EVALUATION UNDER COMMERCIAL CONDITIONS OF A MODEL OF PREDICTION OF THE YIELD AND QUALITY OF CUCUMBER FRUITS

A mechanistic model was developed to predict the weekly fresh weight y ield of cucumber fruits and the fresh weight and developmental stage o f the individual fruits at harvest. The latter two being major criteri a of fruit quality. The model consists of modules for greenhouse light transmission, light interception by the crop, leaf and canopy photosy nthesis, assimilate partitioning, dry matter production, fruit growth, fruit dry matter content and fruit harvest. A sensitivity analysis sh owed the total yield to increase with increasing radiation, CO2 concen tration and temperature. The harvest strategy of the grower (frequency of harvesting and threshold weight for harvest) had a great impact on simulated fruit size and fruit developmental stage at harvest. The la tter was lowest in summer time, which may have consequences for the sh elf life of the fruits. The model was Validated by comparing simulatio n results with production data of 10 commercial growers in 1996 and 14 growers in 1997 (January-May). Input data used for validation were we ek numbers of planting and removing the crop, weekly data on global ra diation outside the glasshouse and glasshouse air temperature and dayt ime CO2 concentration. The weekly harvest of total fresh weight averag ed over all growers was simulated well by the model. The average error of the weekly prediction of the fresh weight yield was 12.6%, while t he error of the annual yield was only 0.3% in 1996. The simulated aver age fruit size corresponded reasonably well with growers' data, showin g an average weekly error of 6.6%. The accuracy of prediction of cucum ber yields largely depends on accuracy of the weather prediction. (C) 1998 Elsevier Science B.V. All rights reserved.