Analyses of the soil and tree nutrition and fruit quality of Satsuma mandarin in orchards at different latitudes in Hunan province

Abstract：【Objective】The soil nutrition, leaf and fruit nutrition and fruit quality of Satsuma mandarin in orchards at different latitudes in Hunan province were analyzed in order to provide reference for soil management in orchards.【Methods】Soil nutrients in 147 Satsuma mandarin orchards in north, central and south Hunan, and leaves nutrition and fruit quality in these orchards were analyzed for 6 consecutive years, from 2011 to 2016. When fruit matured, soil samples were collected from 15-20 sampling points arranged in an S shape in each orchard and leaf and fruit samples were taken at the same time from positions evenly distributed in the tree canopy. Leaf blades at the 2 nd or 3 rd node from the top of the current season spring shoots were sampled. Soil samples at depths of 20-40 cm were taken 10 cm inward from the drip line at two opposite sides of the tree. The relationships among the soil nutrient, leaf nutrition and fruit quality were analyzed in order to find problems of soil nutrition in orchards at differ-ent latitudes.【Results】All the soil p H values in the orchards in north, central and south Hunan were lower than the appropriate range (5.5-5.6) . The percentage of orchards with appropriate soil pH in the three regions was only 8.3%-19.0%. The organic matter content was generally suitable in these orchards. Available Fe, Mn, Cu, Zn, Ca, Mo and Mg in the soils in most of the orchards were appropriate or excessive, while the contents of alkaline N, available P and K were low in north, central and south Hunan, with a percentage of N deficient orchards of 51.7%, 80.6% and 83.0%, respectively. 72.7%-100% of the orchard had a soil effective B below the appropriate value. P and B in the leaves were in slight shortage and N, K and Zn were insufficient. The percentage of the orchards with Ca and Mg deficiency was 85.0%-88.7% and 81.3%-96.2%, respectively. 100% of the orchards showed deficiency of Mo. The average content of Fe was 135-178 mg · kg-1 and the average content of Mn 68-90 mg · kg-1, both being excessive. Soil p H, available N, K, Fe, Cu, Zn and Mg were the highest in northern Hunan, and the organic matter, available P, Mn, Ca, B and Mo were the highest in the south Hunan. No orchards in central Hunan had soils with suitable proportion of nutrients. The regression equation of fruit K content vs latitude was y=-0.024 x+1.231. There was no significant difference in other fruit quality attributes. No significant correlation was found between mineral element contents in the soil and in the fruit. Latitude had some influence on soil and leaf nutrition and fruit quality. The contents of available K and Mn decreased from north to south; those of Fe and Mg in leaves decreased gradually from north to south while those of K, Mn, B and Mo increased. The contents of K and TSS in the fruit increased from north to south. The analysis on the soil and fruit quality indicated that the soil nutrient factors obtained from multiple linear stepwise regressions were significantly different from those obtained from simple correlation analysis screening. The main soil elements influencing fruit quality were organic matter, available Zn, Ca, Mg, and B.【Conclusion】Improving soil p H is needed for Satsuma mandarin orchards at different latitudes in Hunan province. N and B fertilizers should be supplemented in soil fertilization throughout the province. P and K fertilizer should be supplemented regionally. For foliar fertilization, N, K, Zn, Ca, Mg and Mo elements should be added. Improving soil environment improves root vigor and promotes the absorption of nutrients by the trees. Fruit quality attributes in different latitudes were similar. The correlations among most mineral nutrients in soil, leaf and fruit were not significant.Therefore, soil and foliar fertilization should be differentiated in different regions. The key points of soil management for the Satsuma mandarin orchards in Hunan include improvement of the soil p H value and increases in organic matter, alkaline N and available P, K and B.