Relationships Between Fruit Quality And Soil-plant Nutrients Of Nanfeng Tangerine And Regulation By Fertilization Application

The nutrient factors influencing poor fruit quality of Nanfeng tangerine(Citrus reticulata Blanco cv. Kinokuni) were confirmed by correlation analyses between fruit quality parameters and nutrients in soils, leaves and fruit from a 5-year investigation in Nanfeng county. A 3-year field experiment was also conducted in a red soil orchard to focus on fruit mastication quality and sourness. The main results were as follows:1. Tangerine mastication quality was significantly negatively related to Membranes toughness and Firmness of tangerine pulp. Compared with Shatang tangerine(ST, Citrus reticulata Blanco cv. Kinokuni) and Ponkan(PG, Citrus reticulata Blanco cv. Kinokuni), fruit pulp of Nanfeng tangerine(NM, Citrus reticulata Blanco cv. Kinokuni) was inferior mastication quality, and its dietary fiber content was significantly higher. The segment membrane cells were closer, and more isotropic and homogeneous in NM than those in ST and PG. There was evident destruction in the middle lamella area of ST and PG segment membranes, exhibiting empty regions. However, the cell wall of NM fruit segment membranes consisted of tightly packed fibrous substances and conspicuous middle lamella. The dense structure formation of fruit segment membrane cell walls with tightly packed fibrous substances and narrow gaps could be the key mechanism leading to inferior mastication characteristic of tangerines.Shear force and work were determined to measure the mastication quality of tangerine, as shear force > 15 N or shear work > 0.17 J was worse mastication quality, 15 N > shear force > 11 N or 0.17 J > shear work> 0.13 J was in middle quality, and 11 N > shear force or 0.13 J > shear work was better mastication quality.2. Fruit quality parameters of Nanfeng tangerine were 21 N for shear force, 0.22 J for shear work, 30 g in fruit weight, 76% edible ratio, 0.9% titratable acid, 15% TSS and 230mg/kg Vc. Principal component analysis showed fruit weight, shear force and shear work belonged to a mastication quality factor, edible ratio and TA belonged to a sour quality factor, TSS and TTS/TA belonged to a flavor quality factor, and Vc belonged to a nutritional quality factor.There were significant relationships between the various fruit quality parameters. There were positive correlations between total soluble solids(TSS) and Vc, Vc andtitratable acid(TA), TA and TSS, shear force and work, shear force and fruit weight, shear force and fruit weight, shear force and edible ratio, shear work and edible ratio. In contrast there were negative correlations between TSS/TA and Vc, TSS/TA and TA, fruit weight and TSS, fruit weight and Vc, fruit weight and TA, shear force and TSS, shear work and TSS.3. The mastication quality factor was significantly related to the fruit N and P concentrations. The segment shear force and shear work were decreased exponentially as the peel, pulp and fruit N concentrations increased. In addition, shear force, shear work and fruit weight increased as quadratic functions with the peel P(above 0.07%), pulp P(above 0.15%) and fruit P(above 0.13%) concentrations. In the case of edible ratio, there were trends of initial increases followed by decreases with pulp N and P concentrations increasing as quadratic functions. TA was significantly positively correlated with fruit K concentrations. The flavor quality factor was significantly related to the fruit P and K concentrations. TSS decreased with the pulp P concentrations following an exponential function. TSS/TA was decreased with increasing fruit P concentrations when fruit P concentrations was below 0.13%, and decreased with increasing peel, pulp and fruit K. Vc concentrations decreased with increasing fruit N and P concentrations, but increased with increasing fruit K concentrations.4. The mastication quality factor was significantly related to the leaf N and K concentrations. The segment shear force and fruit weight increased significantly with increasing leaf K concentrations, and shear work decreased with increasing leaf N concentrations. The sour quality factor was significantly related to leaf Ca, since TA decreased with increasing leaf Ca while the edible ratio initially decreased then increased with increasing the leaf Ca concentrations. The flavor quality factor was significantly related to leaf N, P, K and Ca concentrations. TSS increased with increasing leaf N concentrations(above 2.5% N), but decreased with the leaf N below 2.5% N, and increased with increasing Ca concentrations. TSS/TA increased with increasing leaf N concentrations, but decreased with increasing leaf P concentrations. Vc concentrations decreased with increasing leaf Ca and N concentrations(below 3.3% N), but increased with increasing leaf N concentrations(above 3.3% N). Based on leaf nutrient status and the correlation relationships between fruit quality and leaf nutrients, N, K and Ca were determined to be the factors on influencing poor fruit quality of Nanfeng tangerine.5. Soils overall had low p H and available N, a lack of exchangeable Ca, exchangeable Mg and available B, and a surplus of available P and K.Fruit weight was significantly negatively related to soil available N, K and Mg. There were significant positive relationships between TSS and soil available N, P and K, but negative relationships to soil p H and available Mn. Vc concentrations was significantly related to soil available Mg, Fe and Zn. Segment shear force was significantly negatively related to soil available N and B, and shear work was also significantly negatively related to soil available B.N, Ca and Mg concentrations were significantly positively related between soil and leaf. Soil available K significantly was positively related to leaf N, Mg and Cu, and soil available Ca and Mg were significantly negatively related with leaf K.6. Shear force, shear work and titratable acid were significantly decreased by application of N to Nanfeng tangerine. Leaf N concentrations were increased by applied N while Vc was showed an initial increase and then decreased with increasing rate of N applied. Compared with the N1K2(0.45 kg N and 0.50 kg K2 O per tree) treatment, titratable acid was significantly reduced in the N2K2(0.68 kg N and 0.50 kg K2 O per tree) treatment. K concentrations were increased in leaves, peel and pulp by higher K application rates, and production was increased. Compared with the N1K1(0.45 kg N and 0.45 kg K2 O per tree) treatment, the N1K2(0.45 kg N and 0.50 kg K2 O per tree) treatment improved the mastication and flavor quality. However fruit mastication quality was worse and the TSS/TA was reduced in the N3K2(0.90 kg N and 0.50 kg K2 O per tree) treatment, in which the most N and K were applied. In conclusion, the optimal application amounts of N and K in practice are 0.68 kg N and 0.5 kg K2 O per tree.7. The fruit pulp’s shear force and insoluble dietary fiber(IDF) contents of the Ca and Mg applied treatment were significantly lower than those of the other treatment, and leaf potassium K was lower, whereas the leaf Mg concentration was higher in the Ca and Mg applied treatment than in the other treatments. We concluded that the fruit pulp mastication characteristics were significantly related to dietary fiber of the fruit pulp, so the mastication characteristic of Nanfeng tangerine fruit pulp could be improved by combining 0.68 kg N, 0.31 kg P2O5 and 0.50 kg K2 O fertilization rates with 500 g lime and 100 g magnesium oxide per tree.