Abbreviations: BGM, black plastic and gravel-sand mulches; GM, gravel-sand mulch; LAI, leaf area ... more Abbreviations: BGM, black plastic and gravel-sand mulches; GM, gravel-sand mulch; LAI, leaf area index (m 2 m −2); NM, no mulch; TGM, transparent plastic and gravel-sand mulches; WGM, white plastic and gravel-sand mulches; a, albedo (-); D, diffuse shortwave radiation (Wm −2 or MJ m −2 day −1); S, shortwave radiation (W m −2 or MJ m −2 day −1); S n , net shortwave radiation (W m −2 or MJ m −2 day −1); ρ, greenhouse cover shortwave radiation reflectance (-); τ, greenhouse shortwave radiation transmission (-) ⁎ Corresponding author.
The stable isotope 15N was used to assess the recovery of mineral N fertilizer applied to fertiga... more The stable isotope 15N was used to assess the recovery of mineral N fertilizer applied to fertigated and drip-irrigated spring muskmelon and autumn-winter sweet pepper crops grown in greenhouse soil plots. They received 92–96% of mineral N fertilizer as NO3−. 15N-labeled Ca (NO3)2 fertilizer was applied to crops during vegetative growth and fruit production phases. Crops were grown with either conventional management or combined improved N and irrigation management. Improved management for both irrigation and N was based on the combined use of models, to estimate crop requirements, and of monitoring of soil parameters. In sweet pepper, from conventional management, 15N recoveries from the 15N applications made during vegetative growth and fruit production were 66% and 58%, respectively. With improved management in sweet pepper, the corresponding 15N recoveries were 82% and 77%. In muskmelon, 15N recoveries from conventional management from the 15N applications made during vegetative...
This work was mainly aimed at studying the spatio-temporal distribution of water content (θ w), b... more This work was mainly aimed at studying the spatio-temporal distribution of water content (θ w), bulk (EC a) and soil solution (EC SS) electrical conductivity measured with a dielectric sensor (GS3) and a tension lysimeter (suction cup) throughout three drip-irrigated tomato crops in Mediterranean greenhouses. The mean θ w (GS3) for the wet bulb was well estimated by measuring at representative positions, especially at the centre of the wet bulb. The EC SS substantially increased in the wet bulb, irrespective of the soil position, reaching relatively high values (6-7 dS m −1) in the second half of the cycles, mostly due to sodium and chloride accumulation. The mean EC SS for the wet bulb was narrowly and linearly related to that measured at any of four representative positions in the wet bulb, which presented similar seasonal dynamics and absolute values throughout most of the crops. The mean EC SS for the wet bulb can be well estimated by measuring at one of these positions, since the errors of using measurements from these positions were relatively low. The relationship between the EC SS estimated from GS3 and that measured with suction cup varied depending mostly on soil position and cropping year, but the GS3 did not generally provide accurate EC SS estimates, especially in the second half of the cycles, when salts accumulated in the soil. Despite this, measurements of EC a and EC SS from GS3 at the centre of the wet bulb might be useful for identifying tendencies or relevant salinity changes for automated irrigation systems. The solution concentration for main salts and nutrients can be fairly well monitored by sampling at any of the four representative positions of the wet bulb. However, it appears advisable to measure at the centre of the wet bulb, as samples from this position might respond faster to changes in the nutrient solution supply or the root activity, especially for very mobile elements, such as nitrate.
ABSTRACT This work studies the effect of different potassium rates applied by fertigation on the ... more ABSTRACT This work studies the effect of different potassium rates applied by fertigation on the soil-plant system of a Green Bean Crop under greenhouse conditions. The experiment was conducted on a greenhouse green bean crop Helda, on a sand-mulched sandy loam soil and trickle irrigation. Three different treatments were established: K1 (83 kg K ha-1), K2 (195 kg K ha-1), and K3 (295 kg K ha-1) applied by fertigation. The experimental determinations included the concentration of assimilable potassium in soil at the start and end of the experiment, the element plant extractions by tissue analysis in different plant aerial parts, and the total fruit yield. The concentration of assimilable potassium in soil at the end of the cropping cycle was not affected by the fertigation dose. The K concentration extracted by the aerial part was 17, 19 and 23 g m-2, for treatments K1, K2, and K3 respectively. There was no significant effect of the potassium rate on fruit yield, oscillating between 2.30 and 2.56 kg m-2.
