| In order to find out the changes of nutrient element contents of N (nitrogen), P (phosphorus), K (potassium) and their correlations in different types of leaf shoots of four significant growing phenophase (spring shoots budding period, summer shoots budding period, autumn shoots budding period and fruit maturity), we collected leaves from Newhall navel orange(Citrus sinensis Osbeck) trees on10years old trifoliate orange (Poncirus trifoliata (L.) Raf.) root stocks. Besides, we used hyperspectral imaging system to extract the spectral information and analyse characteristics of citrus leaves so that we could obtain the optimal pretreatment methods and leaf types to establish prediction models. Minewhile, it is heplful for us to establish a real-time monitoring system to guide reasonable fertilization.The main results of the study were as follows.1. N, P and K content changes in Newhall navel orange LeavesWhen the spring shoots, summer shoots and autumn shoot leaves turn green, the summer shoot leaves had the highest nitrogen content(3.19%), spring shoot leaves was3.13%and autumn shoot leaves was the lowest (2.73%). The nitrogen content and its deceleration of summer shoot leaf had the biggest decline, decreasing by10.97%from autumn shoots budding period to fruit maturity period. Autumn shoots leaves had the highest P content (0.21%), spring shoot leaves was0.20%, summer shoot leaves was the lowest (0.18%). Summer shoot leaf nitrogen content and deceleration had the biggest decline, from summer shoots budding period to fruit maturity period decreased by20%. Summer shoots leaves had the highest K content (2.03%), spring shoot leaves was1.76%, autumn shoots leaves was the lowest (1.02%). The K content and deceleration of summer shoots leaves had the biggest decline, decreasing by39.9%from autumn shoots budding period to fruit maturity period. N, P and K content of the20-month-old spring flush leaves in the nutritional diagnostic criteria were also suitable for low volume or moderate levels, indicating that spring shoots leaves had the function of nutrition output with two consecutive anniversary, it should be noted in the cultivation and management of protection leaves.2. The correlation of N, P and K content of different types and periods leaves in citrus leaves.(1) The correlation of N, P and K content in identical types leaves:The N, P, K content had multiple correlations in various kinds of leaves which bud current year. The N, P, K content showed a significant positive correlation among each other in summer shoots leaves on autumn budding period. P had significant correlation with N and K in spring shoots leaves during the fruit mature period, the correlation coefficient was0.43**and0.50**respectively. Summer and autumn shoots leaves’N content had significant correlation with P and K, P also had positive significant correlation with K. This result shown that the nutrient elements of N, P, K had positive correlation in identical types leaves of citrus.(2) The correlation of N, P and K content in different types of leaves during the same period:The N, P, K contents in different citrus leaf types affected each other in the same period. For example:in autumn budding period, the K content of spring shoots showed a positively significant correlation with the N and K contents of summer shoots, which were0.50and0.55respectively. The spring and summer shoots showed a significant relationship with each other, which were0.35. In fruit maturity period, the K content of spring shoots showed a significant relationship with N, P, K content of summer shoots, which were0.40,0.32and0.64respectively; The P contents of summer shoots were significantly positively correlated with the N contents of the autumn shoot leaves, which were-0.35; The K contents of summer shoots were significantly correlated with the K contents of the autumn shoot leaves, which were0.40. The results indicated that the previous period of leaves may significantly influence the later budding leaves in different types of leaves on the same period.(3) The correlation of N, P and K content in different types and different period citrus leaves:The K contents of spring shoot leaves on autumn budding period had significantly positively correlation with the spring and summer shoot leaves in fruit mature period, the correlation coefficient were0.50**and0.37*. The N contents of spring shoot leaves on autumn shoots period was significantly negatively correlated with the P contents of summer shoots leaves in fruit mature period, the correlation coefficient were-0.32*; The N and K contents of summer shoots leaves in autumn budding period were significantly positively correlated with the K contents of spring shoot leaves the fruit mature period, the correlation coefficient were0.46**and0.52**respectively. The results indicated that the nutrient elements of citrus leaves affected each other in different types and different periods. So, we must consider long-term effect and interwork at the time of citrus fertilizer application.(4) N and P content of last year’spring shoots leaves on spring budding period, N content of last year’spring shoots leaves on summer and autumn budding period, N and K content of summer shoots leaves on fruit mature period, N content of autumn shoots leaves on fruit mature period, these samples collecting periods have a±5%range (0.932-1.073) with standard sample collecting period. So we could use these leaves uncover citrus’nutritional status3. N、P and K spectral diagnosis of citrus leaves(1) The best type of leaf used for N diagnosis was the current spring shoots in the summer leaves budding period, The PLS model for N with Rc=0.790, RMSECV=0.269, Rp=0.798, RMSEP=0.166, which was established by the spectral pretreatment of standard normal variable (SNV).(2) The best type of leaf used for P diagnosis was the current spring shoots in the autumn leaves budding period, The PLS model for K with Rc=0.864, RMSECV=0.009, Rp=0.798, RMSEP=0.012, which was established by the spectral pretreatment of SNV.(3) The best type of leaf used for K diagnosis were the last year’s spring shoots in the autumn leaves budding period, The PLS model for K with Rc=0.782, RMSECV=0.250, Rp=0.793, RMSEP=0.299, which was established by the spectral pretreatment of SNV.4. SPAD spectral diagnosis of citrus leavesSPAD reflect the level of leaf chlorophyll content and photosynthetic capacity. The results showed that:the best leaf type for SPAD spectral diagnosis was spring shoot of current year on the autumn shoot budding period. The PLS model for SPAD with Rc=0.965, RMSECV=0.659, Rp=0.924and RMSEP=0.1.616, which was pretreated by standard normal variable (SNV).5. Hyper spectral prediction of chlorophyll components of citrus leavesCitrus leaves contain a variety of chlorophyll components, this study had a research of chlorophyll a and b contents. The results showed that:the spectral data were preprocessed by multiple scatter correction method (MSC) and the model based on least squares support vector machine (LS-SVM) to predict the content of chlorophyll a was better, the Rp was the largest (0.8983), RMSEP was the minimum (0.1404). Using standard normal variable (SNV) preprocessing, the LS-SVM model similarly had a better prediction of the content of chlorophyll b, Rp was0.9123and RMSEP was0.0426. |
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