Optimizing planting density for production of high-quality apple nursery stock in China

In China, apple (Malus x domestica Borkh.) nursery stock is generally of low quality because of extremely high planting density. The objective of this study was to determine the optimum planting density of 2-year-old grafted apple trees. Tree growth (height, trunk diameter, leaf area index) increased as density decreased. Trees grown at high densities (14.3-50 plants/m(2)) were the shortest with the smallest trunk diameters and leaf areas, whereas trees grown at lower densities (4.8-10 plants/m(2)) were generally largest in terms of height, diameter and leaf area. Trees grown at lower densities tended to have higher bud dry weight, leaf dry weight, nitrogen content, total soluble sugar concentration and total non-structural carbohydrate content. Higher levels of these parameters were generally observed with tree densities at or below 10 plants/m(2). Therefore we conclude that 10 plants/m(2) is the optimum density for maximizing the number of trees produced per unit land area while maintaining tree quality of nursery stock.