Abstract:

【Objective】The aim of this study was to research and construct a diagnosis system for mineral nutrients in the leaves of Duweiwendan Pomelo (Citrus grandis (L.) Osbeck. cv. Duweiwendan), so as to deduce a shared optimization method for the mineral nutrition balance diagnosis and recommendation integrated system (BDRIS).【Method】From 2016 to 2018, 20 representative orchards with different managers were selected in the production area of Xianyou county in Fujian Province. 200 individual leaf samples and 8 660 single fruit samples were collected, and 48 pairs of heteromorphic fruits (H-FSI normal fruit and L-FSI cracking fruit) with the same axillary growth were collected, and the contents of N, P, K, CA, Mg, Cu, Zn, Fe, Mn, B, Mo and S elements in leaves and pericarps were measured. The internal and external quality of fruits and the width of top crack were also measured. Based on the difference between the total soluble solids (TSS) and the crack average index (FCAI) of the fruit, a BDRIS diagnosis system for major mineral elements and a diagnostic criterion for critical values of trace elements were constructed.【Result】According to the difference analysis of TSS, rich N, P, K and lack of Mo significantly reduced TSS. According to the FCAI12 difference analysis, except that the suspected B toxicity excess (>177 mg·kg^-1) significantly increased the fruit cracking, no significant causal relationship was found between other mineral elements and the fruit cracking, but no evidence of fruit cracking caused by B toxin was found; in addition, no significant difference was found in the paired comparative analysis of the elements in pericarp of twin shaped fruit. The distribution of N, P, K, CA, and Mg elements in the selected samples met the requirements of BDRIS modeling, P (normal) ≥0.12. According to BDRIS construction, it was found that the tree age was significantly negatively correlated with BDRIS index, and significantly positively correlated with TSS, that is to say, with the growth of tree age, the mineral nutrition of tree body tended to the origin of nutrition balance, and the fruit quality was also better, which gave a new explanation of the common sense of fruit tree cultivation that “the older the tree is, the sweeter the fruit will be”. BDRIS had no significant correlation with FCAI12; by correlation method, only when K was in morbid excess could thicken the peel, so as to reduce the cracking, which had no practical significance in correcting fruit cracking in production. It was suggested that the diagnostic standard of critical value of mineral elements in leaves should be “elements (over)”: N (<2.29%; 2.41%- 2.87%; >2.99%), P (<0.09%; 0.10%-0.14%; >0.15%), K(<1.17%; 1.39%-2.24%; >2.46%), Ca (<1.74%; 2.26%-4.21%; >4.72%), Mg (<0.20%; 0.24%-0.41%; >0.46%), Cu (<4 mg·kg ^-1; 6-25 mg·kg^-1; >30 mg·kg^-1), Zn (24-40 mg·kg^-1), Fe (60-140 mg·kg^-1), Mn (25-140 mg·kg^-1), B (<15 mg·kg^-1; 30-65 mg·kg^-1; >150 mg·kg^-1), Mo (<0.05 mg·kg^-1; 0.1-1.0 mg·kg^-1), and S (0.2%-0.4%). The shared optimization algorithm of BDRIS diagnosis parameters Mean, Std and r was provided to effectively expand the application scope of BDRIS.【Conclusion】In this study, the BDRIS diagnosis system for major mineral elements and the diagnostic criterion for critical values of trace elements were established based on the high-yield and high-quality population. In addition, there was no significant correlation between fruit cracking and the plant mineral nutrition.

Key words: Duweiwendan pomelo, mineral nutrients, appropriate standard, BDRIS