| Lettuce is one of main soilless cultural of vegetable, it is very popular this year. Our research group had researched the effects of temperature and PAR on lettuce growth, and so on, used environment factors to simulated lettuce growth program empirically. Based on their research, two varieties of lettuce (cv. Hongnong and cv. Lvling) were investigated, the relationships between environment factors and the growth and development of lettuce were also investigated in this study, some models were established to simulate the photosynthesis and dry matter production program. Some spectral and physiological characteristics were measured in this paper, spectroscopic technology was used to analysis nitrogen nutrition of lettuce under hydroponic conditions. The parameters as length, width and leaf areas of individual leaf were collected many times in the whole growth program of lettuce, regression analysis method was used to build models between the parameters and individual leaf area, and independent data was used to validate the models. The main results as following:1.Based on the existed models, the PAR and temperature data of April to June of 2009 were collected, the production of PAR and effective temperature was taken as the parameter to establish the model of leaf area for per-plant. According to the leaf area model, the PAR was used as parameter to establish the model of photosynthesis and dry matter accumulation. The data of weather and six varieties lettuce cultivated with soil in plastic tunnels were used to validate models of leaf area and photosynthesis and dry matter accumulation, all of the correlation coefficients between observed and simulated value were above 0.9, and the RE (relative prediction error) values were relative low, the models developed in this study can give satisfactory predictions.2. The lettuce variety of "Hongnong" was used to investigate the effects of nitrogen on some physiological and spectral characteristics of lettuce. In this study, the standard lettuce nutrient solution was control, eight different nitrogen concentrations of solution as 1/16-N,1/8-N,1/4-N,1/2-N,3/2-N,2-N,5/2-N and 3-N were used. The SPAD values, chlorophyll (a+b) contents, nitrogen contents were measured, the results showed that:the correlation coefficients between SPAD values and chlorophyll (a+b) contents, chlorophyll (a+b) contents and nitrogen contents, SPAD values and chlorophyll (a+b) contents were 0.95,0.92,0.95, respectively, SPAD values can be used to estimate nitrogen nutrient condition of lettuce simply. This study collected the spectral reflectances of lettuce leaves cultivated with 1/4-N,1-N and 3-N solution at different growth stages, the differences of reflectances of wavelength between 750 nm and 950 nm was significant in middle growth stage. So, nitrogen spectral estimation and analysis of hydroponic lettuce can be made in middle growth stage between 750 nm and 950 nm.3. Leaf lengths and widths and Leaf areas of "Hongnong"and "Lvling" were measured for many times after planting, length, width and the production of length and width and so on were used as parameters, regression analysis were carried out between these parameters and leaf areas, the power function equation LA=0.654X0.6513 which the production of length and square of width (X=LW2) as factor was chosed, the data of lettuce cultivated with different shading, different nitrogen concentrations and six varieties was used to validated the equation, the results showed that this simulated values were closed to observed, this model can estimate the leaf area of lettuce exactly. |
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