ABSTRACT The increasingly water demand and the lack of natural resources in arid and semi-arid ar... more ABSTRACT The increasingly water demand and the lack of natural resources in arid and semi-arid areas justify the present interest in the re-use of wastewater. Since 1995 purified and ozone-treated wastewater from Almería (Spain) has been used to irrigate greenhouse crops. The higher nutrient content levels of this effluent requires special management strategies. Melon Galia in a spring cycle (124 days) and tomato Daniela in an autumn-winter cycle (185 days) were grown under greenhouse conditions. The crops were irrigated with groundwater or with purified wastewater. Purified wastewater was obtained from the Almería Purifying Plant after an ozone tertiary treatment, ground water was obtained by desalinizing underground water. To prepare the nutrient solution the chemical composition of each type of water was determined and N and K were added accordingly to obtain similar nutrient solutions. Effluents provided significant amount of N, P and K; this had positive effects on the addition of fertilizer salts since the input of nutrients was reduced. As no significant differences were found among treatments on the tested production parameters in both crops, the nutrient use efficiency was higher in the wastewater treatment. Foliar concentrations of N, P and K were similar in both treatments and crops.
The combined use of fertigation and drip irrigation to frequently apply small amounts of N throug... more The combined use of fertigation and drip irrigation to frequently apply small amounts of N throughout a crop provides the technical capacity for precise N and irrigation management. A prescriptive–corrective management (PCM) package, based on modeling and monitoring approaches, was developed for combined irrigation and N management to take advantage of this technical capacity in a greenhouse-based vegetable production system. For irrigation, the prescriptive component of PCM was the calculation of historical ETc using the simulation model PrHo to calculate ETc with long term climatic data, and the corrective component was the use of tensiometers. For N, the prescriptive component was based on simulation of crop N uptake, using the simulation model Nup, developed in the present study, and the corrective component was based on controlling soil solution [NO 3 − ] in the immediate root zone of the plants. Combined PCM for both N and irrigation management was compared with conventional m...
Small analytical systems enabling rapid on-farm analysis may be useful for monitoring crop and so... more Small analytical systems enabling rapid on-farm analysis may be useful for monitoring crop and soil nutrient status. Two commercially available, rapid analysis systems were evaluated for analysis of [NO 3-] in aqueous standard solutions (AS), and in soil solution (SS), plant sap (PS) and fertigation nutrient solutions (NS) obtained from tomato crops. The systems were the Merck RQFlex reflectometer and the Hanna Instruments C115 Grow Master colorimeter. [NO 3-] in AS covered the analytical range of each instrument, being 0.3-3.2 and 0.3-16.1 mmol L-1 , respectively, for the reflectometer and colorimeter. [NO 3-] were 5-14 mmol L-1 for SS, 2.3-33 mmol L-1 for NS, and 63-158 mmol L-1 for PS. Accuracy was evaluated using linear regression against (i) known concentration for AS, and (ii) laboratory analysis for SS, PS and NS. For the reflectometer with AS, SS and PS, the linear regression had slopes of 1±0.08 and intercepts of <0.6 mmol L-1. In NS up to 9 mmol L-1 , there was a similar slope, with an intercept of 1.3 mmol L-1. In the three most concentrated NS samples, there was a larger relative error that was attributed to faulty dilution. Coefficients of determination were always r 2 ≥0.94. The reflectometer was generally accurate for all media examined; it was rapid (1 min per analysis) and simple to use. The colorimeter was generally similarly accurate; however, it was slower, required reagent preparation and was subject to colour interferences. This work demonstrated that the reflectometer can provide rapid and accurate on-farm measurement of [NO 3-] in SS, PS and NS.
