Effect of diurnal temperature alternations on plant growth and mineral composition in cucumber, melon and watermelon.

This study investigated plant growth and mineral composition in three cucurbit crops of cucumber, melon and watermelon grown under four constant day and night temperatures (DIF) of 25/15, 22.5/17.5, 17.5/22.5 and 15/25 degrees C. As expected, the growth and development of the three cucurbits were strongly temperature dependent. Plant height and relative chlorophyll content of the three crops decreased linearly along with decreases in day temperature. Leaf and stem dry weight decreased significantly under negative DIFs and the lowest value was in DIF plot 15/25 degrees C. However, the negative DIF of 15/25 degrees C resulted in increased content of all mineral nutrients (N, P, K, Ca, Mg, Mn and Cu) in both the leaf and stem of the three cucurbit crops. The data suggest that a negative DIF as low as 15/25 degrees C may be beneficial to greenhouse-grown cucurbit crop producers, by controlling vegetative growth that facilitates crop management, with no negative effect on or enhancement of the uptake rates of mineral nutrients which are required to determine yield and fruit quality at the production stage. Effective utilization of diurnal temperature alternations is one strategy that can be used to reduce energy consumption in greenhouses.