Predicting The Coupling Effects Of Water And Nitrogen On External Quality Of Standard Cut Chrysanthemum In Solar Greenhouse

Water and nitrogen are important factors affecting the external quality of chrysanthemum. The aim of this study was to develop a simple model for the coupling effects of soil water and nitrogen on the external quality of standard cut chrysanthemum (Chrysanthemum morifolium) in order to optimize water and nitrogen management of the crop grown in solar greenhouses. Experiments of standard cut chrysanthemum (cv'Jinba') with different planting dates and levels of water and nitrogen treatment were conducted in a solar greenhouse located at Beijing (39°39'N,116°37'E) from 2006 to 2008. The plant based photo-thermal index (PTI), defined as the daily total photosynthetically active radiation received per plant multiplied by the daily average normalized thermal time, was used as a driving variable to describe the seasonal changes of the external quality traits. Effects of substrate water potential and accumulated leaf nitrogen content on the dynamics of plant height, number of leaves per plant, flower head diameter, peduncle length were quantified based on the experimental data. Based on these quantitative relationships, a model for predicting the coupling effects of water and nitrogen on the external quality indices of standard cut chrysanthemum was developed. Independent experimental data were used to validate the model. The results show that the model gives satisfactory predictions of the external quality indices of the standard cut chrysanthemum grown under different water and nitrogen supply conditions. The main research results are as follows:(1) Based on the plant based photo-thermal index (PTI), a simple model for predicting the effects of substrate water potential on the external quality of standard cut chrysanthemum grown in a solar greenhouse was developed. Independent experimental data were used to validate the model. The results show that the the model gives satisfactory predictions of the external quality indices of the standard cut chrysanthemum grown under different water supply conditions. The coefficient of determination (r2) between the predicted and measured results were, respectively,0.93 for plant height,0.92 for number of leaves,0.92 for flower head diameter and 0.90 for peduncle length. And the relative root mean square error (rRMSE) between the predicted and measured results were, respectively, 0.15 for plant height,0.13 for number of leaves,0.12 for flower head diameter and 0.11 for peduncle length.(2) Based on the plant based photo-thermal index (PTI), a simple model for predicting the effects of accumulated leaf nitrogen content on the external quality of standard cut chrysanthemum grown in a solar greenhouse was developed. Independent experimental data were used to validate the model. The results show that the the model gives satisfactory predictions of the external quality indices of the standard cut chrysanthemum grown under different nitrogen supply conditions. The coefficient of determination (r2) between the predicted and measured results were, respectively,0.95 for plant height,0.95 for number of leaves,0.93 for flower head diameter and 0.88 for peduncle length. And the relative root mean square error (rRMSE) between the predicted and measured results were, respectively, 0.14 for plant height,0.10 for number of leaves,0.11 for flower head diameter and 0.10 for peduncle length.(3) Based on the plant based photo-thermal index(PTI), using the substrate water potential and accumulated leaf nitrogen content as indicators of substrate water and plant nitrogen, respectively, a simple model for predicting the coupling effects of water and nitrogen on the external quality of standard cut chrysanthemum grown in a solar greenhouse was developed. Independent experimental data were used to validate the model. The results show that the the model gives satisfactory predictions of the external quality indices of the standard cut chrysanthemum grown under different water and nitrogen supply conditions. The coefficient of determination (r2) between the predicted and measured results were, respectively,0.92 for plant height,0.88 for number of leaves,0.84 for flower head diameter and 0.82 for peduncle length. And the relative root mean square error (rRMSE) between the predicted and measured results were, respectively,0.19 for plant height,0.17 for number of leaves,0.17 for flower head diameter and 0.14 for peduncle length.(4) The coupling coefficients were,0.9127 for growth rate of plant height,1.0614 for unfolding rate of leaf,1.0759 for flower head diameter,1.1213 for growth rate of peduncle length, and 0.9757 for PTI accumulated from planting date to the date of canopy closure and 0.8917 for PTI accumulated from planting date to the date of bud break, respectively. And the critical substrate water potential for standard cut chrysanthemum (Chrysanthemum morifolium'Jinba') grown in the solar greenhouse was determined as -20kPa, and the critical accumulated leaf nitrogen content for standard cut chrysanthemum (Chrysanthemum morifolium'Jinba') grown in the solar greenhouse was determined as-1.70 g m-2. The model developed in this study can be used for optimizing water management for standard cut chrysanthemum production in solar greenhouses.Using the planting date, planting density, initial plant height and number of leaves at planting date, air temperature at 1.5m above ground and PAR above canopy inside the greenhouse as input, our model can give satisfactory predictions of the examined traits of standard cut chrysanthemum grown under different levels of water and nitrogen conditions. Hence, our model can be used for decision making for precision management of water and nitrogen in greenhouse chrysanthemum production.