The VegSyst simulation model was developed to assist with N and irrigation management of sweet pe... more The VegSyst simulation model was developed to assist with N and irrigation management of sweet pepper grown in plastic greenhouses in the Mediterranean Basin. The model was developed for use in an on-farm decision support system with the requirement for readily available input data. Dry matter production (DMP), crop N uptake and crop evapotranspiration (ET c) are simulated on a daily basis. DMP is calculated from daily fraction of intercepted photosynthetically active radiation (PAR), PAR radiation, and radiation-use efficiency. Fraction of intercepted PAR is calculated from relative thermal time. Crop N uptake is calculated as the product of DMP and N content which is described by a power function of DMP. ET c is the product of daily reference evapotranspiration (ET o) using an adapted Penman-Monteith equation, and a daily simulated crop coefficient value. The VegSyst model for soil-grown, greenhouse pepper was calibrated in one crop and validated in three different crops. In the validation, the model accurately simulated crop growth, N uptake and ET c. Relative to measured values, simulated DMP at final harvest was 0.89-1.06, and crop N uptake was 0.97-1.13. Simulated cumulative ET c for complete crops was 0.95-1.05 of measured values. Communicated by K. Stone.
h i g h l i g h t s " Cationic polyelectrolytes are efficient flocculants for freshwater microalg... more h i g h l i g h t s " Cationic polyelectrolytes are efficient flocculants for freshwater microalgae. " Low doses allows recover 90% of microalgae biomass with concentration factors of 35. " Polyelectrolytes improves the viability of producing biofuels from microalgae.
h i g h l i g h t s Oxygen mass transfe r in raceway reactors mainly occur s place in paddlewheel... more h i g h l i g h t s Oxygen mass transfe r in raceway reactors mainly occur s place in paddlewheel and sump. Mass transfer capacity of raceway reactors is a limiting factor for productivity. Productivity increases at high mass transfer outwe igh the higher power consumption.
The fluid dynamic characterization of a 100 m length  1 m wide channel raceway photobioreactor w... more The fluid dynamic characterization of a 100 m length  1 m wide channel raceway photobioreactor was carried out. The effects of water depth, liquid velocity and the presence, or absence, of sump baffles to improve the CO 2 supply transfer were considered in relation to on the power consumption, residence time and mixing in the reactor was studied. When operated at a depth of 20 cm, the power consumption was between 1.5 and 8.4 W m À3 depending on the forward velocity, with higher values occurring when the baffle was in place. Residence times and the degree of mixing at each section of the raceway (paddlewheel, bends, channels and sump) were measured experimentally. Mixing occurred mainly in the sump, paddlewheel and bends, with a maximum dispersion coefficient of 0.07 m 2 s À1. These sections, however, only contributed a small fraction to the total volume of the raceway. Bodenstein numbers from 200 to 540 for the channel sections indicated plug-flow characteristics. Mixing times ranged from 1.4 to 6 h, with the presence of the baffle greatly increasing these times despite higher specific power consumption. A total of 15e20 circuits of the raceway were needed to achieve complete mixing without the baffle, compared to 30e40 cycles with the baffle. Vertical mixing was very poor whereas axial mixing was similar to that achieved in closed photobioreactors. The methodologies applied were shown to be useful in determining the fluid dynamics of a raceway photobioreactor. Equations useful in simulating the power consumption as a function of the design and operation parameters have been validated.
