Comprehensive assessment of fertilization, spatial variability of soil chemical properties, and relationships among nutrients, apple yield and orchard age: A case study in Luochuan County, China

Abstract Data on fertilization and spatial characterization of soil chemical properties are crucial for developing sustainable apple production systems. However, such information at regional scale is scarce. We conducted a survey asking farmers in Luochuan County about their current use of fertilizers, and collected 290 soil samples from 0 to 20 cm and 20–40 cm depths, respectively, to examine the spatial variability of eight chemical properties, and analyze the possible relations between soil quality index (SQI), apple yield, and stand age. Results showed apple orchards were severely overfertilized, with chemical N-P2O5-K2O fertilizers of 1230–795–1080 kg  ha−1 yr−1 and organic fertilizers applied at the rates of 74.7 kg N ha−1 yr−1, 66.1 kg P2O5 ha−1 yr−1, and 75.8 kg K2O ha−1 yr−1. With the exception of pH, both coefficient of variation and variogram range showed a moderate to high variability (16.5–77.7%) and spatial dependency (7.10–47.8%) for selected parameters. Distribution maps illustrated that the 0–20 cm soil depth was characterized by typically higher soil nutrient contents compared with that of 20–40 cm depth. Relative to the data observed in the 1980s, the averaged pH values decreased by ~0.20 units across 0–40 cm depth, while soil organic matter, total N, available N, P, K and Zn, and exchangeable Ca (Ex-Ca) increased markedly (26.2–508%) in the 0–20 cm depth, whilst few changes ( 9.84–178%) occurred at 20–40 cm depth. Correlation analysis revealed that Ex-Ca was the unique variable that was significantly (P