Crop load management (CLM) for sustainable apple production in China

Abstract

Biennial bearing is a common problem encountered in perennial fruit crops. In order to determine a suitable crop load for sustainable development of dryland apple orchards, we defined the concept of “appropriate productivity” and examined five crop load levels in an apple orchard ecosystem on the Loess Plateau, in Changwu, Shaanxi province, China. The orchards were planted with Fuji apple (Malus domestica Borkh.) trees on M. sieversii rootstock since 1996. Crop load was limited to 53–54 (I), 67–68 (II), 80–81 (III), 94–95 (IV), and 107–108 (V) fruit per tree, using flower and fruit thinning by hand. Volumetric soil water content, total nutrient (N, P, and K) contents of branches, and economic benefit were then analyzed under each treatment over a 5-year period. Soil water content was found to be closely related to rainfall, with three seasonal periods recognized annually. Average water content in 2009–2013 ranked treatment II (21.98%)>III (21.57%)>I (20.61%)>IV (20.31%)>V (20.11%), in which treatments II and III were significantly higher than other treatments. With increasing soil depth, the water content showed an “increasing-decreasing-increasing” trend, with the highest value tending to occur within a depth of 40–100cm. The nutrient contents of branches under treatments I–III were good and trees showed strong resistance to apple Valsa canker. From an economic perspective, the percentage of high-quality fruit increased as did the economic benefits in treatments I–III. In conclusion, controlling fruit crop load effectively reduced fluctuations in production, increased the economic benefits, and maintained the health of the orchard ecosystem. The appropriate crop load level for mature apple orchards in the gully region of the Loess Plateau was deemed to be 67–81 fruit per tree.