Tree growth and leaf mineral nutrient contents in dense-planting 'Fuji'/M.26/seedling apple trees with good fruit quality and high productivity

摘要

To determine the criterion of nutritional diagnosis for good fruit quality and high productivity without off-year cropping in dense-planting 'Fuji'/M.26/seedling apple orchards, three orchards (coded orchard A, B, and C) were selected. The plantingdensity per ha and tree height were 1,250 trees and 4.0 m in orchard A, and 1,670 trees and 2.5 m in orchards B and C. Total 60 trees sampling 20 trees from each orchard were investigated for shoot growth, cropping, fruit quality, and leaf mineral nutrient contents for four years. Trees showing average estimated yield of 56 +- 18 kg/tree with 70 +- 23 t centre dot ha~(-1) were cropped in orchard A for four years, 34 +- 18 kg/tree with 58 +- 24 t centre dot ha~(-1) for orchard B, and 36 +- 16 kg/tree with 61 +- 13 t centre dot ha~(-1) for orchard C. The investigated trees in orchards A and C did not show off-year cropping, but lots of trees in orchard B showed off-year cropping once during four years. Fruit qualities such as soluble solids/acidity and fruit skin color were better in orchard A than in orchard C, but the shoot growth was less vigorous in orchard A than in orchard C, and leaf N content was lower in orchard A than in orchard C. The productivity of the trees without off-year cropping withinthe same orchard varied, but there were no differences among them in fruit quality, shoot growth status, and leaf mineral contents in these highly productive orchards. Therefore, it was reasonable that tree vigor and nutritional conditions of orchard A,having highest productivity without off-year and higher fruit quality among investigated orchards, were considered as the standards for nutritional diagnosis in dense-planting 'Fuji'/M.26/seedling apple trees. To produce 56 +- 18 kg/tree and 70+-23 t centre dot ha~(-1) with fruit qualities of 300 g. 14 deg Brix and 0.27 percent acidity, the criteria for stable tree vigor and optimal levels of leaf mineral nutrient were determined as follows. For stable tree, growth, the average shoot (over 5 cm) lengthof 18 +- 3 cm on the two-year-old branches was desired with shoot regrowth rate of below 10 percent. The optimal levels of leaf mineral nutrient in late July were 24.2 +- 1.7 g centre dot kg~(-1) for N, 1.78 +- 0.30 g centre dot kg~(-1) for P, 10.5 +- 1.7 g centre dot kg~(-1) for K, 11.5 +- 1.5 g centre dot kg~(-1) for Ca, 3.8 +- 0.8 g centre dot kg~(-1) for Mg, and 26 +- 3 mg centre dot kg~(-1) for B. A decrease of leaf mineral contents N, P, and K was observed from late May to late October, while anincrease in Ca and no fluctuations in Mg and B.