The combined use of fertigation and drip irrigation to frequently apply small amounts of N throug... more The combined use of fertigation and drip irrigation to frequently apply small amounts of N throughout a crop provides the technical capacity for precise N and irrigation management. A prescriptive-corrective management (PCM) package, based on modeling and monitoring approaches, was developed for combined irrigation and N management to take advantage of this technical capacity in a greenhouse-based vegetable production system. For irrigation, the prescriptive component of PCM was the calculation of historical ETc using the simulation model PrHo to calculate ETc with long term climatic data, and the corrective component was the use of tensiometers. For N, the prescriptive component was based on simulation of crop N uptake, using the simulation model Nup, developed in the present study, and the corrective component was based on controlling soil solution [NO 3 − ] in the immediate root zone of the plants. Combined PCM for both N and irrigation management was compared with conventional management (CM) for pepper and muskmelon crops. In both crops, fruit production was very similar in the CM and PCM treatments. Using PCM, total irrigation volume was reduced by 17% in pepper and by 20% in muskmelon; total drainage was reduced by 53 and 49%, respectively. Total applied N was reduced by 35% in pepper and by 29% in muskmelon. Total NO 3 − leaching loss was reduced by 58% in pepper and by at least 49% in muskmelon. The Nup simulation model of crop N uptake was calibrated and validated for pepper and muskmelon. This study demonstrated the effectiveness of combined PCM of both N and irrigation to take advantage of the advanced technical capacity of combined fertigation and drip irrigation systems for precise N and irrigation management.
Like many intensive vegetable production systems, the greenhouse-based system on the southeastern... more Like many intensive vegetable production systems, the greenhouse-based system on the southeastern (SE) Mediterranean coast of Spain is associated with considerable NO 3 − contamination of groundwater. Drip irrigation and sophisticated fertigation systems provide the technical capacity for precise nutrient and irrigation management of soil-grown crops which would reduce NO 3 − leaching loss. The VegSyst crop simulation model was developed to simulate daily crop biomass production, N uptake and crop evapotranspiration (ET c). VegSyst is driven by thermal time and consequently is adaptable to different planting dates, different greenhouse cooling practices and differences in greenhouse design. It will be subsequently incorporated into a practical on-farm decision support system to enable growers to more effectively use the advanced technical capacity of this horticultural system for optimal N and irrigation management. VegSyst was calibrated and validated for muskmelon grown in Mediterranean plastic greenhouse in SE Spain using data of four melon crops, two grown in 2005 and two in 2006 using two management strategies of water and N management in each year. VegSyst very accurately simulated crop biomass production and accurately simulated crop N uptake over time. Model performance in simulating dry matter production (DMP) over time was better using a double radiation use efficiency (RUE) approach (5.0 and 3.2 g MJ −1 PAR for vegetative and reproductive growth phases) compared to a single RUE approach (4.3 g MJ −1 PAR). The simulation of ET c over time, was very accurate in the two 2006 muskmelon crops and somewhat less so in the two 2005 crops. The error in the simulated final values, expressed as a percentage of final measured values was −1 to 6% for DMP, 2-11% for crop N uptake, and −11 to 6% for ET c. VegSyst provided effective simulation of DMP, N uptake and ET c for crops with different planting dates. This model can be readily adapted to other crops.
Suboptimal regimes of air and soil temperature usually occur under unheated greenhouses during wi... more Suboptimal regimes of air and soil temperature usually occur under unheated greenhouses during winter crop cycles. This work analyses the effects of three soil surface treatments (no plastic mulch, NM; transparent mulch, TM, and black mulch, BM) on the air-soil heat exchanges and the resulting soil and aerial microclimate. Experiments were conducted in unheated greenhouse compartments located in an area of mild winter climate (South-East Spain) during autumn and winter periods. In all treatments, the soil consisted of an artificial layer of 0.10 m gravel-sand material placed above a 0.3 m layer of imported loamy soil. When vents were closed, soil heat flux, ground net radiation and both air and root-zone temperature were higher in BM than in TM, while NM presented intermediate performances between BM and TM. When vents were open, heat storage and soil warming were substantially reduced with respect to unventilated conditions. This reduction was greater in BM, and so the advantages of BM with respect to the other treatments were only marginal under ventilated conditions. The main conclusions were: (i) The combination of black mulch + greenhouse appears to be a simple and low-cost passive heating system that can be recommended for the early stages of crop cycles starting at the end of autumn or in winter, when canopy leaf area index is small and most of the soil surface is free of vegetation; and (ii) ventilation had a negative effect on the benefits of mulching, implying that greenhouse ventilation management should reflect a compromise between maximizing greenhouse heat storage and fulfilling ventilation requirements for suitable crop growth.
