Simulation model of cucumber healthy indexes based on radiation and thermal effectiveness

In order to improve the predicting ability of healthy degree of cucumber seedlings, the relationships of both temperature and photosynthetically active radiation (PAR) with the root-shoot ratio, G value（the proportion of the total dry weight to the numbers of days of seedling）and healthy index of greenhouse cucumber was investigated. Using two different ecotypes of cucumber varieties ‘Jinchun No. 4’ and ‘Deltastar’ as tested materials, the models of cucumber healthy indexes based on thermal effectiveness and PAR (TEP) were developed through different sowing date test and regression analysis, and models were further verified by independent test data. The results showed that root-shoot ratio was poor fitting with TEP, and G value simulation model had low compliance between simulated and observed values, unsuitable for simulatiion taking photothermal product as a variable in this experiment. Healthy index simulation model was well fitting with TEP. The root mean squared error (RMSE) between the simulated and measured values of healthy index was 0.0040, showing a high predictive accuracy; and the determination coefficients(R2) between the simulations and measurements for the healthy indexes were 0.9854（Jinchun No. 4）and 0.9761 (Deltastar) respectively. They all passed F test, and there were extremely significant level, showing an excellent conformity between simulated and measured values. Based on the results it is concluded that the healthy index simulation model can give a satisfactory prediction of healthy degree of cucumber seedlings. The model developed in this study is applicable with few parameters and can provide an effective method to predict the healthy degree of cucumber seedlings and decision support for the temperature and light and temperature management of greenhouse cucumber seedling cultivation.