productivity biomass: 48.91      		kg/m327.91Water productivity was lower in the closed hydroponic system.[17]
      Open system-dripOpen systemWater productivity: 21.84.
      Water productivity biomass: 34.42      		41.88
      Drip systemWales, United KingdomTomato (Solanum lycopersicum) cv. Forticia F1DripFW fruit/L of transpired water0.0072−0.0099kg/L8.55Hydroponic systems had higher WUE than soil.[6]
      Deep water cultureDeep water0.0059−0.01249.15
      soilSoil0.0035−0.00443.95
      NFTTulkarm, Palestine-Lettuce (Lactuca sativa)Four growing methodsDW/kg water applied121kg/m3121WUE was higher in NFT.[10]
      FW – fresh weight, DW – dry weight, NFT – nutrient film technique.

      Table 1. 

      Studies that evaluated water use efficiency (WUE) in different hydroponic systems.

    • SystemLocationCropTreatmentEquationNUEUnitMain FindingsRef.
      NFT (flow of nutrients)Totori, JapanSwiss Chard (Beta vulgaris spp. Cicla)Different flow rates - 2, 4, 6 and 8 L/minDry wt./nutrient uptake of whole plant20–25g/g DWHighest NUE at 8 L/m flow rate[14]
      Drip recirculating hydroponicsKashiwanoha, JapanTomato (Solanum lycopersicum) cv. Momotaro YorkDifferent cultivarsRatio of fruit fresh FW/total nitrogen uptake per plant at first harvest111.9kg/FW kgJaguar had greater NUE than Momotaro York[5]
      Tomato (Solanum lycopersicum) cv. Jaguar221.1
      Drip systemPunjab, IndiaCucumber (Cucumis sativus) var. Kafka, Multistar & PBRK-4Three fertigation levels and three varietiesYield/nutrient applied229.6–281.8g/plantFertigation level affected NUE[13]
      NFT – nutrient film technique.

      Table 2. 

      Studies conducted on nutrient use efficiency (NUE) in hydroponic systems.

    • SystemLocationCropTreatment (T)EquationUnitWUEMain findingsRef.
      Aeroponic towerKerman, IranCucumber
      (Cucumis sativus)      		Different flow rates and spray duration:
      125 mL/min, 10 min      		WUE = (YS )/∑WU (Total water consumed)kg (total yield)/m394.4Applying insufficient or excess water affected WUE more than changing the application duration. The optimum rate was 233.59 mL/min with an application time of 16.06 min.[21]
      125 mL/min, 15 min98.8
      125 mL/min, 20 min98.2
      250 mL/min, 10 min109.2
      250 mL/min, 15 min111.8
      250 mL/min, 20 min105.8
      375 mL/min, 10 min91.1
      375 mL/min, 15 min87.2
      375 mL/min, 20 min85
      Root chambersBenha, EgyptLettuce
      (Lactuca sativa)      		Different flow rates: 0.5 L/hWUE = CY/CWUkg (crop plant yield)/m3 (modelled water uptake)/plant3.87After the 50 d growing period, higher WUE with 0.5 L/h flow rate (3.87 kg/m3). Lowest at 1.5 L/h rate (3.02 kg/m3). A higher flow rate gave longer roots and reduced fresh biomass.[22]
      1 L/h3.47
      1.5 L/h3.02
      Aeroponic towerCairo, EgyptLettuce
      (Lactuca sativa)      		Number of sprinklers:
      1 nozzle Mini sprinkler      		WUE = (total fresh yield, kg)/(total applied
      irrigation water, m3)      		kg fresh yield/m3 water8Adding nozzles resulted in higher WUE in both crops because higher biomass production was achieved.[23]
      2 nozzle Mini sprinkler8.8
      4 nozzle mini sprinkler11.2
      Celery (Apium Graveolens)Number of sprinkler:
      1 nozzle mini sprinkler      		WUE = (total fresh yield, kg)/(total applied
      irrigation water, m3)      		kg fresh yield/ m3 water9.75[23]
      2 nozzle mini sprinkler12.4
      4 nozzle mini sprinkler12.8
      Root chambersKalamata, GreeceOnion
      (Allium cepa)      		Irrigation frequency:
      Daily 1 min ON/3 min OFF      		WUE = g (Bulb FW)/L (Nutrient solution consumed)g/L25.36Aeroponics outperformed an NFT system in WUE, plant biomass, bulb size, and total yield.[24]
      Root chambersChangchun, ChinaLettuce
      (Lactuca sativa L.
      var. ramosa Hort)      		Different nutrient solution
      and pH: T1: total nutrient solution, pH 5      		WUE = g (Total yield fresh weight)/L (Total water use). Total water use = sum of cumulative water uptake and water lossg FW/L29.68Half nutrient solutions with pH of 6 produced higher WUE. EC based fertilization method resulted in the highest WUE even in low pH.[25]
      T2: half nutrient solution, pH 541.88
      T3: adjusting EC, pH 5127.8
      T4: total nutrient solution, pH 630.81
      T5: half nutrient solution, pH 691.08
      T6: adjusting EC, pH 6142.91
      T7: total nutrient solution, pH 735.74
      T8: half nutrient solution, pH 763.57
      T9: adjusting EC, pH 7130.19
      EC − Electrical conductivity, CY − Crop yield, CWU − Crop water use.

