H.-P. Liebig
Protected cultivation of Kohlrabi - in Germany the normal cropping method in the cold season - requires considerable amount of heating energy, not only for sufficient growth but also to avoid bolting. To improve control algorithms for the heating system in order to save energy the buffering capacity of Kohlrabi growth against fluctuating temperature regimes was examined.

Measurements of the net CO2-uptake per day (24h) and the tuber diameter growth under controlled fluctuations of temperature and radiation led to the following hypothesis:

  1. Photosynthesis is predominantly determined by the amount of radiation (PAR)
  2. Assimilates produced flow into a reserve pool
  3. Tuber growth (fresh weight) is predominantly determined by temperature dependent water uptake.

Comparative measurements and calculations from even more drastic reductions of light or temperature conditions supported the idea of considerably changing dry matter contents - the buffering system. Estimations of the buffering capacity were made by assuming that there was no increment in dry matter production or in tuber diameter.

It was concluded that there exists a large temperature integration potential if periods of extreme temperature regimes compared to the light regime do not exceed approximately 7 days.

In a glasshouse experiment conventionally fixed temperature set points were tested against a control program that led to much more changing temperatures. Growth rates of the different regimes were compared by mean of a plant growth model. No disadvantage caused by heavy changing temperatures could be detected. Although not significant tuber growth rates were even slightly enhanced. Further investigations are needed to develop control algorithms using better the temperature integration potential of Kohlrabi and presumably other plants.

Liebig, H.-P. (1989). TEMPERATURE INTEGRATION BY KOHLRABI GROWTH. Acta Hortic. 248, 277-284
DOI: 10.17660/ActaHortic.1989.248.33

Acta Horticulturae