Modeling net photosynthesis of greenhouse cucumber compared to measured dry weight

Abstract

This study was done for two growing seasons (Fall 94 and Spring 95) in order to compare the actual total dry weight (TDW) of cucumber, Cucumis sativus L. cv. Figaro F1, with the calculated net photosynthesis. The experiment took place in two compartments, double polyethylene greenhouse at The Ohio Agricultural Research and Development Center, the Ohio State University, Wooster, Ohio. One of two compartments was shaded with 33%-shade (nominal) black net. Sixteen of 204 plants were marked in each compartment for vegetative and reproductive data collection. Plant height, leaf-blade length and width, internode length, and fruit diameter and length were measured weekly. Fruits were harvested and weighed as soon as they reached marketable size. Leaf area and fruit fresh weight were calculated from their dimensions. Dry weight samples of entire plant parts were collected two times in each season to calibrate measured estimates. TDW was the sum of vegetative (leaf, stem and root) and productive dry weights (flowers and fruits). Solar radiation, air temperature and CO<inf>2</inf> were measured and averaged over 10-minute intervals. Optimum values for the mean hourly total solar radiation of 168 and 175 W· m ^-2 were determined with correlation coefficients between actual and calculated TDW of 0.82 and 0.85 for fall and spring crops, respectively. Using saturation values for hourly total solar radiation of 168 and 175 W· m^-2 for the fall and spring season, respectively, gave the best predicted dry weight rate compared to using the actual radiation or any other assumed saturation values. A conversion factor for estimating TDW from net photosynthesis that was a function of leaf area index and night temperature is suggested.