Abbreviations: BGM, black plastic and gravel-sand mulches; GM, gravel-sand mulch; LAI, leaf area ... more Abbreviations: BGM, black plastic and gravel-sand mulches; GM, gravel-sand mulch; LAI, leaf area index (m 2 m −2); NM, no mulch; TGM, transparent plastic and gravel-sand mulches; WGM, white plastic and gravel-sand mulches; a, albedo (-); D, diffuse shortwave radiation (Wm −2 or MJ m −2 day −1); S, shortwave radiation (W m −2 or MJ m −2 day −1); S n , net shortwave radiation (W m −2 or MJ m −2 day −1); ρ, greenhouse cover shortwave radiation reflectance (-); τ, greenhouse shortwave radiation transmission (-) ⁎ Corresponding author.
The stable isotope 15N was used to assess the recovery of mineral N fertilizer applied to fertiga... more The stable isotope 15N was used to assess the recovery of mineral N fertilizer applied to fertigated and drip-irrigated spring muskmelon and autumn-winter sweet pepper crops grown in greenhouse soil plots. They received 92–96% of mineral N fertilizer as NO3−. 15N-labeled Ca (NO3)2 fertilizer was applied to crops during vegetative growth and fruit production phases. Crops were grown with either conventional management or combined improved N and irrigation management. Improved management for both irrigation and N was based on the combined use of models, to estimate crop requirements, and of monitoring of soil parameters. In sweet pepper, from conventional management, 15N recoveries from the 15N applications made during vegetative growth and fruit production were 66% and 58%, respectively. With improved management in sweet pepper, the corresponding 15N recoveries were 82% and 77%. In muskmelon, 15N recoveries from conventional management from the 15N applications made during vegetative...
This work was mainly aimed at studying the spatio-temporal distribution of water content (θ w), b... more This work was mainly aimed at studying the spatio-temporal distribution of water content (θ w), bulk (EC a) and soil solution (EC SS) electrical conductivity measured with a dielectric sensor (GS3) and a tension lysimeter (suction cup) throughout three drip-irrigated tomato crops in Mediterranean greenhouses. The mean θ w (GS3) for the wet bulb was well estimated by measuring at representative positions, especially at the centre of the wet bulb. The EC SS substantially increased in the wet bulb, irrespective of the soil position, reaching relatively high values (6-7 dS m −1) in the second half of the cycles, mostly due to sodium and chloride accumulation. The mean EC SS for the wet bulb was narrowly and linearly related to that measured at any of four representative positions in the wet bulb, which presented similar seasonal dynamics and absolute values throughout most of the crops. The mean EC SS for the wet bulb can be well estimated by measuring at one of these positions, since the errors of using measurements from these positions were relatively low. The relationship between the EC SS estimated from GS3 and that measured with suction cup varied depending mostly on soil position and cropping year, but the GS3 did not generally provide accurate EC SS estimates, especially in the second half of the cycles, when salts accumulated in the soil. Despite this, measurements of EC a and EC SS from GS3 at the centre of the wet bulb might be useful for identifying tendencies or relevant salinity changes for automated irrigation systems. The solution concentration for main salts and nutrients can be fairly well monitored by sampling at any of the four representative positions of the wet bulb. However, it appears advisable to measure at the centre of the wet bulb, as samples from this position might respond faster to changes in the nutrient solution supply or the root activity, especially for very mobile elements, such as nitrate.
ABSTRACT This work studies the effect of different potassium rates applied by fertigation on the ... more ABSTRACT This work studies the effect of different potassium rates applied by fertigation on the soil-plant system of a Green Bean Crop under greenhouse conditions. The experiment was conducted on a greenhouse green bean crop Helda, on a sand-mulched sandy loam soil and trickle irrigation. Three different treatments were established: K1 (83 kg K ha-1), K2 (195 kg K ha-1), and K3 (295 kg K ha-1) applied by fertigation. The experimental determinations included the concentration of assimilable potassium in soil at the start and end of the experiment, the element plant extractions by tissue analysis in different plant aerial parts, and the total fruit yield. The concentration of assimilable potassium in soil at the end of the cropping cycle was not affected by the fertigation dose. The K concentration extracted by the aerial part was 17, 19 and 23 g m-2, for treatments K1, K2, and K3 respectively. There was no significant effect of the potassium rate on fruit yield, oscillating between 2.30 and 2.56 kg m-2.
