Abstract
Effects of supplemental lighting, semi-closed greenhouse and split-root fertigation on weekly to seasonal heat and electricity use and CO2 emissions in cucumber growing were estimated in Finland. With moderate lighting (170 W m-2 above rows, 60 W m-2 inter-row) in a ventilated greenhouse, seasonal electricity and heat use (MJ kg-1 cucumber) were 20–50 and 10–25, 17–30 and 3–8, 38–55 and 10–18 in spring, summer and autumn to mid-winter, respectively. In summer, a semi-closed greenhouse improved energy use efficiency by 20–30% and split-root fertigation by 0–15%. Raising light intensity and applying inter- row lighting allowed higher yields in autumn to mid-winter without affecting electricity use efficiency. In other seasons, increasing the lighting decreased the efficiency. The emissions largely resulted from electricity use. Direct emissions (kg CO2-eq kg-1) based on propane and electricity from the national grid were 2.5, 1.5 and 3.3 in spring, summer and autumn to mid-winter, respectively. Efficiency of using solar and supplemental PAR was markedly lower in summer than in other seasons. The results provide profile of energy use and emissions and point to ways to reduce them.
Highlights
The Nordic countries are the northernmost producers of greenhouse vegetables in significant volumes
This study aims to set a temporally dynamic reference for energy use and CO2 emissions from heating and lighting for cucumber
In other seasons a greenhouse covered by a single layer of glass can be maintained mostly closed without the semi-closed technology in Finland
Summary
The Nordic countries are the northernmost producers of greenhouse vegetables in significant volumes. In Finland, located mainly between 60 and 63 °N, 79 thousand tonnes (Kt) of vegetables were produced on 248 hectares in (Puutarhatilastot 2013). Kt vegetables were grown on 114 hectares in 2013 (Skörd av trädgårdsväxter 2013), and in Denmark 32 Kt were produced on 96 hectares in 2012, (Danmarks statistic 2014). In the Netherlands, a major European production area, at about 52 °N, 1701 Kt of vegetables were produced on 4881 hectares in 2013 (Statline 2014). In Alaska, which is at the same latitude as Finland, vegetables were produced on only 2.1 hectares in 2012 (US Department of Agriculture 2014). In Canada, where greenhouses are located mainly between 42 and 51 °N, 286 Kt of vegetables were produced on 574 hectares in 2013 (Statistics Canada 2013)
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