ABSTRACT: Nitrate pollution due to excessive N fertirrigation in greenhouse tomato production is a persisting environmental concern
in the Mediterranean region. Driven by productivity rather than sustainability, growers continue to use very high N concentrations
of more than 11 mM in greenhouse tomato production. A greenhouse study was conducted in Barcelona, Spain, over two growing
seasons to analyze the effect of N concentrations from 5 mM to 11 mM (control) on tomato yield and physical quality. The relative
environmental impact was calculated by using the life cycle assessment method (LCA). Our results show that N concentration
in the nutrient solution can be reduced from 11 mM (control) to 7 mM under a daily mean drainage volume of 30%. This finding
implies a 70% decrease in nitrate leaching without reducing tomato yield or quality. According to life cycle assessment, a
reduction of 36% in N fertilizers leads to a 60% decrease in the potential impact of eutrophication, 50% decrease in the potential
impact of climate change, and 45% decrease in the potential impact of photochemical oxidants.
Lycopersicon esculentum L.–water-use efficiency–LCA–hydroponics
Agronomy for Sustainable Development 04/2012; 28(4):489-495. · 3.33 Impact Factor
ABSTRACT: The object of this work was to determine and model the air exchange rate of greenhouses with insect-proof screens over the vents. Experimental tests were conducted on multi-span tunnel greenhouse with two types of ventilation openings, one with continuous roof vents and the other with an insect-proof screen which was able to replace a flexible roll-up plastic cover.Ventilation rates of the experimental greenhouses were measured using the tracer gas technique. Discharge coefficients were determined in a 1:3 scale model replica of the experimental greenhouses. A simple model that includes the global effect of the wind on the greenhouse ventilation was developed and compared with the measured air exchange values.The main results determine the reduction in the discharge coefficient when an insect-proof screen is incorporated. It was found that vents located in lateral spans have a higher discharge coefficient than those located in central spans. Some practical considerations for the design of more efficient ventilation systems can be derived from this fact.The global wind effect coefficient was found to be dependent on the type of vent, insect-proof screen and wind speed. Some results are not in agreement with others previously published, but obtained under different environmental conditions. This coefficient is derived from empirical measurements which makes its general application questionable.In spite of its simplicity, the theoretical model describes accurately the ventilation rate of the greenhouse with both types of vents. The roll-up roof vent provides a ventilation rate about three times greater than the continuous roof vent. It has an acceptable air exchange, while acting as a barrier against the entrance of undesirable pests.
Journal of Agricultural Engineering Research.
Horticultura: Revista de frutas, hortalizas, flores, plantas ornamentales y de viveros, ISSN 1132-2950, Nº 192, 2006, pags. 8-13.
ABSTRACT: Most transpiration studies of greenhouse crops have been undertaken under cool conditions in northern and central Europe. These conditions are greatly exceeded in most greenhouses of the Mediterranean basin or in other zones where the climate is warmer. This article presents some measured transpiration data of Geranium, Pelargonium zonale grown under high vapour pressure deficit (VPD) (up to 3.4 kPa) and temperature (up to 36°C). Calculated transpiration values from the Penman–Monteith equation averaged over 30 min intervals were compared with measured transpiration by weighing plant on an electronic balance. To calculate the energy used in transpiration, the radiation term of the Penman–Monteith equation was set equal to the net radiation above the plant canopy times (1−exp(kL)), where k is the extinction coefficient and L is the leaf area index. The best correlation was obtained for k=0.61 (R2=0.93). Leaf resistance was estimated as a function only of solar radiation, since leaf resistance derived from porometer measurements showed no dependence on VPD or temperature. The agreement between measured and calculated transpiration was good for the wide range of temperature, radiation and humidity levels that occurred during the 42 days of the test. The effect of air humidity and temperature on canopy resistance was estimated from measurements of crop water use by rearranging the Penman equation. No reduction of canopy resistance was found for VPD values from 1.4 to 3.4 kPa and ambient temperature from 26 to 36°C. A simplified model of daytime transpiration based on easily measured variables is also presented.
Agricultural and Forest Meteorology.