Screening a cucumber crop during leaf area development reduces yield

In order to reduce heat energy consumption in greenhouse cucumber production, (transparent) screens may be used also during the day, particularly in the early growth phase when high temperatures are required to achieve rapid leaf area development. However, energy savings must be optimised against light reduction‐induced yield loss. For this reason, two experiments were conducted to quantify the effect on photosynthesis and growth of screening cucumber plants during their early growth phase, and on yield in the following generative phase. Screening with different light transmission coefficients was simulated using shading nets. Shading the plants during the first 5 weeks under Central European winter conditions reduced the leaf area by 0.40% per 1% reduction in photosynthetic active radiation (PAR). Moreover, potential leaf net photosynthesis decreased by 0.46% per 1% PAR reduction. A major impact was that the leaf dry matter content, leaf starch content and leaf sugar content of shaded plants diminished significantly. In the course of the following 2 weeks under full light, the leaf photosynthesis of the plants previously shaded recovered fully and the leaf area index rose to 3.3 m² m^?2, considered sufficient for optimal crop photosynthesis. The yield from plants previously shaded diminished slightly as early as from the first harvest week on. These yield losses increased further over the next few weeks, measuring approximately 0.8 kg m^?2 per 1 mol m^?2 day^?1 PAR reduction in the early growth phase. The effect of PAR on plant growth was proportional when relating the PAR integral over the entire experimental period to the total yield and to the total dry matter production, respectively.