The effects of propagation temperature, CO2concentration and early post-harvest night temperature on the fruit yield of January-sown cucumbers

Abstract

SummaryGrowth and fruiting responses of four January-sown cucumber cultivars to two propagation temperatures (day 21°C, night 19°C and day 24°C, night 17°C), three levels of CO2 enrichment (400, 1000 and 1600 vpm) and three stages of post-planting night temperature reduction (0, 3 and 6 weeks after first harvest) were examined in a glasshouse experiment. Early (4-week) fruit yield and monetary returns were significantly increased when the higher day temperature treatment was combined with the 1600 vpm CO2. The early advantage was soon lost and after 20 weeks harvesting there were no differences between the propagation temperature treatments. After two weeks of CO2 treatment total dry weight of aerial parts, leaf area and stem length were increased by 88, 73 and 69% respectively when the CO2 level was raised from 400 to 1000 vpm. A further rise from 1000 to 1600 vpm produced no further increases indicating that 1000 vpm is probably near the optimum concentration for growth at the temperatures applied. In the early (4-week) harvest period, fruit yield and gross monetary returns increased by c. 30% when CO2 was raised from 400 to 1000 vpm but there was little or no difference between plants grown in 1000 or 1600 vpm. The early yield advantage from enrichment at 1000 vpm CO2 was maintained throughout the season (20 weeks of harvesting). The most economic level of CO2 enrichment for January-sown cucumbers was c. 1000 vpm. Lowering night temperature at the start of harvesting reduced fruit yield and monetary value compared with lowering the temperature 3 or 6 weeks after fruit picking commenced. The estimated savings in fuel from this treatment were too small to offset the loss of revenue from the crop. The most economic time to reduce night temperature in the January-sown crop was 3 weeks after the start of harvesting.