Unique method of establishing solar radiation saturation levels for greenhouse cucumber production

Abstract

Hydroponically grown cucumbers, Cucumis sativus L. 'Figaro F1.', were studied in Ohio. Two crops were grown; one in fall of 1994 and on in spring of 1995; in two compartments. One of the two compartments was shaded with 33%-shade (nominal) black cloth. Total plant dry weight samples were collected two times in each season while harvested fruit, plant height, leaf number, and leaf areas were collected on a weekly basis for 15 successive weeks. Total solar radiation at the plant level was integrated and recorded every 10 minutes. Results showed that solar radiation and daily/weekly dry weight gains were uncorrelated (R ²=0.03) and it was later assumed the plants were saturating at some much lower radiation level than anticipated. After constructing a series of potential optimum values for the mean hourly total solar radiation, the highest correlation coefficients were found for radiation levels below 100 W·m^-2 for both fall and spring crops.