The effect of terrain and management on the spatial variability of soil properties in an apple orchard

Soil variability has implications in farm workability, nutrient and pesticide management, and sustainability. The aims of this study were to investigate how management practises and topography influence the variability of key soil properties and to test the efficacy of various analytical techniques for predictive high resolution soil mapping. We sampled soil properties measured in an intensively managed orchard in the Adelaide Hills, South Australia using a stratified sampling design for alleys and tree-lines in order to distinguish potential management effects (extrinsic factors) from effects of natural soil variability (intrinsic factors). Key soil properties were determined using standard techniques and predictions using mid-infrared partial least-squares (MIR-PLS). Total organic carbon and electrical conductivity (EC) were significantly lower in the tree-line than in the alley. The distribution of coarse fraction (> 2 mm) was also very different between tree-line and alley, most likely because of ripping during orchard establishment. Terrain parameters had varying effect on distribution of soil properties. The degree of correlation between soil properties and terrain parameters was influenced by the different management regimes in the alley and the tree-line. Within-field management practises impose marked short-range variability in soil properties. Soil sampling in intensively managed orchards in which there has been major landform modification must be stratified.