ABSTRACT The increasingly water demand and the lack of natural resources in arid and semi-arid ar... more ABSTRACT The increasingly water demand and the lack of natural resources in arid and semi-arid areas justify the present interest in the re-use of wastewater. Since 1995 purified and ozone-treated wastewater from Almería (Spain) has been used to irrigate greenhouse crops. The higher nutrient content levels of this effluent requires special management strategies. Melon Galia in a spring cycle (124 days) and tomato Daniela in an autumn-winter cycle (185 days) were grown under greenhouse conditions. The crops were irrigated with groundwater or with purified wastewater. Purified wastewater was obtained from the Almería Purifying Plant after an ozone tertiary treatment, ground water was obtained by desalinizing underground water. To prepare the nutrient solution the chemical composition of each type of water was determined and N and K were added accordingly to obtain similar nutrient solutions. Effluents provided significant amount of N, P and K; this had positive effects on the addition of fertilizer salts since the input of nutrients was reduced. As no significant differences were found among treatments on the tested production parameters in both crops, the nutrient use efficiency was higher in the wastewater treatment. Foliar concentrations of N, P and K were similar in both treatments and crops.
The combined use of fertigation and drip irrigation to frequently apply small amounts of N throug... more The combined use of fertigation and drip irrigation to frequently apply small amounts of N throughout a crop provides the technical capacity for precise N and irrigation management. A prescriptive–corrective management (PCM) package, based on modeling and monitoring approaches, was developed for combined irrigation and N management to take advantage of this technical capacity in a greenhouse-based vegetable production system. For irrigation, the prescriptive component of PCM was the calculation of historical ETc using the simulation model PrHo to calculate ETc with long term climatic data, and the corrective component was the use of tensiometers. For N, the prescriptive component was based on simulation of crop N uptake, using the simulation model Nup, developed in the present study, and the corrective component was based on controlling soil solution [NO 3 − ] in the immediate root zone of the plants. Combined PCM for both N and irrigation management was compared with conventional m...
Small analytical systems enabling rapid on-farm analysis may be useful for monitoring crop and so... more Small analytical systems enabling rapid on-farm analysis may be useful for monitoring crop and soil nutrient status. Two commercially available, rapid analysis systems were evaluated for analysis of [NO 3-] in aqueous standard solutions (AS), and in soil solution (SS), plant sap (PS) and fertigation nutrient solutions (NS) obtained from tomato crops. The systems were the Merck RQFlex reflectometer and the Hanna Instruments C115 Grow Master colorimeter. [NO 3-] in AS covered the analytical range of each instrument, being 0.3-3.2 and 0.3-16.1 mmol L-1 , respectively, for the reflectometer and colorimeter. [NO 3-] were 5-14 mmol L-1 for SS, 2.3-33 mmol L-1 for NS, and 63-158 mmol L-1 for PS. Accuracy was evaluated using linear regression against (i) known concentration for AS, and (ii) laboratory analysis for SS, PS and NS. For the reflectometer with AS, SS and PS, the linear regression had slopes of 1±0.08 and intercepts of <0.6 mmol L-1. In NS up to 9 mmol L-1 , there was a similar slope, with an intercept of 1.3 mmol L-1. In the three most concentrated NS samples, there was a larger relative error that was attributed to faulty dilution. Coefficients of determination were always r 2 ≥0.94. The reflectometer was generally accurate for all media examined; it was rapid (1 min per analysis) and simple to use. The colorimeter was generally similarly accurate; however, it was slower, required reagent preparation and was subject to colour interferences. This work demonstrated that the reflectometer can provide rapid and accurate on-farm measurement of [NO 3-] in SS, PS and NS.
