Effects of Planting Practices on Soil Organic Carbon during Old Apple Orchards' Reconstruction on the Loess Plateau

Changes in the soil organic matter are related to the land-use change of sustainable agricultural production. However, few studies have been reported on the effects of changes in planting practices on SOC during the reconstruction period of old apple orchards. In this study, 4 treatments were applied during the reconstruction period of old apple orchards (more than 20 years old) on the Loess Plateau: thinning and replanted apple saplings (TR); all felled and planted corn (CR); all felled and planted millet (MT); all felled and planted potato (PT). It was found that: SOC was ranked as MT > PT > CR > TR, and decreased with soil depth, obeying the power function law; this first decreased and then increased, with the lowest ranking of the year being obtained in August in a year; MT was the most effective in increasing SOC, with an average annual growth rate of 0.54 g/(kg center dot year). In this study, the complex relationship between rainfall, temperature, solar radiation, soil moisture content, and soil organic carbon was established. The results not only provide a reference for the reconstruction of old apple orchards, but also provide support for sustainable agricultural production in the fragile ecological zone of the Loess Plateau.