      Table 3. 

      Studies conducted on water use efficiency (WUE) in aeroponic systems.

    • SystemLocationCropTreatmentEquationUnitsNUEMain findingsRef.
      Root chamberShimla, IndiaPotato (Solanum tuberosum var. Kufri Gaurav)T1: 0.75 mM N with 30 s ON and 5 min OFFNUE = Plant dry matter accumulation/crop N supplyg/mM~0.85Lower nitrogen applied resulted in higher NUE[26]
      T2: 7.5 mM N with 30 s ON and 5 min OFF~ 0
      Root chamberShimla, IndiaPotato (Solanum tuberosum var. Kufri Jyoti)T1: 0.75 mmol/L N with 30 s ON and 5 min OFFNUE = Plant dry matter accumulation/crop N supplyg/g~1.6Kufri Gaurav had the highest NUE when the 0.75 mmol/L supply of N was applied[27]
      T2: 7.5 mmol/L N with 30 s ON and 5 min OFF~0.20
      Potato (Solanum tuberosum var. Kufri Gaurav)T1: 0.75 mmol/L N with 30 s ON and 5 min OFF~2.1
      T2: 7.5 mmol/L N with 30 s ON and 5 min OFF~ 0.15
      Root chamberShimla, IndiaPotato (Solanum tuberosum)T: 56 seed potato varieties.
      2 mM N with 30 s ON and 5 min OFF      		NUE = Plant dry matter accumulation/crop N supplyg/g0.28 (Kufri Shailja) to 2.95 (Kufri Frysona)Kufri Frysona had the highest NUE of all potato seed varieties tested[28]
      Root chamberOntario,
      Canada      		Corn (Zea mays)T1: Low N with 10 s ON and 50 s OFFNUE = shoot dry weight/ N supplyg/mmol3.1The Teosinte variety of corn had higher NUE when using low N in an aeroponic system when compared to modern day corn using the same amount of N treatments.[29]
      T2: High N with 10 s ON and 50 s OFF2.1
      Teosinte (Zea mays spp. Parviglumis)T1: Low N with 10 s ON and 50 s OFF5.5
      T2: High N with 10 s ON and 50 s OFF3.6
      Root chamberChangchun, ChinaLettuce (Lactuca sativa L. var. ramosa Hort)T1: total nutrient solution, pH 5NUE = Total yield dry matter/Total nitrogen use (gDM/N)
      		gDM N
      		7.84T5 (half nutrient solution at pH 6) was found to have the greatest NUE.[25]
      T2: half nutrient solution, pH 55.17
      T3: adjusting EC, pH 511.12
      T4: total nutrient solution, pH 66.75
      T5: half nutrient solution, pH 616.53
      T6: adjusting EC, pH 613.82
      T7: total nutrient solution, pH 77.87
      T8: half nutrient solution, pH 78
      T9: adjusting EC, pH 710.68

      Table 4. 

      Studies conducted on nutrient use efficiency (NUE) in aeroponics.