Semi-closed greenhouse photosynthesis measurements – a future standard in intelligent climate control

Abstract

The present study evaluates the potential of measuring canopy photosynthesis in large semi-closed greenhouses. The hypothesis was that since the airflow through the canopy can be measured, the CO2 exchange rate (CER) can be measured and thus biomass production can be calculated quite accurately from hour to hour. A semi-closed 9,447 m2 greenhouse was constructed in the southwestern part of Norway (58.7°N, 5.5°E). A defined airflow (varying from 30 to 60 m3 m-2 h-1) moved from the bottom (inlet air) to the top (outlet air) of the tomato canopy. The CO2 concentration was controlled by adding exhaust gases from the combustion of natural gas used for heating. Every fifth minute, CER was calculated on the basis of the difference between the inlet and outlet air, and the flowrate. The CER was measured from June until the end of October, and results from selected time periods with different ratios between daylight and artificial light, are presented. Generally, canopy photosynthesis as a mean for the whole greenhouse increased from-1.0 to 6 g CO2 m-2 h-1 when PFD increased from 0 to 600–1,000 μmol m-2 s-1 and the CO2 concentration increased from 400 to 1,000 μmol mol-1. The highest daily CER was about 30 g CO2 m-2 day-1. It was concluded that measuring photosynthesis on a large-scale basis using the present method is possible. A lot of new information about canopy responses to climate from hour to hour can be acquired and will probably have a significant influence on future greenhouse management.