The VegSyst simulation model was developed to assist with N and irrigation management of sweet pe... more The VegSyst simulation model was developed to assist with N and irrigation management of sweet pepper grown in plastic greenhouses in the Mediterranean Basin. The model was developed for use in an on-farm decision support system with the requirement for readily available input data. Dry matter production (DMP), crop N uptake and crop evapotranspiration (ET c) are simulated on a daily basis. DMP is calculated from daily fraction of intercepted photosynthetically active radiation (PAR), PAR radiation, and radiation-use efficiency. Fraction of intercepted PAR is calculated from relative thermal time. Crop N uptake is calculated as the product of DMP and N content which is described by a power function of DMP. ET c is the product of daily reference evapotranspiration (ET o) using an adapted Penman-Monteith equation, and a daily simulated crop coefficient value. The VegSyst model for soil-grown, greenhouse pepper was calibrated in one crop and validated in three different crops. In the validation, the model accurately simulated crop growth, N uptake and ET c. Relative to measured values, simulated DMP at final harvest was 0.89-1.06, and crop N uptake was 0.97-1.13. Simulated cumulative ET c for complete crops was 0.95-1.05 of measured values. Communicated by K. Stone.
h i g h l i g h t s " Cationic polyelectrolytes are efficient flocculants for freshwater microalg... more h i g h l i g h t s " Cationic polyelectrolytes are efficient flocculants for freshwater microalgae. " Low doses allows recover 90% of microalgae biomass with concentration factors of 35. " Polyelectrolytes improves the viability of producing biofuels from microalgae.
h i g h l i g h t s Oxygen mass transfe r in raceway reactors mainly occur s place in paddlewheel... more h i g h l i g h t s Oxygen mass transfe r in raceway reactors mainly occur s place in paddlewheel and sump. Mass transfer capacity of raceway reactors is a limiting factor for productivity. Productivity increases at high mass transfer outwe igh the higher power consumption.
The fluid dynamic characterization of a 100 m length  1 m wide channel raceway photobioreactor w... more The fluid dynamic characterization of a 100 m length  1 m wide channel raceway photobioreactor was carried out. The effects of water depth, liquid velocity and the presence, or absence, of sump baffles to improve the CO 2 supply transfer were considered in relation to on the power consumption, residence time and mixing in the reactor was studied. When operated at a depth of 20 cm, the power consumption was between 1.5 and 8.4 W m À3 depending on the forward velocity, with higher values occurring when the baffle was in place. Residence times and the degree of mixing at each section of the raceway (paddlewheel, bends, channels and sump) were measured experimentally. Mixing occurred mainly in the sump, paddlewheel and bends, with a maximum dispersion coefficient of 0.07 m 2 s À1. These sections, however, only contributed a small fraction to the total volume of the raceway. Bodenstein numbers from 200 to 540 for the channel sections indicated plug-flow characteristics. Mixing times ranged from 1.4 to 6 h, with the presence of the baffle greatly increasing these times despite higher specific power consumption. A total of 15e20 circuits of the raceway were needed to achieve complete mixing without the baffle, compared to 30e40 cycles with the baffle. Vertical mixing was very poor whereas axial mixing was similar to that achieved in closed photobioreactors. The methodologies applied were shown to be useful in determining the fluid dynamics of a raceway photobioreactor. Equations useful in simulating the power consumption as a function of the design and operation parameters have been validated.
