OPTIMIZING CROP PRODUCTION TO LOW COSTS IN PROTECTED VEGETABLE CULTIVATION

E. Fölster
During the last years in North Europe the protected vegetable cultivation was confronted with an enormous increase of energy costs. As the prices for the vegetable products didn't follow to the same extent, especially the consumption of energy has to be reduced for getting an economical production.

The main possibilities to save energy in protected vegetable cultivation are:

  • reducing the heat losses of the greenhouses and
  • lowering the heat consumption of the cultivated crops.

In the following special attention is paid to the last point. Lowering the heat consumption of the cultivated crops presumes a good knowledge of the climatic requirements of the plants. Until recently the reaction of our vegetable plants to temperature and radiation are only known to a small extent (Krug, Fö1ster, Kling, 1974). For an economic calculation however, these data are of fundamental importance. Therefore in 1976 we started experiments with different vegetable crops to obtain these basic data. The vegetable crops tested at different set points of the temperature and different growing periods (radiation) are shown in table 1. The results of the experiments enable us to relate crop growth or yield to the main climatic growth factors (radiation and temperature) (see Krug, Liebig). We get data about the growing period - for example lambs lettuce to 2 g fresh weight/plant depending on the sowing date and the set point of the heating system as shown in figure 1. Or for vegetables with a continuous harvest we get information about the period from planting - 1 kg fruit/m2 and the total yield/m2 depending on the set point of the temperature and the time of planting. Results (average of the years 1976 – 79) are shown in table 2. It is to be seen that for the period from planting - 1 kg fruit/m2 the tomatoes in the range tested show a stronger reaction to the set point of the temperature than the cucumbers. The total yield (kg/m2) at the different temperatures differs only about 10 %.

Furthermore the experiments show, the temperature reaction of the vegetable plants varies with increasing age and radiation. Lettuce for example in the period from planting - 50 g fresh weight/plant reacts more strongly to the set points of the heating system than in the period from 50 – 200 g/plant (table 3). For optimal use of energy therefore the set points of the heating systems had to be adapted to the age of the plants and the natural radiation. From the results of our experiments and with regard to the present economic aspects we recommend the following set points for day and night temperature and ventilation for vegetable production in greenhouses in the conditions of Northern Germany (table 4). In addition to the period from sowing

Fölster, E. (1981). OPTIMIZING CROP PRODUCTION TO LOW COSTS IN PROTECTED VEGETABLE CULTIVATION. Acta Hortic. 115, 475-484
DOI: 10.17660/ActaHortic.1981.115.53
https://doi.org/10.17660/ActaHortic.1981.115.53

Acta Horticulturae