Quantifying The Effects Of Nitrogen On External Quality Of Standard Cut Chrysanthemum In Solar Greenhouse

Nitrogen is an important nutrient affecting growth, development and formation of external quality. The aim of this study is to quantitatively investigate the effects of nitrogen on external quality of solar greenhouse standard cut chrysanthemum. Experiments of standard cut chrysanthemum (Chrysanthemum morifolium. 'Shenma') with different planting dates and different levels of nitrogen application rates were conducted in a solar greenhouse in Beijing during October, 2005 and July, 2006. Effects of the accumulated leaf nitrogen content at bud showing stage on the dynamics of the quality indexs (plant height, stem diameter, leaf number, diameter of flowerhead, length of flowerneck) were quantified based on experimental data. Based on these quantitative relationships, a model for predicting the effects of nitrogen on external quality of standard cut chrysanthemum in solar greenhouse was developed. Independent experimental data were used to validate the model. The results showed that the model developed in this study can predict the external quality indexs of plants of the solar greenhouse standard cut chrysanthemum. The detailed results are described as follows:(1) The analysis of variance of effects of nitrogen on external qulity of standard cut chrysanthemum 'shenma' in solar greenhouse. The results showed that, in the range of nitrogen available in the soil during experimental season (57.2-160.2 kg·hm^-2), there were no effect of nitrogen on plant height and leaf number and obvious effect of nitrogen on stem diameter, diameter of flowerhead, length of flowerneck and fresh weight.(2) Quantifying the effects of nitrogen on quality index of standard cut chrysanthemum in solar greenhouse. The integrated photo-thermal index, the product of thermal effectiveness, PAR and day length (PTEP), was used to describe the changes of each external quality index. Effects of the accumulated leaf nitrogen content at bud showing stage on the dynamics of the quality indexs were quantified based on experimental data. Based on these quantitative relationships, a model for predicting the effects of nitrogen on external quality of standard cut chrysanthemum in solar greenhouse was developed. The result showed that the relation between the stem diameter, diameter of flowerhead and length of flowerneck of cut chrysanthemum and PTEP after transplanting were described as follows:DS=DS_h*(1-exp(-a*(PTEP+89)/DS_h))When the accumulated leaf nitrogen content at bud showing stage (N_l) increased, the increasing rate of stem diameter (a) decreased, the increasing rate of flower head diameter (DF_r) and the increasing rate of the flower neck length (LN_r) increased. The relation between the stem diameter at harvest (DS_h) and the increasing rate of stem diameter and the intercept of the changing flower head diameter (b) and the increasing rate of flower head diameter and the length of flower neck at harvest (LN_h) and the increasing rate of length of flower neck and the accumulated leaf nitrogen content at flower bud showing stage (N_l) can be described by the funcations as follows:DS_h=7.25*(1-exp(-28.13*(N_L-0.44)/7.25)) R²=0.98 SE=0.047 a=0.149/(1+exp(0.036*N_L/0.149)) R²=0.92 SE=0.0009b=4.6*(1-exp(-21.53*(N_L-0.78)/4.6)) R²=0.99 SE=0.061DF_r=0.023*(1-exp(-0.071*(N_L-0.60)/0.023)) R²=0.99 SE=0.0003 LN_h=2.2*(1-exp(-6.68*(N_L-0.55)/2.2)) R²=0.94 SE=0.058LN_r=0.047*(1-exp(-0.13*(N_L-0.42)/0.047)) R²=0.98 SE=0.0006Independent experimental data were used to validate the model, the results showed that the coefficient of determination (R²) between the simulated and measured value of stem diameter, diameter of flower head and length of flower neck of the standard cut chrysanthemum plants based on the 1:1 line were 0.96, 0.97, 0.98, respectively; and the relative prediction error (RSE) between the simulated and measured value of stem diameter, diameter of flower head and length of flower neck of the standard cut chrysanthemum plants were 3.04%, 10.92%, 9.22%, respectively.(3) The confirmation of fitting accumulated leaf nitrogen content at flower bud showing stage, and the relationship between that and nitrogen available in soil during experimental season. Based on the quantitative relationship between accumulated leaf nitrogen content at flower bud showing stage and the external quality indices, and the relation between the accumulated leaf nitrogen content at flower bud showing stage and the nitrogen available in soil during experimental season, the optimal accumulated leaf nitrogen content at flower bud showing stage was determined as 1.62g·m^-2 (the leaf nitrogen concentration was 4.7%), and the corresponding optimal nitrogen available in soil during the chrysanthemum growing season was determined as 125.5kg·hm^-2 (the corresponding nitrogen concentration in soil was 56mg·kg^-1).The model developed in this study can predict the value of stem diameter, diameter of flower head and length of flower neck of the standard cut chrysanthemum plants grown in the solar greenhouse satisfactorily using planting date, nitrogen content with quick result in the soil, quantum of nitrogen fertilized, and the information of air temperature and radiation in each hour, as input, hence, can be used for optimization nitrogen management for solar greenhouse standard cut chrysanthemum production.