The combined use of fertigation and drip irrigation to frequently apply small amounts of N throug... more The combined use of fertigation and drip irrigation to frequently apply small amounts of N throughout a crop provides the technical capacity for precise N and irrigation management. A prescriptive-corrective management (PCM) package, based on modeling and monitoring approaches, was developed for combined irrigation and N management to take advantage of this technical capacity in a greenhouse-based vegetable production system. For irrigation, the prescriptive component of PCM was the calculation of historical ETc using the simulation model PrHo to calculate ETc with long term climatic data, and the corrective component was the use of tensiometers. For N, the prescriptive component was based on simulation of crop N uptake, using the simulation model Nup, developed in the present study, and the corrective component was based on controlling soil solution [NO 3 − ] in the immediate root zone of the plants. Combined PCM for both N and irrigation management was compared with conventional management (CM) for pepper and muskmelon crops. In both crops, fruit production was very similar in the CM and PCM treatments. Using PCM, total irrigation volume was reduced by 17% in pepper and by 20% in muskmelon; total drainage was reduced by 53 and 49%, respectively. Total applied N was reduced by 35% in pepper and by 29% in muskmelon. Total NO 3 − leaching loss was reduced by 58% in pepper and by at least 49% in muskmelon. The Nup simulation model of crop N uptake was calibrated and validated for pepper and muskmelon. This study demonstrated the effectiveness of combined PCM of both N and irrigation to take advantage of the advanced technical capacity of combined fertigation and drip irrigation systems for precise N and irrigation management.
Like many intensive vegetable production systems, the greenhouse-based system on the southeastern... more Like many intensive vegetable production systems, the greenhouse-based system on the southeastern (SE) Mediterranean coast of Spain is associated with considerable NO 3 − contamination of groundwater. Drip irrigation and sophisticated fertigation systems provide the technical capacity for precise nutrient and irrigation management of soil-grown crops which would reduce NO 3 − leaching loss. The VegSyst crop simulation model was developed to simulate daily crop biomass production, N uptake and crop evapotranspiration (ET c). VegSyst is driven by thermal time and consequently is adaptable to different planting dates, different greenhouse cooling practices and differences in greenhouse design. It will be subsequently incorporated into a practical on-farm decision support system to enable growers to more effectively use the advanced technical capacity of this horticultural system for optimal N and irrigation management. VegSyst was calibrated and validated for muskmelon grown in Mediterranean plastic greenhouse in SE Spain using data of four melon crops, two grown in 2005 and two in 2006 using two management strategies of water and N management in each year. VegSyst very accurately simulated crop biomass production and accurately simulated crop N uptake over time. Model performance in simulating dry matter production (DMP) over time was better using a double radiation use efficiency (RUE) approach (5.0 and 3.2 g MJ −1 PAR for vegetative and reproductive growth phases) compared to a single RUE approach (4.3 g MJ −1 PAR). The simulation of ET c over time, was very accurate in the two 2006 muskmelon crops and somewhat less so in the two 2005 crops. The error in the simulated final values, expressed as a percentage of final measured values was −1 to 6% for DMP, 2-11% for crop N uptake, and −11 to 6% for ET c. VegSyst provided effective simulation of DMP, N uptake and ET c for crops with different planting dates. This model can be readily adapted to other crops.
Suboptimal regimes of air and soil temperature usually occur under unheated greenhouses during wi... more Suboptimal regimes of air and soil temperature usually occur under unheated greenhouses during winter crop cycles. This work analyses the effects of three soil surface treatments (no plastic mulch, NM; transparent mulch, TM, and black mulch, BM) on the air-soil heat exchanges and the resulting soil and aerial microclimate. Experiments were conducted in unheated greenhouse compartments located in an area of mild winter climate (South-East Spain) during autumn and winter periods. In all treatments, the soil consisted of an artificial layer of 0.10 m gravel-sand material placed above a 0.3 m layer of imported loamy soil. When vents were closed, soil heat flux, ground net radiation and both air and root-zone temperature were higher in BM than in TM, while NM presented intermediate performances between BM and TM. When vents were open, heat storage and soil warming were substantially reduced with respect to unventilated conditions. This reduction was greater in BM, and so the advantages of BM with respect to the other treatments were only marginal under ventilated conditions. The main conclusions were: (i) The combination of black mulch + greenhouse appears to be a simple and low-cost passive heating system that can be recommended for the early stages of crop cycles starting at the end of autumn or in winter, when canopy leaf area index is small and most of the soil surface is free of vegetation; and (ii) ventilation had a negative effect on the benefits of mulching, implying that greenhouse ventilation management should reflect a compromise between maximizing greenhouse heat storage and fulfilling ventilation requirements for suitable crop growth.
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