A study on leaf mineral nutrition diagnosis in Vaccinium uliginosum L. at fruit ripening stage in the Greater Khingan Mountains

Abstract: 【Objective】Leaf is very sensitive to mineral element supply, and the contents of mineral elements in the leaf represent the utilization of nutrients of the tree. Leaf nutrition diagnosis is an effective means to evaluate the nutrition status of the tree and provides an important basis to understand the fertilizer requirement of the tree. In this study, the theoretical basis for rational fertilization scheme for the cultivation of V. uliginosum was provided by determining suitable value of mineral element contents in the leaves and nutrition diagnosis was implemented to the orchards in the Greater Khingan Mountains.【Methods】The study was carried out in the Greater Khingan Mountains areas in China. V. uliginosum grown in four types of biotopes(meadow bog with soil layer, meadow bog without soil layer, undergrowth sparse forest, and slope land of forest edge)were used as the test the materials. A total of 66 samples of leaves and fruit were collected during the ripening stage in August 2018. Total nitrogen(N) in the leaf was analyzed using an elemental analyzer(EURO EA3000, Italy). Samples for total phosphorus(P)and potassium(K) analysis were digested using H2 SO4-H2 O2 and determined using an ultraviolet visible spectrophotometer(Thermo Fisher Evolution300, USA) and an atomic absorption spectrophotometer(Thermo Fisher 3500, USA), respectively. Calcium(Ca), magnesium(Mg), manganese(Mn), iron(Fe),copper(Cu) and zinc(Zn) were determined using an atomic absorption spectrophotometer after digestion using HNO3-HClO4(3∶1). Fruit yield of per unit area was collected, and the high-yield, middle-yield and low-yield regions were determined using K-means cluster analysis of SPSS 20.0. The suitable mineral element contents in the leaf of V. uliginosum were determined by probability grading method and the high-yield area method. Nutrient balance condition in the leaves of trees grown in the high-, middle-and low-yield regions was quantified by the nutrient imbalance index(NBIm), and the degree of mineral nutrient deficiency and the order of fertilizer requirement were diagnosed according to the deviation from optimum percentage(DOP).【Results】(1) In the wetland biotope of Greater Khingan Mountains region, the yield of V. uliginosum was the highest(high yield region); the V. uliginosum growing in the undergrowth sparse forest biotope had a medium productivity(middle-yield region); and the V. uliginosum growing in the forest edge slope biotope had the lowest yield(low-yield region).(2) The average content of major elements in the leaves in descending order was N > K > P > Ca > Mg; the average content of trace elements was in the order of Mn > Fe > Zn > Cu. The coefficient of variation of the contents of the nine mineral elements was between 8.95% and 36.10%, and the largest was Zn, and the smallest was N. Except for N with weak spatial variation, all the other elements showed moderate spatial variation. The overall variation degree of the 9 element contents was in the order of Zn>Fe>Ca>P>Mg>Mn>Cu>K>N. The contents of N, P, K, Fe, Mn and Cu in the leaves of V. uliginosum in the high-yield regions were lower, and the contents of Ca, Mg and Zn were higher than those in the low-and middle-yield regions.(3) There were positive correlations between Zn and Mg(p < 0.01), P and Fe, and Ca and Mg(p<0.05) in the high-yield regions. There were positive correlations between Mg and Zn(p <0.01)and between P and Mn(p < 0.05), and negative correlations between P and Ca and between K and Mg(p <0.05) in the middle-yield regions. There were a positive correlation between Fe and Cu(p < 0.05) and negative correlations between Ca and Cu and between Mg and Mn in the low-yield regions(p < 0.05). At the same time, there was a significant positive correlation between Zn and yield(p < 0.05), while a very significant positive correlation between K and yield(p < 0.01). The results showed that the synergetic and antagonistic effects of mineral elements were coexisting in the middle-and low-yield regions, while in the high yield-regions, synergetic effect dominated, and the importance of Zn and K to the productivity of V. uliginosum was revealed.(4) The suitable value of N content in the leaf of V. uliginosum was17.90 to 19.67 g·kg-1, P 3.56 to 4.60 g·kg-1, K 5.22 to 6.13 g·kg-1, Ca 3.13 to 3.88 g·kg-1, Mg 1.90 to 2.27 g · kg-1, Fe 109.19 to 158.85 mg · kg-1, Mn 262.05 to 311.14 mg · kg-1, Cu 5.44 to 6.42 mg · kg-1, and Zn17.33 to 24.87 mg · kg-1.(5) According to the nutrient imbalance index(NBIm), the nutrient balance of V.uliginosum leaves in the high-yield regions was better than that in the middle-and low-yield regions.DOP diagnosis showed that N, Fe and Mn in the leaves of V. uliginosum in the high-yield regions were low; P, K and Cu were deficient; Mg was high, and Ca and Zn were excessive. The order of fertilizer requirement was P > K > Cu > Mn > Fe > N. P, Ca and Mg in the leaves of V. uliginosum in the middleyield regions were low, Zn was deficient, N, Mg and Cu were high, and Fe was excessive, and the order of fertilizer requirement was Zn>P>Ca>Mg. Mg in the leaves of V. uliginosum in the low-yield regions was equilibrium; N and Ca were low; the Zn was deficient; K, Mn and Cu were high; and P and Fe were excessive. The order of fertilizer requirement being Zn>N>Ca.【Conclusion】The yield can be further increased by applying N, P, K, Fe, Mn and Cu fertilizers in high production areas; the yield in the middleyield areas could be increased by P, Ca, Mg and Zn application; and N, Ca and Zn fertilizers are needed in the low-yield areas for yield increase. All the areas had rooms for yield improvement.